Contaminants in the Mississippi River, 1987-92 (Index) 

 

Contaminants in the Mississippi River, 

1987-92

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995

Edited by Robert H. Meade

Circular 1133 cover

CONTENTS

Conversion Factors

Acknowledgments

Executive summary

R.H. Meade and J.A. Leenheer 

Introduction

R.M. Hirsch 

Setting: Geology, hydrology, sediments, and engineering of the Mississippi River

R.H. Meade 

Setting: Chemical character of the Mississippi River

J.A. Moody and W.A. Battaglin 

Sampling the big rivers

R.H. Meade, J.A. Moody, and H.H. Stevens, Jr. 

Heavy metals in the Mississippi River

J.R. Garbarino, H.C. Hayes, D.A. Roth, R.C. Antweiler, T.I. Brinton, and H.E. 

Taylor 

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Nutrients in the Mississippi River

R.C. Antweiler, D.A. Goolsby, and H.E. Taylor 

Pesticides in the Mississippi River

D.A. Goolsby and W.E. Pereira 

Polychlorinated biphenyls and other synthetic organic contaminants associated with 

sediments and fish in the Mississippi River

C.E. Rostad, L.M. Bishop, G.S. Ellis, T.J. Leiker, S.G. Monsterleet, and W.E. 

Pereira 

Organic contamination of the Mississippi River from municipal and industrial 

wastewater

L.B. Barber, II, J.A. Leenheer, W.E. Pereira, T.L. Noyes, G.A. Brown, C.F. Tabor, 

and J.H. Writer 

Potential deleterious effects of chlorinating Mississippi River water for drinking purposes

R.E. Rathbun 

FIGURES

1. Dissolved Contaminants

Map showing average water discharges and graphs showing average concentration of 

dissolved contaminants in the Mississippi River and some of its major tributaries (116K 

JPEG) 

2. Contaminants in Suspended Sediment

Map showing average suspended-sediment discharges and graphs showing average 

concentrations of contaminants adsorbed on suspended-silt particles in the Mississippi 

River and some of its major tributaries(99K JPEG) 

3. Contaminants in Bed Sediments

Map showing navigation pools and graphs showing concentrations of contaminants 

stored in bed sediments of the Upper Mississippi River (99K JPEG) 

4. Geologic Settings

Maps and Vignettes of the Mississippi River showing different geologic settings (132K 

JPEG) 

5.Water Discharge

Map and graphs showing long-term averages, year-to-year, and seasonal variations in 

suspended-sediment discharge of the Mississippi River (99K JPEG) 

6. Suspended-Sediment Discharge

Maps and graphs showing long-term averages, year-to-date, and seasonal variations 

in suspended-sediment discharge of the Mississippi River.(83K JPEG) 

7. Particle Sizes of Sediments

Graphs showing particle sizes of suspended and bed sediments of the Mississippi River 

(83K JPEG) 

8. Effects of Reservoirs

Graphs and photographs showing the effects of reservoirs on sediment in the 

Mississippi River and its tributaries (99K JPEG) 

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9. Engineering Activities

Photographs showing engineering works and activities along the Mississippi River: 

levees, wing dams, bank revetment, and dredging (99K JPEG) 

10. Major Engineering Works

Photographs and graphs of major navigation and water-diversion structures on the 

Mississippi(83K JPEG) 

11. Discharge of River Water

Graph showing mean annual water discharge of the Mississippi River (33k JPEG) 

12. Dissolved Solids in River Waters

Graph and map showing dissolved-solids concentrations in the Mississippi River and its 

major tributary basins (116K JPEG) 

13.Hardness or River Waters

Graph and map showing hardness of waters in the Mississippi River and its major 

tributary basins (116K JPEG) 

14. Nitrate in River Waters

Graph and map showing concentrations of nitrate in waters of the Mississippi river and 

its major tributary basins (116K JPEG) 

15. Population Stress

Graph and map showing population stress on waters of the Mississippi River and its 

major tributary basins (116K JPEG) 

16. Research Vessel

Photograph of Research Vessel Acadiana from which most samples were collected (66K 

JPEG) 

17. Sampled Sites

Maps showing principal sites where flowing waters were sampled (66K JPEG) 

18. Sampling Flowing Waters

Graph and photographs of techniques and equipment used to sample flowing waters 

(99K JPEG) 

19. Sampling Navigation Pools

Maps showing navigation pools of the Upper Mississippi River and a typical areal 

pattern of sampling of bed sediments (99K JPEG) 

20. Sampling Bed Sediments

Photographs or techniques and equipment used to sample bed sediments (17K JPEG) 

21. Sources and Sinks of Heavy Metals

Diagram showing principal sources, transfer mechanisms; and sinks of heavy metals in 

the Mississippi River (83K JPEG) 

22. Lead in River Waters and Sediments

Map and pie diagrams showing distributions of lead in waters and suspended 

sediments of the Mississippi River during July-August 1991 (99K JPEG) 

23. Mercury in River Waters and Sediments

Map and pie diagrams showing distributions of mercury in waters and suspended 

sediments of the Mississippi River during October-November 1991 (99K JPEG) 

24. Lead in Silts and Colloids

Graph showing concentrations of lead absorbed by suspended silts and colloids in the 

Mississippi River, July-August 1991 (66K JPEG) 

25. Range of Lead Dissolved in River Waters

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Graph showing concentrations of dissolved lead in water of the Mississippi River, 1987-

92 (50K JPEG) 

26. Uranium and Copper Dissolved in River Waters

Graphs showing concentrations and transports of dissolved uranium and copper in the 

Mississippi River, April-May 1992 (83K JPEG) 

27. Mercury Dissolved in River Waters

Graph showing concentration of dissolved mercury in the Mississippi River, SeptemberOctober 1991 (50K JPEG) 

28. Metals Dissolved in River Waters

Graph showing ranges of concentrations of dissolved cadmium, chromium, copper, 

lead, mercury, and uranium in the Mississippi River, 1991-92 (33K JPEG) 

29. Lead and Mercury in Bed Sediments

Map and graphs showing concentrations of lead and mercury, in relation to those of 

fine particles and organic carbon, in the bed sediments of the Upper Mississippi River, 

1991-92 (83K JPEG) 

30. Nutrients Dissolved in River Waters

Graphs showing ranges of concentrations of dissolved nitrate, orthophosphate, 

ammonium, and nitrite in the Mississippi River and its tributaries, 1979-92 (66K JPEG) 

31. Nitrate in River Waters

Graph showing annual mean concentrations of nitrate plus nitrite at five sampling 

stations on the Mississippi River, 1979-92 (50K JPEG) 

32. Nitrate Variations Through Time

Map and graphs showing time series of nitrate concentrations in the Mississippi, 

Illinois, Missouri, and Ohio Rivers, March 1991-September 1991 (99K JPEG) 

33. Ammonium Variations Through Time

Map and graphs showing time series of ammonium concentrations in the Mississippi, 

Illinois, Missouri, and Ohio Rivers, March 1991-September 1992 (99K JPEG) 

34. Nutrient Concentrations

Graphs showing concentrations of orthophosphate, nitrate, nitrite, and ammonium in 

the Mississippi River, June-July 1991, and March-April 1991 (99K JPEG) 

35. Nutrient Transports

Graph showing transports of orthophosphate, nitrate, nitrite, and ammonium in the 

Mississippi River, June-July 1991 (66K JPEG) 

36. Nitrate Sources

Pie diagrams showing sources of nitrate and water discharge in the Mississippi River 

and its drainage basin (33K JPEG) 

37. Nitrogen Applied to Croplands

Map showing use of nitrogen fertilizers on croplands in the United States, 1991 (99K 

JPEG) 

38. Harvested Croplands

Map showing areal distribution of harvested croplands in the United States (99K JPEG) 

39. Herbicides Applied to Croplands

Graph showing 20 most-used herbicides, and map showing use of atrazine in the 

United States (132K JPEG) 

40. Pesticides in the River 

Graph showing concentrations of 32 pesticides and pesticide-degradation products in 

the Mississippi River, 1987-92 (99K JPEG) 

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41. Atrazine Variations Through Time

Map and graphs showing time series of atrazine concentrations in the Mississippi, 

Missouri, and Ohio Rivers, April 1991-September 1992 (99K JPEG) 

42. Herbicide Variations Through Time

Graph showing time series of streamflow and concentrations of atrzine, cyanazine, and 

metolachlor in the Mississippi River at Baton Rouge, Louisiana, April 1991-September 

1992 (50K JPEG) 

43. Atrazine at Vicksburg

Graph showing annual maxima, means and minima of concentration of atrzine in the 

Mississippi River at Vicksburg, Mississippi, 1976-92 (50K JPEG) 

44. Atrazine Along the River

Graph showing concentrations of atrzine in the Mississippi River during five sampling 

cruises, 1990-92 (50K JPEG) 

45. Herbicide Transports

Maps and graphs showing transports of atrazine, cyanazine, metolachlor, and alachlor 

in the Mississippi, Illinois, Missouri, and Ohio Rivers during April 1991-September 1992 

(99K JPEG) 

46. Hexachlorobenzene and PCBs in Silts

Graphs showing concentrations of hexachlorobenzene and polychlorinated biphenyls 

(PCBs) on suspended silts in the Mississippi River during March 1989 and June 1989 

(66K JPEG) 

47. PCBs from Ohio and Missouri Rivers

Graphs showing concentrations of polychlorinated biphenyls (PCBs) on suspended silts 

in the Lower Mississippi River when the major source of suspended sediment was the 

Ohio River (March 1990) and the Missouri River (June 1990) (50K JPEG) 

48. PCBs in Silts and Colloids

Graphs showing the concentration and transport of polychlorinate biphenyls (PCBs) 

adsorbed by suspended silt and colloid in the Mississippi River, July-August 1991 (66K 

JPEG) 

49. PCBs in Bed Sediments

Graphs showing the concentrations of polychlorinate biphenyls (PCBs) in bed 

sediments stored in the navigation pools of the Upper Mississippi River (66K JPEG) 

50. Chlordane and PCBs in Catfish

Graphs showing concentrations of chlordane and polychlorinate biphenyls (PCBs) in 

catfish in the Mississippi River, July-August 1987 (50K JPEG) 

51. Fate of Contaminants in the River

Diagram showing processes controlling the fate of organic contaminants in the 

Mississippi River (99K JPEG) 

52. Surfactants in the River

Graph showing annual ranges of concentration of methylene-blue-active substances in 

the Mississippi River, 1963-76, 1992 (66K JPEG) 

53. Fecal Coliforms in the River (Not Available)

Graph showing annual ranges of concentration of methylene-blue-active substances in 

the Mississippi River, 1963-76, 1992 

54.Wastewater Contaminants along the River

Graphs showing temperature and specific conductance, and concentrations of 

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Contaminants in the Mississippi River, 1987-92 (Index) 

sulfonate, and adsorbable organic halogen in the Mississippi River, 1991-92 (116K 

JPEG) 

55. Wastewater Contaminants in Bed Sediments

Graphs showing concentrations of linear alkybenzenesulfonate, coprostanol, and 

polynuclear aromatic hydrocarbons in bed sediments stored in the navigation pools of 

the Upper Mississippi River (83K JPEG) 

56. Caffeine and EDTA in River Waters

Graphs showing the concentrations of dissolved caffeine and 

ethylenediaminetetraacetic acid (EDTA) in the Mississippi River and its tributaries, 

1992-92 (83K JPEG) 

57. TTT and Flame Retardants in River Waters

Graphs showing the concentrations of dissolved 1,3,5-trimethyl-2,4,6-triazinetrione 

and trihaloalkylphosphates in the Mississippi River and its tributaries, 1987-92 (83K 

JPEG) 

58. Volatile Contaminants in the River

Graphs showing concentrations of volatile organic compounds detected in the 

Mississippi River, 1991-92 (66K JPEG) 

59. Graphs showing potentials for forming trihalomethane 

and nonpurgeable total organic halides from Mississippi River water collected during 

summer 1991 and adjusted to three level of acidity (33K JPEG) 

60.Graphs showing reaction times for forming trihalomethane 

and nonpurgeable total organic halides from Mississippi River water collected at 

Minneapolie, Minnesota, Memphis, Tennessee, and New Orleans, Louisiana, during 

summer 1991 (33K JPEG) 

TABLES

1. Classification of naturally occurring metals according to their toxicity and availability in the 

hydrologic environment.

2. U.S. Environmental Protection Agency maximum contaminant levels for heavy-metal 

concentrations in drinking water and water supporting aquatic life, and criteria for openwater disposal of polluted sediments.

3. Selected heavy metals presently or formerly used in major industries along the Mississippi 

River.

4. Average releases of heavy metals into the Mississippi River from a large metropolitan 

wastewater-treatment plant in St. Paul, Minnesota.

5. U.S. Environmental Protection Agency maximum contaminant levels (MCLs) for 

nitrogenous nutrients in drinking water.

6. Sources of nutrients in surface waters.

7. Summary statistics of nutrient concentrations during 1991-92 in the Mississippi River and 

all measure tributaries.

8. Physiochemical properties, health-based limits for drinking water, and aquatic-life 

guidelines for selected major pesticides in the Mississippi River Basin.

9. Estimated loads of pesticides, in kilograms, transported by the Mississippi River and major 

tributaries, April 1991 through March 1992.

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10. Organic compounds measured to evaluate wastewater contamination of the Mississippi 

River, 19987-92.

11. Summary assessment of organic contaminants in the Mississippi River and its major 

tributaries. 

U.S. DEPARTMENT OF THE INTERIOR,

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY,

GORDON P. EATON, Director

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

This is an electronic version of a U. S. Geological Survey publication. 

The original paper copy of this report may be obtained free on 

application 

to the 

 U.S. Geological Survey

 Information Services

 Box 25286

 Denver Federal Center

 Denver, CO 80225 

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Contaminants in the Mississippi River, 1987-92 (Index) 

Library of Congress Cataloging-in-Publication Data

 

Contaminants in the Mississippi River, 1987-92/edited by Rober H. Meade

p. cm.--(U.S. Geolgoical Survey circular:1133)

INCLUDES BIBLIOGRAPHICAL REFERENCES.

1. WATER--Pollution--Mississippi River.

I. Meade, Robert H., 1930- . II. SERIES.

[TD223.4.C657] 1996 96-202

363.73'942'0977--dc20 CIP

 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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CONVERSION FACTORS

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

CONVERSION FACTORS AND ABBREVIATED WATER-QUALITY UNITS

 Multiply By To obtain

 

 meter (m) 3.281 foot

 kilometer (km) 0.6214 mile

 square kilometer (km2) 0.3861 square mile

 cubic kilometer (km3) 0.2399 cubic mile

 centimeter (cm) 0.3937 inch

 millimeter (mm) 0.03937 inch

 micrometer (μm) 0.00003937 inch

 liter (L) 1.057 quart

 milliliter (mL) 0.03381 fluid ounce

 kilogram (kg) 2.205 pound, avoirdupois

 metric ton 2205 pound, avoirdupois

 cubic meter per second (m3/s) 35.31 cubic foot per 

second

kilogram per square kilometer (kg/km2) 0.008924 pounds per acre

 Concentration unit Equals

 

 milligram per gram (mg/g) part per thousand

 milligram per kilogram (mg/kg) part per million

 microgram per gram (μg/g) part per million

 nanogram per gram (ng/g) part per billion 

(109) 

 

 

 

 Concentration unit Approximately* 

equals 

 

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CONVERSION FACTORS

 

 gram per cubic meter (g/m3) part per 

million 

 milligram per liter (mg/L) part per million 

 microgram per liter (μg/L) part per billion 

(109) 

 nanogram per liter (ng/L) part per trillion 

(1012) 

 

*At the concentrations encountered in this study, and considering the detection limits of 

the 

analytical methods employed, these units can be considered equal in the context of this 

report.

 Degree Celsius (°C) may be converted to degree Fahrenheit (°F) by using the 

 following equation:

 

 °F=9/5 (°C)+ 32.

 

Sea level: In this report "sea level" refers to the

National Geodetic Vertical Datum of 1929 (NGVD of 1929)--a geodetic

datum derived from a general adjustment of the first-order level nets

of both the United States and Canada, formerly called Sea Level Datum

of 1929.

Continue to ' Acknowledgments ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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Acknowledgments

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

ACKNOWLEDGMENTS

Because it covered so many aspects of water quality, along 3,000 kilometers of the continent's largest 

river system, this study required the collaboration of a large number of people--only a few of whom are 

listed among the chapter authors. Others who made substantial contributions to the investigation, 

execution, and completion of the study are listed below, with our thanks. Those listed without affiliation 

are (or were) members of the U.S. Geological Survey (USGS).

Among those influential in getting the study started, the late Robert C. Averett played a central role, and 

the completion of this report is part of Averett's lasting legacy as our colleague and mentor. Other 

important instigators were E.M. Thurman, R.G. Wolff, and E.D. Andrews.

Once the program was under way, we received help and encouragement at critical junctures from: U.S. 

Senator Rudy Boschwitz; Holly Stoerker, Upper Mississippi River Basin Association; Gail Carmody, U.

S. Fish and Wildlife Service; Dan Helwig, Minnesota Pollution Control Agency; John Sullivan, 

Wisconsin Department of Natural Resources; Donald F. Boesch and Paul W. Sammarco, Louisiana 

Universities Marine Consortium.

In our field operations, we received the unstinting support of the staff of Louisiana Universities Marine 

Consortium (LUMCON): Steven C. Rabalais and Daniel C. Guidry at LUMCON's home base in 

Cocodrie, Louisiana; AcadianaCaptains Wayne G. Simoneaux, Craig J. LeBoeuf, and C.L. Black, who 

were exemplary in their dedication to the scientific effort; Acadiana crew members Cheryl Blanchard, 

George Collier, Bob Cutting, Wilton Delaune, Mike Detraz, Derral Dupre, D.C. Guidry, Jean Hough, 

Kevin Hutchinson, Jonathan Landry, Daniel Lapeyrouse, Suzanne Moody, Ken Olivier, Renee Rizzo, 

David Robichaux, and Elaine Robichaux. Mike Theriot, of Chauvin, Louisiana, was most helpful in 

fabricating unique equipment on short notice and mounting it aboard Acadiana.

Scientists who participated as colleagues in the field but did not, for one reason or another, end up 

among the chapter authors included: Brent McKee, LUMCON; Alan Shiller and Jim Krest, University 

of Southern Mississippi; Patircia Brown, Wesley Campbell, C.C. Cranston, T.F. Kraemer, D.A. Martin, 

James Ranville, T.F. Rees, and R.F. Stallard.

Many people visited in the field to observe our operations, lend a hand, and provide essential scientific 

discourse. Those who were aboard Acadianafor more than a day were: Lesly Conaway, Missouri 

Department of Conservation; Dirk DeBoer, Andre ́ Germain, and Claire Lemieux, Environment Canada; 

Dolly Dieter, National Science Foundation; Daphne Frilot, University of Southern Mississippi; Densie 

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Acknowledgments

Reed, LUMCON; J.M. Sainz, Venezuelan Ministry of the Environment and Renewable Natural 

Resources; John Sullivan, Wisconsin Department of Natural Resources; Harold Wiegner, Minnesota 

Pollution Control Agency; Ellen Axtmann, Briane Adams, Jerry Glenn, William Kaehrle, Donovan 

Kelly, Lois Koehnken, Gail Mallard, Richard Martin, Tim Miller, William Moody, Fred Morris, Charles 

Patton, Dale Peart, James Seeley, Michael Simpson, A. Richard Tagg, E. Michael Thurman, Lisa Torick, 

Peter Voll, Woodrow Want, and Timothy Willoughby.

The U.S. Army Corps of Engineers was exemplary in providing logistic support and supplying 

hydrologic information for planning and carrying out the sampling cruises and interpreting the data. 

Those who were especially helpful in the St. Paul District were Joe Dvorak, Ed Eaton, Dennis Erickson, 

Gordon Heitzman, Jon Hendrikson, Dan Wilcox, and Kelsey Willus; in the Rock Island District, Bob 

Allen, Jerry Bledsoe, Bryan Goodrum, Bill Gratten, Bill Koelner, James Morgen, and Harvey Vance; in 

the St. Louis District, Don Coleman, Ray Kopsky, Paul Kornberger, and Claude Strauser; in the 

Cincinnati District, David Legg; in the Louisville District, Bob Biel; in the Memphis District, Whit 

Barton, Janet Graner, Sam Lehr, and Dorothy Wilson; in the Vicksburg District, Wesley Bird, Henry 

Noble, and Thomas Runnels; in the New Orleans District, Billy Garrett, John Miller, Nancy Powell, and 

Cecil Soileau; in the Lower Mississippi River Valley Division, James Farrell and Don Flowers. The 

lockmasters and crews at the navigation locks of the Upper Mississippi and Lower Ohio Rivers, as well 

as Norrell Lock no. 1 on the Arkansas River, graciously allowed us to tie up for the night at their 

facilities.

Many people along the river provided permission for docking, loading, and repairing the ship and 

equipment, and they often went out of their way to be helpful: Renee Ory and people at Ory Brothers 

Marine Service of America in Hartford, Illinois; Rusty Sutton in Grafton, Illinois; Pablo Lara, Ron 

Brant, and people at the Central Illinois Power Company in Meredosia, Illinois; Daniel Gipe and people 

at Hermann Sand and Gravel Company in Hermann, Missouri; Captain William Carroll and the people 

at Gateway River Cruises in St. Louis, Missouri; Kent Hoffmeister and the workers at Missouri Dry 

Dock and Repair Company in Cape Girardeau, Missouri; the U.S. Coast Guard Station in Keokuk, Iowa, 

and Hickman, Kentucky; John Janoush and the people at Janoush Marine, Inc., in Rosedale, Mississippi; 

Mary Hosemann and the people working on the Spirit of Vicksburgin Vicksburg, Mississippi; and the 

people running the New Roads Ferry at St. Francisville, Louisiana, and the Belle Chasse Ferry at Belle 

Chasse, Louisiana.

Laboratory analyses of our samples were provided by C.J. Anderson, P.J. Cinotto, B.F. Connor, J.A. 

Kammer, C. Klimper, W.J. Matthes, E.K. Naughton, M.C. Noriega, M.P. Pavelich, M.P. Schroeder, M.J. 

Werito, and M.T. Woodworth. Assisting in our laboratories were Johnathan Fischer, P.W. Mahan, Mike 

Meyer, Mike Pomes, and Diana Aga.

John Flager reviewed the entire manuscript three times, at different stages of completion. Eugene 

Hampton reviewed several chapters at early stages of preparation, and provided valuable advice about 

formats. Colleagues who reviewed individual chapters were: I.B. Brenner, Geological Survey of Israel; J.

N. Huckins and C.J. Schmitt, U.S. Fish and Wildlife Service; Ola Saether, Geological Survey of 

Norway; John Sullivan, Wisconsin Department of Natural Resources; Michael Trehy, Monsanto 

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Acknowledgments

Company; G.R. Aiken, M.J. Baedecker, C.R. Demas, M.C. Goldberg, J.W. LaBaugh, G.R. Marzolk, C.J. 

Patton, C.S. Phinney, M.M. Reddy, R.F. Stallard, and E.M. Thurman.

The final preparation and layout of the rpeort was a team effort led by R.J. Olmstead. Other team 

members: C.L. Anderson, N.L. Bruce, J.M. Evans, M.A. Kidd, Aleta Moores, S.A. Rafferty, A.G. 

Sanchez, Ann Marie Squillacci, E.J. Swibas, Margo Van Alstine; and K.A. Jackson of Moonlight 

Mapping.

All photographs were taken by the editor.

Continue to ' Executive Summary ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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Contaminants in the Mississippi River 1987-92-- Executive Summary

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Executive Summary

By Robert H. Meade and Jerry A. Leenheer

This volume contains a selection of some of the more interesting results of a 5-year study conducted by 

the U.S. Geological Survey of contaminants in the Mississippi River and some of its major tributaries. 

During the first 3 years of the study, 1987-90, the rivers were sampled on seven different occasions 

between St. Louis, Missouri, and New Orleans, Louisiana. During the last 2 years of the study, 1991-92, 

the scope of the program was increased to include three further samplings of the full length of the river 

between Minneapolis-St. Paul, Minnesota, and New Orleans. The sampling and analytical efforts were 

focused on three phases of contaminants in the rivers: (1) contaminants transported in the dissolved 

phase, (2) contaminants transported in the adsorbed phase-that is, in association with the suspended silts 

and colloids-and (3) contaminants stored in the bottom sediments in the navigation pools of the Upper 

Mississippi River. 

Contaminants were assessed for the period of sampling, 1987-92. Given that samples were collected no 

more frequently than twice a year, the 5-year period was not sufficiently long to establish any time 

trends-whether, that is, the contaminant levels were increasing or decreasing. Included in the analysis 

were only a few data that had been collected before our study. Yet to be assessed are the subsequent 

effects on river quality of the great flood of 1993. Contaminants are assessed mostly in a spatial rather 

than a temporal context. This report, in other words, is a snapshot rather than a chronicle. 

Some of the findings represent new information, whereas many of the results confirm previously known 

aspects of the distribution of contaminants in the river, as described, for example, in the volumes by 

Costner and Thornton (1989), Scarpino (1985, especially pages 151-186), and Wiener and others (1984). 

This summary includes three figures that demonstrate the three phases of contaminant occurrence listed 

in the first paragraph. Further details of each of the contaminants portrayed here, as well as of other 

contaminants, are given in the chapters that follow. 

SUGGESTIONS FOR READING THIS REPORT

The chapters on the individual contaminant groups (heavy metals, pesticides, nutrients, polychlorinated 

biphenyls, and other organic contaminants) are organized to be read easily at different levels. For readers 

who want an overview in the shortest amount of time, the figures and their captions contain much of the 

relevant information. For readers having more time or interest, the main text of each chapter provides 

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Contaminants in the Mississippi River 1987-92-- Executive Summary

further information and analysis. For readers who want to inspect entire data sets and evaluate analytical 

methods, each chapter contains bibliographic references to the U.S. Geological Survey Open-File 

Reports and Water-Resources Investigations Reports that contain the basic data and complete 

descriptions of the procedures that were used to obtain them. 

Dissolved Contaminants

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Figure 1. -- The waters of the Mississippi River carry dissolved contaminants and bacteria that originate 

from a variety of municipal, agricultural, and industrial sources. The map shows the amounts of water 

discharged by the Mississippi River and its main tributaries during an average year. About 2 percent of 

the average discharge of the Mississippi River comes from municipal and industrial point sources. The 

distribution of contaminants along the Mississippi River depends on the nature and location of their 

sources, the degree of wastewater treatment, the stability of the contaminants, and their dilution by 

receiving waters. The graphs below the map show the concentrations of contaminants dissolved in the 

Mississippi River between Minneapolis-St. Paul and the Gulf of Mexico. The data in the graphs are 

generalized from the results of chemical analyses of representative samples of water collected at 10-15 

sites along the Mississippi River: on as many as 10 separate occasions during 1987-92 downriver of St. 

Louis, and on 3 separate occasions during 1991-92 upriver of St. Louis. 

As the Mississippi River flows southward from its headwaters in the northern Midwest, its discharge is 

more than doubled by the waters it receives from the Illinois and Missouri Rivers. This combined 

discharge is more than doubled again as it is joined by the waters of the Ohio River. About 500 

kilometers upriver of its principal mouth, the Mississippi River bifurcates, and one-fourth of its 

discharge is diverted down the Atchafalaya River to the Gulf of Mexico. 

A

Fecal coliform bacteria derived from human and animal wastes survive only briefly in river 

water, but their average concentrations exceed the maximum contaminant level (MCL) 

established by the U.S. Environmental Protection Agency of 2,000 per liter for recreational use in 

much of the Mississippi River because of incomplete wastewater treatment.

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B

Linear alkylbenzenesulfonate (LAS) is a biodegradable detergent, primarily derived from 

domestic sewage. Its presence in high concentrations in the Mississippi River in the St. Louis 

metropolitan area corresponds with the elevated counts of coliform bacteria, and probably 

reflects the incomplete treatment of wastewaters discharged into the river.

C

Caffeine is a stimulant chemical in coffee and soft drinks. Because it is consumed only by 

humans, it is an indicator of domestic sewage and illustrates the extent to which sewage is diluted 

by the river. Concentrations of caffeine in municipal wastewaters usually range between 20 and 

300 micrograms per liter (mg/L). The much lower concentrations of 0.02-0.04 mg/L of caffeine 

shown in the graph indicate that municipal wastewaters may be diluted as much as a 

thousandfold after they are well mixed into the Mississippi River. 

D and E

Agricultural contaminants enter the rivers from mostly nonpoint sources, usually as runoff from 

croplands during spring and summer. 

D 

Nitrate in the Mississippi River comes mostly from fertilizers. Its concentration in the river 

fluctuates seasonally, depending on when fertilizers are applied to farmlands and the timing of 

rainfall and runoff. Nitrate concentrations are generally smaller in the Mississippi River below 

the confluence of the Ohio River; the major portion of nitrate in the Mississippi River is derived 

from the tributaries that drain intensively farmed regions in Illinois, Iowa, and Minnesota. 

E 

Atrazine is a pre-emergent herbicide used mainly on cornfields. It is nearly ubiquitous in the 

Mississippi River. Atrazine concentrations usually are greatest near St. Louis, Missouri, because 

of inputs from the Missouri, Illinois, and other rivers that drain the farming regions of the Corn 

Belt. Concentrations usually are smaller in the Lower Mississippi because of dilution by water 

from the Ohio River. Atrazine concentrations vary seasonally, and occasionally exceed the 

maximum contaminant level for treated drinking water of 3 micrograms per liter for a few days 

during the spring runoff in the Mississippi River between St. Louis and the Ohio River 

confluence. 

F 

Ethylenediaminetetraacetic acid (EDTA) is the dissolved organic chemical contaminant present 

at the greatest concentration in the Mississippi River. Generally considered nontoxic, this 

chemical is a general indicator of industrial contamination, and it is found in the Mississippi 

River at about one-fourth of the concentration found in some European rivers. 

G and H 

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Two examples of contaminants from industrial point sources are tris-2-chloroethylphosphate 

(TCLEP) and 1,3,5,-trimethyl-2,4,6-triazinetrione (TTT). 

G 

TCLEP is a flame retardant that is added to polyurethane foams and textiles, and, in the 

Mississippi River system, it is derived almost exclusively from the Illinois River Basin. Its 

exclusive source and its persistence in solution make TCLEP a useful tracer and indicator of 

waters from the Illinois River as they mix with waters from other tributaries down the Mississippi 

River. 

H 

TTT is a by-product of the manufacture of methylisocyanate. Its overwhelmingly singular source 

in the Mississippi River system is in the basin of the Kanawha River of West Virginia, a tributary 

of the Ohio River. Proportions of TTT dissolved in the water can be used to follow the mixing of 

the Kanawha River with the Ohio, and the Ohio River with the Mississippi River. 

Contaminants in Suspended Sediment

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Figure 2. -- The suspended sediments that are transported by the Mississippi River and its tributaries 

adsorb and carry contaminants. Organic contaminants such as polychlorinated biphenyls (PCBs) and 

inorganic contaminants such as lead are many times more likely to adhere to sediment particles than to 

remain in the dissolved phase. The map shows the amounts of suspended sediment discharged by the 

Mississippi River and its main tributaries during an average year near 1990. The graphs arranged below 

the map show the concentrations of constituents adsorbed on the sediments in suspension in the mainstem Mississippi River between Minneapolis-St. Paul and the Gulf of Mexico. The data in the graphs are 

generalized from the results of chemical analyses of representative samples of suspended sediment 

collected at 10-15 sites along the Mississippi River: on as many as 10 separate occasions during 1987-92 

downriver of St. Louis, and on 3 separate occasions during 1991-92 upriver of St. Louis. 

Suspended-sediment discharges in the Upper Mississippi River are fairly small when compared to those 

of the major tributaries. The sediment discharge of the Upper Mississippi River is increased five- to 

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tenfold by the sediment discharge of the Missouri River. The average sediment load in the main stem is 

increased by another significant increment by the contribution from the Ohio River. 

A

Organic carbon (expressed here as weight percent of dried suspended silt) is proportionately 

greater in the uppermost Mississippi River, and its proportion decreases downriver. Particulate 

organic carbon in the Mississippi River is mostly natural, but it affects the ways in which 

contaminants, especially organic contaminants, are adsorbed by suspended sediment. The 

Missouri and Illinois Rivers transport suspended sediment in which organic carbon is somewhat 

less concentrated; where these two tributaries enter the Mississippi (near river kilometer 1850), 

the organic carbon percentages are decreased by dilution. Organic carbon percentages in the 

suspended sediment of the Ohio River, on the other hand, are typically greater than those in the 

Missouri and Illinois Rivers, and the organic carbon in suspended sediment is increased slightly 

where the Ohio River joins the Mississippi (river kilometer 1535). 

B

Polychlorinated biphenyls (PCBs), which are organic contaminants that were formerly used 

widely in industrial applications, are typically most concentrated on the suspended sediments in 

the Upper Mississippi River near Minneapolis-St. Paul. The difference between PCB 

concentrations on the suspended sediments near Minneapolis and those near St. Louis is due 

mostly to the greater amounts of suspended sediment in the river at the latter city, rather than an 

indication that Minneapolis-St. Paul contributed 5-10 times more PCBs to the river than did St. 

Louis. The high concentrations in the upper river decrease rapidly downriver, and they are 

increased significantly only as the suspended sediment from the Ohio River, which usually 

contains more PCBs than that in the middle reaches of the Mississippi River, enters and mixes. 

C 

Hexachlorobenzene, another organic contaminant of industrial origin, is predominantly derived 

from two main sources in the Mississippi River Basin: (1) the Ohio River, which enters the 

Mississippi at river kilometer 1535, and (2) the industrial corridor along the lowermost 400 

kilometers of the Mississippi River. 

D 

Lead and other heavy metals are associated with the suspended sediments along the length of the 

Mississippi River. Spatial variations in their concentrations are less pronounced than those of 

PCBs and hexachlorobenzene. However, they do tend to be most concentrated on the suspended 

sediments in the river just downstream from Minneapolis-St. Paul (as in the case of PCBs, 

because of the relative scarcity there of suspended sediment), and they show slight increases 

related to more concentrated inputs from the Ohio River.

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Contaminants in Bed Sediments

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Figure 3. -- The Upper Mississippi River is partly impounded by control structures which form pools 

that trap sediments and their adsorbed contaminants. Twenty-nine locks and dams, built mostly for 

navigation, control the depth and, to a lesser extent, the flow of the river between Minneapolis and St. 

Louis. Twenty-six of these control structures form major pools that trap and retain sediment and 

contaminants in varying degrees. The two largest pools are Lake Pepin, a natural pool formed by the 

partial damming of the Mississippi River by the sand delta of the tributary Chippewa River, and Pool 19, 

the impoundment behind the hydroelectric dam at Keokuk, Iowa, the highest major dam on the upper 

river. 

The bottom sediments of 25 of these pools (1-26, except for Pool 17) were sampled during 1991-92. In 

each pool, 15-20 samples of the surficial sediment stored in the backwater areas of the lower reaches of 

the pool were collected and combined into a composite sample, which was analyzed for a number of 

characteristics and contaminants, some of which are portrayed in the figure. On the horizontal axes of 

the graphs: UP = upper Lake Pepin; LP = lower Lake Pepin. 

A 

Percent clay, a measure of the fineness of the sediment particles stored on the bottoms of the 

pools, is shown in the graph as percent finer than 0.004 millimeter. Fineness is an important 

attribute in the retention of contaminants because the finer sediments have greater total surface 

areas (compared to coarser sediments) with which contaminants may react or onto which 

contaminants may be adsorbed. The most concentrated accumulation of the finest sediments in 

the pools of the Upper Mississippi River is in Lake Pepin. Other large impoundments, Pools 19 

and 26, have trapped sediments that are finer than those in smaller pools. Clay and other fine 

sediment particles have more time and opportunities to settle and be deposited in the larger 

deeper pools than in the smaller shallower ones. 

B 

Particulate organic carbon usually is found most abundantly in association with the finest 

sediments. In the pools of the Upper Mississippi River, organic carbon shows a strong correlation 

(although not an identical distribution) with percent clay. Independent of its associations with 

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especially organic contaminants-by sediments. 

The distributions of the contaminants adsorbed by the bottom sediments in the pools of the Upper 

Mississippi River reflect two main factors: (1) the affinities of the contaminants for fine particles 

and organic carbon, and (2) local sources of contaminants.

C 

Polychlorinated biphenyls (PCBs) are manmade organic compounds, formerly used extensively 

in industrial applications. Although banned for many years, PCBs still persist in the bottom 

sediments in the pools of the Upper Mississippi River. They are found in the greatest 

concentrations in the pools farthest upriver, and especially in the fine-grained carbon-rich 

sediments on the bottom of Lake Pepin. Lower concentrations in the pools farther downriver 

suggest that the principal sources of PCBs in the Upper Mississippi River were centered in and 

near the Minneapolis-St. Paul metropolitan area, and that Lake Pepin has trapped and retained 

most of the PCBs, retarding their further transport downriver. 

D

Lead comes from natural and manmade sources, but its sources in the Upper Mississippi River 

are mostly industrial and municipal. Sediments having concentrations greater than 40 micrograms 

of lead per gram of sediment are considered "moderately polluted." The highs and lows of lead 

concentration in the pools of the Upper Mississippi River mimic almost exactly the highs and 

lows of the percent clay with one notable exception. Pool 12 includes the mouth of the Galena 

River, which drains an area that was mined extensively for lead some years ago; the higher 

concentrations in Pool 12 may reflect the input of lead-bearing sediment. The high concentrations 

of lead in the sediments of Lake Pepin and Pool 19, however, probably reflect mostly the general 

affinity of lead for fine sediment. 

E 

Coprostanol is a fecal sterol found in the excrement of humans and animals. It is not destroyed 

completely by normal sewage treatment, and so its presence in the sediments of the Upper 

Mississippi River is an indicator of human or animal wastes. The high concentrations of 

coprostanol in Lake Pepin and Pool 19 at least partly reflect the affinity of coprostanol for fine 

sediment. The high concentrations of coprostanol in the sediments of Pool 2 reflect the large 

discharges of treated human wastes in the Minneapolis-St. Paul area. Less easy to explain is the 

high concentration of coprostanol in Pool 14, which is upriver of the Quad Cities (Moline-Rock 

Island, Illinois, and Davenport-Bettendorf, Iowa), and therefore cannot be due to a large 

municipal source.

REFERENCES

Costner, Pat, and Thornton, Joe, 1989,

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We all live downstream-The Mississippi River and the national toxics crisis: Washington, D.C., 

Greenpeace USA, 120 p., 1 app. (61 p.) 

Scarpino, P.V., 1985,

Great river-An environmental history of the Upper Mississippi, 1890-1950: Columbia, Missouri 

University Press, 219 p. 

Wiener, J.G., Anderson, R.V., and McConville, D.R., eds., 1984,

Contaminants in the Upper Mississippi River-Proceedings of the 15th Annual Meeting of the 

Mississippi River Research Consortium: Boston, Butterworth Publishers, 368 p. 

Continue to 'Introduction ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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Contaminants in the Mississippi River--Introduction

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Introduction

By Robert M. Hirsch

The U.S. Geological Survey (USGS) is the Nation's principal earth-science agency. Its mission is to 

assess the land, water, and mineral resources of the Nation and to conduct basic and applied research 

designed to improve the understanding of the Earth and to improve approaches to the study of the Earth. 

In 1987, a group of USGS chemists and hydrologists undertook a research project to examine the 

Mississippi River and its tributaries in a way that had not been done before. The project examined a 

variety of intriguing research questions concerning the transport and storage of a variety of contaminants 

in large rivers. At the same time, it created, for the first time, a highly comprehensive set of data 

describing the movement of a wide range of contaminants from the major tributaries and down the main 

stem of this all-important river. With its laboratories and with its broad mix of practitioners of the 

different phases of river science---hydrologists, chemists, physicists, sedimentologists, geologists---the 

USGS was well equipped to undertake such a study.

The Mississippi River is important in several contexts. (1) It serves as drinking-water supply for 70 

cities and towns. Thus, the contaminants in the waters of the Mississippi River have the potential for 

detrimental health effects on these consumers of river water. Some of these contaminants, of course, are 

removed in water-treatment plants, but some persist regardless of the treatment process. The analysis of 

river waters provides an indication of the potential for drinking-water contamination. (2) The birds, fish, 

and other organisms that live in or adjacent to the Mississippi River are affected by contaminants. Thus, 

there is a basis for interest from an ecological perspective as well as from the perspective of the health of 

humans who consume the birds and fish. (3) The Mississippi River is a significant source of water, 

sediment, and nutrients to the Gulf of Mexico. The chemical characteristics of these flows are important 

to the health and productivity of coastal and marine ecosystems. (4) The Mississippi River drains 41 

percent of the conterminous United States, in which area reside 27 percent of the Nation's population. 

The contaminants moving through the river system are an excellent measure of what is being introduced 

into the Nation's waterways by human activities. In a sense, they are "report cards" on the Nation's 

efforts at water-pollution control. Or, to use the analogy of the great tropical ecologist Harald Sioli, 

"River water is the urine of the landscape," and the quality of the waters of the Mississippi is a monitor 

of the health of a substantial portion of the "body" of the Nation. 

The study, the results of which are reported in this volume, included nearly the full length of the 

Mississippi River and sampled the waters within and along the boundaries of 11 different States. Ten 

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research and sampling cruises were completed during 1987 through 1992. The study ended before the 

unprecedented flooding in the summer of 1993. However, the study has provided a baseline for 

comparison that has been used in the analysis of the movement of contaminants during the flood.

By sampling the river repeatedly, in high flows, in low flows, in the different seasons, one may learn 

something of the dynamics of contaminant movement through the river system. For example, one learns: 

what tributary contributes the largest amounts of certain contaminants; what times of year the 

contaminants enter the river; whether a contaminant, once it enters the river, continues to move 

downstream with the water, or is lost from the system as a result of chemical reaction, uptake by 

organisms, volatilization to the atmosphere, or storage on the riverbed or flood plain? Development of 

effective national and regional strategies for water-quality management demands knowledge of the 

sources, movement, and storage of contaminants and their reactions throughout the river system.

The purposes of this report are to provide an overview of the new knowledge developed in this study 

and to provide access to a body of comprehensive and consistent data that can be compared with data 

collected years and decades hence to help understand and evaluate the changes in the river and future 

progress (or lack of it) in water-quality management.

Continue to ' Setting: Geology, hydrology, sediments, and engineering of the Mississippi River ', or 

return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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Contaminants in the Mississippi River--Geologic Settings

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Setting: Geology, Hydrology, Sediments, and 

Engineering of the Mississippi River

By Robert H. Meade

Geologic Settings

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Figure 4. -- The Mississippi River follows the trend of an ancient continental rift system down the 

center of North America, flowing through different landscapes that record different geologic histories 

(Redfern, 1983). Three vignettes (A, B, and C) in this figure exemplify some of the different processes 

that shaped the landscapes during the latest ice ages and during the 10,000 years since the ice melted 

away.

A

The Upper Mississippi River ("Upper" is conventionally assigned to the Mississippi above its 

confluence with the Ohio) flows for much of its length through a valley 1-10 km wide between 

bluffs that stand 50-100 m above the river and its fringing flood plain. The painting, done in 1844 

by John Casper Wild, shows the bluffs above the confluence of the Minnesota (left) and 

Mississippi (right) Rivers, at the site of Fort Snelling, which is now included in the city of 

Minneapolis. The bluff-bordered river valleys here and farther down the Upper Mississippi were 

formed by a combination of glacial and riverine processes. The great ice ages of the Pleistocene 

epoch gave the basin of the Upper Mississippi much of the shape that we consider characteristic 

today. Pre-existing river valleys were widened and deepened by the ice as it pushed its way 

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south. Between and after the ice ages, the rivers transported and rearranged the sediments in the 

valleys by meandering across them and constructing islands and flood plains. The main valley in 

the painting (upper left to lower right) formed mostly when the ice-age predecessor to the 

Minnesota River (called Glacial River Warren) was the main outlet of a large lake, Lake Agassiz, 

that was dammed along its northern margin in southern Canada by the retreating ice sheet. The 

small notch out of which the Mississippi River is flowing (upper right in painting) was cut, 

mostly after the demise of Glacial River Warren, by a retreating headcut that can be seen today at 

St. Anthony Falls, 13 km upriver of the confluence with the Minnesota River.

B

The Lower Mississippi River flows along and through a wide alluvial plain formed by the river 

and its predecessors. Vignette B (taken from R.T. Saucier, 1991) shows the contrast in stream 

patterns between those formed during the latest ice age (left) and those formed since the ice ages. 

Typical of glacial meltwater rivers heavily laden with coarser sediments are the so-called "valley 

trains" like those shown in the western half of the vignette. Even though no great river has flowed 

there for thousands of years, the braided and anastomosing pattern still shows on the landscape 

and is clearly visible from the air. The present pattern, in which the Mississippi River meanders 

through a belt 20-30 km wide defined by the traces and remnants of older meanders through 

which the river once flowed, is typical of most of the length of the lower river.

C

Where the Mississippi River meets the Gulf of Mexico, its delta has a complex history that has 

been described in classic papers by C.R. Kolb and J.R. Van Lopik (1958, 1966). The succession 

of different river channels and delta lobes during the last 5,000 years are numbered from oldest 

(1) to youngest (7) in Vignette C. Let John McPhee (1989, p. 5-6) recount the story:

"Southern Louisiana exists in its present form because the Mississippi River has jumped 

here and there within an arc about two hundred miles wide, like a pianist playing with one 

hand-frequently and radically changing course, surging over the left or the right bank to 

go off in utterly new directions. Always it is the river's purpose to get to the Gulf by the 

shortest and steepest gradient. As the mouth advances southward and the river lengthens, 

the gradient declines, the current slows, and sediment builds up the bed. Eventually, it 

builds up so much that the river spills to one side. Major shifts of that nature have tended 

to occur roughly once a millennium. The Mississippi's main channel of three thousand 

years ago is now the quiet water of Bayou Teche [3], which mimics the shape of the 

Mississippi......Eight hundred years before the birth of Christ, the channel was captured 

from the east [4]. It shifted abruptly and flowed in that direction for about a thousand 

years. In the second century A.D., it was captured again, and taken south, by the now 

unprepossessing Bayou Lafourche [5], which, by the year 1000, was losing its hegemony 

to the river's present course, through the region that would be known as Plaquemines [6, 

7]."

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Water Discharge

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Figure 5. -- The Mississippi River discharges an average of 520 cubic kilometers of water each year 

past the cities of Vicksburg and Natchez, Mississippi. This represents the greatest amount of water 

discharged by the river while it still is confined to a single channel, but it does not represent all water 

that the Mississippi River system discharges to the Gulf of Mexico. The river bifurcates 77 km below 

Natchez, and the lesser of its two main distributaries is joined by another significant tributary, the Red 

River. The two outlets of the Mississippi River eventually discharge a combined average of 580 cubic 

kilometers per year (or about 420 billion gallons per day) of freshwater to the Gulf of Mexico. This 

discharge ranks seventh in the world, being exceeded only by those of the Amazon, Congo (or Zaire), 

Orinoco, Yangtze, the combined Ganges-Brahmaputra, and Yenisey Rivers.

A

Not all parts of the Mississippi River drainage basin contribute water in equal measure. Nearly 

one-half the water discharged to the Gulf is contributed by the Ohio River and its tributaries 

(including the Tennessee) whose combined drainage areas constitute only one-sixth of the total 

area drained by the Mississippi. By contrast, the Missouri River drains 43 percent of the total area 

but contributes only 12 percent of the total water. As the Mississippi flows southward from its 

headwaters in the northern Midwest, its discharge is more than doubled by the waters it receives 

from the Illinois and Missouri Rivers. This combined discharge, in turn, is more than doubled 

again as it joins the waters of the Ohio River.

B

Just as the spatial distribution of sources of water in the Mississippi River is uneven, so is the 

temporal distribution of river flow. Shown here are the yearly flows of the Mississippi since 1930 

at Keokuk, Iowa, and since 1931 at Vicksburg, Mississippi. Keokuk is at the Iowa-Missouri State 

line, 235 and 270 km, respectively, up the Mississippi from its confluences with the Illinois and 

Missouri Rivers. Vicksburg is downriver of the mouth of the Arkansas River and upriver of the 

Atchafalaya diversion (see fig. 10B), and the discharges recorded at Vicksburg represent the 

largest and most integrated flows measured in the Mississippi River system. The two graphs are 

drawn so that the long-term mean discharges at the two stations are represented equally; although 

the mean discharges at the two stations differ by a factor of nine, the scales and ranges of 

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variability can be compared directly by simple visual inspection. Wet years and dry years at the 

two cities generally coincide. The range of flow variation is somewhat less extreme at Vicksburg 

than at Keokuk, which is a reflection of the damping influence of flows from the intervening 

large tributaries, especially the Illinois, Missouri, Ohio, and Arkansas Rivers. The ratio between 

the extreme maximum and minimum yearly discharges shown here (1973 compared to 1934) is 

5.5 at Keokuk but only 3.1 at Vicksburg.

C

Average seasonal differences in river discharge are on the same order as the extreme annual 

differences between wet and dry years. Shown here are mean monthly discharges at Keokuk and 

Vicksburg for the same periods of record as shown in B. In nearly all years along the length of 

the Mississippi River, mean discharges during the high-water months can be expected to be about 

three times the discharges during the low-water months. At Keokuk, spring runoff usually begins 

quickly, in response to the melting of ice on the river. At Vicksburg, the usually high flows from 

the Ohio River during the months of December through March give a more gradual beginning to 

the annual peak of spring runoff. 

Suspended-Sediment Discharge

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Figure 6. -- The Mississippi River now discharges an average of about 200 million metric tons of 

suspended sediment per year past Vicksburg and eventually to the Gulf of Mexico. This sediment 

discharge to the ocean ranks about sixth in the world today, being equaled or exceeded by those of four 

rivers of Asia (the Yellow and Yangtze Rivers of China, the Ganges-Brahmaputra of India and 

Bangladesh, and probably the Irrawaddy River of Burma) and two rivers of South America (the Amazon 

River of Brazil and possibly the Magdalena River of Colombia).

A

The suspended-sediment loads carried by the Mississippi River to the Gulf of Mexico have 

decreased by one-half since the Mississippi Valley was first settled by European colonists. This 

decrease has happened mostly since 1950, as the largest natural sources of sediment in the 

drainage basin were cut off from the Mississippi River main stem by the construction of large 

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reservoirs on the Missouri and Arkansas Rivers (see fig. 8). This large decrease in sediments 

from the western tributaries was counterbalanced somewhat by a five- to tenfold increase in 

sediment loads in the Ohio River-an increase that has resulted from deforestation and rowcrop 

farming. Further complicating the picture today is the controlled diversion of part of the water 

and sediment from the Mississippi River below Vicksburg into the Old River Outflow Channel 

and the Atchafalaya River (see fig. 10B). The average suspended-sediment discharges portrayed 

for 1980-90 are taken mainly from the extensive compilations of M.P. Keown and his colleagues 

(1981, 1986) and of R.S. Parker (1988).

B

Temporal variation of suspended-sediment discharge in the Mississippi River is more 

pronounced than that of water discharge (compare with fig. 5B). Shown here are the yearly totals 

of suspended sediment discharged past three long-term monitoring stations: Burlington, Iowa, 

335 km upriver of the confluence with the Missouri River; St. Louis, Missouri, 25 km downriver 

of the confluence with the Missouri River; Tarbert Landing, Mississippi, 13 km downriver of the 

Atchafalaya diversion at Old River. Sediment discharges shown for Burlington and Tarbert 

Landing are based on data of the U.S. Army Corps of Engineers (Rock Island and New Orleans 

Districts). Although records of sediment at all three stations began some years prior to 1959, only 

partial records are shown here to eliminate the confusion that might have been introduced by 

including pre-reservoir sediment discharges at St. Louis (see fig. 8) and pre-diversion sediment 

discharges at Tarbert Landing (see fig. 10B). The three graphs are drawn so that the long-term 

mean sediment discharges at all three stations are represented equally and the scales and ranges 

of variability may be compared by simple visual inspection. Years of high and low sediment 

discharges generally coincide at all three stations, but the range of year-to-year variation is more 

extreme in the upper river than in the lower river. The ratios between extreme maximum and 

minimum yearly suspended-sediment discharges for the periods of record shown here are 11.7 at 

Burlington, 9.2 at St. Louis, and only 2.8 at Tarbert Landing. Even during 1988 and 1989, when 

sediment discharges in the upper river were especially small, the Ohio River contributed enough 

sediment to damp the extremes of year-to-year variation at Tarbert Landing.

C

Average seasonal differences in river-sediment discharges are of the same order as extreme 

annual differences between wet and dry years in the Upper Mississippi, and they exceed the 

range of year-to-year differences in the Lower Mississippi. Shown here are the monthly average 

suspended-sediment discharges at Burlington, St. Louis, and Tarbert Landing for the same 

periods of record as shown in B. In the Upper Mississippi River (Burlington), average suspendedsediment discharges during the high-water months following ice breakup are nearly ten times 

greater than discharges during midwinter months when the river usually is covered with ice. In 

the Lower Mississippi (Tarbert Landing), the late winter-early spring runoff from the Ohio River 

contributes sediment during the months of December through March. Even with this temporal 

offset in tributary contributions, the maximum monthly sediment discharge (March) in the lower 

river averages five times greater than the minimum monthly discharge (September).

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Particle Sizes of Sediments

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Figure 7.-- Sediment particles in the Mississippi River range in size from the very finest clays or 

colloids to coarse sand and gravel. Different sizes of particles are found in suspension and on the river 

bed, and the interrelations between the sediments being transported in suspension and those stored or 

being transported along the riverbed are complex and variable. The finest particles play the largest role 

in the transport and storage of toxic contaminants.

A

In the freely flowing reaches of the Mississippi River downstream from St. Louis, part of the 

suspended-sediment load interacts with the channel bed and part of it is independent of any such 

interaction. The examples shown here are data collected from the Mississippi River at Thebes, 

Illinois, on June 10, 1989, and at Vicksburg, Mississippi, on March 27, 1989. The channel bed at 

these two sites (and through most of the 1850-km length of the Mississippi between St. Louis and 

the Gulf of Mexico) consists almost entirely of sand and fine gravel, with few particles, if any, 

finer than 0.063 mm (millimeter) in diameter. Some of the finest sand (mostly 0.125-0.25 mm) is 

mobilized from the channel bed to become part of the suspended sediment; hydraulic engineers 

refer to such sand in suspension as "bed-material load" because it usually represents an exchange 

of sand particles between the river waters and the beds over which they flow. Most of the 

sediment in suspension, however, is finer than sand. To aid in understanding the chemistry of the 

suspended matter, we have divided the fine suspended sediment into two fractions called "silt" 

and "colloid." The division between the two fractions is here defined arbitrarily at about 0.001 

mm. The relative volumes of silt and colloid shown in the figure represent the sizes of the 

individual particles after they have been disaggregated in the laboratory with a dispersing agent. 

In the river itself, most of the colloid-size particles are found in aggregates that are large enough 

to be transported and deposited as silt particles.

B

In the Upper Mississippi River, which has been dammed in order to form a series of lakes to 

provide depth sufficient for barge navigation (see fig. 10A), the sizes of the particles in both the 

bed sediments and suspended sediments are distributed differently from those in the 

unimpounded reaches of the lower river. The examples shown here are data collected from the 

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Mississippi River at Hastings, Minnesota, in the upper end of navigation Pool 3 on October 10, 

1991, and from the nonchannel areas of lower Pool 3 on October 11, 1991; and from the 

Mississippi River near Winfield, Missouri, at the upper end of Pool 26 on July 24, 1991, and 

from the nonchannel areas of lower-middle Pool 26 on November 1, 1991. In the navigation 

channels, the bed sediments consist largely of sand, as they do in the channels of the freely 

flowing lower river. Suspended sediments, however, consist almost entirely of silt and colloidal 

particles and contain very little sand except during floods. In the shallow nonchannel areas of the 

navigation pools, which cover the former flood plains of the upper river, the bed sediment is 

typically intermediate in size-finer than the bed material in the main channels but generally 

coarser than the bulk of the sediment in suspension.

Effects of Reservoirs

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Figure 8.-- Reservoirs reduce the sediment discharges of the Mississippi River and its tributaries by 

trapping sediment that otherwise would have been transported downriver.

A

The Missouri River has been the principal supplier of sediment to the Mississippi River since the 

end of the last ice age. The graphs show the annual discharges of suspended sediment measured 

by the U.S. Army Corps of Engineers and the USGS at three gaging stations on the Missouri 

River and two gaging stations on the Mississippi River over a period of about four decades. After 

five large dams were completed for hydroelectric power and irrigation above Yankton, South 

Dakota, between 1953 and 1963, the discharge of sediment from the Upper Missouri River Basin 

virtually was stopped. Following the closure of Fort Randall Dam and Gavins Point Dam in 

1953, downriver sediment discharges were diminished immediately, and the effect could be 

observed all the way down to the mouth of the Mississippi River. Sediment discharges to the 

Gulf of Mexico in 1992 were less than one-half of what they were before 1953.

B

In this downriver view (looking west-southwest) of Lake Cumberland, a reservoir on the 

Cumberland River in Kentucky, sediment-laden brown water can be seen flowing into the upper 

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end of the lake during late winter (February 28, 1988); the sediment gradually settles out to leave 

blue water farther down the lake.

C

Deltas form where rivers flow into reservoirs, especially if the inflowing rivers transport 

substantial amounts of sand. This large sand delta has formed where the Canadian River flows 

into Lake Eufala, a large reservoir in eastern Oklahoma near where the Canadian River joins the 

Arkansas River. The view is down Lake Eufala (looking east-northeast) in early spring (March 

25, 1988). 

Engineering Activities

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Figure 9. -- For more than 270 years, the banks and the channel of the Mississippi River have been 

engineered for various purposes: originally, starting about 1720, for flood control; eventually, starting 

about a century later, for navigation.

A

The Lower Mississippi River from Cairo, Illinois, to the Gulf of Mexico is constrained by a 

system of flood-control levees that is longer than the Great Wall of China. The Z-shaped levee in 

this photograph (view north) separates the active flood plain of the Mississippi River (left of 

levee) from intensively cultivated cropland in the fertile "Delta" region of Mississippi about 30 

km upriver of Vicksburg.

B

Dikes and wing dams are constructed to focus the main flow of the river into the navigation 

channels, and they encourage sediment to deposit in areas of the river that lie outside the 

navigation channels. These dikes have allowed sandbars to grow and stabilize into permanent 

islands along the right (western) bank of the Mississippi River about 10 km upriver of Cape 

Girardeau, Missouri. The sediment stored behind and between dikes such as these is virtually 

immobilized and is unlikely to be resuspended for transport downriver during the foreseeable 

future.

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C

Bank-protection measures are applied along most of the Mississippi to impede erosion and to 

maintain the shape of the navigation channel. Shown here is an articulated concrete mat that is 

laid like carpet on the riverbank by a special machine. Other banks along the Mississippi are 

stabilized by boulder-size rock fragments that are quarried from bluffs near the banks of the 

Upper Mississippi and brought downriver by barge. One effect of the bank stabilization is to 

prevent the remobilization of sediment previously deposited on the flood plains of the river.

D

Despite the controls on water flow and sedimentation that are provided by dikes and other 

engineering works, some reaches of the river require periodic dredging to maintain the depth of 

water necessary for navigation. In the Lower Mississippi, as shown in the photograph, the 

dredged material is frequently piped out to the fast flowing part of the river to be discharged. In 

the Upper Mississippi, where sand is frequently the material dredged, large spoil banks and 

artificial islands have been built alongside the main navigation channel. 

Major Engineering Works

(Click on image for a larger version, 83K)

Figure 10.-- The two most prominent examples of river engineering on the Mississippi are the lock-anddam system on the upper river and the Atchafalaya diversion on the lower river.

A

The entire 1080-km reach of the Upper Mississippi River between Minneapolis, Minnesota, and 

St. Louis, Missouri, is controlled for barge navigation by a series of 29 lock-and-dam structures 

(O'Brien and others, 1992). One of these structures-the first to be completed, in 1913, at Keokuk, 

Iowa-was built to impound water to generate hydroelectric power. The other 28 structures were 

built, mostly during the 1930s, to maintain a minimum river depth of 9 feet (2.7 meters) for barge 

navigation.

Before the dams were built, navigation during low-water periods was extremely hazardous, if not 

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impossible, across rapids such as those at Keokuk and Rock Island, and it was difficult in many 

other reaches of the upper river. The lower reaches of the navigation pools, such as the one 

shown in the photograph, are shallow lakes in which former flood plains, previously inundated 

for infrequent short periods, are now permanently under water. These shallow lakes are storage 

areas for fine-grained sediments and the contaminants adsorbed to them.

B

About 500 km upstream from its main outlet to the Gulf of Mexico, the Lower Mississippi River 

is partly diverted into the Atchafalaya River. About one-fourth, on average, of the water that 

flows down the Mississippi River past Vicksburg is diverted at a place called "Old River" to join 

the waters of the Red and Ouachita Rivers in forming the Atchafalaya River (McPhee, 1989). 

The diagram on the lower right is an excerpt of figure 5A that has been enlarged and rotated 90 

degrees so that the direction of flow is to the right. The accompanying photograph (view east, 

June 1991) shows the Mississippi River flowing from center left to upper right. In the foreground 

is the Old River Outflow Channel (flow west toward the viewer), an artificial channel that joins 

the Red River just off the lower edge of the photograph to form the Atchafalaya. Three artificial 

channels, each containing a control structure, divert water from the Mississippi River into the Old 

River Outflow Channel: (1) the original channel, in the center, contains the Old River Control 

Structure, completed in 1963; (2) the southernmost channel (upper right in photograph) contains 

the Old River Auxiliary Control Structure, completed in 1987; and (3) the northernmost channel 

(left center) contains a low-head hydroelectric power dam, completed in 1990 and having a rated 

capacity of 194 megawatts, which supplies electricity to communities in Louisiana.

REFERENCES

Keown, M.P., Dardeau, E.A., Jr., and Causey, E.M., 1981,

Characterization of the suspended-sediment regime and bed-material gradation of the Mississippi 

River Basin: U.S. Army Engineer Waterways Experiment Station Potamology Program (P-1) 

Report 1, 2 vols., 62 p., 7 app. 

___ 1986, 

Historic trends in the sediment flow regime of the Mississippi River: Water Resources Research, 

v. 22, no. 11, p. 1555-1564. 

Kolb, C.R., and Van Lopik, J.R., 1958,

Geology of the Mississippi River deltaic plain, southeastern Louisiana: U.S. Army Engineer 

Waterways Experiment Station Technical Report 3-483, 120 p. 

___ 1966,

Depositional environments of the Mississippi River deltaic plain-Southeastern Louisiana, in

Shirley, M.L., and Ragsdale, J.A., eds., Deltas in their geologic framework: Houston Geological 

Society, p. 17-61. 

McPhee, John, 1989, 

Atchafalaya, in The control of nature: New York, Farrar Straus Giroux, p. 3-92. 

O'Brien, W.P., Rathbun, M.Y., O'Bannon, Patrick, and Whitacre, Christine, 1992,

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Gateways to commerce-The U.S. Army Corps of Engineers' 9-foot channel project on the Upper 

Mississippi River: National Park Service, Rocky Mountain Region, 238 p. 

Parker, R.S., 1988, 

Uncertainties in defining the suspended sediment budget for large drainage basins, in Bordas, M.

P., and Walling, D.E., eds., Sediment budgets: International Association of Hydrological 

Sciences Publication 174, p. 523-532. 

Redfern, Ron, 1983,

Fluvial plain, in The making of a continent: New York, Times Books, p. 159-178. 

Saucier, R.T., 1991,

Geomorphology, stratigraphy, and chronology, inAutin, W.J., and others, Quaternary geology of 

the Lower Mississippi Valley, in Morrison, R.B., ed., Quaternary nonglacial geology: Geological 

Society of America, The Geology of North America, v. K-2, p. 550-564. 

Continue to ' Setting: Chemical character of the Mississippi River ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

http://water.er.usgs.gov/pubs/circ1133/geosetting.html 

Maintainer: h2o Webserver Team 

Last Modified: 1230 01 Oct 96 ghc 

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Chemical Character of the Mississippi River

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Setting: Chemical Character of the Mississippi 

River

John A. Moody and William A. Battaglin

Discharge of River Water

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Figure 11. -- To understand the chemical character of the Mississippi River, we first have to understand 

how the river is nourished by its tributaries. The effects of tributaries on river chemistry depend less on 

their absolute water discharges than on their relative contributions to the local water discharge of the 

Mississippi River. Tributaries whose discharges would hardly qualify them as significant contributors to 

the Lower Mississippi River are highly significant contributors of water, sediment, and contaminants to 

the Upper Mississippi River. In this graph are plotted the mean discharges of the Mississippi River for 

the period of record prior to 1989 (data from U.S. Army Corps of Engineers and USGS; for a somewhat 

different portrayal of the same data, see figure 5A). The mean water discharge in the Mississippi River 

at a site 8 km upstream from the Minneapolis city limits is 225 cubic meters per second (m3/s). Thirtytwo kilometers farther downstream, the average discharge is increased by about 50 percent as the 

Minnesota River joins the Mississippi in downtown Minneapolis. For the next 772 kilometers, the 

average water discharge of the Mississippi River increases slowly to about 1,810 m3/s at Keokuk, Iowa. 

Just upstream from St. Louis, Missouri, the contributions from the Illinois and Missouri Rivers more 

than double the mean water discharge to 5,140 m3/s. In a relatively short distance of 290 km 

downstream from St. Louis, the Ohio River again more than doubles the water discharge so that just 

downstream from the Mississippi-Ohio confluence the Lower Mississippi River discharge averages 

13,500 m3/s. The Lower Mississippi River is now transporting so much water that, in a relative sense, 

the White and Arkansas Rivers are the only major tributaries between the Ohio River and the Gulf of 

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Mexico. Their combined contribution is only about 10 percent of the Lower Mississippi River's 

discharge but this equals the discharge of the Upper Mississippi River at Keokuk, Iowa. Tributaries like 

the Hatchie River in Tennessee and the Big Black River in Mississippi have mean discharges similar to 

that of the Minnesota River but only contribute about 1 percent of the mean discharge of the Lower 

Mississippi River. Even though the Hatchie and Big Black Rivers contribute as much water as the 

Minnesota River, their local effects on the discharge of the Mississippi River are only about one-fiftieth 

of the local effect of the Minnesota River.

Dissolved Solids in River Waters

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Figure 12. -- The amount of dissolved chemicals or dissolved solids in river water depends on the 

solubility of the rocks and soil and the rainfall within a drainage basin. The map shows the dissolved 

solids (DS, in milligrams per liter, or mg/L) added to the Mississippi River by some of its tributaries; the 

median concentration of dissolved solids shown for each basin is the median value in water samples 

collected at the gaging station closest to the mouth of the tributary. The graph on the left side of the 

figure shows the variation of the median concentration of dissolved solids along the length of the 

Mississippi River for the period from 1970 through 1991. Triangles on the map show the locations of the 

gaging stations that are represented as dots on the graph. The median concentration of DS in the 

Mississippi River upstream from St. Paul, Minnesota, is about 170 mg/L. This increases sharply with the 

addition of water from the Minnesota River (median concentration is 550 mg/L)-a western tributary 

draining plains developed on fairly soluble sedimentary rocks in a region of relatively low mean annual 

precipitation (50-70 cm/yr; all precipitation figures are taken from U.S. Geological Survey, 1970, p. 97-

99). Downstream from the Minnesota River, the eastern tributaries (St. Croix, Chippewa, and Wisconsin 

Rivers) drain terranes varying from glacial gravel and sand deposits in the northeast to sandstone and 

limestone hills along the Mississippi River and receiving slightly greater precipitation (70-80 cm/yr). 

These tributaries contribute water with low DS concentrations (74 to 129 mg/L) which dilute the DS 

concentration in the Mississippi River below St. Paul, Minnesota. However, downstream from Clinton, 

Iowa, the Rock, Iowa, Des Moines, Illinois, and Missouri Rivers have median DS concentrations 

between 280 and 380 mg/L and thus increase the DS concentration of the Mississippi River in a series of 

steps, up to a maximum of 300 mg/L at Thebes, Illinois. These tributaries drain a predominantly 

agricultural region (with the exception of the Illinois River, which also drains the urban areas of 

Chicago, Peoria, and Springfield, Illinois) consisting of plains underlain by relatively soluble 

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sedimentary rocks and receiving a wider range of precipitation (40-100 cm/yr). The Ohio River drains 

mostly hilly and mountainous terranes composed of predominantly insoluble rocks that receive 

relatively high precipitation (100-130 cm/yr) resulting in a high discharge (7,750 m3/s) with a relatively 

low DS concentration (170 mg/L). When this large amount of Ohio River water mixes with the Upper 

Mississippi River water, the DS concentration in the Mississippi is reduced to about 220 mg/L. The 

concentration in the Mississippi River remains nearly constant at sites farther downstream to New 

Orleans because the eastern tributaries (like the Yazoo River) to the Lower Mississippi River drain the 

alluvial plain and adjacent uplands that receive the highest precipitation (130-150 cm/yr), contain low 

DS concentrations (53-75 mg/L), and discharge relatively small volumes of water into the Lower 

Mississippi River.

Hardness of River Waters

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Figure 13. -- Both natural and human-influenced sources contribute chemicals to the dissolved solids of 

the Mississippi River. The chemicals can be separated into two groups based upon their electrical 

charge. The major positively charged chemical ions (cations) are calcium, magnesium, sodium, and 

potassium, and the major negatively charged chemical ions (anions) are bicarbonate, chloride, sulfate, 

and nitrate. The hardness of water increases as more calcium and magnesium ions are dissolved by 

tributary water flowing over naturally occurring rock sources in each river basin. Hardness is reported as 

the equivalent concentration of calcium carbonate in milligrams per liter. The value of hardness shown 

in the map for each basin is the median value in water samples collected at the gaging station closest to 

the mouth of the tributary. The graph on the left side of the figure shows the variation of the median 

hardness along the length of the Mississippi River for the period from 1970 through 1991. The water in 

the Mississippi River upstream from St. Paul, Minnesota, is hard (median value is 151 mg/L), but the 

water becomes very hard when it mixes with the very hard water of the Minnesota River (median value 

is 419 mg/L). The waters of the St. Croix, Chippewa, and Wisconsin Rivers are soft to moderately hard 

(median values range from 59 to 98 mg/L), and these tributaries again effectively dilute, downstream 

from St. Paul, Minnesota, the concentration of calcium and magnesium ions that determine the water 

hardness. In a pattern similar to that for dissolved solids, tributary inflows from the Rock, Iowa, Des 

Moines, Illinois, and Missouri Rivers increase the hardness of the Mississippi River downstream from 

Clinton, Iowa, in a series of steps to a maximum hardness of 208 mg/L (very hard) at Thebes, Illinois, 

just upstream from the confluence of the Mississippi and Ohio Rivers. The Ohio River, which is 

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Chemical Character of the Mississippi River

moderately hard (117 mg/L), decreases the hardness of the Mississippi River from very hard to hard. 

The water remains hard (140-154 mg/L) at gaging stations between the Mississippi-Ohio River 

confluence and New Orleans, Louisiana.

Nitrate in River Waters

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Figure 14. -- A wide range of human activities adds chemicals to rivers. The use of common salt, 

sodium chloride, to deice highways has contributed to the chloride concentration in rivers. Burning 

fossil fuels creates sulfur compounds that are major sources of sulfate for river water (Hem and others, 

1990). In fact, the contribution of sulfur to rivers from anthropogenic sources may now be about onehalf as much as from natural sources (Berner, 1971). Spreading fertilizers consisting of phosphate, 

nitrite, and nitrate compounds on cropland eventually adds to the total concentration of these chemicals 

in rivers as do other human activities such as the disposal of sewage effluents from metropolitan areas. 

Wastes from livestock production also add nitrogen compounds. The pattern of nitrate and nitrite 

concentration in the Mississippi River differs from the pattern for dissolved solids and hardness. The 

figure shows the combined nitrate and nitrite concentration (predominantly nitrate) in milligrams of 

nitrogen per liter. The value of nitrate and nitrite shown on the map for each basin is the median value in 

samples collected at the gaging station closest to the mouth of the tributary. The graph on the left side of 

the figure shows the variation of the median nitrate and nitrite concentrations along the length of the 

Mississippi River for the period from 1970 through 1991. Upstream from St. Paul, Minnesota, the 

median concentration of nitrate plus nitrite is 0.16 mg/L but then steadily increases step by step with 

each downstream addition of water from the Minnesota (2.8 mg/L), Rock (2.9 mg/L), Iowa (5.5 mg/L), 

Des Moines (3.7 mg/L), and Illinois (3.5 mg/L) Rivers. At Alton, Illinois, just upstream from the 

Mississippi-Missouri confluence near St. Louis, Missouri, the median concentration of nitrate and nitrite 

in the Mississippi River reaches a maximum of 2.6 mg/L. Downstream from Alton, the Missouri (1.1 mg/

L) and Ohio Rivers (1.0 mg/L) successively dilute the nitrate and nitrite concentration so that it remains 

nearly constant at about 1.4 mg/L at gaging stations in the Lower Mississippi River. Although maximum 

concentrations for the Mississippi River have never exceeded the maximum contaminant level for 

drinking water of 10 mg/L, concentrations in several of the tributaries (Minnesota, Iowa, and Des 

Moines Rivers) in heavily farmed regions have exceeded the maximum contaminant level on occasion. 

Further details of nitrate and nitrite are discussed in the chapter, "Nutrients in the Mississippi River."

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Population Stress

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Figure 15. -- The concentrations of contaminants in the water represent stresses on the river system that 

depend upon the human population within a tributary basin and the capacity (as measured by the mean 

discharge) of the Mississippi River and its tributaries to reduce the concentration of contaminants by 

dilution. The population stress has been computed for 23 gaging stations in tributary basins and for 14 

gaging stations on the Mississippi River as the ratio of the human population upstream from the gaging 

station to the mean discharge (in cubic meters per second) at each gaging station. The populations 

upstream from the gaging stations on the Mississippi River were taken from the 1990 census (U.S. 

Bureau of the Census, 1990). The mean water discharge is based on the period of record prior to 1989. 

The graph on the left side of the figure shows the variation of the population stress along the length of 

the Mississippi River. The dense population of St. Paul and Minneapolis, Minnesota, (about 3.2 million 

people) and the small water discharge (310 m3/s) combine to create a high population stress of about 

10,000 people per cubic meter per second. This initial high population stress decreases as each 

downstream tributary adds more water to the Mississippi River, until at Keokuk, Iowa, it reaches a 

minimum of 4,600 people per cubic meter per second. It increases near St. Louis, Missouri, along the 

reach of the river downstream from the mouth of the Illinois River, which has the highest population 

stress of the tributary basins (14,600 people per cubic meter per second), caused by the population of the 

Chicago metropolitan area. Another increase on the main stem occurs along the reach of the river 

between Baton Rouge and New Orleans, Louisiana. The population stress suggests that within and 

downstream from these three reaches of the Mississippi River (Minneapolis-St. Paul, St. Louis, and 

Baton Rouge-New Orleans), one should expect increases in anthropogenic contaminants. The chapters 

that follow contain numerous examples of such increases.

REFERENCES

Ackermann, W.C., Harmeson, R.H., and Sinclair, R.A., 1970,

Some long-term trends in water quality of rivers and lakes: EOS American Geophysical Union 

Transactions, v. 51, p. 516-522. 

Berner, R.A., 1971,

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Worldwide sulfur pollution of rivers: Journal of Geophysical Research, v. 76, p. 6597-6600. 

Hem, J.D., 1985,

Study and interpretation of the chemical characteristics of natural water (3d ed.): U.S. Geological 

Survey Water-Supply Paper 2254, 263 p. 

Hem, J.D., Demayo, Adrian, and Smith, R.A., 1990,

Hydrogeochemistry of rivers and lakes, in Wolman, M.G., and Riggs, H.C., eds., Surface water 

hydrology: Geological Society of America, The Geology of North America, v. O-1, p. 189-231. 

Livingstone, D.A., 1963,

Data of geochemistry-Chemical composition of rivers and lakes (6th ed.): U.S. Geological 

Survey Professional Paper 440-G, 64 p. 

U.S. Army Corps of Engineers, 1988-90,

Stages and discharges of the Mississippi River and tributaries-Annual reports of the District 

Engineers as follows: 1988, New Orleans District; 1989, Vicksburg District; 1990, Memphis 

District. 

U.S. Bureau of the Census, 1990, 

Census of population and housing, 1990: Washington, D.C., U.S. Department of Commerce, 

Data Users Service Division. 

U.S. Geological Survey, 1970, 

The national atlas of the United States of America: Washington, D.C., U.S. Geological Survey, 

417 p. 

Continue to ' Sampling the big rivers ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

http://water.er.usgs.gov/pubs/circ1133/chemsetting.html 

Maintainer: h2o Webserver Team 

Last Modified: 1230 01 Oct 96 ghc 

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Contaminants in the Mississippi River--Sampling the Big Rivers

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Sampling the Big Rivers

Robert H. Meade, John A. Moody, and Herbert H. Stevens, Jr.

History of the Study: 1987-92

This study of the Mississippi River and its tributaries began in 1987 when a group of scientists in the U.

S. Geological Survey (USGS) joined forces to pursue some of the intriguing research questions 

concerning the transport and storage of contaminants in large rivers. The assemblage of researchers 

included hydrologists, chemists, physicists, sedimentologists, and geologists who collectively had 

enough aggregate expertise to begin a study of the continent's largest river. At least three research 

questions piqued the collective interests of the group and were amenable to a multidisciplinary 

approach: (1) How are contaminants partitioned between the dissolved and adsorbed phases-that is, does 

the contaminant travel in the river in true solution (as salt is dissolved in sea water) or does it travel 

piggyback, adsorbed onto the particles of sediment that are suspended in the river? (2) How do 

contaminants, dissolved or adsorbed, mix at large river confluences? (3) How are sediments and their 

adsorbed contaminants stored and remobilized in big rivers? In addition to the research results of these 

questions, a principal outcome of the study was an assessment of the status of selected contaminants in 

the Mississippi River. In the course of pursuing research goals in a riverwide context, making repeated 

sampling trips at different seasons of the year, a body of information inevitably accumulated that could 

shed new light on the levels of many contaminants in the river. This assessment, rather than the original 

research goals, is the subject of the present report.

Research Vessel

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Figure 16. -- A program to sample a river as large as the Mississippi (specifically, a total length of 2,800 

river kilometers between the uppermost station near Minneapolis/St. Paul and the lowermost station 

below New Orleans) is best carried out aboard a ship that can serve simultaneously as sampling 

platform, laboratory, and dormitory. The ship that filled all these functions was Research Vessel (R/V) 

Acadiana, owned and operated by the Louisiana Universities Marine Consortium. Acadiana is 17 meters 

long, 5.5 meters wide, and has a shallow enough draft (1.2 meters) to operate in most parts of the 

Mississippi River and in many of its major tributaries. In the configuration shown here, Acadiana has 

two onboard laboratories and bunk space for seven scientists plus a crew of two. 

During the first 3 years of the study, July 1987 to June 1990, seven research and sampling cruises were 

made aboard the research vessel, Acadiana. Sampling usually began at Winfield, Missouri, 100 

kilometers upstream from St. Louis and 30 and 70 kilometers, respectively, upstream from the 

confluences of the Mississippi with the Illinois and Missouri Rivers. Downriver from Winfield, the 

primary strategy was to sample the Mississippi main stem and several of the major tributaries (Illinois, 

Missouri, Ohio, White, Arkansas, and Yazoo Rivers) in a downstream sequence, trying to follow 

approximately the same mass of water downriver. Although we did not always succeed in following the 

same mass of water, we usually were able to observe the changes that occurred in the water after the 

Mississippi had received inflows from the major tributaries or after the water and its load of sediment 

and contaminants had traveled several hundred kilometers downstream. The initial phases of the study 

were focused on the Lower Mississippi River, downriver of the navigational locks and dams, because of 

the availability of new techniques for sampling the freely flowing waters of large rivers and because of 

our initial reluctance to deal with the extra complexity of the transport and deposition of contaminants in 

a river that was impounded by a series of large dams.

All this was to change during 1990. During the second half of 1988, after the first three of our sampling 

cruises had been completed, the Greenpeace ship Beluga conducted a well-publicized trip along the 

Illinois and Mississippi Rivers and, in December 1989, Greenpeace released its report, "We All Live 

Downstream: The Mississippi River and the National Toxics Crisis". In January 1990, the USGS was 

contacted by the office of then Senator Rudy Boschwitz of Minnesota, who asked the USGS to extend 

its existing study into the Upper Mississippi River, especially into the reach of the river between St. 

Louis and The Twin Cities of Minneapolis and St. Paul, and produce a report summarizing our results. 

Soon thereafter, members of Congress from other States along the Mississippi-Arkansas, Illinois, Iowa, 

Louisiana, Missouri, Tennessee, Wisconsin-joined Senator Boschwitz in his request.

The response to this request was a change in the goals of our program from mainly research to mainly 

assessment, and an expansion of the scope of the program to include the much different hydrologic 

setting of the upper river. This expansion required an augmentation of the primary strategy for sampling 

the contaminants carried by the flowing waters to include a second strategy for sampling the 

contaminants that were stored with the sediment deposited on the bottoms of the navigation pools of the 

Upper Mississippi.

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Sampled Sites

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Figure 17. -- The flowing waters of the Mississippi River and its principal tributaries were sampled 

repeatedly at critical sites during our studies.

A

During 1987-90, our studies focused on the lower and middle reaches of the Mississippi Riverfrom the vicinity of its confluences with the Illinois and Missouri Rivers to a point a few 

kilometers below New Orleans.

B

During 1991-92, the emphasis shifted to the Upper Mississippi River, while the sampling of the 

Lower Mississippi was continued at a reduced number of sites. Furthermore, time-series samples 

were collected at three sites on the Mississippi River and at three sites on major tributaries. 

Sampling the Flowing Waters

The flowing waters of the big rivers are sampled to measure the contaminants transported in solution as 

well as the contaminants adsorbed onto the sediment particles suspended in the water. To measure a 

dissolved contaminant being transported by the river, one needs to know: (1) the water discharge 

(expressed as the number of cubic meters of water that flows by a point along the river each second); 

and (2) the concentration of the contaminant (expressed as the number of grams per cubic meter of 

water). By multiplying discharge times concentration, one obtains what is called "load," or the number 

of grams of dissolved contaminant flowing downriver each second. To measure a contaminant adsorbed 

on suspended sediment, one needs to know: (1) the water discharge; (2) the concentration of suspended 

sediment (expressed as the number of kilograms per cubic meter of water); and (3) the concentration of 

the adsorbed contaminant (expressed as grams of contaminant per kilogram of suspended sediment). The 

load of adsorbed contaminant (grams per second or tons per day) is the product of water discharge times 

suspended-sediment concentration times contaminant concentration.

Two principal methods were used to collect water samples for determining concentrations and loads. 

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Both methods take into consideration that the velocity of flow and the concentrations of suspended 

sediment and even dissolved matter are not distributed uniformly across the widths of large rivers. Flow 

velocities usually are greatest at the river surface in midstream and they decrease toward the bottom and 

banks of the river. Sediment concentrations usually are greatest near the river bottom and smallest at the 

river surface. After large tributaries enter the Mississippi, their waters may not mix thoroughly for 100-

200 km downstream. Were it not for these inhomogeneities, one simply could dip a bottle or bucket into 

the middle of the flowing river, analyze the water collected, and multiply the concentrations times the 

discharge to calculate the loads. Indeed, this simple method has been used around the world for many 

years to sample the chemical compositions of rivers large and small. But the results of this sampling 

approach cannot be evaluated for their accuracy because the point at the centroid of water flow and the 

point where the contaminant concentration is the representative average of a river cross section are 

seldom obvious, unless extensive sets of detailed measurements have been collected beforehand.

Our standard method of collecting representative amounts of river water for the analysis of contaminant 

loads samples the full depth and width of the river. By this method, a sampler is lowered to the bottom 

of the river and raised back to the surface, collecting water through the full depth of the river, at a 

number of locations spaced equidistantly across the river from bank to bank. The resulting sample is 

called a depth-integrated composite. The sampler is designed to admit water at the velocity at which it is 

flowing in the river, and the sampler travels to the bottom and back at the same vertical speed each time. 

It collects the most water where the river flows fastest and deepest, and the least water where the river 

flows slowest and shallowest; the resulting sample is thereby weighted for water discharge. This method 

has been the standard for many years for sampling smaller rivers. Scaling it up for larger rivers such as 

the Mississippi is simple in principle but has proven more complicated in actual practice. Working from 

a moving ship in flowing water requires microwave positioning equipment or some other means of 

finding and maintaining the appropriate locations for collecting samples in a cross section of the river. A 

specially designed hydraulic winch and a sampler consisting of an initially collapsed Teflon bag inside a 

plastic bottle are required to collect the fast and deep waters of the Mississippi. Deploying the navigation 

equipment, positioning the ship, and collecting a representative sample in sufficient volume for all the 

required analyses usually kept the ship's crew and half a dozen scientists busy for the better part of a day 

at most of our sampling cross sections.

Sampling Flowing Waters

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Figure 18. -- Obtaining representative samples of the flowing waters of the Mississippi River and its 

larger tributaries required special procedures and equipment, some of which are illustrated here.

A

In a typical cross section of the Mississippi River, representative amounts of water were 

collected, through the full river depth from the surface to the bottom, at locations spaced at 

approximately equal intervals across the river. All the water collected at the locations across the 

river was combined into a single composite sample. At many cross sections, two separate 

composites (shown here as red and yellow) were collected so comparisons could be made to 

assess the precision of the sampling procedure.

B

Sampling from a freely moving vessel in a large river requires a precise means of determining the 

location and motion of the vessel. Microwave positioning equipment served that purpose. Shown 

in the photograph is one of several remote units that were placed at known positions on the 

riverbanks at or near the sampling sites. Aboard the vessel (not shown in the photograph) was a 

master microwave unit that measured the distances from the remote units and thereby determined 

the relative position of the vessel.

C

The array of equipment for measuring water velocity and for sampling the flowing waters and 

suspended sediment consisted of, from top to bottom,

(1) a current meter, similar in design to the familiar anemometer that is commonly used to 

measure windspeed,

(2) a sampling bottle, containing a collapsed Teflon bag (shown here partly filled) that expanded 

as it received the incoming sample, and fitted in front with an isokinetic nozzle that was designed 

to admit water and suspended sediment in proportion to the velocity at which they were moving 

in the river, and

(3) a sounding weight of either 150, 200, or 300 pounds-depending on how fast and deep were 

the waters being sampled.

The hydraulic winch that was used to lower and raise the sampling array is not shown in the 

photograph.

Sampling Navigation Pools

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Figure 19. -- The contaminants adsorbed to the sediments deposited in the backwater areas of the 

navigation pools of the Upper Mississippi River were sampled to obtain representative average 

concentrations for each pool.

A

The Upper Mississippi River between Minneapolis/St. Paul and St. Louis is segmented by 26 

principal navigation pools.

B

A "typical" pool (Pool 8, in this example) consists of three parts: an upper section, characterized 

by riverine channels and emergent flood plains; a middle section, characterized by numerous 

islands, parts of which are deltaic in origin but most of which are the elevated areas of the flood 

plains that flanked the river channels before the pool was inundated; a lower section, 

characterized by a shallow expanse of open water.

C

Sampling was concentrated in the lower sections of the pools (Pool 8 is again the example)-

outside the main navigation channel-because this is where fine-grained sediments and their 

adsorbed contaminants are most likely to be stored. Samples were collected at 15-20 locations 

per pool (shown here as three linear rows of white dots), which was sufficient to obtain a 

representative average, without seeking either "hotspots" or pristine areas.

Representative small amounts of the depth-integrated composite were taken for the analysis of such 

things as herbicides, surfactants, dissolved heavy metals, and suspended sediment. The bulk of the depthintegrated sample was passed first through a centrifuge and then through an ultrafiltration apparatus to 

separate most of the water from the suspended sediment in preparation for chemical analysis for 

adsorbed heavy metals and other inorganic constituents. Every gram of suspended sediment that was 

recovered this way required processing from 5 to 100 liters of river water: 5 to 10 liters in most places in 

the Lower Mississippi where sediment concentrations are moderate to large; 50 to 100 liters of water in 

some places in the Upper Mississippi (downriver of Lake Pepin, especially) where concentrations are 

very small.

Our second principal method for collecting the flowing waters was by pumping them directly out of the 

river. Because the analyses for some of the adsorbed contaminants required larger quantities of 

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suspended sediment than we were able to recover by depth-integrated sampling, we adopted the more 

expedient method of pumping water from the river, usually from a depth halfway between the surface 

and bottom. The pumping method collected 5 to 10 times the amount of water that could be collected in 

the same time by the depth-integrated sampling. Consequently, 5 to 10 times the amount of suspended 

sediment could be recovered, making it increasingly possible to measure many of the industrial and 

other contaminants that are difficult to detect on small quantities of sediment. The quantities of water 

pumped in the different parts of the channel were proportional to the water discharges there. The 

disadvantage of the pumping method is that it does not sample the full depth of the river. However, 

because depth-integrated samples were being collected at the same time at the same locations, 

comparative studies were made to show that, for the suspended particles with which contaminants are 

preferentially associated, the pumped sample was accurately representative of what was being 

transported in the full depth of the river. A typical pumped sample was somewhere between 500 and 

1,000 liters (one-half ton to a ton, that is) of river water, which required 6 to 10 hours to collect and 

many more hours of shipboard processing to separate all the water from the suspended sediment.

Despite its disadvantages, a secondary method of dipping bottles into the surfaces of the rivers was used 

to obtain some samples. This sampling method was used most consistently in the tributaries of the Upper 

Mississippi River that were too shallow to be navigated by R/V Acadiana and had to be sampled from a 

small boat. The procedure consisted simply of dipping bottles into the tributaries near their estimated 

centroids of water discharge. The concentrations of contaminants in these surface-dipped samples are 

useful for computing approximate downriver loads, so long as the contaminant is transported in solution 

and the river waters being sampled are well mixed from top to bottom and from bank to bank. In other 

circumstances, the concentrations of surface-dipped samples may be more indicative than definitive.

Sampling Bed Sediments

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Figure 20. -- The sediments and their adsorbed contaminants on the bottoms of the navigational pools of 

the Upper Mississippi River were sampled by fairly traditional means.

A and B

The shallow backwater areas of most of the navigation pools were sampled from a small boat. 

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Sampling equipment consisted of a clamshell grab (midboat) and gravity corer (forward). Also 

measured were current velocity (aft) and the position of the boat (microwave unit atop the pole).

C

In the deeper pools such as Pool 19 (shown here) or Lake Pepin, bottom-sediment samples were 

collected directly from Research Vessel Acadiana.

D

From the sediment recovered in the clamshell grab, separate subsamples were taken for the 

analysis of organic constituents such as PCBs and coprostanol. Samples for heavy-metal analysis 

were taken separately with a plastic gravity corer so as to avoid any error caused by the 

introduction of extraneous metal from the sampling equipment itself.

Sampling the Stored Sediments in the Pools of the Upper River

The Upper Mississippi River between St. Louis and Minneapolis/St. Paul is controlled, mostly for 

navigation, by a series of 29 locks and dams, and its hydrologic characteristics are markedly different 

from those of the freely flowing middle and lower river between St. Louis and the Gulf of Mexico. Each 

dam between Minneapolis and St. Louis artificially deepens, widens, and slows the river above it, 

allowing sediment to settle in the pool that forms behind the dam. These pools form a series of small 

lakes that trap and store some of the sediment and adsorbed contaminants that are being transported 

downriver. How much of the incoming contaminant load is stored in one of these pools, or for how long, 

depends on a number of things: the size and shape of the pool, how often the pool is flushed by large 

floods, and whether the contaminant in question is transported in solution or is adsorbed onto sediment 

particles. In general, the contaminants most likely to remain in storage are those adsorbed onto sediment 

particles that have been deposited in the backwater areas of large pools.

The contaminants adsorbed onto the sediments stored in the pools of the Upper Mississippi River were 

sampled by conventional means. A clamshell grab and a small plastic corer were used to collect samples 

of the uppermost 10 cm of the silt or mud that lay on the bottom at 15 to 20 places in the shallow or 

backwater areas of the navigation pools. In only the two largest pools, Lake Pepin and Pool 19, were the 

waters sufficiently deep to allow the bed samples to be collected directly from Acadiana. In the 

remainder of the pools, samples were collected over the side of a 14-foot-long boat. The locations in the 

pools where the samples were collected were fixed by their distances (determined by microwavedistancing equipment) and bearings from objects or landmarks whose positions were known. Sampling 

the stored bed sediments of a pool took four people most of a day. Equal quantities of each of the 15 to 

20 grab samples collected in each pool were combined into a single batch sample for analysis of organic 

compounds such as PCBs and sewage contaminants such as coprostanol. Core samples were kept 

separate for individual analyses for heavy metals.

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Sampling the Length of the River

A third major strategy employed in this study was longitudinal sampling along the center line of the 

river. This was an opportunistic strategy that exploited the long traverse that Acadiana had to make at 

the beginning of each sampling cruise from her home port near New Orleans, Louisiana, to the farthest 

upriver point where the regular downriver sampling was begun (Winfield, Missouri, or Minneapolis, 

Minnesota). On the upriver traverse, the vessel took 10-11 days to reach Minneapolis, depending on the 

strength of the river currents. So as not to waste this opportunity to sample the river continually along its 

full length, a strategy was devised whereby the vessel was slowed down sufficiently every 10 miles or so 

to collect samples of water from about a meter below the river surface. Samples usually were taken in 

the middle of the river, but, where the waters were not well mixed (below major tributary confluences, 

for example), samples were collected at several points across the river. This procedure would not have 

been valid for sampling constituents associated with sediment particles, but it provided unique 

information on the spatial and temporal distributions of such compounds as herbicides and dissolved 

sewage contaminants.

Time-Series Sampling at Fixed Locations

A limited number of contaminants were sampled at fairly frequent intervals, usually once or twice a 

week, for limited periods at fixed stations on the Mississippi River and some of its tributaries. The 

specific contaminants that were sampled in this manner were herbicides and nutrients, for which the 

Mississippi River main stem was sampled at Clinton, Iowa, Thebes, Illinois, and Baton Rouge, 

Louisiana. Tributaries sampled in this manner were the Illinois, Missouri, and Ohio Rivers.

Further Information

More detailed accounts of the procedures used to sample the Mississippi River are given in the 

following reports.

Leenheer, J.A., Meade, R.H., Taylor, H.E., and Pereira, W.E., 1989,

Sampling, fractionation, and dewatering of suspended sediment from the Mississippi River for 

geochemical and trace-contaminant analysis, in Mallard, G.E., and Ragone, S.E., eds., U.S. 

Geological Survey Toxic Substances Technical Meeting, Phoenix, Arizona: U.S. Geological 

Survey Water-Resources Investigations Report 88-4220, p. 501-511. 

Meade, R.H., and Stevens, H.H., Jr., 1990,

Strategies and equipment for sampling suspended sediment and associated toxic chemicals in 

large rivers-with emphasis on the Mississippi River: The Science of the Total Environment, v. 

97/98, p. 125-135. 

Moody, J.A., 1993,

Evaluation of the Lagrangian scheme for sampling the Mississippi River during 1987-90: U.S. 

Geological Survey Water-Resources Investigations Report 93-4042, 31 p. 

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___ ed., 1995,

Chemical data for water samples collected during four upriver cruises on the Mississippi River 

between New Orleans, Louisiana, and Minneapolis, Minnesota, May 1990-April 1992: U.S. 

Geological Survey Open-File Report 94-523, 297 p. 

___ ed., 1995,

Hydrologic, sedimentologic, and chemical data describing surficial bed sediments in the 

navigation pools of the Upper Mississippi River, July 1991-April 1992: U.S. Geological Survey 

Open-File Report 95-708. 

Moody, J.A., and Meade, R.H., 1992,

Hydrologic and sedimentologic data collected during three cruises at low water on the 

Mississippi River and some of its tributaries, July 1987 through June 1988: U.S. Geological 

Survey Open-File Report 91-485, 143 p. 

___ 1993,

Hydrologic and sedimentologic data collected during four cruises at high water on the 

Mississippi River and some of its tributaries, March 1989 through June 1990: U.S. Geological 

Survey Open-File Report 92-651, 227 p. 

___ 1994,

Evaluation of the method of collecting suspended sediment from large rivers by dischargeweighted pumping and separating it by continuous-flow centrifugation: Hydrological Processes, 

v. 8, p. 513-530. 

___ 1995,

Hydrologic and sedimentologic data collected during three cruises on the Mississippi River and 

some of its tributaries from Minneapolis, Minnesota, to New Orleans, Louisiana, July 1991-May 

1992: U.S. Geological Survey Open-File Report 94-474, 159 p. 

Moody, J.A., and Troutman, B.M., 1992, 

Evaluation of the depth-integration method of measuring water discharge in large rivers: Journal 

of Hydrology (Amsterdam), v. 135, p. 201-236. 

Rees, T.F., Leenheer, J.A., and Ranville, J.F., 1991,

Use of a single-bowl continuous-flow centrifuge for dewatering suspended sediments-Effect on 

sediment physical and chemical characteristics: Hydrological Processes, v. 5, p. 201-214.

Continue to ' Heavy metals in the Mississippi River ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

http://water.er.usgs.gov/pubs/circ1133/big-sample.html 

Maintainer: h2o Webserver Team 

Last Modified: 1230 01 Oct 96 ghc 

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Contaminants in the Mississippi River--Heavy Metals in the Mississippi River

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Heavy Metals in the Mississippi River

John R. Garbarino, Heidi C. Hayes, David A. Roth, Ronald C. Antweiler, 

Terry I. Brinton, and Howard E. Taylor

Introduction

Metals in the Mississippi River come from natural as well as artificial sources. Metals that are naturally introduced into the river come primarily from 

such sources as rock weathering, soil erosion, or the dissolution of water-soluble salts. Naturally occurring metals move through aquatic environments 

independently of human activities, usually without any detrimental effects. However, as the valleys of the Mississippi River and its tributaries were 

settled and industrialized, the metals added by human activities have affected the water quality of the Mississippi River and ultimately the Gulf of 

Mexico. Some of these metals are essential for proper metabolism in all living organisms yet toxic at high concentrations; other metals currently thought 

of as non-essential are toxic even at relatively low concentrations.

Sources and Sinks of Heavy Metals

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Figure 21.--Heavy metals are released to the Mississippi River from numerous sources. Typical sources are municipal wastewater-treatment plants, 

manufacturing industries, mining, and rural agricultural cultivation and fertilization. Heavy metals are transported as either dissolved species in water or 

as an integral part of suspended sediments. Heavy metals may be volatilized to the atmosphere or stored in riverbed sediments. Toxic heavy metals are 

taken up by organisms; the metals dissolved in water have the greatest potential of causing the most deleterious effects. 

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Health Significance of Metals in the Environment

The metallic elements can be categorized into two groups. The heavy metals are those having densities five times greater than water, and the light metals, 

those having lesser densities. Well-known examples of heavy metallic elements are iron, lead, and copper. Examples of light metals are sodium, 

magnesium, and potassium. Humans consume metallic elements through both water and food. Some metals such as sodium, potassium, magnesium, 

calcium, and iron are found in living tissue and are essential to human life-biological anomalies arise when they are depleted or removed. Probably less 

well known is that currently no less than six other heavy metals including molybdenum, manganese, cobalt, copper, and zinc, have been linked to human 

growth, development, achievement, and reproduction (Vahrenkamp, 1979; Friberg and others, 1979). Even these metals, however, can become toxic or 

aesthetically undesirable when their concentrations are too great. Several heavy metals, like cadmium, lead, and mercury, are highly toxic at relatively 

low concentrations, can accumulate in body tissues over long periods of time, and are nonessential for human health. Table 1 lists metals according to 

their toxicities.

No specific health guidelines for heavy metals associated with suspended or bed sediments have been established by the U.S. Environmental Protection 

Agency. This lack of national guidelines based on concise scientific criteria causes difficulty when evaluating the environmental effects of heavy metals 

in sediments. Several different criteria have been defined, primarily on the basis of observed effects on aquatic life (Lyman and others, 1987). Table 2 

(page 57) lists criteria for open-water disposal of polluted sediments that can be used for comparison purposes.

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Sources of Metals in the Mississippi River

Heavy metals in the Mississippi River originate from either natural processes or human activities. Natural erosion and weathering of crustal materials 

take place over long periods of time and the amount of heavy metals released is small. However, the potential for contamination is increased when 

mining exposes metal-bearing ores. When compared to the natural exposure of ore bodies through erosion, the exposure rate through mining is over ten 

times faster for lead and zinc (Massachusetts Institute of Technology, 1970). Leaching of mine tailings and drainage from mined areas can introduce 

substantial amounts of metals into the river.

Two of the largest lead-zinc mining areas in the world are located along the Mississippi River. The reach of the Mississippi River between Prairie du 

Chien, Wisconsin, and Galena, Illinois, passes through the Upper Mississippi Valley lead-zinc district of southwest Wisconsin, northwest Illinois, and 

northeast Iowa. The New Lead Belt lies in southeast Missouri adjacent to the Mississippi River downriver of St. Louis, Missouri.

Lead in River Waters and Sediments

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Figure 22. --Like most of the heavy metals in the Mississippi River, lead is transported largely in association with the suspended sediments. The areas of 

the dots and pie diagrams on the left side of the figure are proportional to the quantities of lead that were being transported down the Mississippi River at 

12 sites sampled during July-August 1991; the dots and pie diagrams on the right side of the figure show the inputs from four main tributaries (complete 

tabulations of the data are given by Hayes, 1993). The lead loads transported by suspended sediment, both silt and colloid, were larger than the dissolved 

loads because lead is a strongly "hydrophobic" element-that is, it adsorbs onto sediment particles more readily than remaining in solution by a factor of 

thousands to one. The suspended silt loads are greater than the colloidal loads because the river transports much more silt than colloid. The quantities of 

colloid in suspension, for example, were so low at the two most downstream sites sampled during this trip that not enough could be collected for 

chemical analysis.

Both the silt and colloid fractions were analyzed further to determine in detail how the lead is associated with the sediments. More than one-half the lead 

in the sediment phases is designated "inorganic," which means that it is an inorganic salt or a component of the iron and manganese hydroxides that coat 

the surfaces of the sediment particles. The second largest percentage of the lead is called "residual," meaning lead sulfide (galena) or other minerals that 

contain lead. Usually less than 10 percent of the lead is associated with organic material in the suspended sediment. The blank pie diagrams for St. 

Anthony Falls and Hastings indicate that there was not enough material to obtain the distribution of lead in the suspended colloid. However, enough 

colloid was available to determine the total amount of lead present and therefore calculate the corresponding load.

Cadmium is distributed in suspended sediment in much the same way as lead, with the largest proportion being inorganic. Chromium and copper, on the 

other hand, have much greater residual than inorganic components.

Mercury in River Waters and Sediments

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Figure 23. -- The transport of mercury in the Mississippi River differs from that of lead in three important respects. First, there is considerably less 

mercury than lead in the river; notice the difference in the scales between this and the preceding figure. Second, a greater proportion of mercury is 

transported in the dissolved phase. Third, most of the mercury in the sediment phases is residual, most likely as mercury sulfides, and the remainder is 

associated with the organic matter in suspension. The dots and pie diagrams in the figure represent samples collected during the downriver cruise of 

October-November 1991 at 12 sites on the Mississippi River (left) and in 4 major tributaries (right). Complete tabulations of the data are given by Roth 

(1994). The percentage of mercury in the organic phase of the silt increased downriver of Thebes. Toxicological implications of this increase are strong 

because the human body absorbs organic forms of mercury 14 times more readily than inorganic forms (Task Group on Metal Accumulation, 1973). 

Mercury concentrations in both silts and colloids at Trempealeau, Lock & Dam 9, and Keokuk were not determined; therefore, loads could not be 

calculated.

Major sources of toxic metals arising from human activities are domestic and industrial wastewaters and their associated solid wastes. On the average, the 

USEPA estimates that 81 percent of the metals introduced into wastewater treatment plants comes from various regulated industries that dispose of their 

wastes into municipal sewer systems and that about 19 percent comes from consumer households in the form of common household products (U.S. 

Environmental Protection Agency, 1986). Cadmium, chromium, copper, lead, and mercury are used extensively in industries along the Mississippi River 

(table 3,}. The two main by-products of municipal treatment plants are solid wastes and treated wastewater. In the most common form of treatment, 70 to 

90 percent of cadmium, chromium, copper, lead, and zinc are removed as solid wastes (Lester, 1983). The other 10 to 30 percent of these heavy metals 

remain dissolved in the water that is released back into the river. The concentration and transport of several heavy metals in treated effluent from a 

wastewater- treatment plant are shown in table 4 . Note that, in undiluted wastewater, the concentrations of cadmium, chromium, copper, and mercury 

exceed USEPA aquatic life standards, and concentrations of cadmium, chromium, lead, and mercury exceed the USEPA drinking water standards listed 

in table 2. The solid waste or sewage sludge is commonly disposed in landfills or sold as fertilizer. Heavy metals can be released through leaching of 

sewage sludge in landfills. Sewage sludge also contains plant nutrients and compares favorably to other fertilizers in crop production. The amount of 

sewage sludge that can be applied to cropland is regulated by the USEPA and depends on the concentration of heavy metals in the sludge and the soil 

chemistry of the cropland. Some toxic heavy metals, especially cadmium, have been found at elevated concentrations in corn kernels harvested from soils 

fertilized with sewage sludge (Kiemnec and others, 1990).

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Rural cropland and pasture land abound along the Mississippi River and its tributaries. Soil cultivation accounts for at least 90 percent of the soil erosion 

in the more humid areas of the United States, and it increases the amount of sediment introduced into the streams and rivers (McElroy and others, 1975). 

Millions of tons of fertilizers and pesticides are applied to croplands every year. Cultivated soils can become enriched with toxic metals associated with 

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these applications. Although the concentrations may vary between specific formulations, many of these fertilizers contain chromium, copper, iron, 

manganese, nickel, and zinc. Selected pesticides use heavy metals such as mercury as an integral component. During the late spring and early summer, 

after fertilizers and pesticides have been applied, the runoff from rain flushes these contaminants into the Mississippi River. For example, the uranium 

concentration in the Mississippi River is 20 times that found in the Amazon River, a result linked to the specific use of phosphate fertilizers (Spalding 

and Sackett, 1972).

The atmosphere is also a source of metal contamination to aquatic environments. Metal-containing particulates that are washed from the atmosphere by 

rain and snow are deposited in drainage basins and find their way into lakes and rivers. As of 1973, the total nationwide airborne particulate emissions 

were distributed basically among three sources: 51 percent from industrial processes, 29 percent from fossil-fuel combustion, and 20 percent from 

miscellaneous burning practices (Magee and others, 1973). Since 1973, vehicle emissions (and perhaps other emissions as well) have decreased. Stone 

and rock crushing, iron and steel foundries, grain-handling operations, and cement production emit the greatest percentage of the particulates. Coal, used 

extensively for power generation, often contains significant concentrations of metals such as vanadium, copper, nickel, chromium, zinc, lanthanum, 

cobalt, molybdenum, gallium, germanium, tin, and mercury (Magee and others, 1973). Automobile fuels have historically contained lead additives for 

valve lubrication, but their usage is slowly being phased out.

Lead in Silts and Colloids

(Click on image for a larger version, 66K)

Figure 24. -- Concentrations of lead in suspended sediments are greater and more variable in the Upper Mississippi than in the Lower Mississippi River. 

Lead concentrations shown in these graphs are the totals of inorganic, organic, and residual (see fig. 22). Complete data are tabulated by Hayes (1993).

A

Lead concentration in colloidal sediments is generally greater than or equal to the concentration in silts. Data shown in this graph are from 

suspended sediments collected during the down-river cruise of July-August 1991. Lead concentrations in colloids decrease markedly downriver; 

concentrations in silts also decrease downriver, but less markedly. Concentrations of lead at some sites in the uppermost river exceed the guideline 

of 60 micrograms per gram (ug/g) for heavily polluted sediments. Cadmium, chromium, and copper concentrations were similar to those of lead in 

that they were greater in the colloidal fraction, decreased downriver, and reached a fairly constant level downriver of Winfield, Missouri. 

Suspended sediment was heavily polluted with chromium and copper at 75 percent of all the locations sampled on the Mississippi River main 

stem.

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B

The variability of concentrations of lead in suspended silts in the Mississippi River main stem decreases markedly downriver. Shown in this graph 

are the concentrations of lead in suspended silts collected during the three downriver cruises of July-August 1991, October-November 1991, and 

April-May 1992. Concentrations in the upper river differed seasonally by factors of two or more; those in the lower river registered seasonal 

differences of only 10 to 15 percent. The greater variability in the upper river probably reflects a diversity of sediment sources and the 

impoundment of sediment behind the navigation dams. The downriver increase in the uniformity of the concentration probably reflects the 

progressive homogenization of the suspended sediment by repeated episodes of deposition and resuspension. The concentrations of 27 to 34 ug/g 

that were measured during 1991-92 in the lowest reaches of the Mississippi River are similar to the 32 3 ug/g measured by Trefry and others 

(1985) in samples collected there during 1982-83.

Range of Lead Dissolved in River Waters Range of Lead Dissolved in River Waters

(Click on image for a larger version, 50K)

Figure 25. -- None of the concentrations of dissolved heavy metals that were measured in the Mississippi River during 1987-92 exceeded the USEPA 

standards for drinking water or the standards for aquatic life. Shown in the graph are the concentrations of dissolved lead measured in depth-integrated 

composite samples collected during 1987-92 between Minneapolis and New Orleans (complete tabulations of the data are given by Brinton and others, 

1995, and Garbarino and others, 1995). All the concentrations shown here were less than the drinking-water standard by a factor of at least 100. More 

than one-half of the samples collected had dissolved lead concentrations too small to be measured; in the fraction given at the lower end of each bar, the 

denominator is the total number of samples analyzed from that site, and the numerator is the number of analyses in which the concentration of lead was 

less than the detection limit of 0.06 ug/L. The principal tributaries sampled generally contained metal concentrations greater than the main stem 

Mississippi River. However, these concentrations decreased downstream from the confluences through simple dilution, precipitation, or adsorption onto 

sediments. The concentrations of heavy metals are controlled by the volume of the flow of the Mississippi River and are greater during the late fall and 

winter when freezing temperatures decrease river flow and sediment concentrations than in the spring and early summer when runoff is high. Some 

fluctuations in concentrations can be attributed to seasonal releases of metals from specific sources.

The Fate of Metals in the Mississippi River

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The numerous studies of the heavy-metal water quality of the Mississippi River that have been conducted over the last several decades have emphasized 

mostly the water quality in specific regions of either the lower reaches of the river (Everett 1971; Hartung, 1974; Presley and Trefry, 1980; Shiller and 

Boyle, 1983; Newchurch and Kahwa, 1984; Trefry and others, 1986) or the upper reaches of the river (Eisenreich and others, 1980; Water Quality Work 

Group of the Great River Environmental Action Team, 1980a, 1980b; Bailey and Rada, 1984; Buhl and McConville, 1984; Wiener and others, 1984). 

The water quality of the Mississippi River at selected locations has also been reported (Briggs and Ficke, 1978; DeLeon and others, 1986; Smith and 

others, 1987; Costner and Thornton, 1989; Taylor and others, 1990). However, our study assesses the heavy-metal contamination through the full length 

of the Mississippi River from Minneapolis, Minnesota, to the Gulf of Mexico. Over the 5-year assess ment period, the effects of seasonal variation and 

changes in the river flow rate could be evaluated. The water and sediment samples were collected by the same group of scientists during the entire study 

using proven sampling protocols. In addition, all samples were analyzed by one group of scientists in a single laboratory using state-of-the-art 

instrumentation and meth odology. Heavy metals released into the Mississippi River, by both natural processes and human activities, can be distributed 

among several different forms within the water environment as shown in figures 22 and 23. Metals can be either transported with the water and 

suspended sediment or stored within the riverbed bottom sediments. Heavy metals are transported as (1) dissolved species in the water, (2) suspended 

insoluble chemical solids, or (3) components of the sus pended natural sediments. Metals dissolved in the water can exist as hydrated metal ions or as 

aqueous metal complexes with other organic or inorganic constituents. Water-insoluble inorganic (non-carbon-containing, except for car bonates) 

chemical solids such as metal hydroxides may be formed, as may organic (carbon-containing) chemical solids, such as those associated with compounds 

derived from the decay of living organisms. Both inorganic and organic solids can be transported with the water as individual entities or as chemical 

coatings on sus pended sediments. In addition, mineral components of suspended sediments themselves can contain heavy metals. Heavy-metal solids 

can also be stored in river-bottom sediments. Suspended sediments and metallic chemical solids are stored in riverbed sediment after they aggregate to 

form large, denser-than-water particles that settle from the water when the river's flow is not sufficient to keep them in suspension.

Uranium and Copper Dissolved in River Waters

(Click on image for a larger version, 83K)

Figure 26. -- Although they are well within drinking-water standards, concentrations and loads of dissolved heavy metals in the Mississippi River give 

clues to their sources. The data for dissolved uranium and dissolved copper shown here were collected during the downriver sampling cruise of AprilMay 1992. Represented in the figure are depth-integrated composite samples of the flowing main stem (circles) and four tributaries (the Minnesota, 

Illinois, Missouri, and Ohio Rivers: squares and bars), areally composited samples of backwaters in the navigation pools (triangles), and samples of water 

dipped from surfaces of tributaries other than the four listed above (squares and bars). The complete data are tabulated by Garbarino and others (1995). 

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A

Uranium dissolved in the Mississippi River comes, in large part, from phosphate fertilizers applied to croplands. Uranium occurs naturally in 

phosphate rock that is mined for fertilizer. Rain falling on fertilized croplands washes some uranium-containing fertilizer from the fields into 

streams and rivers. Concentrations of dissolved uranium are greatest in the Upper Mississippi River. Tributaries like the Minnesota and Des 

Moines Rivers, which drain areas that are farmed intensively for corn and other grains, have high concentrations of dissolved uranium that 

increase the concentrations in the Mississippi River downstream from their confluences. 

B

Copper dissolved in the Mississippi River comes mostly from industrial and municipal wastewaters. Concentrations of dissolved copper generally 

increase in the downriver direction, especially near urban centers. Some tributaries carry greater concentrations of copper than the main stem 

Mississippi, but their influences on main stem concentrations seem to be minimal. 

C

The transport of dissolved uranium downriver depends on water discharge as well as on the concentration of the element in solution. Transports 

usually are greater during high-flow periods such as spring runoff (shown here) than during periods of lower flow. For example, the transport of 

dissolved uranium measured at Vicksburg during the spring sampling trip shown here was twice the transport measured at the same site the 

previous November--even though the dissolved concentrations were virtually the same. During the sampling trip shown here, the Mississippi 

River was receiving high loads of dissolved uranium from the Minnesota and Des Moines Rivers (because of their high concentrations) and from 

the Missouri and Ohio Rivers (because of their high water discharges). The abrupt decrease in uranium transport near river kilometer 500 

represents the Old River Outflow where about one-fourth of the flow of the Mississippi River is diverted into the Atchafalaya River. 

D

The transport of dissolved copper in the Mississippi River, like that of dissolved uranium, varies directly with the water discharge. The most 

significant increases in the transport of dissolved copper occur at the confluences of the Mississippi with the Missouri and Ohio Rivers. 

Mercury Dissolved in River Waters

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Figure 27. -- Mercury dissolved in the Mississippi River is derived (like copper) from municipal and industrial sources. The distribution of dissolved 

mercury in the Mississippi can be shown in more detail than that of other heavy metals (such as uranium and copper, shown in the previous figure) 

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because samples were collected specifically for mercury analyses during upriver transects. Shown in the graph are the concentrations of dissolved 

inorganic mercury in samples collected from the river surface at 15- to 20-kilometer intervals between New Orleans and Minneapolis during the upriver 

cruise of September 25-October 4, 1991 (a complete tabulation of the data is given by Roth, 1994). The line in the graph represents the average of the 

concentrations of each three adjacent samples (that is, a 3-point moving average) over 45- to 60-kilometer reaches of the river. Mercury concentrations 

were lowest in the upper reaches and gradually increased downriver. Large concentrations were measured downstream from tributaries such as the Des 

Moines, Illinois, and Missouri Rivers and near large metropolitan and industrial centers, specifically St. Louis, Missouri, Vicksburg, Mississippi, and 

below Baton Rouge, Louisiana. Farther downstream from each of these inputs, the concentration of dissolved mercury appears to have decreased; these 

decreases may be due to transformations of inorganic mercury to organic forms or to its adsorption onto sediment rather than to a decrease in the overall 

concentration of mercury in the river.

The different chemical forms of heavy metals in the river influence their availability and toxicity to organisms. Heavy metals are readily available to 

aquatic organisms and pose a significant health hazard when they are present as dissolved inorganic or organic species in the water or loosely adsorbed to 

particulate surfaces. When heavy metals are present as components of particulates, such as inorganic metal-hydroxide coatings or metal-organic 

compounds, some chemical alterations are required before they can be released and become biologically available. Even stronger chemical reactions are 

required to release heavy metals that are integral parts of the minerals composing river sediments.

The water chemistry of the Mississippi River, the aqueous chemistry of individual heavy metals, the type and surface area of the particulates present in 

the Mississippi River, and other hydrologic factors control where the metals will be found. The water chemistry is controlled by many complex factors 

such as water acidity and the type and concentration of the major inorganic compounds, organic compounds, and suspended sediment. Many of these 

factors are also influenced by seasonal variation in river flow and temperature, and the decomposition of vegetation. The Mississippi River, like the 

majority of natural waters in the United States, can be described as having bicarbonate-type water because bicarbonates, especially calcium bicarbonate, 

predominate as the dissolved salt (Water Quality Work Group of the Great River Environmental Action Team, 1980b). Bicarbonate water is slightly 

alkaline rather than acidic. An aqueous solution of baking soda is a good example of an alka-line solution, whereas orange juice is an acidic solution. The 

major fraction of heavy metals released into alkaline natural waters becomes associated with either the suspended particulates or the bed sediments. This 

association reduces or eliminates dissolved heavy metals, which are usually the most toxic form. For example, dissolved lead and zinc compounds from 

mine wastes tend to be adsorbed onto natural silt and clay sediments or organic matter, rather than staying dissolved in the water of the Mississippi River 

(Jennett and others, 1973). In contrast, most of the light metals tend to remain as dissolved species in the water.

Heavy-Metal Water Quality of the Mississippi River

The brief glimpse at the heavy metals in the Mississippi River described in this chapter generally was based on data collected during the summer and 

autumn of 1991 and the spring of 1992. Data that were collected in the Lower Mississippi River during 1987-90 (Brinton and others, 1995) reinforce the 

findings presented here. Concentrations of toxic heavy metals dissolved in the water in the 2,900 km reach of the Mississippi River from Minneapolis, 

Minnesota, to Belle Chasse, Louisiana, are well below USEPA guidelines for drinking water and water that supports aquatic life. However, heavy metals 

associated with suspended sediments exceeded the pollution guidelines at many of the main-stem sampling locations. Heavy-metal concentrations in the 

suspended sediments were generally greater in the small colloidal-sized particles than the larger silt-sized particles. Even though the colloids compose a 

significantly lower percentage of the total suspended sediment, their heavy-metal concentrations are greater, and they are small enough to pass through 

some of the filtering systems used in water-treatment facilities. Sediments stored in pools upstream from every lock and dam of the Upper Mississippi 

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River also have elevated heavy-metal concentrations. The biological accessibility to heavy metals associated with suspended and stored sediment also 

depends on the chemical form in which the metal exists. A high percentage of the heavy metals in all the sediment sizes exist in chemical forms that can 

be dissolved if appropriate conditions driven by chemical or biological processes are present.

Concentrations of dissolved heavy metals and those associated with suspended sediment vary seasonally. Dissolved heavy-metal concentrations are 

generally greater during periods when the river flow is low, during droughts and winter months, because the decrease in water volume decreases dilution 

effects and the decrease in suspended sediment concentrations decreases metal-scavenging processes. Conversely, the increases in river flow during the 

warmer months either dilute heavy metal concentrations with greater volumes of water or decrease dissolved metal concentrations through increased 

scavenging processes resulting from higher suspended-sediment concentrations. As a result, heavy-metal transport on suspended sediment increases 

during high-flow periods. Wastewater treatment, agricultural practices, and mining activities all influence the water quality. Crop fertilization 

periodically introduces specific heavy metals into the hydrologic system after spring applications and spring runoff. Discharges from wastewatertreatment facilities and industrial manufacturing activities cause increases in heavy-metal concentrations near major urban areas.

Whether the loads and concentrations of heavy metals in the Mississippi River have increased or decreased in recent years is difficult to determine. 

Although most of the heavy metals in the river are associated with sediment, most of the previous studies have focused on the dissolved metals. Even for 

the dissolved metals, comparisons are difficult to draw between earlier and more recent data because analytical laboratory techniques have become 

markedly more sensitive in the last decade and field sampling techniques have not been adequately standardized. Specific conclusions about increases or 

decreases in heavy metals with time in the Mississippi River are tenuous at best.

Metals Dissolved in River Waters

(Click on image for a larger version, 33K)

Figure 28. -- Statistical analysis of dissolved heavy-metal concentrations measured at all main-stem locations of the Mississippi River during the JulyAugust 1991, October-November 1991, and April-May 1992 cruises indicate that cadmium, chromium, copper, lead, and uranium varied little with 

season. Of 36 samples collected during this period only one cadmium concentration was greater than the detection limit of 0.1 ug/L. In 11 of the 36 

samples, concentrations of chromium were less than the detection limit of 0.2 ug/L. In 20 of the 36 samples, lead concentrations were less than the 

detection limit of 0.06 ug/L. Dissolved mercury was less than the detection limit of 0.004 ug/L in 15 of the 36 samples. All the samples contained 

measurable concentrations of copper and uranium.

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Lead and Mercury in Bed Sediments

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Figure 29. -- The bed sediments stored in the nonchannel (backwater) areas of the navigation pools of the Upper Mississippi River contain substantial 

quantities of heavy metals. However, the concentrations of lead and mercury in these bed sediments are generally less than those measured in the 

suspended sediments in transport; and, in the case of lead, the concentrations usually are less than the criterion value of 40 ug/g for moderately polluted 

sediment. Data used in this figure are the concentrations measured in a composite sample derived from 15-20 bed samples collected from the lower 

reaches of each navigation pool. The difference between lead and mercury concentrations measured in the bed sediments and in suspended sediments is 

mostly due to the differences in sediment particle size. Bed sediment samples were composed of a wide variety of particle sizes that ranged from coarse 

sand to colloid (see fig. 7B), markedly different than the suspended sediment. In addition, bed sediment samples were not separated into individual 

particle-size fractions prior to analysis, as was the case for suspended sediment, but rather were analyzed as a whole. As a result, the heavy-metal 

concentrations measured in the bed sediments would be expected to be lower because of the presence of less metal-laden sand particles. Complete data 

are tabulated in the reports by Hayes (1993) and Roth and others (1995).

A

The distribution of bed-sediment particle sizes in navigation pools of the Upper Mississippi River depends on factors such as pool size and 

configuration. More than 80 percent of the bed sediment collected from Lake Pepin, Pool 9, Pool 12, Pool 13, and Pool 26 was composed of silt 

and colloid particles (shown here as percent finer than 63 micrometers); more than 70 percent of the sediment collected in Pools 2, 3, 11, and 19 

was silt and colloid. 

B

The bed sediments collected from the rest of the pools contained significantly lower percentages of silt and colloid. In bed sediments collected 

from 25 navigation pools of the Upper Mississippi River between July 1991 and April 1992, the greatest concentrations of lead were in Lake 

Pepin, Pool 12, Pool 19, and Pool 26. Lake Pepin, a large and narrow natural lake, is known to trap large proportions of the suspended sediment 

that the Mississippi River delivers to it from the north. Pool 12 receives inflow from the Galena River, which drains a lead and zinc mining 

district. Lead leaching from the lead mines has an affinity for sediment. However, the relation of the high lead concentration in Pool 12 to the 

nearby mining district has not been confirmed. The high lead concentrations could simply be a result of the large proportion of fine bed-sediment 

material present in the pool. Pool 19 is the largest of the artificial pools, not as large as Lake Pepin, but more likely than the other smaller pools to 

trap and retain sediments and their associated contaminants. Elevated lead concentrations in the bed sediment of Pool 26 suggest a link to the 

input of lead-laden sediment from the Illinois River. Grab samples of the bed sediment collected from the Illinois River near Hardin, Illinois, 

contained 25 ug/g of lead, or about twice the concentration found in the bed sediments from Pool 25. Cadmium, chromium, copper, nickel, and 

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zinc followed nearly the same trend as lead, with bed-sediment concentration maximums at Lake Pepin, Pool 12, Pool 19, and Pool 26. Only bed 

sediments from Lake Pepin, and possibly from Pool 12, can be described as moderately polluted in lead. In most pools, approximately 50 percent 

of the lead in the bed sediment was associated with the inorganic component, 40 percent with the residual component, and 10 percent with the 

organic component. The greatest proportions of the inorganic component were found where the lead concentrations were highest. Therefore, most 

of the lead in the pool bed-sediment environment may be readily accessible and could be released if the proper conditions existed. Other heavy 

metals-cadmium, chromium, and copper-had their greatest percentages in the residual component. Except for cadmium, the proportions of heavy 

metals designated as inorganic, organic, and residual were similar to those in the main-stem suspended sediments. The concentrations shown in 

the figure are similar to earlier data collected by Bailey and Rada (1984), who reported the following average concentrations of lead in bed 

sediments: 40 ug/g in Lake Pepin, 13 ug/g in Pool 5, and 14 ug/g in Pool 9.

C and D

Mercury concentrations in pool bed sediments of the Upper Mississippi River can be correlated to the organic carbon content of the sediments. 

Mercury concentrations in the bed sediments of most pools, except for Lake Pepin, were not large enough to cause adverse toxicological effects. 

Bed-sediment mercury concentrations in Lake Pepin exceeded 0.18 ug/g, a level that has been shown to increase the mortality rates in fish 

embryos, eggs, and larvae (Birge and others, 1977). Mercury can bioaccumulate in many aquatic organisms, especially fish, by direct ingestion of 

suspended or bed- sediment particles. High organic-carbon concentrations in the presence of mercury in the bed sediments increase the 

methylation rate of mercury and subsequently increase the absorption and retention of mercury in fish and human tissues. Lake Pepin, Pools 2, 3, 

12, 19, and 26 are the most likely areas in which this might occur because of the high percent organic carbon in their bed sediments.

REFERENCES

Bailey, P.A., and Rada, R.G., 1984,

Distribution and enrichment of trace metals (Cd, Cr, Cu, Ni, Pb, Zn) in bottom sediments of navigation Pools 4 (Lake Pepin), 5, and 9 of the 

Upper Mississippi River, in Wiener, J.G., Anderson, R.V., and McConville, D.R., eds., Contaminants in the Upper Mississippi River: Boston, 

Butterworth Publishers, p. 119-138. 

Birge, W.J., Black, J.A., Westerman, A.G., Francis, P.C., and Hudson, J.E., 1977,

Embryopathic effects of waterborne and sediment-accumulated cadmium, mercury, and zinc on reproduction and survival of fish and amphibian 

populations in Kentucky: U.S. Department of the Interior, Research Report 100, Washington, D.C., 28 p. 

Boyer, H.A., 1984,

Trace elements in the water, sediments, and fish of the Upper Mississippi River, Twin Cities metropolitan area, in Wiener, J.G., Anderson, R.V., 

and McConville, D.R., eds., Contaminants in the Upper Mississippi River: Boston, Butterworth Publishers, p. 195-230. 

Briggs, J.C., and Ficke, J.F., 1978, 

Quality of rivers of the United States, 1975 water year: U.S. Geological Survey Open-File Report 78-200, 436 p. 

Brinton, T.I., Garbarino, J.R., Peart, D.B., Taylor, H.E., and Antweiler, R.C., 1995,

Concentration and transport data for dissolved inorganic constituents in water collected during seven cruises on the Mississippi River and some of 

its tributaries, July 1987-June 1990: U.S. Geological Survey Open-File Report 94-524, 102 p. 

Buhl, K.J., and McConville, D.R., 1984, 

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Heavy metal accumulation in selected sessile components of Fountain City Bay, Pool 5A, of the Upper Mississippi River, in Wiener, J.G., 

Anderson, R.V., and McConville, D.R., eds., Contaminants in the Upper Mississippi River: Boston, Butterworth Publishers, p. 171-194. 

Costner, Pat, and Thornton, Joe, 1989,

We all live downstream-The Mississippi River and the national toxics crisis: Washington, D.C., Greenpeace USA, 120 p., l app. (61 p.). 

Dean, J.G., Bosqui, F.L., and Lanouette, V.H., 1972, Removing heavy metals from waste water: Environmental Science and Technology, v. 6, p. 518-

522. DeLeon, I.R., Byrne, C.J., Peuler, E.A., Antoine, S.R., Schaeffer, Jeffrey, and Murphy, R.C., 1986, 

Trace organic and heavy metal pollutants in the Mississippi River: Chemosphere, v. 15, no. 6, p. 795-805. 

Eisenreich, S.J., Hoffmann, M.R., Rastetter, D., Yost, E., and Maier, W.J., 1980,

Metal transport phases in the upper Mississippi River, in Kavanaugh, M.C., and Leckie, J.O., eds., Particulates in water: American Chemical 

Society, Advances in Chemistry Series No. 180, p. 135-176. 

Everett, D.E., 1971,

Hydrologic and quality characteristics of the lower Mississippi River: Louisiana Department of Public Works Technical Report 5, 48 p. 

Friberg, L., Nordberg, G.F., and Vouk, V.B., eds., 1979,

Handbook on the toxicology of metals: Amsterdam, Elsevier/North-Holland Biomedical Press, 709 p. 

Garbarino, J.R., Antweiler, R.C., Brinton, T.I., Roth, D.A., and Taylor, H.E., 1995, 

Concentration and transport data for selected dissolved inorganic constituents and dissolved organic carbon in water collected from the 

Mississippi River and some of its tributaries, July 1991-May 1992: U.S. Geological Survey Open-File Report 95-149, 149 p. 

Great Lakes Water Quality Board, Dredging Subcommittee, 1982,

Guidelines and register for evaluation of Great Lakes dredging projects: International Joint Commission, Great Lakes Regional Office, 365 p. 

Hartung, R., 1974,

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Ecosystems: Ottawa, National Research Council of Canada, p. 93-98. 

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Metal associations in suspended sediments and bed sediments from the Mississippi River: Golden, Colorado School of Mines, Department of 

Chemistry and Geochemistry, M.S. thesis, 131 p. 

Jennett, J.C., Wixson, B.G., Bolter, E., and Gale, N., 1973,

Transport mechanisms of lead industry wastes, in Proceedings of Industrial Waste Conference, 28th, Purdue University: Boston, Butterworth 

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Significance and behavior of heavy metals in waste water treatment processesÑsewage treatment and effluent discharge: The Science of the Total 

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Lyman, W.J., Glazer, A.E., Ong, J.H., and Coons, S.F., 1987,

An overview of sediment quality in the United States: U.S. Environmental Protection Agency, Monitoring and Data Support Division, Office of 

Water Regulations and Standards, Contract No. 68-01-6951, Task 20, 111 p., 3 app. 

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Man's impact on the global environment-Report of the study of critical environmental problems: Cambridge, Massachusetts Institute of 

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Water pollution from non-point sources: Water Research, v. 9, p. 675-681. 

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Presley, B.J., and Trefry, J.H., III, 1980,

Heavy metal inputs to Mississippi delta sediments-A historical view: Water, Air, and Soil Pollution, v. 13, no. 4, p. 481-494. 

Roth, D.A., 1994,

Ultratrace analysis of mercury and its distribution in some natural waters in the United States: Fort Collins, Colorado State University, 

Department of Chemistry, Ph.D. dissertation, 309 p. 

Roth, D.A., Garbarino, J.R., and Taylor, H.E., 1995,

Major and trace elements, in Moody, J.A., ed., Chemical data for water samples collected during four upriver cruises on the Mississippi River 

between New Orleans, Louisiana, and Minneapolis, Minnesota, May 1990-April 1992: U.S. Geological Survey Open-File Report 94-523, p. 127-

209. 

Roth, D.A., Hayes, H.C., Antweiler, R.C., Brinton, T.I., Garbarino, J.R., Peart, D.B., and Taylor, H.E., 1995,

Major and trace elements, and nutrients, in Moody, J.A., ed., Hydrologic, sedimentologic, and chemical data describing surficial bed sediments 

and water in the navigation pools of the Upper Mississippi River, July 1991- April 1992: U.S. Geological Survey Open-File Report 95-708. 

Shiller, A.M., and Boyle, Edward, 1983, 

Trace metals in the plume of the Mississippi River [abs.]: EOS American Geophysical Union Transactions, v. 64, p. 1021. 

Smith, R.A., Alexander, R.B., and Wolman, M.G., 1987,

Water-quality trends in the Nation's rivers: Science, v. 235, p. 1607-1615. 

Spalding, R.F., and Sackett, W.M., 1972,

Uranium in runoff from the Gulf of Mexico distributive province: anomalous concentrations: Science, v. 175, p. 629-631. 

Task Group on Metal Accumulation, 1973,

Accumulation of toxic metals with special reference to their absorption, excretion, and biological half-times: Environmental Physiology and 

Biochemistry, v. 3, p. 65-107. 

Taylor, H.E., Garbarino, J.R., and Brinton, T.I., 1990,

The occurrence and distribution of trace metals in the Mississippi River and its tributaries: The Science of the Total Environment, v. 97/98, p. 369-

384. 

Taylor, H.E., and Shiller, A.M., 1995, 

Mississippi River methods comparison study-Implications for water quality monitoring of dissolved trace elements: Environmental Science and 

Technology, v. 29, p. 1313-1317. 

Taylor, H.E., Shiller, A.M., Garbarino, J.R., and Brinton, T.I., 1995, 

Intercomparison experiments on dissolved trace-metal data from the Mississippi River and some of its tributaries, 1989-90: U.S. Geological 

Survey Open-File Report 93-628, 28 p. 

Trefry, J.H., III, Metz, S., and Trocine, R.P., 1985, 

A decline in lead transport by the Mississippi River: Science, v. 230, p. 439-441. 

Trefry, J.H., III, Nelson, T.A., Tocine, R.P., Metz, S., and Vetter, T.W., 1986,

Trace metal fluxes through the Mississippi River delta system, in Kullenberg, G., ed., Contaminant fluxes through the coastal zone: Rapports et 

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Proces-Verbaux des Reunions, Conseil International pour I'Exploration de la Mer, v. 186, p. 277-288. 

U.S. Environmental Protection Agency, 1982,

Maximum contaminant levels (subpart B of part 141, National interim primary water regulations): U.S. Code of Federal Regulations, Title 40, 

Parts 100 to 149, revised as of July 1, 1982, p. 315-318. 

___ 1986, 

Report to Congress-Discharge of hazardous wastes to publicly owned treatment plants, (530/SW-86-004): Environmental Protection Agency, 

February 28, 1986. 

___ 1992,

Drinking water regulations and health advisories: U.S. Environmental Protection Agency, Office of Water, unpublished. 

Vahrenkamp, H., 1979

, Metalle in Lebensprozessen: Chemie in Unserer Zeit, v. 7, p. 97-105. Water Quality Work Group of the Great River Environmental Action 

Team, 1980a, Water quality, sediment & erosion: GREAT I, Study of the Upper Mississippi River, v. 4, 125 p., 2 app. 

___ 1980b, 

Water quality work group appendix: GREAT II, Study of the Upper Mississippi River (Guttenberg, Iowa, to Saverton, Missouri), 216 p. 

Wiener, J.G., Jackson, G.A., May, T.W., and Cole, B.P., 1984,

Longitudinal distribution of trace elements (As, Cd, Cr, Hg, Pb, and Se) in fishes and sediments in the Upper Mississippi River, in Wiener, J.G., 

Anderson, R.V., and McConville, D.R., eds., Contaminants in the Upper Mississippi River: Boston, Butterworth Publishers, p. 139-170. 

Wood, J.M., 1974,

Biological cycles for toxic elements in the environment: Science, v. 183, p. 1049-1052.

Continue to ' Nutrients in the Mississippi River ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

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Contaminants in the Mississippi River--Nutrients in the Mississippi River

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Nutrients in the Mississippi River

By Ronald C. Antweiler, Donald A. Goolsby, and Howard E. 

Taylor

Nutrients are chemical elements and compounds in the environment from which living things synthesize 

living matter: their body cells and tissues, their genetic material, their energy-bearing molecules, and 

their reproductive cells. In this discussion of water quality in the Mississippi River, four nutrient 

compounds are described: nitrate (NO3

-), nitrite (NO2-), ammonium (NH4+), and orthophosphate (PO4-

3). These are the most significant inorganic forms of two elements, nitrogen and phosphorus, that 

commonly limit the productivity of plants.

Nitrate and nitrite at high concentrations are known to have toxic effects on humans. The U.S. 

Environmental Protection Agency (USEPA), mandated by Public Laws 89-753 (the Clean Water 

Restoration Act of 1966) and 92-500 (the Federal Water Pollution Control Act Amendments of 1972), 

has established drinking-water standards for both of these to protect public health (Sceery, 1992; U.S. 

Environmental Protec-tion Agency, 1991a, 1991b; table 5). If the concentration of nitrate or nitrite is 

high in the raw water supply (for example, the Mississippi River), the cost of treatment increases. 

Ammonia also is known to be toxic to aquatic organisms, and the USEPA also has established criteria 

for this compound in surface waters (U.S. Environmental Protection Agency, 1985, 1992). Maximum 

contaminant levels have not been established for orthophosphate.

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Plant productivity caused by nutrients is another factor of concern. In lakes, nutrient enrichment almost 

always increases algal production, a condition known as cultural eutrophication. One effect of 

eutrophication is that an abundance of algae may cause taste and odor problems in drinking-water 

supplies. A second effect of eutrophication is the increased uptake of dissolved oxygen by bacteria in 

response to higher concentrations of organic matter. If oxygen is taken up by decaying organic matter 

faster than it is imported from the atmosphere or produced by photosynthesis, it becomes depleted, and 

the aquatic species that require it are adversely affected. Furthermore, oxygen depletion causes basic 

changes in the chemical environment that allow materials (including many metals) that were formerly 

precipitated or tied to the sediments to become soluble and, therefore, mobile.

Nutrients Dissolved in River Waters

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Figure 30. -- Of four major nutrient compounds in the Mississippi River and its tributaries, only nitrate 

is found in concentrations approaching the U.S. Environmental Protection Agency (USEPA) maximum 

contaminant level (MCL). Orthophosphate usually is present in low concentrations, and concentrations 

of ammonium and nitrite usually are insignificant. The box plots show the medians and ranges of values 

determined in the Mississippi River main stem (Ml, M2) and in tributaries (Tl, T2). Values determined 

during 1991-92 are labeled Ml and T1 (see table 7 for a statistical summary of the data; see Antweiler 

and others, 1995, and Garbarino and others, 1995, for a detailed listing of the data), and those at 

monitoring stations of the U.S. Geological Survey's National Stream Quality Accounting Network 

(NASQAN) during 1979-91 are labeled M2 and T2.

In large turbid rivers such as the Mississippi, rapid stream velocities and reduced light penetration into 

the water may inhibit primary productivity. In the Mississippi River, eutrophication may be limited to 

slow-flowing reaches behind locks and dams and to backwaters and eddies. The major response of 

plants to the nutrients in the Mississippi River is delayed until the water reaches the estuarine regions 

along the coast of the Gulf of Mexico, where velocities decrease and sediment settles out of the water, 

allowing light to penetrate and algae to bloom. For example, the fish production of the Barataria Basin, 

one of these estuarine regions, has become endangered by eutrophication (Hanor, 1988; Madden and 

others, 1988; Craig and Day, 1976); thus, the nutrients supplied by the Mississippi River are of concern 

to the coastal areas of the Gulf of Mexico.

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The sources of nutrients in surface waters can be broadly divided as natural and anthropogenic (see 

table 6). Natural sources are generally ubiquitous; however, their contribution is usually low because, 

over the course of time, natural systems have established balances between the production and 

consumption of nutrients. Anthropogenic sources arise from many activities. In the agricultural setting 

of the Mississippi River drainage, farmers increase the productivity and yield of their crops by use of 

chemical fertilizers. If more fertilizers are applied than are used by the crops, they can move into ground 

and surface waters and become a major source of nutrients in rivers. Other major sources of nutrients in 

surface waters are domestic and animal wastes. Although municipal wastewater is treated, only a 

fraction of the nutrients is removed. In addition to the nutrients derived from human sewage, municipal 

wastewater also contains nutrients from such things as lawn fertilizers and household cleaners and 

detergents. Other anthropogenic sources of nutrients are industrial, either from the manufacture of 

fertilizers or as by-products of other manufacturing processes.

During the last 80 years, there has been a marked increase in the concentration of nitrate in the Lower 

Mississippi River that has been attributed to the increasing use of fertilizers (Turner and Rabalais, 1991). 

Before 1940, nitrate concentrations ranged from 0.2-0.4 milligram of nitrogen per liter (mg N/L); since 

1940, they have ranged from 1.0-1.2 mg N/L. In the last 10 to 15 years, however, nitrate concentrations 

do not appear to have changed.

Time-series data collected at Baton Rouge and elsewhere were combined and integrated to estimate that 

the Mississippi River delivered about 900,000 metric tons of nitrate and 35,000 metric tons of 

orthophosphate to the Gulf of Mexico during the year, April 1991-April 1992. If we assume that all 

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nitrate in the Mississippi River before 1940 originated from natural sources, the increase since 1940 

provides a rough estimate that at least 75 percent of the nitrate in the Mississippi River today is 

anthropogenic in origin. Most of that 75 percent apparently comes from nonpoint agricultural sources. It 

is estimated that more than 5.5 million metric tons of nitrogen fertilizer were applied to cropland in the 

Mississippi River Basin in 1991 (U.S. Department of Agriculture, 1992; J.J. Fletcher, West Virginia 

University, unpubl. data,1992). The 900,000 metric tons of nitrate discharged by the Mississippi River 

into the Gulf of Mexico was therefore equivalent to about 16 percent of the nitrogen fertilizer applied to 

cropland in one year. In contrast, most of the ammonium that enters the Mississippi River probably 

originates from either industrial or municipal waste. 

Nitrate in River Waters

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Figure 31. -- During the last decade and a half, there has been no significant change in the 

concentrations of nitrate and nitrite in the Mississippi River. Shown here are the yearly mean 

concentrations of nitrate plus nitrite at monitoring stations of the U.S. Geological Survey's National 

Stream Quality Accounting Network (NASQAN) on the Mississippi River. The lower four lines 

represent the upper river at Royalton, Minnesota (upriver of the Twin Cities), and Alma, Wisconsin 

(Lock and Dam 4), and the lower river at Memphis, Tennessee, and St. Francisville, Louisiana. The 

uppermost line shows considerably more scatter than the other four, which probably is related to 

variable inputs of nitrate from the Illinois River; the Illinois enters the Mississippi at Grafton (a few 

kilometers upriver of Alton), and it usually contains higher concentrations of nitrate than the other major 

tributaries of the Mississippi (see fig. 32).

Nitrate Variations Through Time

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Figure 32. -- Nitrate concentrations in the Mississippi River and its tributaries vary seasonally, usually 

being higher in winter, spring, and early summer and lower in late summer and early autumn. The data 

shown in the graphs are from samples collected at weekly or biweekly intervals between March 1991 

and September 1992 at six sites: three on the Mississippi River main stem and three in the lower reaches 

of principal tributaries. For a complete listing of the data, see Coupe and others (1995). The maximum 

contaminant level for nitrate in drinking water (10 milligrams of nitrogen per liter, a level that 

corresponds to the top of the graphs) was not exceeded in any of the samples collected at the six sites 

during the period shown here. The highest concentrations of nitrate were recorded in the Illinois River, 

which drains extensive agricultural areas and receives municipal wastes from Chicago and other cities.

Virtually all of the sharp increases of ammonium concentration in samples, such as those illustrated in 

figures 34 and 35, corresponded to metropolitan centers on the river. This association, coupled with data 

on fecal coliforms and surfactants (see the chapter, "Organic contamination of the Mississippi River 

from municipal and industrial wastewater"), suggests that most ammonium ions in the river originate 

from municipal waste.

The source of nitrite is more difficult to assess. Although there was probably a significant contribution 

from non-point sources, nitrite, like ammonium, was being removed by biotic utilization or conversion 

to nitrate, and hence this contribution was minimized. 

To summarize: In terms of human health, nitrate is the only nutrient compound that represents a problem 

in the Mississippi River system; nitrate concentrations in many of the Mississippi River's tributaries in 

Iowa, Minnesota, and northern Illinois approach and occasionally exceed the USEPA drinking-water 

standard (table 5; see also Lucey and Goolsby, 1993). In addition to the public health question, nitrate 

represents an ecological problem as well. Because it is not removed quickly, nitrate is accumulating in 

the Gulf of Mexico; each year, the Mississippi delivers a large quantity (900,000 metric tons between 

April 1991 and April 1992) to the Gulf and therefore merits concern in terms of potential eutrophication. 

The largest sources of this nitrate are most likely fertilizers used in agriculture. Although the 

concentrations of nitrate in the Mississippi River have increased since the turn of the century, these 

levels have been virtually unchanged over the last 10 to 15 years. Hence, although nitrate concentrations 

may be high, they appear to have stabilized.

Ammonium Variations Through Time

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(Click on image for a larger version, 99K)

Figure 33. -- Ammonium concentrations generally are highest in winter (December through March) 

when river water temperatures are lowest. This pattern is not so much related to seasonal supplies of 

ammonium as it is to water temperatures. During the warmer months, ammonium is less persistent in 

oxygenated river water because it is more rapidly utilized by bacteria and algae or more rapidly oxidized 

to nitrate or nitrite. Data shown in the graphs are based on the same samples as the nitrate data shown in 

figure 32 (see Coupe and others, 1995, for a complete listing).

Nutrient Concentrations

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(Click on image for a larger version, 99K)

Figure 34. -- Spatial variations of nutrients along the length of the Mississippi River demonstrate the 

interplay between the input sources that increase their concentrations and the processes of dilution and 

decomposition that decrease their concentrations. Data shown here in A and B were collected during two 

upriver cruises (see "Sampling the Length of the River") wherein samples were taken approximately 

every 10 miles near the center of the river. Complete tabulations of the data are given by Antweiler and 

others (1995).

A

Data collected during the upriver cruise of June 23-July 2, 1991, showed (1) increases and 

decreases in nitrate and orthophosphate that were related mainly to inputs and dilutions by 

tributaries, and (2) downstream decreases of nitrite and ammonium that were related mostly to 

uptake by organisms or oxidation to nitrate. Concentrations of nitrate (NO3-) and orthophosphate 

(PO4

-3) fluctuated in near parallel fashion, showing the following features, in downriver 

sequence: highest concentrations just below the mouth of the Minnesota River; rapid decreases in 

concentration between the mouth of the Minnesota River and kilometer 2500 (northern border of 

Iowa) owing mostly to dilution by tributary inflows that have lower concentrations; rapid 

increases in concentration as the river flowed past Iowa and northern Illinois, probably owing to 

more concentrated inputs from rivers like the Iowa and Des Moines; no appreciable changes in 

concentration at or below the mouth of the Missouri River; marked dilutions from the less 

concentrated waters of the Ohio River; few large changes in concentration in the lower 

Mississippi River, except for peaks between river kilometers 650 and 1100 that probably 

reflected pulses of runoff of stormwaters that fell a few weeks earlier in agricultural areas of Iowa 

and Illinois. Ammonium (NH4

+) concentrations showed as three distinct spikes that appeared and 

disappeared rapidly: one below the Minnesota River and the Twin Cities, one below the Des 

Moines River and Keokuk, and one below St. Louis. Once ammonium has been introduced into 

the river, it decreases quickly as it is assimilated by bacteria and algae, converted to nitrate or 

nitrite, or removed by adsorption onto sediments. After reaching a peak concentration downriver 

of Lake Pepin (near river kilometer 2700), nitrite (NO2

-) showed a general decrease downriver, 

punctuated most notably by an increase between kilometers 2400 and 2100 and another small 

increase near St. Louis. Nitrite, like ammonium, is removed by natural processes--its utilization 

by bacteria and algae and its oxidation to nitrate are the most likely possibilities--but not as 

rapidly as ammonium. Like ammonium, most of the nitrite probably originates from point 

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sources.

B

Data collected during the upriver cruise of March 25-April 4, 1992, show substantial differences 

when compared with the data collected the previous summer (shown in A). These differences in 

concentrations reflected seasonal differences in the sources of nutrients and in the rates at which 

nutrients are utilized or transformed in the river. Nitrate (NO3

-) concentrations again were highest 

in the Minneapolis-St. Paul area and decreased downriver to about kilometer 2400, below which 

point they remained fairly constant until they were diluted by the waters of the Ohio River. 

Orthophosphate (PO4

-3) concentrations were lower than during the previous summer, especially 

in the upper river; the spikes or peaks of concentration between river kilometers 1100 and 650 

may have resulted from storm events upriver that flushed in waters that were rich in 

orthophosphate. Ammonium (NH4

+) concentrations again appeared as spikes, but these spikes 

were broader, reflecting the slower rates of removal or utilization during the early spring that are 

related to lower temperatures, slower growth cycles, or less incident radiation (sunlight). 

Persistent concentrations of nitrite (NO2

-) along most of the length of the river suggest that 

mechanisms for its disappearance, such as uptake or oxidation, also were retarded during the 

early spring period of March-April 1992.

Nutrient Transport

(Click on image for a larger version, 66K)

Figure 35. -- When nutrient data are graphed in terms of their fluxes or transports rather than their 

concentrations, they show that the transports of nitrate (NO3

-) and orthophosphate (PO4-3) mostly 

increase downriver. This means that the processes that add nitrate and orthophosphate to the river are 

more prevalent than the processes that remove them. Transports of nitrite (NO2

-) and ammonium (NH4

+), on the other hand, generally decrease downriver because, in their cases, the removal mechanisms 

prevail. Shown here are the data from the upriver cruise of June 23-July 2, 1991: concentrations shown 

in figure 34A have been multiplied by water discharges to compute the downriver transports of 

dissolved nutrients in tons per day (1 metric ton = 1000 kg = 2205 pounds). Significant inputs from 

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tributaries are shown by bars near the center of the graph; the individual nutrients are identified by bar 

colors which correspond to those of the curves. Concentrations of nitrate and orthophosphate showed 

parallel fluctuations during the sampling period. The initial loading to the Mississippi River from the 

Minnesota River represented the total transport of these two compounds for the next 600 km (to river 

kilometer 2250); this implies that over this distance, additions of nitrate and orthophosphate from 

tributaries and point sources were negligible, or that gains of these ions were balanced by their losses. 

From kilometer 2250 (near the confluence with the Iowa River) downriver to St. Louis (kilometer 1800), 

loads increased steadily from contributions from tributaries. The Iowa River at kilometer 2240, the Des 

Moines River at kilometer 2100, and the Missouri River at kilometer 1850 each added a large increment 

of nitrate and orthophosphate (see the bars in the middle of the graph). Because the Ohio River added 

relatively small amounts of nutrients, its effect can barely be distinguished on the graph. The large 

increases in the curves at about kilometer 1100 (south of Memphis, Tennessee) probably were caused by 

a storm event several weeks earlier in Iowa or Illinois, which flushed large quantities of these 

compounds into the river. The decreases in the curves at about kilometer 500 are caused by the Old 

River outflow, which removes substantial amounts of the water and dissolved nutrients from the 

Mississippi River. Ammonium (NH4

+) loads were introduced into the river from point sources, most 

likely municipal wastes, and they decreased within relatively short distances downriver. Nitrite (NO2

-) 

load behaved in a fashion somewhere between nitrate load and ammonium load: its points of 

introduction were generally not spikes, yet it clearly was being utilized or converted to other forms of 

nitrogen faster than it was being introduced--as reflected in the downriver decrease in nitrite load. Places 

where nitrite was introduced were not always related to entering tributaries; the sharp increase in nitrite 

load near river kilometer 2700 (Lake Pepin), for example, cannot be related to tributary inputs.

Nitrate Sources

(Click on image for a larger version, 33K)

Figure 36. -- Disproportionately large quantities of the nitrate in the Mississippi River, on average, are 

derived from the upper-basin States of Minnesota, Iowa, and Illinois. Slightly more than one-half the 

total nitrate load in the system is derived from the Upper Mississippi River Basin, which supplies less 

than one-fourth of the total water. Conversely, the Ohio River supplies 41 percent of the total water, but 

only 21 percent of the total nitrate load. The Missouri River is the only major tributary whose nitrate 

load corresponds closely to its proportion of the water discharge.

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SELECTED REFERENCES

Antweiler, R.C., Patton, C.J., and Taylor, H.E., 1995, 

Nutrients, in Moody, J.A., ed., Chemical data for water samples collected during four upriver 

cruises on the Mississippi River between New Orleans, Louisiana, and Minneapolis, Minnesota, 

May 1990-April 1992: U.S. Geological Survey Open-File Report 94-523, p. 89-125. 

Battaglin, W.A., and Goolsby, D.A., 1995,

Spatial data in geographic information system format on agricultural chemical use, land use, and 

cropping practices in the United States: U.S. Geological Survey Water-Resources Investigations 

Report 94-4176, 87 p. 

Coupe, R.H., Goolsby, D.A., Iverson, J.L., Markovchick, D.J., and Zaugg, D.S., 1995,

Pesticide, nutrient, water discharge, and physical-property data for the Mississippi River and 

some of its tributaries, April 1991- September 1992: U.S. Geological Survey Open-File Report 

93-657, 116 p. 

Craig, N.J., and Day, J.W., Jr., 1976,

Barataria Basin eutrophication case history: Baton Rouge, Report to Louisiana State Planning 

Office, June 1976, 24 p. 

Fletcher, J.J., 1992,

Unpublished nitrogen fertilizer use database: Morgantown, West Virginia University. 

Garbarino, J.R., Antweiler, R.C., Brinton, T.I., Roth, D.A., and Taylor, H.E., 1995,

Concentration and transport data for selected dissolved inorganic constituents and dissolved 

organic carbon in water collected from the Mississippi River and some of its tributaries, July 

1991-May 1992: U.S. Geological Survey Open-File Report 95-149, 149 p. 

Goolsby, D.A., Coupe, R.C., and Markovchick, D.J., 1991,

Distribution of selected herbicides and nitrate in the Mississippi River and its major tributaries, 

April through June 1991: U.S. Geological Survey Water-Resources Investigations Report 91-

4163, 35 p. 

Goolsby, D.A., and Battaglin, W.A., 1993,

Occurrence, distribution and transport of agricultural chemicals in surface waters of the 

Midwestern United States, in Goolsby, D.A., Boyer, L.L., and Mallard, G.E., eds., Selected 

papers on agricultural chemicals in water resources of the Midcontinental United States: U.S. 

Geological Survey Open-File Report 93-418, p. 1-25. 

Hanor, J.S., 1988,

Effects of discharge of municipal waste on water quality of the lower Mississippi River: 

Environmental Geology and Water Sciences, v. 12, p. 163-175. 

Lucey, K.J., and Goolsby, D.A., 1993,

Effects of short-term climatic variations on nitrate concentrations in the Raccoon River, Iowa: 

Journal of Environmental Quality, v. 22, p. 38-46. 

Madden, C.J., Day, J.W., and Randall, J.M., 1988,

Freshwater and marine coupling in estuaries of the Mississippi River deltaic plain: Limnology 

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and Oceanography, v. 33, p. 982-1004. 

Sceery, W.M., 1992,

Drinking water update: Environmental Testing and Analysis, v. 1, p. 26-30. 

Turner, R.E., and Rabalais, N.N., 1991, 

Changes in Mississippi River water quality this century-Implications for coastal food webs: 

Bioscience, v. 41, p. 140-147. 

U.S. Department of Agriculture, 1992,

Agricultural resources--Inputs situation and outlook: U.S. Department of Agriculture, p. 13-20. 

U.S. Environmental Protection Agency, 1985,

Criterion document: Washington, D.C., U.S. Environmental Protection Agency, 3 p. 

___ 1991a,

Drinking water regulations and health advisories: Washington, D.C., U.S. Environmental 

Protection Agency, Office of Water, 12 p. 

___ 1991b,

Summary of Phase II regulations--National Primary Drinking Water Regulation for 38 inorganic 

and synthetic organic chemicals--EPA Phase II Fact Sheet Series (Nitrate, no. 3 of 14, and 

Nitrite, no. 4 of 14): Office of Ground Water and Drinking Water, U.S. Environmental Protection 

Agency publication #570, 9-91-022, October. 

___ 1992,

Revised tables for determining average freshwater ammonia concentrations: Washington, D.C., U.

S. Environmental Protection Agency memorandum, dated July 30, 1992, 3 p.

Continue to ' Pesticides in the Mississippi River ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

http://water.er.usgs.gov/pubs/circ1133/nutrients.html 

Maintainer: h2o Webserver Team 

Last Modified: 1230 01 Oct 96 ghc 

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Contaminants in the Mississippi River--Pesticides in the Mississippi River

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Pesticides in the Mississippi River

Donald A. Goolsby and Wilfred E. Pereira

Introduction

The Mississippi River basin contains the largest and most intensively farmed region in the Nation. In order to 

increase yields from crops, large amounts of pesticides are used to protect against weeds, insects, and other pests. 

The major categories of pesticides are herbicides, insecticides, and fungicides. It is estimated that about two-thirds 

of all pesticides used for agriculture in the United States are applied to cropland and pasture land in the 

Mississippi River Basin (Gianessi and Puffer, 1990). The intense use of pesticides is of concern because of 

potential adverse effects on the quality and use of water resources. The most immediate concerns are for aquatic 

life and for the 18 million people in the basin who rely on surface-water sources for drinking water.

Nitrogen Applied to Croplands

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Figure 37. -- An estimated 5.5 million metric tons of nitrogen fertilizer were applied to croplands in the 

Mississippi River Basin during 1991. This map was prepared by W.A. Battaglin of the U.S. Geological Survey to 

show the geographical distribution of the estimated use of nitrogen fertilizer in the Nation during 1991. County 

estimates were made by J.J. Fletcher of West Virginia University, using fertilizer expense estimates from the 1987 

Census of Agriculture. State totals were compiled by the National Fertilizer and Environmental Research Center 

of the Tennessee Valley Authority. Agricultural lands of the Corn-Belt States of Iowa, Illinois, Indiana, and 

Minnesota clearly are potential sources of nutrients in the Mississippi River.

Harvested Croplands

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(Click on image for a larger version, 99K)

Figure 38. -- Cropland in the United States is concentrated most heavily in the areas drained by the Mississippi 

River. In this map, prepared by W.A. Battaglin of the U.S. Geological Survey from data supplied by the U.S. 

Department of Commerce, Bureau of the Census, Census of Agriculture, harvested cropland is expressed as a 

percentage of the total area of each county. The Mississippi River Basin contains about 65 percent of the total 

harvested cropland in the Nation, producing about 80 percent of the corn and soybeans, and much of the cotton, 

rice, sorghum, and wheat (U.S. Department of Agriculture, 1985; U.S. Department of Commerce, 1989).

Many of the pesticides used in the basin are present in the Mississippi River and its tributaries. A regional-scale 

study of a 10-State area in the upper Midwest showed that large amounts of herbicides are flushed into streams 

during storm runoff in late spring and summer each year, following application of herbicides to cropland 

(Thurman and others, 1992). Storm runoff produces high concentrations of many herbicides in streams across the 

upper Midwest from Nebraska to Ohio for periods of several weeks to several months. Concentration of herbicides 

in some small streams may exceed 100 micrograms per liter (μg/L) for short periods of time. Flow from these 

streams, in turn, transports significant amounts of herbicides into large rivers such as the Missouri, Ohio, and 

Mississippi, and eventually to the Gulf of Mexico (Pereira and Rostad, 1990; Goolsby and others, 1991; Pereira 

and Hostettler, 1993).

Sources and Properties of Pesticides

Pesticides include a wide variety of synthetic organic and inorganic compounds used to control weeds, insects, 

nematodes and other pests. The U.S. Environmental Protection Agency (Aspelin and others, 1992) estimated that 

in 1991 about 490 million kilograms (kg) of pesticides were used annually in the United States. These include 

herbicides (285 million kg), insecticides (113 million kg), and fungicides (54 million kg). About three-fourths of 

the total annual pesticide use is for agriculture (Aspelin and others, 1992). In 1991, about 218 million kg of 

pesticides were used on major field crops alone, of which about 84 percent were herbicides (U.S. Department of 

Agriculture, 1992).

Pesticides derived from point and nonpoint sources in the Mississippi River basin are transported into the 

Mississippi River in runoff from agricultural and urban areas, discharge from reservoirs and aquifers, and 

atmospheric deposition (Nations and Hallberg, 1992). The physiochemical properties of the pesticides themselves, 

as well as other factors such as usage, rainfall, and farming practices, are important in governing the amounts and 

concentrations that actually occur in streams. Several important physiochemical properties of the most widely 

used pesticides in the Mississippi River basin are given in table 8. These include water solubility, soil half-life, 

and soil sorption coefficient (Koc). Water solubility determines how easily pesticides wash off soil and crop 

residues and how easily they leach through the soil. Pesticides with solubilities greater than about 30 milligrams 

per liter (mg/L) are considered to be soluble and more likely to wash off the soil during storms. Soil half-life is the 

length of time required for pesticides to degrade in the soil to one-half their previous concentration. The longer the 

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soil half-life the more persistent the pesticide, and the longer it will be available to wash off in storm runoff. The 

half-life of pesticides, once they are in surface water, is generally much longer than in soil because water contains 

much less organic matter and fewer micro-organisms to degrade the pesticides. Many pesticides are highly 

persistent in streamwater and in reservoirs, but very little specific information is available on pesticide half-lives 

in natural water bodies. The soil sorption coefficient is a measure of the tendency of a pesticide to attach to soil 

particles. The larger the Koc value the more strongly the pesticide will be adsorbed to soil. Those with Koc values 

less than about 500 tend to be transported primarily in the dissolved phase. Those with Koc values of more than 

1000 are transported primarily on suspended-sediment particles.

Herbicides Applied to Croplands

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(Click on image for a larger version, 132K)

Figure 39. -- Most of the pesticides used in the Mississippi River Basin are herbicides used for weed control. Data 

portrayed in this figure, representing the years 1987--89, were obtained from Resources for the Future (Gianessi 

and Puffer, 1990).

A

The 20 most heavily used herbicides are shown in this graph. The most heavily applied herbicides are 

atrazine, alachlor, and metolachlor, which are used in the production of corn and soybeans.

B

Atrazine is used most heavily in the upper Midwest, generally to control broad-leaved weeds in cornfields. 

Other herbicides used extensively on corn and soybean fields have geographical patterns of use similar to 

that of atrazine, but the amounts are somewhat less. 

The physiochemical properties listed in table 8 indicate that relatively soluble and mobile compounds such as 

atrazine, alachlor, metolachlor, and many other herbicides are transported primarily in the dissolved phase.

This group of compounds includes the majority of pesticides in use today. However, soil half-life and other factors 

such as intensity of use, application methods, and climatic conditions are also important in determining transport 

in surface water. Most of the older "first generation" chlorinated insecticides, such as DDT, chlordane, and 

dieldrin (not shown in table 8), are insoluble in water, have long soil half-lives, and large Koc values. 

Consequently, they are transported primarily on sediment particles. Most of these first-generation chlorinated 

insecticides are banned and are no longer used in the United States, but continue to persist in the Mississippi River 

Basin from previous use because of long soil half-lives. Also, because these chlorinated insecticides are relatively 

insoluble in water and have large Koc values, they partition into the organic coatings of sediments or accumulate 

in the fatty tissues of fish and other stream biota (Moore and Ramamoorthy, 1984), which is not true for most 

pesticides currently in use.

Pesticides in the River

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(Click on image for a larger version, 99K)

Figure 40. -- The concentrations of 32 pesticides and pesticide-degradation products dissolved in waters collected 

from the main-stem Mississippi River during 1987--92 are shown here in dot plots. These plots show the 

distribution and range in concentration for each pesticide. Each dot represents one sample. The dot plots 

summarize a diverse body of data that represents concentrations during different seasons of the year at numerous 

locations. The samples on which the plots are based were collected (1) during 10 downriver sampling trips 

between July 1987 and May 1992 and (2) approximately weekly at 3 fixed stations on the Mississippi River 

(Clinton, Iowa; Thebes, Illinois; Baton Rouge, Louisiana) from April 1991 through September 1992. The 

concentrations of pesticides measured near the mouths of tributaries that flow into the Mississippi River generally 

are slightly higher than those shown in this figure. Specific sampling locations and analytical data are given by 

Coupe and others (1995) and Pereira and others (1995).

Drinking-Water Standards and Aquatic-Life Guidelines

The maximum contaminant levels (MCLs), or drinking-water standards, that have been established by the U.S. 

Environmental Protection Agency (1995) for several pesticides also are shown in table 8. MCLs are based on 

annual average concentrations and are legally enforceable under the Safe Drinking Water Act. MCLs are based on 

analyses of a minimum of four samples per year, and a violation occurs only if the average concentration in these 

samples exceeds the MCL. Further, MCLs apply to water delivered at the tap and not the raw water source. 

However, conventional water treatment removes very little of the water-soluble pesticides currently used in the 

Mississippi River Basin. At present (1995) MCLs are established only for individual compounds and do not 

consider the possible effects of complex mixtures of pesticides and their degradation products.

Health advisories (HAs) have been established for many other pesticides (table 8). HAs are the recommended 

maximum concentrations in drinking water for lifetime exposure and are not legally enforceable. However, in 

time, the lifetime HAs for many pesticides may become enforceable MCLs.

Many pesticides may have adverse effects on aquatic life, but at present (1995), the U.S. Environmental Protection 

Agency has established standards or criteria for aquatic life for very few current-generation pesticides. However, 

Environment Canada has established water-quality guidelines for specific water uses in Canada that include 

drinking water, aquatic life, and agricultural uses of water (Wong and Kent, 1988). The guidelines are numerical 

concentrations recommended to support and maintain a designated water use. Because U.S. guidelines or criteria 

for aquatic life do not presently exist for most pesticides in current use, the Canadian pesticide water-quality 

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guidelines, where available, have been included in table 8 as points of reference for pesticide concentrations 

measured in the Mississippi River Basin.

Occurrence and Temporal Distribution of Pesticides in Water

More than 40 pesticides and pesticide degradation products were detected during 1987--92 in water samples 

collected from the Mississippi River or from the mouths of large rivers that flow directly into the Mississippi 

(Goolsby and Battaglin, 1993). Thirty-two pesticides and pesticide degradation products that were detected in 5 

percent or more of the nearly 600 water samples collected during the study period are shown in figure 40. The 

pesticides detected most frequently and in highest concentrations were the most extensively used compounds with 

low Koc values such as atrazine, alachlor, metolachlor, and cyanazine. In contrast, several other extensively used 

compounds such as butylate, EPTC, and trifluralin (fig. 39A) were detected infrequently and in low 

concentrations. The most persistent compounds were alachlor, atrazine, cyanazine, desethylatrazine (an atrazine 

degradation product), metolachlor, and simazine, all of which are herbicides. These herbicides were detected in 

low concentrations in more than 75 percent of the samples analyzed. Two herbicides, atrazine and metolachlor, 

were detected in more than 95 percent of the samples. Although numerous pesticides were detected in many 

samples, only three compounds, atrazine, alachlor, and cyanazine, exceeded MCLs or HAs in only a small 

percentage of samples. The average annual concentrations were far below MCLs or HAs. Atrazine and cyanazine 

concentrations in a few samples also exceeded the Canadian aquatic-life guidelines (compare concentrations 

shown in figure 40 with the guidelines listed in table 8).

For a period of several weeks during May through July, atrazine, cyanazine, and to a lesser extent alachlor 

concentrations in the Mississippi River main stem and in tributaries may exceed MCLs or HAs. However, because 

the annual average concentrations of these compounds are well below health-based limits, there is no violation of 

the Safe Drinking Water Act and the water would be considered suitable for public supply from the standpoint of 

pesticides.

Atrazine Variation Through Time

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Figure 41. -- Pronounced seasonal variations are typical of pesticide concentrations in the Mississippi River and 

its tributaries. Atrazine, the example portrayed in this figure, is more concentrated during late spring and early 

summer than during other parts of the year. Concentrations shown here are based on samples collected 

approximately weekly (more frequently during late spring and early summer, less frequently at other times). 

Runoff caused by rainstorms following the application of atrazine to cornfields early in the growing season flushes 

a portion of the atrazine into streams that eventually flow into the Mississippi River. Most other major herbicides 

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show a seasonal pattern of runoff similar to that of atrazine. Data from two growing seasons, 1991 and 1992, are 

shown here. The differences in concentrations between 1991 and 1992 probably are caused by differences in the 

intensity and timing of rainfall. Pesticides will be transported in storm runoff as long as their residues remain on 

the soil or on plant surfaces. As the growing season progresses and wanes, concentrations of pesticides in storm 

runoff decrease to low levels. For a few weeks of 1991 and 1992, concentrations of atrazine, cyanazine, and (to a 

lesser extent) alachlor reached or exceeded maximum contaminant levels (MCLs) or health advisories (HAs). 

However, the average annual concentrations of these compounds were well below these health-based limits. 

Therefore, these pesticide concentrations did not violate the Safe Drinking Water Act or make the water unsuitable 

for public supply.

Spatial Distribution of Pesticides in Water

The majority of all pesticides used in the Mississippi River Basin are applied in the upper part of the basin. 

Consequently, streams draining Illinois, Iowa, Indiana, eastern Nebraska, and southern Minnesota contribute the 

largest quantities of pesticides to the Mississippi River. As water flows downriver from the Minneapolis area, 

inflow from tributary streams results in large and often dramatic increases in pesticide concentrations during May 

through July, as illustrated in figure 44.

Mass Transport of Pesticides

Two major objectives of our Mississippi River study were to determine the predominant source areas for 

pesticides and to estimate the mass transport of these chemicals from major tributaries into the Mississippi River 

and to the Gulf of Mexico for a 1-year period. The transport for each pesticide of interest was calculated for each 

day of the year using either measured or estimated daily pesticide concentrations and mean daily streamflow. 

Pesticide concentrations were estimated by linear interpolations for days on which no samples were collected. The 

estimated daily transports were then summed to obtain an estimate of annual transport. Mass-transport estimates 

were made in this manner for the six sites where approximately weekly samples were collected. The annual mass 

transport of pesticides to the Gulf of Mexico was estimated from concentrations measured at Baton Rouge, 

Louisiana, and streamflow at Baton Rouge plus the streamflow diverted from the Mississippi into the Atchafalaya 

River upstream from Baton Rouge (fig. 45). Loads of 21 major pesticides and degradation products transported by 

the Mississippi River at four locations and by three major tributaries during a 1-year period (April 1, 1991, 

through March 31, 1992) are given in table 9.

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Iowa and Illinois are the predominant sources for most pesticides transported by the Mississippi River. The Upper 

Mississippi River Basin, excluding the Missouri River Basin, constitutes about 22 percent of the total Mississippi 

River drainage basin, but contributes about 40 percent of the atrazine, and 50 percent or more of many other 

pesticides transported by the Mississippi River (table 9). The area receives essentially all of the streamflow 

discharged from Iowa and Illinois, which contain the most intensive crop-production areas in the basin (fig. 38). 

These two States apparently also are the sources for much of the agricultural chemicals transported by the 

Mississippi River. The Ohio River Basin is the source of about one-half the butylate and most of the simazine 

transported by the Mississippi River (table 9), and the Missouri River Basin is the predominant source for 

trifluralin.

Although the annual mass transport appears to be large for several pesticides (table 9), it represents only a small 

fraction, generally less than 3 percent, of the pesticide mass applied annually to cropland in the basin. The mass of 

pesticides discharged from the Mississippi River Basin to the Gulf of Mexico during April 1991 through March 

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1992 expressed as a percentage of the annual mass applied to cropland was 0.2 percent for alachlor, 0.8 percent 

for metolachlor, 1.6 percent for atrazine and cyanazine, and 2.7 percent for simazine. A similar fraction of the 

mass of these pesticides applied in the Illinois, Ohio, and Missouri River Basins was discharged from these rivers. 

These percentages may be higher or lower in other years, depending on rainfall patterns.

Herbicide Variations Through Time

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Figure 42. -- Temporal variations in the concentrations of herbicides in the Mississippi River reflect two factors: 

(1) the application of the herbicides on croplands, and (2) the rainfall and runoff events that follow the 

applications. This figure shows the concentrations of three herbicides measured in the Mississippi River at Baton 

Rouge, Louisiana, at weekly to biweekly intervals between April 1991 and September 1992. Plotted in the figure 

is the streamflow at Baton Rouge plus the flow diverted into the Atchafalaya River above Baton Rouge. The 

heavier rainfalls during the planting and post-planting periods in 1991 resulted in greater streamflows, more 

flushing of herbicides from the fields, and higher herbicide concentrations than in 1992. 

Summary

Most streams throughout the Midwestern United States contain water with high concentrations of pesticides for 

several weeks to several months following the application of pesticides to farmlands. Concentrations generally are 

largest and may briefly exceed health-based limits for drinking water during runoff from the first storms after 

application. Concentrations decrease during later runoff events. More than 40 pesticides and pesticide degradation 

products were detected in the Mississippi River. Most of these were at concentrations less than 0.5 μg/L. 

Maximum concentrations during 1991--92 of the most extensively used herbicides such as alachlor, atrazine, 

cyanazine, and metolachlor ranged from 3 μg/L to about 6 μg/L in large rivers such as the Mississippi, Missouri, 

and Ohio, compared to 50 to more than 100 μg/L reported in previous studies of smaller tributaries. These high 

concentrations generally represent extreme conditions that do not persist past midsummer. The average annual 

concentrations of all pesticides measured in the Mississippi River are well below health-based limits and do not 

violate the Safe Drinking Water Act. Low concentrations (0.05 to 0.2 μg/L) of a few pesticides are detectable yearround in the Mississippi River Basin owing to storage and subsequent discharge from surface- and ground-water 

reservoirs. The total mass of pesticides discharged from the Mississippi River and its major tributaries from April 

1991 through March 1992 represents a small fraction (from less than 0.1 to about 3 percent) of the amounts 

applied. About 40 percent of the atrazine mass and more than 50 percent of the mass of many other heavily used 

pesticides discharged to the Gulf of Mexico originate in the Upper Mississippi River Basin, above the confluence 

with the Missouri River. This area constitutes only about 22 percent of the drainage area of the Mississippi River 

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Basin. Varying climatic conditions cause considerable variation in the maximum annual pesticide concentrations 

and in the annual loads. Wet years with intense rainfall shortly after application of pesticides tend to have the 

highest pesticide concentrations in streams and the highest loads.

Atrazine at Vicksburg

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Figure 43. -- Long-term records on atrazine concentrations in the Lower Mississippi River at Vicksburg, 

Mississippi, are shown in this figure. Concentration data for 1976--90 were collected by Ciba Geigy (the 

manufacturer of atrazine), its contractors, and other chemical companies, and are based on 11--51 samples per 

year (Tierney, 1992). Concentration data for 1991--92 are those shown in figures 41 and 42 for the station at 

Baton Rouge (Coupe and others, 1995). Mean annual streamflows are those measured in the Mississippi River at 

Vicksburg, Mississippi. The minimum, mean, and maximum values of atrazine concentration show no apparent 

upward or downward trends during the 17 years portrayed here, but after the mid-1980s the mean and maximum 

concentrations do tend to parallel the year-to-year increases and decreases of streamflow.

Atrazine Along the River

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Figure 44. -- Atrazine concentrations in the Mississippi River are consistently low for the first 600 kilometers 

below Minneapolis, and they increase rapidly downriver as the river collects water from tributaries that drain the 

Corn Belt. Shown here are measurements of atrazine in waters collected from the Mississippi River during five 

different sampling trips: the discrete points connected by straight-line segments represent samples collected in 

downstream sequences; the continuous line labeled June-July 1991 represents samples collected from the river, at 

10-mile intervals, in upriver sequence. Highest concentrations were measured during the months immediately 

following the application of atrazine (June 1990, June-July 1991). Details are best shown in the data of June-July 

1991, which represent the most intensive sampling: a doubling of atrazine concentrations between river kilometers 

2250 and 2000, where the Rock, Cedar, and Des Moines Rivers deliver pesticides, including atrazine, from 

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northern Iowa and Illinois; another significant increase below river kilometer 1900 as a result of inflows from the 

Illinois and Missouri Rivers; a decrease near kilometer 1530 where the Mississippi is diluted by inflow from the 

Ohio River. The variability in atrazine concentration between river kilometer 1530 and Baton Rouge probably 

results from short-term storm runoff pulses entering the Mississippi from the Missouri River and other major 

tributaries (Moody and Goolsby, 1993). These runoff pulses have high concentrations of pesticides and can 

produce water masses in the Mississippi River that are interspersed with water containing lower concentrations. 

This is analogous to turning on a point source of pesticide for a few days and then turning it off. This kind of 

spatial variability was also observed during another upriver transect (not shown in the figure) made in late May 

1990, and to a lesser extent in upriver transects conducted in late September 1991 and late March 1992. Details of 

procedures for collecting and analyzing the samples and complete listings of the data represented in the figure are 

given by Goolsby (1995) and Pereira and others (1995). 

Herbicide Transports

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Figure 45. -- The four pesticides (all herbicides) transported in the largest quantities by the Mississippi River are 

atrazine (plus two of its metabolites, desethylatrazine and desisopropylatrazine), cyanazine, metolachlor, and 

alachlor. 

A

The loads of these four herbicides discharged to the Gulf of Mexico during the 1-year period from April 1, 

1991, through March 31, 1992, ranged from 365,700 kg for atrazine and its metabolites to 33,700 kg for 

alachlor. This was a period of slightly greater than average streamflow, so these figures might represent 

herbicide transports somewhat greater than average. Most of the herbicides discharged into the Mississippi 

River originate in the Upper Mississippi, Missouri, and Ohio River Basins. Except for atrazine, there 

appear to be no significant inputs of most herbicides between the Ohio River confluence and Baton Rouge, 

a distance of about 1,160 river kilometers. This distance represents a traveltime in the river of about 10 

days. The annual alachlor load in this reach decreased from 47,900 kg below the Ohio River confluence to 

33,700 kg at Baton Rouge, a decrease of about 30 percent. This decrease is believed to be due primarily to 

degradation (and, possibly, volatilization) of alachlor in the Mississippi River. 

B

Temporal distributions of the rates at which the four major herbicides were transported by the Mississippi 

River to the Gulf of Mexico have been calculated here from the data on streamflow and concentrations, 

much of which was shown earlier in figure 42. For complete data, see Coupe and others (1995). Most of 

the herbicide transport during this period of study occurred during May and June, shortly after herbicide 

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application. Maximum transport rates were about 6,500 kg per day for atrazine and two of its metabolites, 

about 3,000 kg per day for metolachlor, about 2,000 kg per day for cyanazine, and about 700 kg per day for 

alachlor. Other herbicides were transported at much lower rates. The rates of transport and total masses of 

these four herbicides transported were considerably lower in 1992 than in 1991, probably as the result of 

less intense rainfall and less flushing of herbicides from cropland in 1992.

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Aspelin, A.L., Grube, A.H., and Toria, R., 1992, 

Pesticide industry sales and usage, 1990 and 1991 market estimates: Washington, D.C., U.S. 

Environmental Protection Agency, 37 p. 

Becker, R.L., Herzfeld, D., Ostlie, K.R., and Stamm-Katovich, E.J., 1989,

Pesticides: Surface runoff, leaching, and exposure concerns: University of Minnesota, Minnesota Extension 

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Coupe, R.H., Goolsby, D.A., Iverson, J.L., Markovchick, D.J., and Zaugg, S.D., 1995, 

Pesticide, nutrient, water-discharge, and physical-property data for the Mississippi River and some of its 

tributaries, April 1991-September 1992: U.S. Geological Survey Open-File Report 93-657, 116 p. 

Gianessi, L.P., and Puffer, C.M., 1990,

Herbicide use in the United States: Resources for the Future, 127 p. [Revised 1991]. 

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Dissolved herbicides, in Moody, J.A., ed., Chemical data for water samples collected during four upriver 

cruises on the Mississippi River between New Orleans, Louisiana, and Minneapolis, Minnesota, May 1990-

April 1992: U.S. Geological Survey Open-File Report 94-523, p. 19--87. 

Goolsby, D.A., and Battaglin, W.A., 1993, 

Occurrence, distribution and transport of agricultural chemicals in surface waters of the Midwestern United 

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Goolsby, D.A., Coupe, R.H., and Markovchick, D.J., 1991,

Distribution of selected herbicides and nitrate in the Mississippi River and its major tributaries, April 

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Kent, R.A., Pauli, B.D., Trotter, D.M., and Gareau, J., 1991, 

Canadian water quality guidelines for metolachlor: Ottawa, Environment Canada Scientific Series no. 184, 

34 p. 

Kent, R.A., Taché, P.-Y., and Pauli, B.D., 1992,

Canadian water quality guidelines for trifluralin: Ottawa, Environment Canada Scientific Series no. 190, 92 

p. 

Moody, J.A., and Goolsby, D.A., 1993,

Spatial variation of triazine herbicide concentrations in the lower Mississippi River: Environmental Science 

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Moore, J.W., and Ramamoorthy, S., 1984,

Organic chemicals in natural waters---Applied monitoring and impact assessment: New York, SpringerVerlag, 289 p. 

Nations, B.K., and Hallberg, G.R., 1992,

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Pesticides in Iowa precipitation: Journal of Environmental Quality, v. 21, p. 486--492. 

Pauli, B.D., Kent, R.A., and Wong, M.P., 1990, 

Canadian water quality guidelines for metribuzin: Ottawa, Environment Canada Scientific Series no. 179, 

44 p. 

___ 1991a, 

Canadian water quality guidelines for cyanazine: Ottawa, Environment Canada Scientific Series no. 180, 

26 p. 

___ 1991b, 

Canadian water quality guidelines for simazine: Ottawa, Environment Canada Scientific Series no. 187, 29 

p. 

Pereira, W.E., and Hostettler, F.D., 1993,

Nonpoint source contamination of the Mississippi River and its tributaries by herbicides: Environmental 

Science and Technology, v. 27, no. 8, p. 1542--1552. 

Pereira, W.E., Moody, J.A., Hostettler, F.D., Rostad, C.E., and Leiker, T.J., 1995,

Concentrations and mass transport of pesticides and organic contaminants in the Mississippi River and 

some of its tributaries, 1987--89 and 1991--92: U.S. Geological Survey Open-File Report 94-376, 169 p. 

Pereira, W.E., and Rostad, C.E., 1990,

Occurrence, distribution, and transport of herbicides and their degradation products in the lower 

Mississippi River and its tributaries: Environmental Science and Technology, v. 24, p. 1400--1406. 

Task Force on Water Quality Guidelines, undated,

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chap. 3, p. 36. 

Thurman, E.M., Goolsby, D.A., Meyer, M.T., and Kolpin, D.W., 1992,

A reconnaissance study of herbicides and their metabolites in surface water of the Midwestern United 

States using immunoassay and gas chromatography/mass spectrometry: Environmental Science and 

Technology, v. 26, no. 12, p. 2440--2447. 

Tierney, D.P., 1992,

A review of historical surface water monitoring for atrazine in the Mississippi, Missouri, and Ohio Rivers, 

1975--1991: Greensboro, N.C., Ciba Geigy Corporation. Technical Report 6-92, 69 p. 

Trotter, D.M., Baril, A., Wong, M.P., and Kent, R.A., 1990, 

Canadian water quality guidelines for atrazine: Ottawa, Environment Canada Scientific Series no. 168, 106 

p. 

Trotter, D.M., Kent, R.A., and Wong, M.P., 1989,

Canadian water quality guidelines for carbofuran: Ottawa, Environment Canada Scientific Series no. 169, 

34 p. 

U.S. Department of Agriculture, 1985, 

Agricultural statistics: Washington, D.C., U.S. Government Printing Office, 551 p. 

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Drinking water regulations and health advisories: U.S. Environmental Protection Agency, Office of Water, 

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Wong, M.P., and Kent, R.A., 1988, 

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Developing Canadian water quality pesticide guidelines for the protection of aquatic life: Water Pollution 

Control Research Journal of Canada, v. 23, no. 4, p. 500--509.

Continue to ' Polychlorinated Biphenyls and other Synthetic Organic Contaminants Associated with Sediments 

and Fish in the Mississippi River ', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

http://water.er.usgs.gov/pubs/circ1133/pesticides.html 

Maintainer: h2o Webserver Team 

Last Modified: 1230 01 Oct 96 ghc 

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Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Polychlorinated Biphenyls and other Synthetic 

Organic Contaminants Associated with 

Sediments and Fish in the Mississippi River

Colleen E. Rostad, LaDonna M. Bishop, Geoffrey S. Ellis, 

Thomas J. Leiker, Stephanie G. Monsterleet, and Wilfred E. 

Pereira

Hexachlorobenzene and PCBs in Silts

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Figure 46. -- Many of the sparingly soluble organic contaminants found in the Mississippi River, such 

as hexachlorobenzene and PCBs (polychlorinated biphenyls), are associated with the suspended 

sediments. Their distributions on the sediments in the river reflect the sources of the contaminants. Once 

they are in the river, many of these contaminants are most concentrated in the fractions of the sediment 

that contain the most organic carbon. Data shown here are for suspended silts collected from the river 

during downriver sampling cruises in March 1989 and June 1989. Total PCBs are defined here as the 

sum of the penta-, hexa-, hepta-, and octachlorinated biphenyl homologs. Complete data are tabulated in 

the report by Rostad, Bishop, and others (1995).

A

Concentrations of hexachlorobenzene in the suspended silt of the Mississippi River main stem 

clearly show the two principal sources of this contaminant. The marked increases near river 

kilometer 1530 are due to the input from the Ohio River, which supplies many times more 

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hexachlorobenzene than does the Upper Mississippi River. A further increase in 

hexachlorobenzene occurs as the Lower Mississippi River flows through Louisiana between St. 

Francisville (river kilometer 428) and Belle Chasse (river kilometer 117); this increase is 

probably related to the large number of halogenated hydrocarbon manufacturing industries along 

this part of the river between Baton Rouge and New Orleans.

B

Organic carbon in the suspended sediment is a strong determinant in the adsorption of sparingly 

soluble organic contaminants like hexachlorobenzene. When the contaminant concentrations are 

normalized to organic carbon, as they are in this graph, some of the irregularities in the 

contaminant-silt relation are smoothed out. The suspended silt collected at river kilometer 1920 

(Winfield, Missouri) during March 1989 contained a very high proportion of organic carbon and 

a high concentration of hexachlorobenzene for the silt of the Upper Mississippi River (fig. 46A). 

However, when the hexachlorobenzene concentration is expressed in relation to organic carbon, 

as it is here in figure 46B, the concentration is consistent with concentrations measured at other 

times and locations in the upper river.

C

The concentrations of total PCBs in the suspended silt in the middle and lower reaches of the 

Mississippi River are less visibly related to specific sources than those of a contaminant like 

hexachlorobenzene. One reason for this is that the sources of PCBs have been more diverse and 

disseminated than those of hexachlorobenzene. Perhaps even more important is that in the nearly 

two decades since the disposal of PCBs into the river has been curtailed, the repeated deposition 

and resuspension of contaminated silts has resulted in a partial homogenization of PCB 

concentrations along the length of the river and a blurring of some of the more abrupt changes in 

distribution that indicated specific sources.

D

PCBs also are strongly associated with the organic carbon in the suspended sediments of the 

Mississippi River. By expressing the PCB concentrations in relation to organic carbon, this graph 

eliminates the seemingly anomalous concentration of PCBs measured at kilometer 1920 during 

March 1989 (fig. 46C) and emphasizes the marked increase in PCB concentration associated with 

the influx of suspended sediment from the Ohio River.

Introduction

Suspended material in the Mississippi River transports the following sparingly soluble synthetic 

chlorinated pesticides and industrial chemicals: aldrin, chlorthalonil, chlordane, DCPA, DDT, DDE, 

DDD, dieldrin, endrin, heptachlor, heptachlor epoxide, hexachloro-benzene, lindane, methoxychlor, 

mirex, pentachloroanisole, pentachlorobenzene, polychlorinated biphenyls (PCBs), and trifluralin. 

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Although our analyses detected all of these compounds, the discussion here is focused on four, whose 

sources are industrial, agricultural, or residential. The PCBs are a very stable family of industrial 

chemicals previously used primarily in urban and industrial areas in electrical transformers and 

capacitors, heat-transfer and hydraulic fluids, lubricants, plasticizers, and many other products. 

Chlordane or chlordan, sold under many names such as Toxichlor, Chlortox, Dowchlor, and Octachlor, 

is a broad-spectrum insecticide formerly used on agricultural land for control of corn rootworm and on 

residential land for control of household and lawn pests. DCPA, also called chlorthal, is sold as Dacthal 

or Dacthalor for nonsystemic pre-emergence control of grasses for both agricultural (radishes, onions, 

broccoli and cauliflower) and residential uses. Of these, only DCPA is currently in use. 

Hexachlorobenzene, sometimes called HCB or perchlorobenzene, is marketed as Anticarie, Bent-cure, 

Bent-no-more, and No Bunt (Royal Society of Chemistry, 1991). It is a selective fungicide formerly 

used on wheat seed but is also a common starting material or by-product used in the chemical industry. 

Some of these compounds were first introduced into the environment as long as 40 years ago, and, 

although the use of PCBs and chlordane has been banned in the United States, they still persist in the 

environment today because they are not easily degraded. These compounds were found in sediments 

from most of the sites we sampled.

Many toxic chemicals, including most heavy metals and the majority of the U.S. Environmental 

Protection Agency (USEPA) Priority Pollutants, are primarily associated with sediments (Ongley and 

others, 1992). These sparingly soluble compounds may be transported in the environment by direct 

surface runoff or by resuspension of contaminated bed sediments in rivers. Because they are not water 

soluble, they associate with sediment or move into organisms and thus enter into food chains. They can 

bioaccumulate; for example, after a fish eats a contaminated insect, the contaminants are not degraded or 

metabolized but instead are retained by the fat in the fish tissue. The fish eats many insects and 

continues to accumulate the contaminants. As additional contaminated insects are consumed, higher 

concentrations build up in the fish tissue. Biomagnification takes place, when each level of the food 

chain contains higher concentrations than the level below it. If a bird eats this highly contaminated fish, 

the bird may also retain the contaminant in its tissue. If a human eats the fish, the contaminant can also 

accumulate in human tissue. 

PCBs, chlordane, DCPA, and hexachlorobenzene usually are detected in association with the suspended 

material in the river but not in the water itself. This behavior is expressed numerically as "partition 

coefficients," which for these compounds are large. The partition coefficient is a laboratory-determined 

ratio of the amount of a compound associated with the sediment to the amount associated with the 

aqueous phase. It is characteristic of each chemical and ranges from 1 to 10,000,000. This ratio allows 

prediction of how the compound behaves in the environment, because it indicates whether a compound 

will be found in the aqueous phase or the sediment phase. A small partition-coefficient value means the 

compound will have an affinity for the aqueous phase, not the sediment phase, and will most likely 

remain dissolved under most conditions. A large value means the compound will instead associate with 

an organic phase, like the organic carbon of sediments, or in the fat of fish tissue. Compounds with large 

partition coefficients are more likely to be found associated with available organic matter, whether it is 

bed sediment, suspended sediment, fish tissue, or aquatic insects.

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Synthetic compounds enter the river from point and nonpoint sources. Point sources are discrete, such as 

manufacturing plants or accidental spills. Although there can be many point sources, each has an 

individual effect on the environment at that point as well as downstream. Nonpoint sources are more 

general, reflecting overall widespread usage of chemicals in the environment, such as atrazine from 

farmlands. PCBs, which probably came from industrial point sources in the past, are now widely 

distributed in the environment, and as a result, are now considered to be from nonpoint sources. 

Chlordane was used extensively on corn and, more recently, on lawns and in residences for termite 

control before it was banned by USEPA. DCPA use is currently residential and agricultural. Both 

chlordane and DCPA have been so widely used that their sources are now considered nonpoint. 

Hexachlorobenzene, however, has specific industrial uses as well as agricultural uses, and therefore can 

come from point sources as well as nonpoint sources.

The toxicity of these compounds is quite high to some organisms. Most of the time, however, only trace 

concentrations of these compounds are present in environmental waters. The precise health effects of 

such trace concentrations are often subtle and, therefore, difficult to pinpoint in the environment or the 

general human population. For example, chlordane is classified by USEPA as a probable human 

carcinogen (U.S. Environmental Protection Agency, 1986). Because chlordane is present in trace 

amounts in food and water (Cochrane and others, 1975), and because humans can barely metabolize it, 

the amount present in human fatty tissue has been found to increase with age. The main target organ for 

carcinogenic effect from chlordane is the liver, but other organs of the body are also susceptible to its 

effects. In a 1973--74 study conducted in Mississippi and Arkansas, 54 percent of human breast milk 

samples contained chlordane residues at trace levels or higher (Strassman and Kutz, 1977). At large 

concentrations, chlordane is known to cause blood anemia, leukemia, and problems of the central 

nervous system.

PCBs from Ohio and Missouri Rivers

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Figure 47. -- Concentrations of organic contaminants on suspended sediment in the Mississippi River 

are variable, depending on which major tributary is contributing the most sediment at the time of 

sampling. Shown here are concentrations of total PCBs on suspended silts in the Lower Mississippi 

River during two periods of 1990---one when most of the silt in the main stem was being supplied by the 

Ohio River, and another when most was being supplied by the Missouri River. Complete data are 

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tabulated in the report by Rostad, Bishop, and others (1995).

A

During March 1990, most of the silt being transported in the Mississippi River system was in or 

from the Ohio River, and PCB concentrations were accordingly high. Data in this graph extend 

from Uniontown, Kentucky, on the Ohio River, down the Ohio to its confluence with the 

Mississippi River, and down the Mississippi to the Gulf of Mexico. That is, the uppermost 400 

kilometers on the graph represent the lowermost 400 km of the Ohio River, and the Upper 

Mississippi is represented as a tributary to the Ohio and Lower Mississippi Rivers. 

Concentrations of total PCBs on the suspended silts were greatest in the Ohio River. All the 

major tributaries that joined the Ohio (Wabash, Cumberland, Tennessee, and Upper Mississippi 

Rivers) transported silts whose PCB concentrations were less than those in the Ohio River, which 

drains a more industrialized area.

B

During June 1990, most of the silt being transported in the Mississippi River was coming from 

the Missouri River, and PCB concentrations were accordingly lower than they had been during 

March. Data in the graph show PCB concentrations in the main-stem Mississippi River from 

Grafton, Illinois, to below New Orleans, Louisiana. PCB concentrations on silts were greater in 

the tributary Illinois and Ohio Rivers than in the main stem. Although most of the silt was 

coming from the Missouri River, no silt sample was taken at the time from the Missouri River 

itself. The probable concentration range of 10--40 nanograms per gram (ng/g) shown in the graph 

for PCBs in the Missouri River was inferred from the five other measurements that were made 

between 1988 and 1991 on suspended silts from the Missouri. Of the major tributaries to the 

Mississippi River that were sampled from 1988 through 1992, the Missouri River consistently 

supplied suspended silts having the smallest concentration of PCBs.

Contaminants Associated with Suspended Silt

PCBs were detected in almost every silt sample we analyzed. They were most prevalent in the Ohio 

River, which is the principal source of PCBs to the Lower Mississippi River (figs. 46C, 46D). The 

suspended sediments of other tributaries---the Missouri, White, Arkansas, and Yazoo Rivers---contain 

significantly smaller concentrations of PCBs than those of the Ohio. Within the Upper Mississippi 

River, PCB concentrations on suspended silts are greatest between Minneapolis-St. Paul and Lake 

Pepin, but they decrease markedly downriver because Lake Pepin acts as a trap for suspended sediment 

and its associated contaminants.

Chlordane also was detected in almost every silt sample we analyzed from the Mississippi River and its 

tributaries. In general, its distribution parallels that of PCBs throughout the river system: highest 

concentrations in the Upper Mississippi are found near Lake Pepin; largest inputs to the Lower 

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Mississippi come from the Ohio River. Local exceptions do occur, such as the elevated concentrations of 

chlordane detected near Keokuk, Iowa, during July and October 1991. The higher concentrations of 

chlordane associated with the silt at this site also are reflected in the fish, for which the State of Missouri 

has issued a fish-consumption advisory, (Missouri Department of Health, 1990).

Total chlordane in this study is the sum of cis-chlordane, trans-chlordane, and trans-nonachlor. Of the 

three components, trans-nonachlor is the most resistant to environmental degradation. The ratio of cisand trans-chlordane to trans-nonachlor is an indicator of the proportion of recently released chlordane to 

"weathered" chlordane. It does not, however, provide a specific time estimate of the weathering period 

involved. Weathered chlordane was associated with the silt during sample periods of spring runoff 

(March 1989 and 1990), which indicated the source of the chlordane to be resuspension of bed sediment 

or runoff of previously contaminated sediment rather than more recent environmental inputs of 

chlordane.

DCPA also is ubiquitous on the suspended silts of the Mississippi River and its principal tributaries. 

Concentrations of DCPA on silts usually do not vary widely from one part of the river to another, which 

indicates that DCPA comes from widely dispersed nonpoint sources rather than from specific regions or 

tributaries.

Hexachlorobenzene, in contrast, has more specific sources in the Mississippi River Basin. Suspended 

silts of the Ohio River carry concentrations of hexachlorobenzene that are consistently greater than those 

of the Upper Mississippi and its tributaries (Illinois and Missouri Rivers) by factors of 5 or more. The 

concentration of hexachlorobenzene increases significantly between St. Francisville (above Baton 

Rouge) and Belle Chasse (below New Orleans), Louisiana, as the river flows through an industrial 

corridor.

PCBs in Silts and Colloids

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Figure 48. -- Large proportions of the organic contaminants are associated with the colloidal fraction of 

the sediments suspended in the Mississippi River. "Colloid" was defined operationally in this study as 

the suspended matter that passed through the ultracentrifuge but was removed by the ultrafilter (see the 

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chapter on "Sampling the Big Rivers"). In effect, the boundary between "colloid" and "silt" was about 

0.1 micrometer, or one ten-thousandth of a millimeter. Data shown in the figure are from samples 

collected in the Mississippi River and four major tributaries during the downriver sampling cruise of 

July-August 1991. Complete data are tabulated in the report by Rostad, Monsterleet, and others (1995).

A

In suspended sediments of the Mississippi River, concentrations of total PCBs usually are greater 

for colloids than for silts---not only because the colloidal material has more exposed surface area 

onto which PCBs can be adsorbed, but because colloids usually contain larger proportions of 

organic carbon. Data in the graph show that PCB concentrations are greatest in the uppermost 

Mississippi River for both the silt and colloid. Throughout most of the river system and the major 

tributaries, however, concentrations for the colloids are consistently greater than those for the 

silts.

B

In terms of the total loads of PCBs transported by the Mississippi River, silt transport is more 

important than colloidal transport, simply because there is much more silt than colloid in 

suspension in the river. Transports shown in the graph are computed by multiplying the 

concentrations shown in figure 48A by the concentrations of silt and colloid in suspension and 

the discharge of the water. Even though concentrations of PCBs in colloids may exceed those in 

silts by factors of 2 or 3, the quantities of silt in suspension usually exceed those of colloids in 

suspension by factors near 10. Therefore, the total quantities of PCBs transported down the 

Mississippi River by silts are usually 3 to 5 times greater than those transported by colloids.

Contaminants Associated with Suspended Colloid

Colloids are very small organic or mineral particles that can barely be seen by the naked eye (Rees and 

Ranville, 1989). They make the water slightly turbid and do not settle out with time. Recent studies of 

contaminant solubility in natural waters have found higher concentrations in the aqueous phase than 

thought possible. These findings were attributed to the possible presence of colloidal-sized particles 

(Baker and others, 1986). Separation of colloids from the aqueous phase is difficult and very little is 

known about their composition and behavior. Enough colloidal material was isolated during the July and 

October 1991 cruises for analysis of specific organic contaminants. Colloids in the Mississippi River 

average about 10 percent by weight of the total suspended material. Although the concentration of silt 

varies, the concentration of colloid seems to be fairly consistent.

Most toxic compounds travel in association with organic carbon, and the attribute of colloids that makes 

them especially important in the transport of pollutants is their high content of organic carbon. The 

colloid sampled in the Mississippi River averaged 15 percent organic carbon, which was substantially 

higher than that of the silt (3 percent). Colloidal material from the Upper Mississippi River was higher in 

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organic carbon content than that from the Lower Mississippi River.

Colloid particles do not settle. Once a contaminant is adsorbed to a colloidal particle, its transport is 

probably consistent along the length of the river system. Silt transport, however, varies greatly in 

response to the variations in velocity, turbulence, and discharge of the river. The amount of 

contaminants transported by the colloids should be consistent, whereas the amount transported by the silt 

may vary widely.

Contaminants Associated with Fish

Fish-consumption advisories have been issued at many sites along the Mississippi River, especially for 

carp and channel catfish. Most of these warnings are based on high concentrations in the fish of the 

ubiquitous compounds that are also found associated with the suspended material: PCBs, chlordane, 

DDT, and dieldrin. According to the U.S. Fish and Wildlife Service, concentrations of PCBs and 

chlordane in the fish in the Mississippi River remained relatively constant from 1976 to 1981 (Schmitt 

and others, 1983, 1985). The PCBs were most concentrated in fish in the Mississippi River near Pepin, 

Wisconsin, and in the Ohio River. Chlordane residues in fish were greatest in the Ohio River and in the 

Mississippi River at Cape Girardeau, Missouri. Highest hexachlorobenzene concentrations were in fish 

from the Mississippi River at Luling, Louisiana. DCPA concentrations in fish declined slightly from 

1976 to 1981.

A study by the Tennessee Department of Health and Environment that included more than 500 km of the 

Mississippi River upstream and downstream from Memphis showed how, in addition to the consistent 

background of these compounds, concentrations in fish can sharply increase near more heavily 

contaminated areas (Collins and others, 1989). Local studies have found that most severe cases of fish 

contamination occur near large urban areas (Iowa Department of Natural Resources, 1992).

PCBs in Bed Sediments

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Figure 49. -- Concentrations of PCBs stored in the bed sediments in the navigation pools of the Upper 

Mississippi River vary from place to place and according to the times at which the sediments were 

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deposited.

A

In the surficial bed sediments (that is, the sediments no more than 10 cm below the bottoms of 

the pools), the concentrations of total PCBs are large below Minneapolis-St. Paul, reach their 

greatest values in Lake Pepin, and are significantly smaller in the pools downriver of Lake Pepin. 

Data in the graph are from composite samples that were collected during 1991--92 at 15--20 

locations in the lower reaches of each navigation pool and combined into a single sample (one 

per pool) for the analysis of total PCBs. Locations of the navigation pools are shown in the map 

on the left side of the figure. "UP" and "LP" in the graph denote Upper and Lower Lake Pepin. 

Data are tabulated in the report by Iverson and others (1995). Lake Pepin is the only large natural 

lake on the Mississippi River main stem below Minneapolis-St. Paul, and it apparently functions 

as the principal repository of many of the sediment-associated contaminants discharged from the 

metropolitan area. Furthermore, the high concentrations of organic carbon in this region of the 

river (see fig. 29D) probably increase the attraction between PCBs and the local sediments.

B

The history of PCB contamination in the Upper Mississippi River is recorded in the sediments 

that have been deposited and stored in the navigation pools. Shown in the graph are the 

concentrations of total PCBs in a core taken in March 1989 from the bed sediments in a shallow 

backwater in the lower end of Pool 2, a few miles downriver from Minneapolis-St. Paul. Data 

were provided by Dan Helwig of the Minnesota Pollution Control Agency, Water Quality 

Division. Very high PCB concentrations of 2,000--3,000 nanograms per gram (ng/g) are found in 

the sediments deposited when large quantities of PCBs were allowed to enter the river, probably 

during the 1950s and 1960s. Following the cessation of the manufacture of PCBs, and the 

passage of State and Federal regulations restricting their use and disposal during the 1970s, 

concentrations of PCBs on sediments decreased markedly. The uppermost 35 cm of the core 

consisted of sediments in which concentrations consistently averaged about 150 ng/g. Because of 

the proximity to the Twin Cities, even these more recent PCB concentrations are greater than 

those in sediments stored farther downriver.

Chlordane and PCBs in Catfish

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Figure 50. -- Although banned for years, many halogenated organic contaminants persist in rivers and 

are ingested or absorbed by fish. Shown in the graphs are the concentrations of chlordane and PCBs in 

catfish taken from the Mississippi River and four of its tributaries during July-August 1987. One to four 

fish caught by hook and line at each location were homogenized in a blender and analyzed for PCBs and 

chlordane, as well as for other compounds such as hexachlorobenzene, DCPA, and DDT and its 

degradation products. Complete data are tabulated in the report by Leiker and others (1991).

A

Chlordane is especially concentrated in catfish. Concentrations of chlordane shown here are 

substantially greater than those on the suspended sediment in the Mississippi River, which are 

almost always less than 10 (often less than 5) nanograms of chlordane per gram of suspended silt. 

Chlordane is especially lipophilic-that is, especially soluble in the fatty tissues of the fish-and 

difficult to metabolize. The action level for chlordane of 300 nanograms per gram, specified by 

the U.S. Food and Drug Administration (USFDA, 1986) corresponds to the top of the graph.

B

PCB concentrations in catfish in the Mississippi River are comparable to those on suspended 

sediment. Although the "total" PCB shown here refers to the sum of the tetra-, penta-, hexa-, and 

heptachlorobiphenyls, this total is comparable to that of the penta-, hexa-, hepta-, and 

octachlorobiphenyls portrayed in the other figures of this chapter. The action level for PCBs of 

2,000 nanograms per gram, specified by USFDA (1986), is well above the range of values shown 

here. 

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Compliance policy guide 7141.01: Pesticide residues in food and feed--enforcement criteria, 

chap. 41--Pesticides. 

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Continue to ' Organic Contamination of the Mississippi river from Municipal and Industrial Wastewater

', or return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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Contaminants in the Mississippi River, 1987-92--Organic Contamination of the Mississippi River from Municipal and Industrial Wastewater

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Organic Contamination of the Mississippi River from 

Municipal and Industrial Wastewater

Larry B. Barber, II, Jerry A. Leenheer, Wilfred E. Pereira, 

Ted I. Noyes, Greg K. Brown, Charles F. Tabor, and 

Jeff H. Writer

Fate of Contaminants in the River

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Figure 51. -- The most significant factors controlling the concentrations of organic contaminants in rivers are the 

physical processes of dispersion and dilution. Within this physical framework, the most significant chemical and 

biological processes controlling the fate of organic contaminants in the Mississippi River are (1) sorption to the 

sediment and removal by deposition, (2) desorption and diffusion of contaminants from bed sediments back into the 

water, (3) biological transformation to intermediate compounds, or biodegradation for complete removal, (4) 

volatilization to the atmosphere, (5) bioconcentration and magnification in the food chain, (6) photolysis, or the 

breakdown of contaminants under the influence of sunlight, and (7) hydrolysis, or the decomposition of contaminants 

by taking up the elements of water. Organic compounds of the type called "hydrophobic" (meaning that they prefer 

being sorbed onto sediment or organic particles to being dissolved in water) can be adsorbed onto sediments in 

concentrations that are a thousand to a million times greater than in the associated water. Once they are sorbed, the 

contaminants can be deposited and eventually become buried as sediments continue to accumulate. Buried 

contaminants can be remobilized, however, by resuspension of the sediments. Likewise, the sedimentary organic 

matter may decompose, reintroducing its sorbed contaminants to the river by desorption and diffusion of organic 

colloids. If the contaminants are sorbed onto the sediments in high concentrations, they can adversely affect bottomdwelling organisms. The tendency of a contaminant to sorb onto the sediment is frequently indicative of its capacity 

to bioconcentrate and become magnified in the food chain.

Many organic contaminants are biodegraded in rivers. Readily degradable compounds may have a biodegradation 

half-life (time for one-half of the mass of a compound to be removed) in a river environment of less than 1 day, 

depending on factors such as temperature, population of bacteria, availability of oxygen, and availability of nutrients. 

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Other organic contaminants are resistant to biodegradation and have half-lives on the order of years. Compounds that 

are rapidly biodegraded under aerobic conditions, such as those found in a flowing stream, may persist under the 

anaerobic conditions that exist in buried sediments.

Some organic contaminants are volatile, and the major pathway for their removal from water is transfer to the 

atmosphere. The rate of volatilization is a function of the vapor pressure and water solubility of the compound, water 

temperature, and amount of turbulence in the water. A typical half-life for volatile organic compounds is on the order 

of a few hours; thus, even high concentrations can be rapidly attenuated in river systems.

All these processes---sorption, biodegradation, and volatilization, as well as photolysis and hydrolysis---interact in 

complex ways in the natural environment. For example, biotransformations can increase the solubility of a 

hydrophobic organic contaminant, which results in less sorption and greater mobility in the river. The Mississippi 

River is dynamic, and the distribution of contaminants between air, water, sediment, and organisms is continually 

changing with variations in the chemical, hydrological, and climatic regimes. The transportation of sediment-bound 

contaminants, for example, is episodic; most of the transport occurs during periods of high flow and bed scouring. 

Instream biodegradation rates usually decrease at lower temperatures. Ice cover during cold weather decreases the 

importance of volatilization as a removal pathway. High concentrations of dissolved organic matter can affect 

sorption, biodegradation, and volatilization of organic contaminants.

Introduction

The Mississippi River receives a variety of organic wastes, some of which are detrimental to human health and 

aquatic organisms. Urban areas, farms, factories, and individual households all contribute to contamination of the 

Mississippi River by organic compounds. This contamination is important because about 70 cities rely on the 

Mississippi River as a source of drinking water. Considerable gains have been made in the last two decades in 

controlling point-source contamination, but control of nonpoint-source contamination has been more difficult. 

Among the topics that are discussed in this chapter and its figures are (1) a comparison of the present-day water 

quality of the river with historical trends, (2) the environmental processes controlling the occurrence and fate of 

organic contaminants, (3) the distributions and concentrations of organic contaminants in the water and sediments 

along the entire length of the river, and (4) the seasonal variability of some of the contamination patterns. Organic 

contaminants in the Mississippi River were assessed by collecting water and sediment samples between MinneapolisSt. Paul, Minnesota, and New Orleans, Louisiana, during 10 sampling cruises conducted in 1987--92, and analyzing 

the samples for the organic contaminants and indicator compounds listed in table 10.

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Trends in Water Quality: A Historical Perspective

The relation between water pollution and public health has been recognized since the Colonial period, and increasing 

efforts have been made during the last century in the field of water pollution control. The earliest concerns with water 

pollution were about transmission of pathogenic diseases, such as typhoid, and obstruction of waterways by refuse 

from domestic and commercial sources. Anecdotal evidence from early reports indicates that development of 

metropolitan areas along the Mississippi River and its tributaries during the 1800s and early 1900s had a negative 

effect on water quality. The status of the Mississippi River at Minneapolis-St. Paul is illustrated by the following 

quotations:

"In 1888, the Engineers were called to remove a bar forming near the St. Paul waterfront. Dredging discovered that 

this bar was formed entirely of garbage dumped into the river by St. Paul. This area of the river had been shoaling for 

several years; the Corps was called in only when the smell became so objectionable that private citizens obtained an 

injunction against the governments of Minneapolis and St. Paul. Minneapolis dumped 500 tons of garbage a day just 

below the Falls of St. Anthony, and St. Paul added even more than that." (Tweet, 1984, p. 125-126.)

"During the months of low flows recorded for June, July, and August (1926), the pool above the High Dam was in a 

septic condition with the ebullition of large quantities of gas at the surface. On many occasions the surface of the 

pool was covered with sewage sleek, the oily floating substances contained in sewage, and was highly discolored for 

a considerable distance below the sewer outlets. Odors were noticeable at times, but usually in the vicinity of the 

larger sewer outlets. Below the High Dam septic conditions also prevailed in the back water pools during the 

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summer." (Wisconsin State Board of Health, 1927, p. 310).

Gross contamination problems like these were gradually eliminated during the mid-1900s, but less obvious problems 

caused the quality of the Mississippi River to decline as population centers continued to grow. After World War II, 

the synthetic-organic chemical industry rapidly expanded and thousands of new chemicals eventually made their way 

into natural waters. Beginning about 1950, investigations into the occurrence of organic chemicals indicated that the 

Mississippi River had been significantly degraded by organic contaminants. Since the passing of pollution-control 

laws during the early 1970s, many of the obvious and readily correctable sources of contamination from industrial 

and municipal wastewater have been eliminated or diminished. Improvements in sewage-treatment plants have 

improved the water quality even though the population has continued to increase.

Municipal-and Industrial-Derived Wastewater: A Perspective on Today

Municipal wastewater is the aggregate of all water used and disposed of in a community. The mean per capita 

domestic wastewater flow rate for the United States is 200--500 liters per person per day. The synthetic-organic 

chemical composition of municipal wastewater is a function of the various products consumed by individual 

households and the contribution of industrial effluents. Sewage effluents also contain a variety of natural organic 

chemicals from human waste and food products, a variety of micro-organisms including bacteria and viruses, and a 

variety of inorganic chemicals.

In many metropolitan areas, domestic and industrial wastes and stormwater runoff are drained into a combined 

sewer. Combined-sewer overflows can contribute high waste loads for short time periods, and pollution loads vary as 

a function of discrete storm events. Combined-sewer overflows vary in composition with the density of population 

and the type of industry.

Municipal sewage and industrial wastewater are typically treated prior to their discharge into surface waters. Most 

municipal wastewater is treated by activated-sludge or trickling-filter methods that rely on sorption and 

biodegradation to remove organic contaminants. Removal efficiency for strongly sorbing, biologically labile, and 

volatile organic compounds ranges from 25 percent for primary treatment, 80 to 98 percent for secondary treatment, 

and greater than 98 percent for tertiary treatment. However, poorly sorbing and biologically recalcitrant compounds 

are not completely removed even during tertiary treatment. Depending on the type of treatment, removal of microorganisms varies from negligible to more than 95 percent.

After effluent is discharged into a river, dilution becomes a major factor regulating the concentrations of dissolved 

chemicals. The stream-dilution factor is a function of streamflow and effluent discharge (stream-dilution factor = 

streamflow divided by cumulative effluent discharge). Stream-dilution factors determined for individual cities along 

the Mississippi River during this study varied: about 50 for Minneapolis-St. Paul, 500 for St. Louis, and 1500 for 

New Orleans. Stream-dilution factors for many small cities along the lower river were greater than 100,000. 

However, cumulative stream-dilution factors, determined using the combined effluent volumes for all upriver 

municipal discharges, including tributaries, were relatively constant along the entire river and ranged from 25 to 50, 

indicating that 2 to 4 percent of the river volume is contributed by municipal wastewater discharges. 

Stream-dilution factors vary as a function of season and long-term hydrological trends. For example, the Mississippi 

River discharges that were sampled during this study varied by a factor of two in the upper river and a factor of four 

in the lower river. Although stream-dilution factors can exceed 100,000, some contaminants such as fecal coliform 

bacteria can have concentrations up to millions of bacteria per liter in treated sewage effluents; thus, even small cities 

can contaminate the river with bacteria.

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In addition to chemicals derived from domestic sources, municipal effluents also have an industrial component that 

varies depending on the type and number of industries present. For a given reach of the river, it may not be possible 

to distinguish contaminants introduced directly through onsite industrial discharges from contaminants introduced by 

industry through municipal wastewater. Likewise, urban runoff through storm sewers or from overland flow is a 

potential source of chemicals that may be difficult to distinguish from treated wastewater effluent. However, some 

synthetic-organic chemicals are unique and can be traced directly to specific industrial discharges.

Other significant sources of organic contamination along the Mississippi River are powerplants and pulp mills. A 

typical power- plant along the Upper Mississippi River uses about 6.6 cubic meters per second (m3/s) of cooling 

water (Water Quality Work Group of the Great River Environmental Action Team, 1980a), which amounts to 

approximately 3 percent of the average Mississippi River discharge at Minneapolis. Power- plants use a variety of 

chemicals in their cooling water, including chlo-rine as a disinfectant to prevent biofouling, and metal-complexing 

agents to prevent scale buildup. Pulp mills also can discharge large quantities of wastewater. The mean discharge for 

six pulp mills located along the Mississippi River and its tributaries is about 1 m3/s (Costner and Thornton, 1989), 

which is equal to about 10 percent of the municipal discharge for St. Louis. However, because of the high organic 

content of pulp-mill effluents, their organic loading to the river can be significant compared with municipal 

wastewaters. Pulp mills use a wide variety of organic chemicals, and the bleaching process produces significant 

amounts of chlorinated organic compounds. Another important source of organic contaminants is the application of 

agricultural chemicals such as fertilizers and pesticides. These chemical formulations are complex and consist of both 

active and inert ingredients. Many of the inert ingredients are solvents, surfactants, and builders that also are common 

in domestic and industrial products. Runoff from feedlots also contains high concentrations of organic matter and 

fecal coliform. 

Surfactants in the River

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Figure 52. -- Anionic surfactants were studied in river waters during the 1950s to 1970s because they caused 

extensive foaming. Consequently, they have been measured for a long enough period (since 1958 in the Mississippi 

River) to provide an example of long-term trends in water quality. The foaming was the result of high concentrations 

of branched-chained alkylbenzenesulfonates (ABS) that were resistant to biological degradation during wastewater 

treatment and residence in rivers. Concentrations were frequently above the foaming threshold of about 0.5 milligram 

per liter (mg/L). Dilution was the primary attenuation mechanism for ABS. To remedy the foaming problem, the 

surfactant-manufacturing industry modified the chemical structure of the molecule to a more biodegradable linear 

side chain (LAS) which resulted in a significant decrease in concentrations during wastewater treatment and 

residence in rivers (Swisher, 1964). From 1959 to 1965, ABS concentrations in the Illinois River ranged from 0.4 to 

9 mg/L; from 1965 to 1966, ABS+LAS concentrations ranged from about 0.2 to 0.3 mg/L (Sullivan and Evans, 1968; 

Sullivan and Swisher, 1969). After 1968, LAS concentrations decreased to less than 0.1 mg/L even though surfactant 

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consumption increased by more than 30 percent. This example shows that it is possible to reverse certain pollution 

effects, in this case by the compulsory introduction of a more biodegradable material. 

The box plots in the figure show the average annual concentrations of anionic surfactants (ABS plus LAS measured 

as methylene-blue-active substances) for all available sampling sites along the Mississippi River from 1963 to 1976 

in the U.S. Environmental Protection Agency's STORET data base. Although the switchover from ABS to LAS 

occurred between 1964 and 1968, the concentrations of anionic surfactants in the Mississippi River continued to rise 

until 1971 or 1972, probably the result of increasing consumption rates and population density. Following 1972, 

concentrations decreased to the levels observed today, reflecting improvements in wastewater-treatment plants as the 

result of the Federal Water Pollution Control Act of 1972, which required secondary treatment of sewage effluents. 

The continued decrease of surfactant concentrations is shown in data collected during 1991--92, which are plotted on 

the right side of the graph.

Fecal Coliforms in the River

(Not Available)

Figure 53. -- Bacterial contamination of water is commonly assessed by measuring fecal coliform bacteria, which are 

present in untreated domestic sewage and animal wastes in extremely large concentrations (1,000 to 100,000 

organisms per milliliter; American Public Health Association, 1992). The current maximum contaminant level for 

whole-body-contact recreation for fecal coliform bacteria is 200 organisms per 100 milliliter (mL). Coliform bacteria 

have been measured at many sites on the Mississippi River from the 1920s to the present. Fecal coliform 

concentrations as great as 100,000 organisms per 100 mL that were measured in the river in 1925--26 resulted from 

untreated sewage inputs near Minneapolis-St. Paul, Minnesota (Wisconsin State Board of Health, 1927). By the 

1970s, improved wastewater treatment had greatly decreased fecal coliform concentrations in most of the river 

although high levels were still reported below Minneapolis-St. Paul and St. Louis, Missouri (Water Quality Work 

Group of the Great River Environmental Action Team, 1980a, 1980b). Fecal coliforms also are derived from animal 

waste and feedlot runoff. 

The box plots in the figure show fecal coliform concentrations along the Mississippi River from 1982 to 1992 

obtained from the U.S. Environmental Protection Agency's STORET data base and the U.S. Geological Survey's 

WATSTORE data base. Data for St. Louis from the Illinois River Watch program and data from the current study for 

1991--92 also are plotted in the figure. Median fecal coliform concentrations exceeded the standard by a factor of 10 

or more near Guttenberg, Iowa, Rock Island, Illinois (Quad Cities), St. Louis and Cape Girardeau, Missouri, and 

Memphis, Tennessee. The standard was exceeded to a lesser extent at several other locations. Standards also were 

exceeded in the Rock, Iowa, Des Moines, Missouri, and Kaskaskia Rivers (data not shown in the figure). Although 

earlier studies (Water Quality Work Group of the Great River Environmental Action team, 1980a) showed the 

standards being exceeded near Minneapolis-St. Paul, our measurements showed coliform counts in that area that 

were lower than the standard, indicating efficient removal during wastewater treatment. The fecal coliform 

contamination near St. Louis during 1991--92 was consistent with data reported by the Water Quality Work Group of 

the Great River Environmental Action Team (1980b), and probably results from lack of chlorination of treated 

sewage effluent in the metropolitan area.

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Wastewater Contaminants Along the River

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Figure 54. -- Distributions and concentrations of dissolved organic contaminants along the length of the Mississippi 

River are best viewed in the context of other physical and chemical properties of the river water. During the three 

upriver cruises in summer 1991, fall 1991, and spring 1992 (see "Sampling the Length of the River"), samples were 

taken and measurements were made near the center of the river approximately every 10 miles between New Orleans 

and Minneapolis. On the left side of the figure are shown the distributions of three "background" variables---

temperature, specific conductance, and dissolved organic carbon---to provide a context for viewing the contaminant 

data. On the right side of the figure are shown the distributions of three groups of dissolved organic contaminants---

surfactants (MBAS and LAS) and adsorbable organic halogen (AOX). Complete tabulations of the data are given by 

Barber, Leenheer, and others (1995).

A

During the upriver cruise of summer 1991, water temperatures were fairly uniform along the length of the 

river and ranged from 22° to 27°C. By early fall 1991, the temperatures near Minneapolis had decreased about 

10° while temperatures near New Orleans remained at summer levels; water temperature between 

Minneapolis and New Orleans showed a regular increase in the downstream direction. By early spring 1992, 

temperatures near Minneapolis were about 15°C lower than the previous summer and they increased 

downstream. During the winter (data not shown) water temperatures between Minneapolis and LaCrosse, 

Wisconsin (kilometer 2660), were near 0°C. A major influence of the various temperature regimes is their 

effect on rates of instream biodegradation, which decreases with decreasing temperature. The rate of 

volatilization also is affected by temperature, and the presence of ice cover during the winter can reduce the 

transfer of contaminants to the atmosphere.

B

Specific conductance is a measure of total inorganic dissolved solids, and the profiles measured during the 

three upriver cruises of 1991--92 generally resemble the long-term average profile of total dissolved solids in 

the Mississippi River shown in figure 12. Maximum values in the upper river were measured immediately 

below the confluence of the Minnesota River, which had the highest specific conductance of any tributary. 

Specific conductance decreased downstream as the result of dilution by low-conductivity tributaries such as 

the St. Croix, Chippewa, Black, and Wisconsin Rivers. The reach between the Illinois and Ohio Rivers 

(kilometers 1890 and 1530) had elevated specific conductance, reflecting the input of high-conductivity water 

from the Missouri River. Specific conductance decreased sharply as the Mississippi River received the more 

dilute waters of the Ohio River, and the lower river had relatively uniform values. There was little seasonal 

variability in specific conductance of the upper river. Seasonal variability in the reach between the Illinois and 

Ohio Rivers was controlled by the relative discharge from the Missouri River. Seasonal variability in the 

lower river was related to discharge, with the highest values recorded during low flow during the fall. Several 

spikes in the profiles were probably the results of point-source inputs and hydrological events that occurred 

upstream.

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C

Dissolved organic carbon (DOC) is a measure of the total dissolved organic matter in the Mississippi River, 

most of which is natural. Wastewaters are only minor contributors of DOC. The most obvious features of the 

DOC profiles shown in the figure were the high concentrations in the upper river that decrease downstream, 

the sharp decreases in concentration below the Ohio River, and the relatively uniform concentrations (about 4 

mg/L) in the lower river. There were distinct seasonal differences in DOC concentrations in the upper river; 

seasonal differences in the lower river were much less pronounced. DOC has important geochemical 

implications for the occurrence and fate of organic contaminants because it can (1) increase the solubility and 

facilitate the transport of organic contaminants, (2) alter rates of biodegradation, (3) form complexes with 

trace metals, and (4) react during water treatment to produce potentially toxic by-products (see next chapter).

D

Surfactants are major ingredients of soaps and detergents, and their presence is an indication of the effect of 

domestic wastewater on the water quality of the Mississippi River. Total anionic surfactants were determined 

as methylene-blue-active substances (MBAS), which is a composite measurement of linear 

alkylbenzenesulfonate (LAS), LAS biological metabolites and impurities, other synthetic-anionic surfactants, 

and naturally occurring compounds such as humic substances. The graph shows that during the upriver cruises 

of 1991--92, MBAS were present throughout the Mississippi River and its tributaries at concentrations 

ranging from about 20 μg/L to 100 μg/L, values that are below the drinking-water standard of 500 μg/L. The 

MBAS profiles showed some of the same general trends as specific conductance and DOC, including values 

in the upper river that were slightly larger than those in the lower river. The greater variability and scatter in 

the MBAS data indicate the effects of multiple point-source inputs from municipal wastewater discharges. 

MBAS concentrations had peaks in the vicinity of major cities and decreased rapidly downstream because of 

dilution, biodegradation, and sorption to the sediments.

E

Specific measurements for linear alkylbenzenesulfonate (LAS) were not strongly correlated with MBAS, and 

many of the samples with elevated MBAS had low levels of LAS. The annual consumption of LAS in the 

United States is about 300,000 metric tons per year (Schirber, 1989). LAS is readily biodegraded under 

aerobic conditions to form intermediate compounds and ultimately carbon dioxide, water, and sulfate 

(Swisher, 1987). Although LAS and its byproducts are nontoxic to humans, aquatic organisms can be 

sensitive to concentrations ranging from 10 to 1000 μg/L (Kimerle and Swisher, 1977; Kimerle, 1989). 

Measurable LAS concentrations in the Mississippi River were found near Minneapolis, St. Louis, and New 

Orleans. However, LAS concentrations drop below detectable levels within 80 km downstream from the 

major sources as the result of dilution and instream biodegradation. The St. Louis area has a stream-dilution 

factor (river discharge divided by municipal effluent discharge) of about 500, but has the highest LAS 

concentrations along the river. In contrast, the stream-dilution factor for Minneapolis is about 50 and 

concentrations are very low. The stream-dilution factor for New Orleans is about 1500, and concentrations are 

similar to those below Minneapolis-St. Paul.

F

Adsorbable organic halogen (AOX) is a measure of dissolved chlorinated organic matter, including both 

volatile and nonvolatile compounds, some of which may be toxic. These compounds are difficult to measure 

individually, so the AOX measurement serves as an overall index of their combined effect on water quality. 

AOX comes from a variety of sources, in particular, the chlorination of natural organic matter during 

disinfection of sewage effluents, biofouling control in powerplant cooling waters, pulp-wood bleaching, and 

other industrial discharges. There also are significant natural sources of AOX. The graph shows AOX profiles 

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for the three upriver cruises of 1991--92. Although concentrations and distributions varied significantly along 

the river and among cruises, spatial trends relative to river reach were not as apparent as for other 

constituents. The greatest concentrations occurred during the spring and may have been the result of flushing 

natural and atmospherically transported AOX from the soils or increased anthropogenic sources during spring 

runoff events. The multiple spikes during the spring and fall probably represent sporadic inputs from point 

sources. The concentrations of AOX in the Mississippi River exceeded those that would be expected from 

discharge of treated municipal sewage effluent, indicating that other sources such as pulp mills and 

powerplants also contribute AOX. For example, a single pulp mill can contribute 840 kilograms (kg) per day 

of AOX (Costner and Thornton, 1989) which is 5--10 percent of the total Mississippi River AOX load near 

the confluence with the Ohio River. A typical powerplant can contribute a daily load of 600 kg per day (Water 

Quality Work Group of the Great River Environmental Action Team, 1980a). In contrast, the municipaltreated sewage discharge from St. Louis contributes an average of about 250 kg of AOX per day.

Wastewater Contaminants in Bed Sediments

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Figure 55. -- The sediments deposited and stored in the navigation pools of the Upper Mississippi River are 

contaminated with organic pollutants derived from municipal and other sources. Data in these three graphs are from 

samples of bed sediment collected during 1991--92 from the shallow areas of the navigation pools. Additional 

samples were collected from the shallow backwater areas of the unimpounded river at St. Louis and at Thebes, 

Illinois, 215 km downriver of St. Louis. Complete tabulations of the data are given in the reports by Writer (1992), 

Tabor (1993), Barber, Writer, and others (1995), and Writer and others (1995).

A

Linear alkylbenzenesulfonate (LAS) is found in soaps and detergents, and its presence in river- bottom 

sediments indicates contamination by domestic and municipal wastes. The concentrations of LAS on bed 

sediments (about 0.1 to 1 milligram per kilogram (mg/kg) of sediment) are one to three orders of magnitude 

greater than those detected in the overlying water (0.00005 to 0.012 milligrams per liter (mg/L) of water). The 

data in the graph show a pattern that can be attributed to inputs from cities such as Minneapolis-St. Paul, 

LaCrosse, and Rock Island. Biodegradation removes LAS from the sediment---at rates that apparently are 

variable enough to complicate patterns of high and low concentrations attributed to local sources.

B

Coprostanol is a fecal sterol that comes from human and livestock wastes. A properly operating wastewatertreatment plant will remove 95--99 percent of the coprostanol, resulting in concentrations ranging from 30 to 

50 micrograms per liter (μg/L) in sewage effluents and from 1,400 to 7,900 mg/kg in sewage sludge (Walker 

and others, 1982). Between 85 and 95 percent of the coprostanol discharged in sewage effluents is associated 

with particulate matter that can be assimilated into bed sediments (Venkatesan and Kaplan, 1990). Data in the 

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figure show that coprostanol concentrations ranged from 0.09 to about 0.8 mg/kg.

Concentrations in excess of 0.1 mg/kg indicate sewage contamination (Hatcher and McGillivary, 1979). 

Coprostanol is biodegraded more slowly than LAS, and its distribution in the upper river can be explained in 

terms of sources and sinks. Obvious sources of coprostanol are Minneapolis-St. Paul (Pool 2). Sites for the 

accumulation and storage of coprostanol-bearing sediments are the two largest pools in the upper river (Lake 

Pepin and Pool 19). During moderate to large flows, the sediments are likely to be swept out of the smaller 

shallower pools of the upper river and deposited in the larger deeper pools.

C

Polynuclear aromatic hydrocarbons (PNAs) are organic compounds that are common contaminants in 

sediments, several of which are sufficiently toxic to be listed as priority pollutants by the U.S. Environmental 

Protection Agency. The sources of PNAs are complex, but they typically come from combustion processes. 

Urban runoff, municipal-wastewater discharges, wood-treatment facilities, petroleum development and 

processing, coal-storage facilities, and transportation networks (both land and river) all contribute PNAs to the 

Mississippi River. PNAs detected on the bed sediments include the priority pollutants naphthalene, 

acenaphthene, acenaphthylene, fluorene, phenanthrene, fluoranthene, anthracene, chrysene, pyrene, benzo[b]

fluoranthene, and benzo[k]fluoranthene. Concentrations of individual compounds ranged from less than 0.2 to 

about 10 mg/kg. Although only the elevated concentrations at Minneapolis-St. Paul (Pools 1 and 2) are clearly 

attributable to municipal sources, many of the PNAs detected in the other samples probably come from 

wastewater discharge and urban runoff.

Caffeine and EDTA in River Waters

(Click on image for a larger version, 83K)

Figure 56. -- Caffeine and EDTA (ethylenediaminetetraacetic acid) are two of the more ubiquitous dissolved organic 

compounds in the Mississippi River. Neither compound is highly toxic to humans, but each is a specific indicator of 

contamination by wastewaters.

A

Caffeine is a stimulant chemical in beverages such as coffee and soft drinks and in a variety of food products. 

Its concentrations in municipal wastewaters range from 20--300 μg/L (Rogers and others, 1986). The graphs 

show the concentrations of caffeine measured in the Mississippi River and its tributaries during the three 

downriver sampling cruises of 1991--92 (a complete tabulation of data is given by Pereira and others, 1995). 

Caffeine is a fairly specific tracer of domestic wastewaters, and its profile illustrates the effect of population 

density on water quality. The concentration gradient between river kilometers 2950 and 2600 shows inputs 

from Minneapolis-St. Paul into the relatively small upper river and the progressive dilution downstream by 

the Minnesota and St. Croix Rivers. The elevated concentrations of caffeine in the Illinois River are from the 

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large population in the Chicago metropolitan area, and the abrupt increase in the Mississippi River near river 

kilometer 1850 is the result of input from the Illinois River. The gradual downstream decreases in caffeine 

concentrations in the river indicate instream degradation through biotic and abiotic processes in addition to 

dilution by tributaries. Caffeine occurs at similar concentrations to EDTA in sewage effluents, but it occurs at 

much lower concentrations in river water because of degradation and because it is not supplied by the 

industrial sources that also introduce EDTA.

B

EDTA is used to form water-soluble complexes with insoluble metals in a wide variety of domestic and 

industrial applications, including stabilization of bleaching agents in laundry detergents, prevention of boiler 

scale formation in powerplants, addition as a preservative and clarifying agent in foods and beverages, use in 

fertilizers as a source of chelated metal micronutrients, and other applications in the metal-plating, 

photography, paper, and textile industries. The 1990 United States production of EDTA was 49,687 metric 

tons (U.S. International Trade Commission, 1990). EDTA is an indicator of total domestic and industrial 

wastewater inputs. EDTA has low toxicity to humans and aquatic organisms. The chief water-quality 

concerns are its ability to mobilize toxic metals from sediments and to stimulate algal growth by increasing 

the availability of nutrients such as iron and zinc. EDTA is not biologically degraded during wastewater 

treatment, but various EDTA salts and metal complexes have been observed to degrade in light (Alder and 

others, 1990). As a consequence of the lack of biodegradation, its high solubility in water, and large rates of 

production and usage, EDTA can be one of the most abundant organic contaminants in surface waters. The 

graphs show EDTA concentrations measured in the Mississippi River and four principal tributaries during the 

three downriver sampling cruises of 1991--92 (L.B. Barber, II, unpub. data, 1995). Concentrations were 

greater in the upper river than the lower river, and the peak concentrations occurred between kilometers 2250 

and 1900 (between Dubuque and Keokuk, Iowa). The EDTA concentrations measured in the river were about 

five times greater than the concentrations that can be attributed to inputs of secondary treated municipal 

wastewaters. It is likely therefore that discharges from powerplants and other industrial sources contribute 

significantly to EDTA concentrations. The greatest tributary EDTA concentration was from the Illinois River, 

which probably reflects industrial and domestic wastewater inputs from the Chicago metropolitan area. In 

general, EDTA concentrations in the Mississippi River were lower than those reported for German rivers, 

which typically range from 10 to 60 μg/L (Frimmel and others, 1989).

Summary

A summary of the major organic contaminants identified, their range of concentrations, their water-quality criteria, 

and their environmental fate is presented in table 11. Fecal coliform bacteria was the only contaminant that exceeded 

health limits. Although concentrations of most organic compounds measured in this study were below regulatory 

limits, their distributions indicate that the entire Mississippi River has been contaminated by point and nonpoint 

sources. Significant sources of organic contaminants include municipal-wastewater discharge, urban runoff, powerplant cooling-water discharges, pulp-mill effluents, feedlot runoff, commercial and recreational river traffic and 

refueling, discharges from industrial facilities, and agricultural runoff.

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The Mississippi River carries higher concentrations of organic contaminants in the vicinity of major metropolitan 

areas. Concentrations are typically greatest in the upper river where the stream- dilution factors are lowest. Major 

tributaries such as the Minnesota, Illinois, Missouri, and Ohio Rivers have significant effects on the organic 

chemistry of the Mississippi River. Seasonal differences are related to hydrologic, climatic, biological, and 

geochemical factors. Concentrations are greatest during periods of low flow (fall) and least during periods of high 

flow (spring). Likewise, concentrations of biologically labile and volatile organic compounds are greatestduring the 

winter when temperatures are lowest.

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Although the data presented here provide only a brief glimpse of the water quality of the Mississippi River, 

comparisons with historical data show trends of improving water quality for several constituents. The improvements 

can be related to: (1) changes made by the chemical manufacturing industry to address the environmental fate of 

problematic chemicals, and (2) improved wastewater treatment by municipal and industrial dischargers. Converting 

primary treatment facilities to secondary treatment has resulted in improved water quality, although chemicals that 

are not completely removed present a challenge for treatment technology.

Much remains to be learned about the sources, fates, and effects of organic contaminants on human health and 

aquatic ecology. The data presented in the figures for this chapter and in the detailed reports of supporting data 

(Barber, Leenheer, and others, 1995; Barber, Writer, and others, 1995; Leenheer, Noyes, and Brown, 1995; 

Leenheer, Barber, and others, 1995; Pereira and others, 1995) represent a benchmark for future reference. They 

indicate critical areas where research is needed to more clearly define potential problems, and provide a baseline 

against which future changes in the water quality in the Mississippi River can be measured. 

TTT and Flame Retardants in River Waters

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Figure 57. -- Some of the organic contaminants that are dissolved in the waters of the Mississippi River can be 

traced to unique sources. Two of these are TTT, an industrial by-product primarily contributed from the Kanawha 

River Valley of West Virginia, and flame retardant additives contributed almost exclusively from the Illinois River 

watershed. Because their sources are so restricted, these compounds can be used as tracers of the waters of their 

source tributaries as they mix with the other waters that make up the Mississippi River. Samples portrayed in the 

graphs were collected during the downriver cruises of 1987--92; complete tabulations of the data are given by Pereira 

and others (1995).

A

TTT (1,3,5-trimethyl-2,4,6-triazinetrione) is a by-product of the manufacture of methylisocyanate. TTT has 

been reported in residual materials from a tank after the leak of methylisocyanate in Bhopal, India (D'Silva 

and others, 1986), in secondary effluent from a municipal and industrial wastewater-treatment plant in Illinois 

(Ellis and others, 1982), and in water from the Ohio River where it continues to be detected at 1--2 μg/L (Don 

Mackell, Louisville Water Company, Louisville, Kentucky, written commun., 1989). During the sampling 

cruises of 1987--92, the Ohio River was the major contributor of TTT to the Mississippi River, and the source 

was eventually traced to a location on the Kanawha River where methylisocyanate is manufactured and 

transported. TTT is a very stable compound and was detected in all water samples collected from the 

Mississippi River between the Ohio River and the Gulf of Mexico, indicating little or no degradation during 

2300 kilometers of river transport.

B

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THAP (trihaloalkylphosphates) are used as flame-retardant additives in flexible and rigid polyurethane foams, 

and in textiles. THAP are relatively water-soluble compounds that have low bioconcentration factors and 

short half-lives in fish. THAP have been reported in municipal water supplies of cities adjoining the Great 

Lakes in Canada (Williams and others, 1982; Williams and Le Bel, 1981), in surface waters of Japan (Japan 

Environmental Agency, 1977--79), and in surface water, ground water, and drinking water in Italy (Galassi 

and Guzella, 1988).

The graphs show the concentrations of total THAP (sum of tris-2-chloroethylphosphate and two isomers of 

tris-2-chloropropylphosphate), that were detected in all water samples collected from the Mississippi River 

and its tributaries during the downriver sampling cruises of 1987--92. In addition to minor sources of THAP 

along the Mississippi River, there is a major source on the Illinois River. THAP are relatively stable and 

degrade only slightly during transport from St. Louis to the Gulf of Mexico, a distance of about 1850 

kilometers.

Volatile Contaminants in the River

(Click on image for a larger version, 66K)

Figure 58. -- Volatile organic compounds (VOC) appear to be short lived in the Mississippi River, as would seem to 

be self-evident from the fact that the compounds are called "volatile." However, considerable effort was spent in 

testing the waters of the Mississippi River for their presence because (1) there are degrees of volatility and (2) some 

of the compounds are highly toxic. Sources of volatile organic compounds are industrial, municipal, and 

transportational (urban runoff and river traffic).

The graphs show several of the volatile organic compounds that were detected in significant concentrations in the 

midriver samples collected during the three upriver cruises of 1991--92. Of the 64 target compounds, for which 440 

samples were analyzed, 32 were detected and only 19 occurred in more than 1 percent of the samples. Concentrations 

of total VOC ranged from 0.2 to 3.1 μg/L and were typically an order of magnitude below maximum contaminant 

levels. There was a seasonal trend in volatile compound concentrations; the greatest frequency of detections and 

highest concentrations occurred during the fall and winter. During the winter (data not shown in the graphs) 

concentrations increase significantly in the reaches of the river that become ice covered. The areas with the most 

significant contamination by volatile organic compounds were the reach downstream from Minneapolis-St. Paul, the 

reach downstream from the confluence of the Ohio and Mississippi Rivers, and the reach between Baton Rouge and 

New Orleans.

SELECTED REFERENCES

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Contaminants in the Mississippi River, 1987-92--Organic Contamination of the Mississippi River from Municipal and Industrial Wastewater

Alder, A.C., Siegriest, H., Gujer, W., and Giger, W., 1990,

Behavior of NTA and EDTA in biological wastewater treatment: Water Research, v. 24, p. 733--742. 

American Public Health Association, 1992,

Standard methods for the examination of water and wastewater, 18th ed.: Washington, D.C., American Public 

Health Association, p. 9--60. 

Barber, L.B., II, Leenheer, J.A., Tabor, C.F., Brown, G.K., Noyes, T.I., and Noriega, M.C., 1995,

Organic compounds and sewage-derived contaminants, in Moody, J.A., ed., Chemical data for water samples 

collected during four upriver cruises on the Mississippi River between New Orleans, Louisiana, and 

Minneapolis, Minnesota, May 1990-April 1992: U.S. Geological Survey Open-File Report 94-523, p. 211--

297. 

Barber, L.B., II, Writer, J.H., Tabor, C.F., and Leenheer, J.A., 1995,

Sterols, polynuclear aromatic hydrocarbons, and linear alkylbenzene sulfonates, in Moody, J.A., ed., 

Hydrologic, sedimentologic, and chemical data describing surficial bed sediments and water in the navigation 

pools of the Upper Mississippi River, July 1991-April 1992: U.S. Geological Survey Open-File Report 95-

708. 

Costner, Pat, and Thornton, Joe, 1989, 

We all live downstream---The Mississippi River and the national toxics crisis: Washington, D.C., Greenpeace 

USA, 120 p., 1 app. (61 p.). 

Curtis, M.W., and Ward, C.H., 1981, 

Aquatic toxicity of forty industrial chemicals---Testing in support of hazardous substance spill prevention 

regulation: Journal of Hydrology, v. 51, p. 359--367. 

D'Silva, T.D.J., Lopes, A., Jones, R.L., Singhawangcha, S., and Chan, J.K., 1986,

Studies of methylisocyanate chemistry in the Bhopal incident: Journal of Organic Chemistry, v. 51, p. 3781--

3788. 

Dufour, A.P., 1984, 

Health effects criteria for fresh recreation waters: Research Triangle Park, N.C., U.S. Environmental 

Protection Agency, EPA-600 11-84-004, 33 p. 

Ellis, D.D., Jone, C.M., Larson, R.A., and Schaeffer, D.J., 1982,

Organic constituents of mutagenic secondary effluents from wastewater treatment plants: Archives of 

Environmental Contamination and Toxicology, v. 11, p. 373--382. 

Frimmel, F.H., Grenz, R., Kordik, E., and Dietz, F., 1989,

Nitrilotriacetate (NTA) and ethylenedinitrilotetraacetate (EDTA) in rivers of the Federal Republic of 

Germany: Vom Wasser, v. 72, p. 175--184. 

Galassi, S., and Guzella, L., 1988,

Organic phosphates in surface, ground, and drinking water, in Angeletti, G., and Bjorseth, A., eds., Organic 

micropollutants in the aquatic environment, Proceedings of the 5th European Symposium, Rome, Italy, Oct. 

20--22, 1987: Boston, Mass., Kluwer Academic, p. 108--115. 

Hatcher, J.P., and McGillivary, P.A., 1979,

Sewage contamination in the New York Bight---Coprostanol as an indicator: Environmental Science and 

Technology, v. 13, p. 1225--1229. 

Japan Environmental Agency, 1977, 1978, 1979,

Environmental Survey Reports: Office of Health Studies, Department of Environmental Health. 

Kimerle, R.A., 1989,

Aquatic and terrestrial ecotoxicology of linear alkylbenzene sulfonate: Tenside, Surfactants, Detergents, v. 26, 

p. 169--176. 

Kimerle, R.A., and Swisher, R.D., 1977,

Reduction of aquatic toxicity of linear alkylbenzene sulfonate (LAS) by biodegradation: Water Research, v. 

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Contaminants in the Mississippi River, 1987-92--Organic Contamination of the Mississippi River from Municipal and Industrial Wastewater

11, p. 31--37. 

Leenheer, J.A., Noyes, T.I., and Brown, P.A., 1995, 

Data on natural organic substances in dissolved, colloidal, suspended-silt and -clay, and bed-sediment phases 

in the Mississippi River and some of its tributaries, 1987--90: U.S. Geological Survey Water-Resources 

Investigations Report 93-4204, 71 p. 

Leenheer, J.A., Barber, L.B., II, Rostad, C.E., and Noyes, T.I., 1995,

Data on natural organic substances in dissolved, colloidal, suspended-silt and -clay, and bed-sediment phases 

in the Mississippi River and some of its tributaries, 1991--92: U.S. Geological Survey Water-Resources 

Investigations Report 94-4191, 47 p. 

Leenheer, J.A., Wershaw, R.L., Brown, P.A., and Noyes, T.I., 1991,

Detection of poly(ethylene glycol) residues from nonionic surfactants in surface water by 1H and 13C nuclear 

magnetic resonance spectrometry: Environmental Science and Technology, v. 25, p. 161--168. 

McLeese, D.W., Zitko, V., Sergeant, D.B., Burridge, L., and Metcalfe, C.D., 1981, 

Lethality and accumulation of alkylphenols in aquatic fauna: Chemosphere, v. 10, p. 723--730. 

Patoczka, J., and Pulliam, G.W., 1990,

Biodegradation and secondary effluent toxicity of ethoxylated surfactants: Water Research, v. 24, p. 965--972. 

Pereira, W.E., Moody, J.A., Hostettler, F.D., Rostad, C.E., and Leiker, T.J., 1995,

Concentrations and mass transport of pesticides and organic contaminants in the Mississippi River and some 

of its tributaries, 1987--89 and 1991--92: U.S. Geological Survey Open-File Report 94-376, 169 p. 

Persaud, D., Jaagumagi, R., and Hayton, A., 1993,

Guidelines for the protection and management of aquatic sediment quality in Ontario: Water Resources 

Branch, Ontario Ministry of the Environment and Energy. 

Pontius, F.W., 1993,

D-DBP rule to set tight standards: American Water Works Association Journal, v. 85, p. 23--30. 

Rogers, I.H., Birtwell, I.K., and Kruzynski, G.M., 1986,

Organic extractables in municipal wastewater, Vancouver, British Columbia: Canadian Journal Water 

Pollution Research, v. 21, p. 187--204. 

Schirber, C.A., 1989,

LAS and AEs: Soap/Cosmetics/Chemical Specialties, April, p. 32--36. 

Sullivan, W.T., and Evans, R.L., 1968,

Major U.S. river reflects surfactant changes: Environmental Science and Technology, v. 2, p. 194--200. 

Sullivan, W.T., and Swisher, R.D., 1969,

MBAS and LAS surfactants in the Illinois River, 1968: Environmental Science and Technology, v. 3, p. 481--

483. 

Swisher, R.D., 1964, 

LAS---Major development in detergents: Chemical Engineering Progress, v. 60, p. 41--45. 

___ 1987, Surfactant biodegradation, 2d ed.: New York, Marcel Dekker, 1085 p. 

Tabor, C.F., Jr., 1993,

The occurrence and fate of linear alkylbenzene sulfonate in the Mississippi River---A molecular indicator of 

sewage contamination: Boulder, University of Colorado, M.S. thesis, 78 p. 

Tabor, C.F., and Barber, L.B., II, 1996,

Fate of linear alkylbenzene sulfonate in the Mississippi River: Environmental Science and Technology, v. 30, 

no. 1. 

Tweet, Roald, 1984, 

A history of the Rock Island District, U.S. Army Corps of Engineers, 1866--1983: U.S. Army Engineer 

District, Rock Island, Illinois, 441 p. 

U.S. Environmental Protection Agency, 1987,

National primary drinking water regulations---Synthetic organic chemicals---Monitoring for unregulated 

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Contaminants in the Mississippi River, 1987-92--Organic Contamination of the Mississippi River from Municipal and Industrial Wastewater

contaminants; Final rule: Federal Register, v. 52, p. 25690--25717. 

___ 1994,

Drinking Water Regulations and Health Advisories: U.S. Environmental Protection Agency, Office of Water, 

Washington, D.C. 

U.S. International Trade Commission, 1990,

Synthetic organic chemicals, U.S. production and sales, 1990: U.S. International Trade Commission Report 

No. 2479. 

Venkatesan, M.I., and Kaplan, I.R., 1990, 

Sedimentary coprostanol as an index of sewage addition in the Santa Monica Basin, California: 

Environmental Science and Technology, v. 24, p. 208--213. 

Verhaar, H.J.M., van Leeuwen, C.J., and Hermens, J.L.M., 1992,

Classifying environmental pollutants. 1: Structure-activity relationships for prediction of aquatic toxicity: 

Chemosphere, v. 25, p. 471--491. 

Walker, R.W., Wun, C., and Litsky, W., 1982,

Coprostanol as an indicator of fecal pollution: CRC Critical Reviews in Environmental Control, v. 10, p. 91--

112. 

Water Quality Work Group of the Great River Environmental Action Team, 1980a, 

Water quality, sediment & erosion: GREAT I, Study of the Upper Mississippi River, v. 4, 125 p., 2 app. 

___ 1980b,

Water quality work group appendix: GREAT II, Study of the Upper Mississippi River (Guttenberg, Iowa, to 

Saverton, Missouri), 216 p. 

Williams, D.T., and Le Bel, G.L., 1981, 

A national survey of tri(haloalkyl)phosphates, trialkylphosphates, and triarylphosphates in Canadian drinking 

water: Bulletin of Environmental Contamination and Toxicology, v. 27, p. 450--45. 

Williams, D.T., Nestmannn, E.R., Le Bel, G.L., Benoit, F.M., Otson, R., and Lee, E.G.H., 1982,

Determination of mutagenic potential and organic contaminants of Great Lakes drinking water: Chemosphere, 

v. 11, p. 263--276. 

Wisconsin State Board of Health, 1927,

Stream pollution in Wisconsin: Madison, Wisconsin State Board of Health, p. 277--321. 

Writer, J.H., 1992,

Sewage contamination in the Upper Mississippi River as measured by the fecal sterol coprostanol: Boulder, 

University of Colorado, M.S. thesis, 99 p. 

Writer, J.H., Leenheer, J.A., Barber, L.B., Amy, G.L., and Chapra, S.C., 1995,

Sewage contamination in the Upper Mississippi River as measured by the fecal sterol, coprostanol: Water 

Research, v. 29, p. 1427--1436.

Continue to ' Potentially Deleterious Effects of Chlorinating Mississippi River Water for Drinking Purposes ', or 

return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

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Potentially Deleterious Effects of Chlorinating Mississippi River Water for Drinking Purposes

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

Potentially Deleterious Effects of Chlorinating 

Mississippi River Water for Drinking Purposes

Ronald E. Rathbun

Introduction

An emerging issue in the treatment of drinking water is the role played by chlorine in the formation of 

toxic compounds. The idea that chlorine might be deleterious seems paradoxical because the addition of 

chlorine to public water supplies, which became a general practice during the early decades of this 

century, perhaps did more to increase human life spans than any other single event in history 

(Fairweather, 1990). Chlorine destroys the microbes that cause typhoid fever, cholera, and amoebic 

dysentery; as a result, these diseases have been virtually eradicated from the developed countries of the 

world. Within the last few decades, however, it has become evident that adding chlorine as a disinfectant 

to natural waters can result in the formation of chloroform and other carcinogenic or mutagenic 

compounds (Rook, 1974; Bellar and others, 1974). The importance of this issue may be summarized by 

the statement of R.J. Bull (1982) who concluded that "no other public health issue affects a larger 

proportion of the U.S. population than drinking water disinfection."

The Mississippi River is used by many of the cities and towns along its banks as a source of drinking 

water. As a standard practice, chlorine is added as a disinfectant to the waters that are extracted from the 

river before they are distributed to consumers through municipal water systems. As part of the 

assessment of the water quality of the Mississippi River, a set of laboratory experiments was done to 

assess the potential for forming toxic substances when river waters are chlorinated.

Background

The toxic by-product compounds formed during the chlorination of natural waters result from the 

reaction of free chlorine used for disinfection with the dissolved organic carbon (DOC) present in the 

water. The DOC is a complex mixture of organic compounds resulting from the decay of soil and plant 

organic matter (Thurman, 1985). Chemical and biological processes within aquatic systems also may 

contribute to the DOC. The DOC is present in varying concentrations and compositions in all natural 

waters. It is the DOC that serves as the precursor for the formation of the by-product compounds.

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The by-products formed during the chlorination of natural waters can be divided into two classes of 

compounds. The first class consists of the trihalomethane (THM) compounds, which are chlorinated and 

brominated derivatives of methane. The four compounds commonly included in this class are 

chloroform (CHCl3), dichlorobromomethane (CHCl2Br), chlorodibromomethane (CHClBr2), and 

bromoform (CHBr3). Chloroform is a known animal carcinogen (Pieterse, 1988). The other THM 

compounds formed during the disinfection process are carcinogenic and mutagenic (Simmon and 

Tardiff, 1978), and positive correlations have been observed between the concentrations of these 

compounds in drinking water and bladder cancer (Cantor and others, 1978). Positive correlations also 

were observed for brain cancer in both males and females and for lymphoma and kidney cancer in 

males. Concerns about possible health effects of these compounds (U.S. Environmental Protection 

Agency, 1975, 1979; National Academy of Sciences, 1977) resulted in the U.S. Environmental 

Protection Agency's establishing a maximum contaminant level (MCL) in drinking water of 100 

micrograms per liter (ug/L) total of the four THM compounds. Other countries have more stringent 

requirements. Germany and Switzerland have an MCL of 25 ug/L (Pieterse, 1988). In addition, 

Amsterdam has stopped the chlorination of drinking water because of health concerns about the 

ingestion of these compounds (Pieterse, 1988).

The second class consists of a complex mixture of relatively nonvolatile compounds that have higher 

molecular weights than the THM compounds. Because of the large number of different compounds 

present in this mixture at small concentrations, identification and quantification of the individual 

compounds is difficult. Consequently, the concentration of these compounds is determined as a bulk 

parameter called the nonpurgeable total organic halide (NPTOX) concentration. As of 1994, no 

maximum contaminant level has been established for the NPTOX concentration in drinking water. 

Experimental Procedure

The experiments evaluated the factors that influence the formation of toxic by-products during the 

chlorination process. These factors are the concentration of free chlorine used in the chlorination 

process, the pH at which the water is chlorinated, the water temperature, and the concentration and 

composition of the DOC of the source water. The distribution of the compounds among the chlorinated 

and brominated compounds depends on the bromide concentration of the source water. The free chlorine 

concentration is determined by the particular water-treatment process being used, and the pH is 

determined by a combination of the pH of the source water and the water-treatment process being used. 

The DOC and bromide concentrations, the composition of the DOC, and the temperature are determined 

by the characteristics of the source water.

Potentials for the formation of THM and NPTOX compounds upon chlorination of Mississippi River 

water were determined in samples that were collected from 12 sites along the river between 

Minneapolis, Minnesota, and New Orleans, Louisiana; the samples were shipped to the laboratory in 

Denver, Colorado, where the experiments were conducted. Formation potentials were determined as a 

function of pH and initial free chlorine concentration for 7 days at a temperature of 25oC. Formation 

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potentials also were determined as a function of reaction time over 7 days for a pH of 8.14 and an initial 

free chlorine concentration of 30 milligrams per liter. Complete details of the experimental procedure 

and the data resulting from this study have been presented in other reports (Rathbun, 1995; Rathbun and 

Bishop, 1993, 1994).

Experimental Results

Potentials for the formation of the THM and the NPTOX compounds when water from the Mississippi 

River is chlorinated are presented in figure 59 as a function of distance above Head of Passes, Louisiana. 

Also presented in figure 59 are the DOC concentrations. The formation potentials decrease with distance 

downstream, in each case paralleling the decrease of the DOC concentration with distance downstream. 

This behavior clearly demonstrates the importance of the DOC as the precursor in the by-product 

formation process.

The effect of pH on the by-product formation process is demonstrated by the fact that NPTOX formation 

potential is considerably larger than the THM formation potential for a pH of 6.73, whereas the THM 

formation potential is slightly larger than the NPTOX formation potential for a pH of 9.70. For the 

intermediate pH of 8.14, the NPTOX formation potential is larger than the THM formation potential, 

although the difference is considerably less than the difference for pH 6.73. These results indicate that 

pH conditions in the water-treatment process that minimize the formation of the THM compounds tend 

to maximize the formation of the NPTOX compounds.

Potentials for the formation of the THM and the NPTOX compounds as a function of reaction time are 

presented in figure 60 for water samples from the river at Minnea-polis, Memphis, and New Orleans. 

Concentrations of both types of compounds increased rapidly during the initial part of the experiment; 

more than one-half of the final concentrations was formed during the first day. Thereafter, the 

concentrations of both types of compounds increased gradually for the balance of the 7-day period.

(Click on image for a larger version, 66K)

Figure 59. -- Results obtained in laboratory experiments show the potential for forming trihalomethane 

(THM) and nonpurgeable total organic halide (NPTOX) compounds during chlorination of waters 

collected at 12 sites along the Mississippi River during the summer of 1991. Potentials are graphed to 

show distance of the sampling sites upriver of Head of Passes, Louisiana, with Minneapolis to the left 

and New Orleans to the right. The graphs show the results of chlorination experiments conducted at 

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three different values of pH: upper graph pH = 6.73 (slightly acid); middle graph pH = 8.14 (moderately 

alkaline); lower graph pH = 9.70 (strongly alkaline). The concentrations of dissolved organic carbon 

(DOC), measured at the beginnings of the experiments (shown by the triangles; same values in all three 

graphs), were greater in the upper-river waters than in the lower-river waters. Potentials of the formation 

of the toxic compounds generally parallel the DOC concentrations, but the relative importance of THM 

(squares) and NPTOX (circles) depends heavily on pH. At slightly acid and moderately alkaline pH 

(upper two graphs), NPTOX compounds form more readily than THM compounds. At strongly alkaline 

pH (lower graph), THM compounds form more readily than the NPTOX compounds.

(Click on image for a larger version, 33K)

Figure 60. -- Results obtained in laboratory experiments show that the formation of trihalomethane 

(THM) and nonpurgeable total organic halide (NPTOX) compounds is initially very fast; the rate of 

formation decreases after about 1 day; several days are required to reach the maximum concentrations 

for both the THM and NPTOX compounds. The experiments portrayed in this figure were conducted on 

waters collected during the summer of 1991 from the Mississippi River at Minneapolis, Memphis, and 

New Orleans. All three experiments were conducted at a pH of 8.14, which is near the characteristic pH 

of most untreated waters of the Mississippi River.

Conclusion

Results of this study indicate that there is sufficient DOC in the Mississippi River that THM and 

NPTOX compounds will be formed when the water is disinfected with chlorine. The DOC concentration 

decreased with distance downstream between Minneapolis and New Orleans; the THM and NPTOX 

concentrations measured in the laboratory formation-potential experiments also decreased with distance 

downstream, paralleling the decrease of the DOC. The pH levels prevalent in the Mississippi River and 

pH values likely to be used in water disinfection are such that the NPTOX compounds are likely to form 

more abundantly than the THM compounds. However, if a more alkaline condition is used in the 

disinfection process, then the THM compounds are likely to form more abundantly than the NPTOX 

compounds. The formation potentials for the THM compounds, although less than the potentials for the 

formation of the NPTOX compounds, were always in excess of the present MCL of 100 ug/L. This 

conclusion should be tempered by the fact that experimental conditions of initial free-chlorine 

concentration and reaction time used in these laboratory experiments were such as to maximize the 

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Potentially Deleterious Effects of Chlorinating Mississippi River Water for Drinking Purposes

formation of the THM and NPTOX compounds. The large formation potentials observed, however, 

indicate that care must be exercised in disinfecting river water with chlorine, particularly in water from 

the Upper Mississippi River.

REFERENCES

Bellar, T.A., Lichtenberg, J.J., and Kroner, R.C., 1974, 

The occurrence of organohalides in chlorinated drinking waters: Journal American Water Works 

Association, v. 66, no. 12, p. 703-706. 

Bull, R.J., 1982,

Health effects of drinking water disinfectants and disinfectant by-products: Environmental 

Science and Technology, v. 16, no. 10, p. 554a-559a. 

Cantor, K.P., Hoover, R., Mason, T.J., and McCabe, L.J., 1978,

Associations of cancer mortality with halomethanes in drinking water: Journal National Cancer 

Institute, v. 61, no. 4, p. 979-985. 

Fairweather, V., 1990, 

Water: Civil Engineering, v. 60, no. 10, p. 59-61. 

National Academy of Sciences, 1977,

Drinking water and health: Washington, D.C., Printing and Publishing Office, 939 p. 

Pieterse, M.J., 1988, 

The potential health risk of trihalomethanes in drinking waterÑ A perspective: South African 

Journal of Science, v. 84, March, p. 166-70. 

Rathbun, R.E., 1995,

Trihalomethane and nonpurgeable total organic-halide formation potentials for the Mississippi 

River and some of its tributaries, March-April 1992: U.S. Geological Survey Open-File Report 

94-336, 55 p. 

Rathbun, R.E., and Bishop, L.M., 1993,

Trihalomethane and nonpurgeable total organic halide formation potentials for the Mississippi 

River and some of its tributaries, June-August 1991: U.S. Geological Survey Open-File Report 

93-158, 57 p. 

___ 1994,

Trihalomethane and nonpurgeable total organic-halide formation potentials for the Mississippi 

River and some of its tributaries, September-October 1991: U.S. Geological Survey Open-File 

Report 94-36, 53 p. 

Rook, J.J., 1974,

Formation of haloforms during chlorination of natural waters: Water Treatment and Examination, 

v. 23, no. 2, p. 234-243. 

Simmon, V.F., and Tardiff, R.G., 1978,

The mutagenic activity of halogenated compounds found in chlorinated drinking water, in Water 

Chlorination, Environmental Impact and Health Effects, v. 2: Ann Arbor, Michigan, Ann Arbor 

Science, p. 417-431. 

Thurman, E.M., 1985,

http://pubs.usgs.gov/circ/circ1133/chlorinating.html (5 of 6)9/29/2005 9:18:35 AM
Potentially Deleterious Effects of Chlorinating Mississippi River Water for Drinking Purposes

Organic geochemistry of natural waters: Boston, Martinus Nijhoff/Dr. W. Junk Publishers, 497 p. 

U.S. Environmental Protection Agency, 1975,

Preliminary assessment of suspected carcinogens in drinking water: Report to Congress: Report 

PB-250 961, National Technical Information Service, 52 p. 

___ 1979, 

National interim primary drinking water regulations; control of trihalomethanes in drinking 

water; final rule: Federal Register, v. 44, no. 231, p. 28641-28642.

Return to ' Contents ' 

Contaminants in the Mississippi River 

U.S. GEOLOGICAL SURVEY CIRCULAR 1133 

Reston, Virginia, 1995 

Edited by Robert H. Meade 

http://water.er.usgs.gov/pubs/circ1133/chlorinating.html 

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