Research by the

U.S. Geological Survey on

Organic Materials in Water

MLMI

GEOLOGICAL SURVEY 

CIRCULAR 744
Research by the

U.S. Geological Survey on

Organic Materials in Water

By Robert A. Baker

GEOLOGICAL SURVEY CIRCULAR 744
United States Department of the Interior

THOMAS S. KLEPPE, Secretary

Geological Survey

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Baker, Robert Andrew, 1925-

Research by the U.S. Geological Survey on organic materials in water.

(Geological Survey Circular 744)

Bibliography: p.

Supt. of Docs. No.: I 19.4/2:744

1. Water-Analysis Research. 2. Organic water pollutants Research. 3. Chemistry,

Organic Research. 4. United States Geological Survey. 

I. Title. II. Series: United States Geological Survey Circular 744. 

QE75.C5 No. 744 [GB658.7] 557.3'08s [628.l'61] 76-608296

Free on application to Branch of Distribution, U.S. Geo/ogtca/Survey/ 7200 South Eods Street, Arlington, VA 22202
CONTENTS

Page Page

Abstract.............................................................................. 1 Humic acids....................................................................... 3

Introduction.................................................................... 1 Field studies....................................................................... 4

Analytical developments.................................................... 1

Dissolved organic carbon................................................... 2 Long-range plans............................................................... 5

Pesticides............................................................................ 3 References cited.................................................................. 5

in
Research by the U.S. Geological Survey on 

Organic Materials in Water

By Robert A. Baker

ABSTRACT

The U.S. Geological Survey has responsibility for investigating the Nation's water resources for source, availability, 

quantity, and quality. This paper describes the Geological 

Survey's research on organic substances in water and fluvial sediments. Results and ongoing studies are examined. Typical 

research includes: Separation, concentration, and chromatographic identification of volatile acids; free-flow electrophoresis fractionation of natural organic materials; identification of chlorinated insecticides in suspended sediments and 

bottom materials; fate of organics following underground 

disposal; determination of humic and fulvic acid stability 

constants and characterizations; identification of low-molecular 

weight chloroorganic constituents in water; PCB (polychlorinated biphenyl compound) distribution in aquatic environments; dissolved organic carbon in ground water; and improvement in separation and concentration schemes prior to analyses.

INTRODUCTION

Evaluation of the organic and biological aspects of 

the Nation's water resources by the U.S. Geological 

Survey coincides with its initiation of research in 

these fields in the 1960's. By 1965 a pesticidemonitoring network was established. Increasingly, 

emphasis has been placed on elucidation of 

principles and relationships necessary for solution 

of practical problems associated with hydrology. 

Although the effort devoted to organic contaminants has been modest, considerable progress 

has been made, and noteworthy results have been 

achieved. A summary of prior and current research 

on this subject is presented.

ANALYTICAL DEVELOPMENTS

The following are representative of analytical 

developments made to support field investigations:

Analysis of formic and acetic acids in aqueous 

solution at relatively low concentrations had often 

presented a problem. A procedure combining steam 

distillation and concentration steps followed by 

flame-ionization detection, gas-liquid chromatography permitted determination of 1.0 mg/1 and 0.03

mg/1, respectively, of formic and acetic acid (White 

and Leenheer, 1974).

Preparative free-flow electrophoresis was found to 

be an efficient method of conducting large-scale 

fractionations of natural organic polyelectrolytes 

occurring in many surface waters and solids. The 

method depends on mass and charge. A decreasing 

mass-charge ratio increases electrophoretic mobility. 

The method obviates the problem of adsorption 

upon a supporting medium. Application of the 

technique to natural samples, as well as associated 

sample-preparation techniques has been defined 

(Leenheer and Malcolm, 1973a). The free-flow 

electrophoresis procedure was applied to soluble 

river organic matter and soil fulvic acids. Significant quantities of virtually colorless organic 

material were found in soil and river preparations. 

Polysaccharides represent 20 to 75 percent of the 

colorless soil fulvic acids but only 3.2 to 7.0 percent 

of river preparations. Polysaccharides were greater 

in Northern than in Southern States. This suggested 

slower degradation in cooler climates (Leenheer and 

Malcolm, 1973b).

Analyses of coextratives during pesticide cleanup 

revealed presence of elemental sulfur. Elemental 

sulfur is often used as a fungicide and miticide and 

appears in hexane extracts. Gas chromatographic 

analysis of aldrin is particularly susceptible to interferences by elemental sulfur. A technique was 

developed to eliminate the interference by extraction on a small drop of elemental mercury (Goerlitz 

and Law, 1971).

Chlorinated napthalenes are produced for uses 

analogous to PCB's (polychlorinated biphenyl compounds). They are employed as engine oil additives, 

fabric dying, impregnation for automobile 

capacitors, electroplating stopoff compounds, and 

carbon electrode impregnation. They can interfere 

in pesticide residual analyses and are often even more 

difficult to detect on conventional electron-capture

1
chromatography. Various methods of identifying 

chlorinated naphthalenes have been examined. 

Combined gas chromatograpy-mass spectrametry is 

the most effective detection procedure. The base peak 

is typically found in the molecular ion cluster, and 

spectra are unique (Goerlitz and Law, 1972).

Water and soil contamination by TNT and RDX 

is likely around munitions manufacturing sites. 

Methodology was developed for measuring the 

presence of these substances. Volatile solvent 

extraction is followed by removal of bulk solvent and 

separation from extraneous material by column 

adsorption chromatography. TNT and RDX are 

measured by electron-capture gas chromatography, 

using two columns of different retention characteristics. Minimum detectable concentrations are 0.005 

/u.g/1 (Goerlitz and Law, 1975).

A novel system of classification, fractionation, and 

analysis of organic solutes in aqueous systems has 

been evolved from ongoing research (J. A. Leenheer, 

written commun., 1975). Attempts to characterize 

such solutes by tractionating the DOC (dissolved 

organic carbon) based on hydrophobic-hydrophilic 

nature and acid-base characteristics led to investigation of Rohm and Haas Amberlite XAD resins. 1 The 

XAD-8 resin series was found to have high sorptive 

capacity for natural organic polyelectrolytes (humic 

and fulvic acids). Alkaline eluants were effective in 

quantitative desorption. Prior experience with other 

resins had led to irreversible sorption and resin 

fouling. The use of XAD-8 resin permitted development of analytical procedures which have since been 

applied to surface and ground waters.

Other ongoing investigations include: Application of lasar-Raman spectroscopy to remote sensing 

of water quality; characterization of organic constituents in domestic sewage effluents and their fate 

on distribution to surface and ground waters; 

characterization and fate of organic contaminants 

released from coal and shale residues; and quantification of organic substances in water and sediment 

from representative rivers, lakes, and ground waters.

DISSOLVED ORGANIC CARBON

Traditionally, semiquantitative measures of 

organic constituents of water have included BOD 

(biochemical oxygen demand) and COD (chemical 

oxygen demand). These measurements are being 

replaced by quantitative procedures including DOC 

and SOC (suspended organic carbon). The techni-

'The use of brand names in this report is for identification purposes only and does not 

imply endorsement by the U.S. Geological Survey.

ques for DOC and SOC have been subjected to 

rigorous testing Malcolm and Leenheer, 1973). DOC 

and SOC are independent of microbial effects, toxic 

substances, and variability with diverse organic 

constituents. Inorganic interferences are readily 

isolated. Combining DOC and SOC provides a 

measure of TOC (total organic carbon). TOC is 

commonly measured as a single value by instrumental means. TOC values, so derived, commonly 

lack the precision and accuracy of combined 

DOC-SOC values.

DOC was shown to provide definitive information regarding the level and areal extent of 

ground-water contamination in Mojave River sediments near Barstow, Calif. (Hughes and others, 

1974). The underlying alluvial aquifer has been 

degraded by industrial and municipal wastes. Concomitantly, DOC values have increased from 0.1 to 6 

or 7 mg/1 in the ground water. The technique serves 

as a tracer of discharge patterns. Two plumes of 

degraded water were shown to exist at different 

depths. Areal distribution suggests selective adsorption of some constituents by the aquifer sediments.

A survey of DOC in ground water was made at 100 

sites in 27 States. Samples were pressure filtered at 

the time of collection and immediately frozen on dry 

ice. Subsequent analyses showed DOC to vary from 

less than the 0.1 mg/1 detection limit to 15 mg/1. The 

DOC values were correlated with various chemical 

and geological properties (Leenheer and others, 

1974).

Six rivers, the Missouri, Neuse (N.C.), Ohio, 

Brazos (Tex.), Mississippi, and Sopchoppy (Fla.), 

were monitored for organic loading (Malcolm and 

Durum, 1976). Annual organic loads of 3.4 billion 

kilograms and 47 million kilograms of the 

Mississippi and Brazos Rivers, respectively, were 

approximately equally distributed between dissolved and suspended phases. The Missouri load of 

725 million kilograms was chiefly in the suspended 

phase. However, the 6.4 and 19 million kilograms 

loads of the Sopchoppy and Neuse Rivers, 

respectively, were chiefly in the dissolved phase. In 

most rivers DOC concentrations were usually less 

than 8 mg/1. SOC concentrations varied widely with 

discharge, ranging between 1 and 14 weight-percent. 

Except for the Mississippi and Sopchoppy Rivers, 

DOC and SOC fluctuated with the seasons. The sediment phase carbon: nitrogen ratio of all these 

systems averaged less than 8:1 as compared with 

12:1, or more, for most soils. This indicates nitrogen 

enrichment of stream sediment.
PESTICIDES

The distribution of pesticides and their 

decomposition products in the Nation's water 

systems has been of continuing concern. A national 

monitoring program has been in operation (Feltz 

and others, 1971). Emphasis was on 20 selected stations in the Western United States in 1968. There 

were 153 stations operating coast-to-coast in May 

1975. The analytical laboratories have devoted continuing effort to improvement of sampling, 

preservation, and handling of samples containing 

pesticides. Cooperative studies have been conducted 

with other governmental units and inhouse research 

has addressed specific needs. The following cases 

typify past investigations.

Organochlorine insecticides were monitored in 

the Everglades of south Florida. DOT and its 

metabolites ODD and DDE in the range 0.00-0.03 

Hg/l were found in water. Underlying marshy soil 

contained up to threefold greater concentrations. 

Similarly increased levels were found in algal mats, 

omniverous crustaceans, and fishes. It was 

postulated that these organochlorine substances 

were introduced by water inflow and aerial transport 

(Kolipinski and others, 1971).

Pesticide monitoring of the streams of Western 

States has been a continuing effort (Brown and 

Nishioka, 1967; Manigold and Schulze, 1969; 

Schulze and others, 1973). From 1968 to 1971 DOT 

was the most frequently occurring insecticide, and 

2-, 4-, 5-T, the most common herbicide. Concentrations were highest in samples containing larger 

concentrations of suspended sediments. Beginning 

in July 1970 parathion, methylparathion, 

malathion, and diazinon were measured monthly at 

20 stations.

Sediment and bottom material represent the transport mode and repository of many organic contaminants including pesticides. Procedures have been 

developed and standardized for pesticide extraction 

and analysis (Goerlitz and Law, 1974a). Acetonehexane extraction is followed by adsorption 

chromatography to isolate the coextractants, polychlorinated biphenyls and polychlorinated 

napthalenes. Sulfur is removed by precipitation.

San Francisco Bay is a principal aquatic resource 

in California. Millions of persons depend on its 

waters for multiple uses. The bay receives waters 

from many tributaries. Bottom materials from 26 

streams tributary to the bay were analyzed for 

pesticides. ODD, DDE, DOT, and PCB residues were 

present in most samples. Chlordane proved equally

ubiquitous. One stream sample contained polychlorinated napthalene residues. Combined gas 

chromatography-mass spectrometry was used to 

identify compounds occurring in concentrations 

greater than 20 ^g/kg (Law and Goerlitz, 1974). 

These same investigators demonstrated that it is 

essential to consider all particle-size fractions in 

bottom-sediment analysis if quantitative results are 

to be obtained (Goerlitz and Law, 1974b).

Interfering materials often pose a problem in gasliquid chromatographic analyses of pesticide 

residues. Rapid and economical cleanup procedures 

for treating samples are necessary. Various 

adsorbents and solvent systems were tested using 

many pesticides (Law and Goerlitz, 1970). Microcleanup column techniques were devised for use 

with surface- and ground-water samples. These techniques have been in regular use for many years.

HUMIC ACIDS

Humic and fulvic acid components of soils, sediments, and natural waters are involved in physical, 

biological, and chemical processes affecting water 

quality. It has long been known that these abundant 

substances are mixtures of chemically different molecular species. However, separation and elucidation 

of the complex mixtures have proved to be difficult. 

Humic acids are characteristically aromatic in 

nature and contain phenolic, quinone, and acidic 

groups. Amine and alcohol groups and ether 

linkages are also present. It will be necessary to 

define these substances if their role in water quality is 

to be properly assessed.

A research project is devoted to investigating these 

complex natural substances. Their isolation, 

properties, and reaction mechanisms with other 

constituents of natural aqueous systems are being 

defined. Adsorption chromatography on Sephadex 

gel has been applied to humic acid salts. The humics 

were extracted from: (1) A North Carolina sandy soil 

of low clay and approximately 0.2-percent organic 

carbon; (2) a Florida sandy soil; (3) a New Mexico 

alpine bog, high in decaying organic material; (4) a 

Washington organic soil made up of peat and undifferendated alluvial soil containing decaying organic 

matter, sand, and clay; and (5) an Alamosa ground 

water from a zone 60-120 m beneath the surface and 

highly colored from peat bed contact. Fractionation 

of the sodium salts is attributed principally to 

adsorption, but molecular sieving and ion exchange 

are also taking place (Wershaw and Pinckney, 

1973a).
The aforementioned fractionation of the humic 

acids was by adsorption chromatography on 

Sephadex G-50 followed by chromatography on 

either a G-25 or a G-100 column. The fractions of 

the solutions were then examined by small-angle X-- 

ray scattering. Three types of aggregation behavior 

were identified: (1) Some fractions show little change 

in aggregation above pH 3.5; (2) one fraction 

aggregates at pH values higher and lower than 7 but 

is completely disassociated at 7; and (3) some fractions show decreased aggregation with increasing 

pH. Some large particles still persist, however, at pH 

11.5. Differences in association tendency are 

attributed to interaction of varying attractive and 

repulsive forces. The multiplicity of active forces in 

humic systems includes hydrogen-bonding, TT - 

bonding between planar aromatic moieties, and 

other coulombic interactions (Wershaw and 

Pinckney, 1973b).

Although there have been other contributions 

emanating from this project, the most promising 

breakthrough involves recent analytical advances. 

Previous research could not fully utilize such systems 

as mass spectroscopy because of limited volatility. A 

new procedure has been developed in which humicacid fractions are dissolved in pyrrolidone and 

methylated with diazomethane. Groups not 

amenable to these steps are derivatized by other 

means. The resulting derivatives are yielding useful 

chemical structural characterizations.

FIELD STUDIES

Although many analytical procedures and basic 

investigations related to organics are conducted in 

the research laboratory, a conscious effort is made to 

extrapolate advances to field application. Technology transfer is accomplished in a variety of ways. 

These include formal classwork, on-site demonstrations by researchers in field situations, and 

cooperative studies with others in public and private 

sectors. The following field studies typify the 

problems under investigation:

CEC (cation exchange capacity) of sediments can 

affect stream water quality. In turn, the parent 

material, age of weathering surface, climatic factors, 

degree of weathering, and dispersion affect CEC. 

Decreasing particle size usually produces an increase 

in CEC. A field study demonstrated these principles 

and the effect of organic loading. Sediment from the 

Mattole River was classified in particle sizes ranging 

from less than 0.2 /xm up to fine gravel (4-9.5 mm).

Carbon content was greatest for the finest 

particulates, 2.58 percent for the aforementioned 

finest clays. Lowest carbon con tent of 0.3 percent was 

in the gravel-size particulates. CEC was greater for 

particles associated with organic matter and ranged 

from approximately 50 meq/100 g at 0.1 /urn to 

approximately 10 meq/100 g at 10 /xm. The 

exchange process is very fast. Equilibration of the 

solids with surrounding liquid is rapid (Malcolm 

and Kennedy, 1970).

PCB's have been established as universally distributed in the environment as a result of industrial 

applications. The extent of their effect, especially in 

aquatic systems, is under intensive study. PCB 

residues have been analyzed by multiple-pesticide 

residue methods for water, suspended sediment, and 

bottom material (Goerlitz and Brown, 1972). 

Residues have been detected in samples from 19 

States throughout the Nation. Unfiltered water 

concentrations ranged from 0.1 to 4.0 /xg/1 while 

bottom sediment concentrations varied from 5.0 to 

3200 /xg/kg. This ongoing survey is intended to 

define the distribution of PCB's in major drainage 

basins of the United States (Crump-Wiesner and 

others, 1973). During the course of this study, the 

presence of significant concentration levels of PCN's 

was detected in water and sediment samples collected 

from a south Florida drainage ditch. The sediment 

samples collected from a south Florida drainage 

ditch. The sediment samples contained a mixture of 

PCN's varying from 1,250 to 5,000 /xg/kg, and the 

water samples averaged 5.7 /xg/kg. Identification 

was confirmed by microcoulometry and GC-MS.

Increasingly underground disposal of wastes is 

being practiced. The effects are not always readily 

evident. A study was made in North Carolina at a 

location where 380 to 7601/min of industrial organic 

wastes were pumped at 10 atm into multiple 

permeable zones 259 to 305 m below the surface. The 

zones consisted of a sand, gravel, and limestone 

aquifer of Late Cretaceous age. Before injection, the 

waste was adjusted by lime to pH 4. The disposal was 

not entirely satisfactory. Wells plugged, and waste 

leakage occurred into shallower aquifers. The wastes 

proved geochemically reactive. These contained 

7100 mg/1 DOC. The major organic constituents in 

order of decreasing abundance were acetic acid, 

formic acid, p-toluic acid, formaldehyde, methanol, 

terephthalic acid, phthalic acid, and benzoic acid. 

Movement of the waste front was monitored by 

observation wells. Methane-rich gas evolved. 

Ferrous iron, hydrogen sulfide, and sulfide pre-
cipitates indicated biochemical reductive processes. 

Organism counts increased to 106/ml at the waste 

front. These were chiefly anaerobic, methanogenic 

bacteria. Concurrent laboratory studies supported 

the field studies. A conceptive model, detailing waste 

reactivity and movement in the subsurface from 

injection point to waste front, was developed 

(Leenheer and Malcolm, 1973c; Leenheer, Malcolm, 

and White, 1976).

The in situ clay mineral dissolution by the aforementioned waste injection has been analyzed 

(Malcolm, Leenheer, and Weed, 1975). The mechanism was postulated to entail organic acid sorption on 

mineral surfaces, complexation of metals by organic 

ligands, and desorption of the ligand-metal 

complex.

LONG-RANGE PLANS

Research and supporting analytical programs 

must be subjected to constant reevaluation to assure 

that they are responsive to priority needs. Subjects 

related to organics in water that currently merit 

priority consideration include:

Improvement in analytical methodology for trace 

organic sampling, preservation, transfer, and 

analyses in salt and brackish waters.

Development of detailed information on microorganic transport and fate at specific sites for sensitivity testing of mathematical models.

Elucidation of metallo-organic interactions in natural and man-stressed aqueous systems.

Clarification of the effect of condensation nuclei, 

such as clay particulates, on organic transport. 

(Sedimentation determines the ultimate benthic 

concentration and transportation of hydrophobic 

constituents, such as pesticides and herbicides.)

Investigation of bioaccumulation of heavy metals 

and potentially carcinogenic trace organics and 

the role of such processes in altering water quality.

Determination of the nature and effect of trace organic contaminants in urban runoff under 

varying climatic, topographic, and land-use 

conditions.

Monitoring the stress on surface and ground waters 

from nonpoint sources of trace organics. (Landfill, land-surface disposal, and deep-well waste injection are typical concerns.)

Improvement of organic sensors to be used in conjunction with automatic data collection platforms and data relay systems for remote, continuous monitoring of water quality.

Even this limited list poses challenges. Manpower 

and facility limitations preclude intensive research 

on all these subjects. However, these needs will have 

to be addressed if water resources demands are to 

match expansion of international requirements for 

food, fiber, and energy. Research on organics by the 

U.S. Geological Survey is expected to be an increasingly important aspect in the elucidation of the 

hydrologic system over the next decade.

REFERENCES CITED

Brown, Eugene, and Nishioka, Y. A., 1967, Pesticides in selected 

western streams A contribution to the national program: 

Pesticides Monitoring Jour., v. 1, no. 2, p. 38-46.

Crump-Wiesner, Hans J., Feltz, H. R., and Yates, M. L., 1973, 

A study of the distribution of polychlorinated biphenyls 

in the aquatic environment: U.S. Geol. Survey Jour. Research, v. 1, no. 5, p. 603-607.

Feltz, H. R., Sayers, W. T., and Nicholson, H. P., 1971, National monitoring program for the assessment of pesticide 

residues in water: Pesticides Monitoring Jour., v. 5, no. 1, 

p. 54-62.

Goerlitz, D. F., and Brown, Eugene, 1972, Methods for analysis 

of organic substances in water: U.S. Geol. Survey Techniques Water-Resources Inv., book 5, chap. 5-A3, 40 p.

Goerlitz, D. F., and Law, L. M., 1971, Note on removal of sulfur 

interferences from sediment extracts for pesticide analysis: 

Bull. Environmental Contamination and Toxicology, v. 6, 

no. 1, p. 9-10.

 1972, Chlorinated naphthalenes in pesticide analysis: 

Bull. Environmental Contamination and Toxicology, v. 7, 

no. 4, p. 243-251.

____1974a, Determination of chlorinated insecticides in suspended sediment and bottom material: Jour. Assoc. Official 

Anal. Chemists, v. 57, no. 1, p. 176-181.

____1974b, Distribution of chlorinated hydrocarbons in 

stream bottom material": U.S. Geol. Survey Jour. Research, 

v. 2, no. 5, p. 541-543. 

-1975, Gas chromatographic method for the analysis of

TNT and RDX explosives contaminating water and soilcore material: U.S. Geol. Survey Open-File Rept. 75-182.

Hughes, J. L., Eccles, L. A., and Malcolm, R. L., 1974, Dissolved organic carbon (DOC), an index of organic contamination in ground water near Barstow, California: Ground 

Water Jour., v. 12, no. 5, p. 283-290.

Kolipinski, M. C, Higer, A. L., and Yates, M. L., 1971, Distribution of chlorinated hydrocarbons in stream-bottom 

material: Pesticides Monitoring Jour., v. 5, no. 3, p. 281-288.

Law, L. M., and Goerlitz, D. F., 1970, Microcolumn chromatographic cleanup for the analysis of pesticides in water: 

Jour. Assoc. Official Anal. Chemists, v. 53, no. 6, p. 1276- 

1286.

____1974, Selected chlorinated hydrocarbons in bottom material from streams tributary to San Francisco Bay, 1974: 

Pesticides Monitoring Jour., v. 8, no. 1, p. 33-36.

Leenheer, J. A., and Malcolm, R. L., 1973a, Preparative freeflow electrophoresis and a method of fractionation of natural organic materials: U.S. Geol. Survey Water-Supply 

Paper 1817-D, 14 p.
 1973b, Fractionation and characterization of natural 

organic matter from certain rivers and soils by free-flow 

electrophoresis: U.S. Geol. Survey Water-Supply Paper 

1817-E, 14 p.

 1973c, Chemical and microbial transformations of an

industrial organic waste during subsurface injections: Proc. 

Inst. Environmental Sci., Anaheim, Calif., Apr. 1-3, 1973, 

p. 351-360.

Leenheer, J. A., Malcolm, R. L., McKinley, P. W., and Eccles, 

L. A., 1974, Occurrence of dissolved organic carbon in selected ground-water samples in the United States: U.S. Geol. 

Survey Jour. Research, v. 2, no. 3, p. 361-369.

Leenheer, J. A., Malcolm, R. L., and White, W. R., 1976, Investigations of the reactivity and fate of certain organic 

components of an industrial waste after deep-well injection: 

Environmental Sci. and Technology. (In press.)

Malcolm, R. L., and Durum, W. H., 1976, Organic carbon and 

nitrogen concentrations and annual organic carbon load 

of six selected rivers of the United States: U.S. Geol. Survey 

Water-Supply Paper 1817-F, 21 p.

Malcolm, R. L., and Kennedy, V. C., 1970, Variation of cation 

exchange capacity and rate with particle size in stream sediment: Jour. Water Pollution Control Federation, v. 42, no. 

5, pt. 2, p. R153-R159.

Malcolm, R. L., and Leenheer, J. A., 1973, The usefulness of 

organic carbon parameters in water quality investigations: 

Anaheim, Calif., Inst. Environmental Sci., Proc. No. 19, 

p. 336-340.

Malcolm, R. L., Leenheer, J. A., and Weed, S. B., 1975, Dissolution of aquifer clay minerals during deep-well disposal 

of industrial organic waste: Mexico City, Proc. Internal. 

Clay Conf., p. 477-494.

Manigold, D. B., and Schulze, J. A., 1969, Pesticides in selected 

western streams A progress report: Pesticides Monitoring 

Jour., v. 3 no. 2, p. 124-135.

Schulze, J. A., Manigold, D. B., and Andrews, F. L., 1973, Pesticides Monitoring Jour., v. 7, no. 1, p. 73-84.

Wershaw, R. L., and Pinckney, D. J., 1973a, The fractionation 

of humic acids from natural water systems: U.S. Geol. Survey Jour. Research, v. 1, no. 3, p. 361-366.

____1973b, Determination of the association and dissociation 

of humic acid fractions by small x-ray scattering: U.S. Geol. 

Survey Jour. Research, v. 1, no. 6, p. 701-707.

White, W. R., and Leenheer, J. A., 1974, Determination of free 

formic and acetic acids by gas chromatography using the 

falme ionization detector: Jour. Chromatographic Sci. 

(In press.)

U.S. GOVERNMENT PRINTING OFFICE 1976-777-034/27