United States Office of Water EPA-822-R-03-023 

Environmental Protection 4304 October, 2003 

Agency

 AMBIENT AQUATIC LIFE WATER QUALITY CRITERIA FOR ATRAZINE - 

REVISED DRAFT 
AMBIENT AQUATIC LIFE WATER QUALITY CRITERIA FOR

 ATRAZINE - REVISED DRAFT 

CAS Registry No. 1912-24-9

October 2003

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF WATER

OFFICE OF SCIENCE AND TECHNOLOGY

HEALTH AND ECOLOGICAL CRITERIA DIVISION

WASHINGTON D.C.
ii

NOTICES

This document has been reviewed by the Health and Ecological Criteria Division, Office of Science and

Technology, U.S. Environmental Protection Agency, and is approved for publication.

Mention of trade names or commercial products does not constitute endorsement or recommendation for

use.

This document is available to the public through the National Technical Information Service (NTIS),

5285 Port Royal Road, Springfield, VA 22161. It is also available on EPA’s web site:

http://www.epa.gov/waterscience/criteria/atrazine.
iii

FOREWORD

Section 304(a)(1) of the Clean Water Act of 1977 (P.L. 95-217) requires the Administrator of

the Environmental Protection Agency to publish water quality criteria that accurately reflect the latest

scientific knowledge on the kind and extent of all identifiable effects on health and welfare that might

be expected from the presence of pollutants in any body of water, including ground water. This

document is a revision of draft criteria published in 2001 based upon consideration of scientific input

received from the public and new information. Criteria contained in this document replace any

previously published EPA aquatic life criteria for the same pollutant.

The term "water quality criteria" is used in two sections of the Clean Water Act, section

304(a)(1) and section 303(c)(2). The term has a different program impact in each section. In section

304, the term represents a non-regulatory, scientific assessment of ecological effects. Criteria presented

in this document are such scientific assessments. If water quality criteria associated with specific

stream uses are adopted by a state as water quality standards under section 303, they become

enforceable maximum acceptable pollutant concentrations in ambient waters within that state. Water

quality criteria adopted in state water quality standards could have the same numerical values or

method resulting in a numerical value as criteria developed under section 304. However, in many

situations states might want to adjust water quality criteria developed under section 304 to reflect local

environmental conditions and human exposure patterns. Alternatively, states may use different data

and assumptions than EPA in deriving numeric criteria that are scientifically defensible and protective

of designated uses. It is not until their adoption as part of state water quality standards that criteria

become regulatory. Guidelines to assist the states and Indian tribes in modifying the criteria presented

in this document are contained in the Water Quality Standards Handbook (U.S. EPA, 1994). This

handbook and additional guidance on the development of water quality standards and other waterrelated programs of this Agency have been developed by the Office of Water.

This draft document is guidance only. It does not establish or affect legal rights or obligations. 

It does not establish a binding norm and cannot be finally determinative of the issues addressed. 

Agency decisions in any particular situation will be made by applying the Clean Water Act and EPA

regulations on the basis of specific facts presented and scientific information then available.

Geoffrey H. Grubbs

Director

Office of Science and Technology
iv

ACKNOWLEDGMENTS

Daniel J. Call 

University of Wisconsin-Superior

Superior, Wisconsin

Larry Brooke 

University of Wisconsin-Superior

Superior, Wisconsin

Tyler K. Linton

Great Lakes Environmental Center

Columbus, OH

Gregory J. Smith

Great Lakes Environmental Center

Columbus, Ohio

Douglas J. Urban

U.S. EPA

Environmental Fate and Effects Division

Office of Pesticide Programs

Washington, D.C.

Stephanie R. Irene

U.S. EPA

Environmental Fate and Effects Division

Office of Pesticide Programs

Washington, D.C.

Frank Gostomski

(document coordinator)

U.S. EPA

Health and Ecological Criteria Division

Office of Water

Washington, D.C.
v

CONTENTS

NOTICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction ........................................................................ 3

Acute Toxicity to Freshwater Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Acute Toxicity to Saltwater Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Chronic Toxicity to Freshwater Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Chronic Toxicity to Saltwater Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Toxicity to Aquatic Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Ecosystem Effects Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Impacts to Plant Communicty Structure and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Endocrine Disruption Effects Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Bioaccumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Other Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Unused Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

National Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
vi

TABLES

Page

A. Selected Freshwater Acute and Chronic Plant Data Taken From Table 4 . . . . . . . . . . . . . . . . . . . . 16

B. Selected Saltwater Acute and Chronic Plant Data Taken From Table 4 . . . . . . . . . . . . . . . . . . . . . . 18

C. Summary of Endocrine Disruption Effects of Atrazine to Freshwater Organisms . . . . . . . . . . . . . . 25

1. Acute Toxicity of Atrazine to Aquatic Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

2a. Chronic Toxicity of Atrazine to Aquatic Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

2b. Acute-Chronic Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

3. Ranked Genus Mean Acute Values with Species Mean Acute-Chronic Ratios . . . . . . . . . . . . . . . . . 71

4. Toxicity of Atrazine to Aquatic Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

5. Bioaccumulation of Atrazine by Aquatic Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

6. Other Data on Effects of Atrazine on Aquatic Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
vii

FIGURES

Page

A. Mesocosm/Microcosm Effects Scores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

B. Plant Species Sensitivity Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

C. Example Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

D. Correlation Between Similarity Index and Brock 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

E. Micro- and Mesocosm Study Effect Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

1. Ranked Summary of Atrazine GMAVs - Freshwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

2. Ranked Summary of Atrazine GMAVs - Saltwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3. Chronic Toxicity of Atrazine to Aquatic Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

4. Ranked Summary of Test Values for Freshwater Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

5. Ranked Summary of Test Values for Saltwater Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

6. Range of Reported Atrazine Lowest Observed Effect Concentrations (LOECs) 

and No Observed Effect Concentrations (NOECs) Excluding Those LOECs 

Where Recovery Was Reported to Occur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
1

EXECUTIVE SUMMARY

Background:

Atrazine is the most extensively used herbicide in the United Sates for control of weeds in

agricultural crops and is toxic to aquatic organisms. EPA has developed ambient water quality criteria

for atrazine for the protection of aquatic life through its authority under section 304(a) of the Clean

Water Act (CWA). These water quality criteria are guidance for Sates and Tribes and in themselves

have no binding legal effect. The criteria may for the basis for State and Tribal water quality standards

and in turn become enforceable through National Pollutant Discharge Elimination System (NPDES)

permits or other environmental programs.

Freshwater Criteria:

For atrazine the criterion to protect freshwater aquatic life freshwater aquatic life and their uses

is an Average Primary Producer Steinhaus Similarity deviation for a site less than 5% (as determined

using CASM or other appropriate model and index) not exceeded more than once every three years on

the average (or other appropriate return frequency sufficient to allow system recovery) and a one-hour

average concentration that does not exceed 1,500 ug/L more than once every three years on the

average. The 5% index for the protection of aquatic plant community should also be protective of most

freshwater animals.

Saltwater Criteria:

For atrazine, the criterion to protect saltwater aquatic life from chronic toxic effects is 17 ug/L. 

This criterion is implemented as a thirty-day average, not to be exceeded more than once every three

years on the average. The criterion to protect saltwater aquatic life from acute toxic effects is 760 ug/L. 

This criterion is implemented as a one-hour average, not to be exceeded more than once every three

years on the average.

The criteria for atrazine were developed by the EPA Office of water (OW) using a large aquatic

toxicity data base and extensive mesocosm and mesocosm data. Adverse effect of atrazine on survival,

growth, and reproduction of aquatic organisms and on plant community structure were demonstrated in

numerous laboratory and field studies.
2

This document provides guidance to States and Tribes authorized to establish water quality

standards under the Clean Water Act (CWA) to protect aquatic life from acute and chronic effects of

atrazine. Under the CWA, States and Tribes are to establish water quality criteria to protect designated

uses. While this document constitutes U.S. EPA’s scientific recommendations regarding ambient

concentrations of atrazine, this document does not substitute for the CWA or U.S. EPA’s regulations;

nor is it a regulation itself. Thus, it cannot impose legally binding requirements on U.S. EPA, States,

Tribes, or the regulated community, and it might not apply to a particular situation based upon the

circumstances. State and Tribal decision-makers retain the discretion to adopt approaches on a caseby-case basis that differ from this guidance when appropriate. U.S. EPA may change this guidance in

the future. 
1

A comprehension of the “Guidelines for Deriving Numerical National Water Quality Criteria for the

Protection of Aquatic Organisms and Their Uses” (Stephen et al. 1985), hereafter referred to as the Guidelines, is

necessary to understand the following text, tables and calculations.

3

INTRODUCTION1

Atrazine is a herbicide with the empirical formula C8H14Cl5N5 and a molecular weight of 215.7. 

It is a white, crystalline solid with a melting point of 173-175o

C, a boiling point of 279oC, and

solubility in water of 33 mg/L at 25o

C (Farm Chemicals Handbook 2000; Hunter et al. 1985). Atrazine

has an n-octanol-water partition coefficient (log P) of 2.82, a vapor pressure of 7.34 x 10-4 mm Hg, a

Henry's Constant of 8.32 x 10-6 atm.

m3/M, and a hydrolysis half-life in excess of 1,000 days (Hunter et

al. 1985). These physico-chemical properties contribute to its environmental partitioning and degree of

persistence in the aquatic environment.

Atrazine is used extensively in the United States, Canada and other countries for the control of

weeds in agricultural crops, especially in crops such as corn, sorghum, wheat and soybeans. It is one of

the most heavily used pesticides in North America, generally being among the top few in terms of total

pounds of herbicide used (Braden et al. 1989; Burridge and Haya 1988; Ciba-Geigy 1994; Council on

Environmental Quality 1984; Moxley 1989; Pike 1985; Richards and Baker 1993). Annual domestic

usage during the past two decades has been in the general range of 30 to 40 million kilograms applied

to approximately 70 million acres of farm land in the U.S. (U.S. EPA 2000). It is also commonly used

in other countries (Bester and Huhnerfuss 1993; Bester et al. 1995; Caux and Kent 1995; Galassi et al.

1992, 1993; Lode et al. 1994). Atrazine is also used in combination with other herbicides including

alachlor, ametryne, linuron, paraquat, propachlor, amitrole, and cyanazine (Farm Chemicals Handbook

2000).

With this magnitude of application, atrazine has commonly been detected in surface waters of

agricultural watersheds where it has been used. Due to its relative mobility from soil, atrazine surface

water concentrations are highest in field runoff, with concentration peaks generally following early

major storm events that occur within a few weeks of application (Glotfelty et al. 1984; Muir et al. 1978;

Triplett et al. 1978; Wauchope 1978; Wauchope and Leonard 1980). Concentrations in the low mg/L

range may be encountered in edge-of-field run-off (Hall et al. 1972; Kadoum and Mock 1978; Klaine et

al. 1988; Roberts et al. 1979). Field run-off is diluted upon entering a stream or lake, resulting in

atrazine concentrations that are generally much lower (e.g., 1-10 μg/L range) in such waters (Frank and

Sirons 1979; Frank et al. 1979; Richards and Baker 1993; Richard et al. 1975; Roberts et al. 1979; Wu

1981). Only trace levels (i.e., <1.0-33 ng/L) were reported in a pesticide monitoring study in California
4

(Pereira et al. 1996). However, individual maximum concentrations may be considerably higher. 

Elevated levels of atrazine $2 μg/L have been documented by Frenzel et al. (1998) in the Platte River

of Nebraska for greater than 60 days, and $5 μg/L for greater than 30 days. When considered over

several years, maximum concentrations reported in some creeks and rivers from midwestern

agricultural areas have ranged from 5 to 70 μg/L (Ciba-Geigy 1992a,b,c,d, 1994; Frank and Sirons

1979; Frank et al. 1979, 1982; Illinois State Water Survey 1990; Muir et al. 1978; Richards and Baker

1993; Roberts et al. 1979). Factors that strongly and positively correlate with the release of atrazine

from soil include sediment organic carbon, landscape position, and tillage (Novak 1999).

Surface waters surrounded by agricultural lands may receive several pulsed doses over the

growing season corresponding to rainfall events (Herman et al. 1986). Annual patterns of atrazine

concentrations in Ohio streams show peak time-weighted mean concentrations of about 6 μg/L in early

June, with a rapid increase from April to June, followed by a rapid decrease from June to August

(Richards and Baker 1993). Time-weighted mean concentrations between August and December are

considerably lower, most frequently being less than 1.0 μg/L. Atrazine concentrations are the lowest,

and uniformly so, between January and April. Also, smaller streams were shown to have higher peak

concentrations, but of shorter duration, than larger streams (Richards and Baker 1993). The annual

cycle is similar in southwestern Ontario, but with the annual peak concentrations occurring at lower

levels and several weeks later than in Ohio (Bodo 1991). Nonetheless, atrazine concentrations in

Ontario have regularly exceeded 2 μg/L, which is the Canadian water quality guideline for aquatic life

protection (Trotter et al. 1990). Exceedances have similarly been reported in surface waters of Quebec

(Caux and Kent 1995).

Among the highest surface water concentrations of atrazine are those in small reservoirs in

southern Illinois. These are currently being intensively monitored (Tierney et al. 1994a). Maximum

concentrations as high as 55 μg/L have been reported from these reservoirs. 

Similar seasonal trends in concentrations of atrazine to those in Ohio streams have been

observed in streams in Illinois (Ciba-Geigy 1992a; Illinois State Water Survey 1990), in Iowa (CibaGeigy 1994), and in other midwestern states (Ciba-Geigy 1992c). In large rivers such as the

Mississippi, Missouri and Ohio Rivers, peak concentrations have most commonly occurred in June,

with mean levels of less than 5.0 μg/L during the spring period (Ciba-Geigy 1992b). The maximum

concentrations were generally between 2 and 8 μg/L, with a single maximum as high as 17.25 μg/L

(Ciba-Geigy 1992b,c). Atrazine concentrations in the Mississippi River between Minneapolis,

Minnesota and New Orleans, Louisiana from July to August, 1991 ranged from 0.054 μg/L to 4.7 μg/L

(Pereira and Hostetler 1993).
5

Atrazine residues in Illinois lakes tended to be lower than those in the streams (with less

pronounced peak values), however, the lower concentrations were sustained for longer durations (CibaGeigy 1992a). It should be noted that the maximum observed atrazine concentration was less than 3.0

μg/L at 61 percent of 42 sites monitored over 6 years between 1975 and 1988 (Ciba-Geigy 1992a).

Atrazine concentrations were considerably lower in Chesapeake Bay and its tributaries (CibaGeigy 1992e). Here, the maximum observed concentration in a tributary was 14.6 μg/L, and only three

out of 600 samples analyzed between 1976 and 1991 exceeded 3.0 μg/L. The highest observed

maxima in the Upper and Lower Chesapeake Bay were 1.7 and 0.38 μg/L, respectively. Models for the

Great Lakes suggest that concentrations should be quite low, not likely to exceed 0.13 μg/L (Tierney et

al. 1994b). Individual measurements from Lake Erie taken at Toledo, Ohio, have not exceeded 0.35

μg/L, while concentrations measured from samples collected in Lake Michigan at Michigan City,

Indiana, have been below 0.20 μg/L (Ciba-Geigy 1992c).

In addition to field run-off, atrazine residues are also transported by volatilization into the

atmosphere and subsequent deposition. Atrazine has been measured in fog (Glotfelty et al. 1987), and

trace amounts have been shown to be transported by the wind (Elling et al. 1987). Atrazine was present

year-round in rainwater samples in Maryland, with the highest concentration of 2.2 μg/L occurring in

May (Wu 1981).

Atrazine has been shown to be enriched at the microsurface layer of water (Wu 1981; Wu et al.

1980). This may be due to the presence of microsurface films which tend to concentrate certain

chemicals. Wu (1981) suggested that atrazine enrichment in the microsurface layer was more likely a

source of direct input rather than a result of atmospheric wet deposition, and that the main source of

atrazine at the site studied in Maryland was agricultural runoff.

Studies of atrazine persistence in water have produced varying results. Huckins et al. (1986)

reported the loss of atrazine from water within 4 days in a simulated prairie pond microcosm. In

shallow artificial streams, a 50 percent loss of atrazine occurred in 3.2 days (Kosinski 1984; Moorhead

and Kosinski 1986). Lay et al. (1984) reported an 82 percent loss in 5 days and a 95 percent loss in 55

days. The half-life of atrazine in wetland mesocosms was from 8 to 14 days (Detenbeck et al. 1996). 

The half-life of 14C-labeled atrazine has been measured in estuarine water as 3 to 12 days, compared to

15 to 30 days in estuarine sediment and 330 to 385 days in agricultural soils (Jones et al. 1982; Kemp et

al. 1982a).

These rapid losses in small artificial systems and in an estuarine environment are contrasted

with reports of a 300-day half-life in a larger lake system (Yoo and Solomon 1981), surface water

losses of only 33 percent in 120 days and 0 percent in 85 days in two separate 0.49 hectare pond
6

applications (Klaassen and Kadoum 1979), and a loss of only 40-50 percent in pond water over a

period of more than 5 months (Gunkel 1983). In two months time, approximately 25-30 percent of

individual 20 and 500 μg/L atrazine applications to a 0.045 hectare Kansas pond had disappeared from

the water (deNoyelles et al. 1982). Approximately 25 percent of the initial applications remained after

12 months. The half-life of atrazine was approximately 3 months in Tasmanian streams (Davies et al.

1994a).

The above information indicates that the persistence of atrazine in water is highly variable,

dependent perhaps upon both the nature of the aquatic system into which it is introduced as well as the

climatic conditions at the exposure site. For example, Comber (1999) determined that significant

hydrolysis of atrazine occurs only at pH values of 4 or less, while photolysis was initiated only by

wavelengths below 300 nm at higher pH (pH 6 to 8). Based on this author’s experiments, the aquatic

half-life of atrazine in sunny upland waters was predicted to be 6 days, but in low land rivers with

higher pH (7 to 8.5), the half-life would be in the order of months rather than days. The opposite is true

for groundwater where the half-life would be in the order of years due to exceedingly slow rates of

hydrolysis.

Biodegradation is considered to be one of the most important processes governing the

environmental fate of atrazine (Radosevich et al. 1996). Microbes isolated from aquatic ecosystems

that are capable of degrading atrazine have been reported. Mirgain et al. (1993) isolated a

Pseudomonas putida/Xanthomonas maltophilia pair with atrazine-degrading ability. Certain soil

bacteria have also been shown to be capable of degrading atrazine both aerobically and anaerobically

(Behki et al. 1993; Radosevich et al. 1995, 1996). Some soil fungi also can degrade atrazine (Donnelly

et al. 1993). In a salt marsh environment, the incorporation of atrazine into the sediment appeared to be

a prerequisite for its degradation (Meakins et al. 1995). Very little degradation occurred in the water

column. 

Seybold et al. (1999) recently examined the fate of atrazine (14C-labeled) from two undisturbed

sediments over a 2-year period. The atrazine was released from the sediment into the water column

primarily through diffusion from the pore water. The amount of atrazine released was affected by

sediment type and temperature. More atrazine residue was released into the water column at 5o

C than

at 24o

C. However, degradation of the atrazine in sediment was high; less than 2 percent of extractable

atrazine and metabolites remained after 2 years. The authors concluded that the accumulation and later

release of atrazine is greatest at cold water temperatures and in sediments with low adsorption capacity. 

Kruger et al. (1996) found that the mobilities of atrazine and its degradates were negatively correlated

with soil organic matter content and positively correlated with sand content of Iowa soils. 
7

The major atrazine degradate in aquatic systems is hydroxyatrazine (U.S. EPA 2000). Others

include deethylatrazine, deisopropylatrazine, and diaminoatrazine. The degradation products of

atrazine were found to be less toxic to algae (Stratton 1984) and submerged aquatic plants (Jones and

Winchell 1984) then the parent compound. Equivalent studies of atrazine degradate toxicity to aquatic

animals is sparse. Results from mammalian studies indicate that some atrazine degradates may be more

toxic than parent compound (U.S. EPA 2000).

The mode of atrazine's toxic action toward plants is blockage of electron transport within the

Hill reaction of photosystem II, thereby inhibiting photosynthesis (Moreland 1980). Vascular plants

and algae are both affected by this mode of action. In this way, atrazine has the demonstrated capacity

to reduce primary productivity in aquatic ecosystems (deNoyelles et al. 1982; Dewey 1986; Herman et

al. 1986; Kosinski and Merkle 1984; Pratt et al. 1988). On the other hand, the mode of toxic action

toward aquatic animals has not been documented, probably because atrazine is not considered acutely

toxic to these species. Recent evidence implicates atrazine as an indirect endocrine disruptor (Dodson

et al. 1999; Petit et al. 1997) that may act by stimulating the activity of the aromatase enzyme that

converts testosterone to estrogen (Sanderson et al. 2000). The occurrence of abnormal gonadal

development (including feminization and hermaphroditism) and reduced laryngeal muscle size in

exposed Xenopus laevis males has been reported at levels ranging from 1 μg/L atrazine (Hayes et al.

2002) to approximately 20-21 μg/L atrazine (Carr et al. 2003; Carr and Solomon 2003; Renner 2002). 

Other investigators have demonstrated that atrazine causes induction of xenobiotic metabolizing

systems (Miota et al. 1999), and enhances the toxicity of organophosphorous insecticides to aquatic

invertebrates (Belden and Lydy 2000; Pape-Lindstrom and Lydy 1997).

Several reviews exist on atrazine and its environmental impact (CCREM 1989; deNoyelles et

al. 1994; Eisler 1989; Huber 1993, 1994; Solomon et al. 1996). These reviews indicated that a few

species of aquatic plants have been shown to be slightly affected by atrazine at concentrations below 10

μg/L. The review by deNoyelles et al. (1994) stated that herbicides have little direct effects upon

animals, and that they tend to produce ecosystem effects from the bottom of the food chain upward, in

contrast to insecticides which act in the opposite direction. Huber (1993) and Solomon et al. (1996)

stated that plants readily recovered from the inhibitory effects of atrazine once the exposure was

reduced or eliminated.

A comprehension of the "Guidelines for Deriving Numerical National Water Quality Criteria

for the Protection of Aquatic Organisms and Their Uses" (Stephan et al. 1985), hereafter referred to as

the Guidelines, and the response to public comment concerning that document (U.S. EPA 1985) are

necessary to understand the following text, tables, and calculations. Results of intermediate
8

calculations such as recalculated LC50 values and Species Mean Acute Values are given to four

significant figures to prevent roundoff error in subsequent calculations, not to reflect the precision of

values. The criteria presented herein are the Agency’s best estimate of maximum concentrations of the

chemical of concern to protect most aquatic organisms or their uses from any unacceptable short- or

long-term effects. Whenever adequately justified, a national criterion may be replaced by a sitespecific criterion (U.S. EPA 1983a), which may include not only site-specific criterion concentrations

(U.S. EPA 1983b), but also site-specific durations of averaging periods and site-specific frequencies of

allowed excursions (U.S. EPA 1991). The latest comprehensive literature search for this document was

conducted in November, 1999. Data in the files of the U.S. EPA's Office of Pesticide Programs

concerning the effects of atrazine on aquatic organisms and their uses have been evaluated for use in

the derivation of aquatic life criteria. Some more recent information received through the submission

of public scientific views on the 2001 document and additional toxicity testing conducted since 2001

was also included.

ACUTE TOXICITY TO FRESHWATER ANIMALS

The data that meet the requirements of the Guidelines concerning the acute toxicity of atrazine

to freshwater organisms are available for 17 species (Table 1). Acute toxicity data for eight freshwater

invertebrate species ranged from 3,000 μg/L for the hydroid coelenterate, Hydra sp. (Brooke 1990) to

49,000 μg/L for the cladoceran, Daphnia magna (Putt 1991). A stonefly (Acroneuria sp.) was the

second most sensitive invertebrate tested, with an EC50 of 6,700 μg/L (Brooke 1990). A cladoceran

(Ceriodaphnia dubia) had a Species Mean Acute Value (SMAV) of >12,120 μg/L (Jop 1991a; Oris et

al. 1991), and the amphipod, Hyalella azteca, had an LC50 of 14,700 μg/L (Brooke 1990). The

remaining invertebrate species tested, the snails (Physa acuta and Physa sp.) and an annelid

(Lumbriculus variegatus), had LC50 values in excess of 20,000, 34,100 and 37,100 μg/L, respectively

(Roses et al. 1999; Brooke 1990).

The rainbow trout (Oncorhynchus mykiss) was the most sensitive freshwater vertebrate species

tested, with an LC50 of 5,300 μg/L (Beliles and Scott 1965). The goldfish, Carassius auratus, was the

most tolerant fish species and is11.32 times less sensitive to atrazine than rainbow trout (Table 1). The

fathead minnow (Pimephales promelas) had a SMAV of 20,000 μg/L (Dionne 1992), while the LC50

for the brown trout (Salmo trutta) was 27,000 μg/L (Grande et al. 1994). The SMAVs for the

remaining vertebrate species, all fishes, were 6,300, >10,000, >10,000, >13,856 and >18,000 μg/L for
9

the brook trout, Salvelinus fontinalis (Macek et al. 1976); largemouth bass, Micropterus salmoides

(Jones 1962); channel catfish, Ictalurus punctatus (Jones 1962); bluegill, Lepomis macrochirus (Beliles

and Scott 1965; Macek et al. 1976); and coho salmon, Oncorhynchus kisutch (Lorz et al. 1979),

respectively. The SMAV was based upon a flow-through test in the case of the fathead minnow, where

other test results were also available.

Three species of amphibians were tested with atrazine (Table 1). The leopard frog (Rana

pipiens), wood frog (Rana sylvatica) and American toad (Bufo americanus) each has a LC50 value of

>20,000 μg/L atrazine. Based on these values, the amphibians evaluated are relatively acutely

insensitive to atrazine.

Freshwater Genus Mean Acute Values (GMAVs) were identical to the SMAVs in all cases with

the exception of Physa and Oncorhynchus, where the two species tested had different SMAVs (Table

3). Two of the four most sensitive freshwater genera to atrazine are invertebrates. The freshwater Final

Acute Value (FAV) for atrazine was calculated to be 3,021 μg/L using the procedure described in the

Guidelines and the GMAVs for invertebrates, fish and amphibians in Table 3. The freshwater FAV is

lower than all available freshwater SMAVs except that for the Hydra, which it is less than one percent

higher (Figure 1).

ACUTE TOXICITY TO SALTWATER ANIMALS

The acute toxicity of atrazine to resident North American saltwater animals has been determined

with eight species of invertebrates and two species of fish (Table 1). Although only two fish species

were tested, fish appear to have a similar sensitivity to atrazine as invertebrates. The saltwater SMAVs

range from 2,324 μg/L for mysids, Americamysis bahia (formerly Mysidopsis bahia), to >30,000 μg/L

for the eastern oyster, Crassostrea virginica. The copepod, Acartia tonsa, had similar LC50 values

resulting from a static unmeasured test (Ward and Ballantine 1985) and two renewal tests (Thursby et al.

1990) with measured values of 94, 91.73 and 210.1 μg/L, respectively. An additional flow-through

measured test (McNamara 1991a) with the same species yielded an LC50 of 4,300 μg/L. It is unclear

why there is such a large difference between the flow-through measured value and the other measured

results. There was nothing unusual about the variability of the chemistry data from the flow-through

tests to indicate a problem (coefficient of variations ranged from 2 to 15 percent). A possible

explanation is that the measured values from the static renewal tests were conducted with 70 percent
10

technical grade atrazine, while the flow-through test used 97.1 percent atrazine. The other 30 percent

may have contributed to the higher toxicity. Because there is no obvious problem with the flow-through

data set for A. tonsa, the Guidelines state that the flow-through measured value must be used. Therefore,

the SMAV for this species is 4,300 μg/L. LC50 values for the copepod, Eurytemora affinis, were 500,

2,600 and 13,200 μg/L at salinities of 5, 15 and 25 g/kg, respectively (Hall et al. 1994a,b). The resultant

SMAV was 2,579 μg/L. The opposite trend was observed for the sheepshead minnow; the LC50 values

were 16,200, 2,300 and 2,000 μg/L at salinities of 5, 15 and 25 g/kg, respectively, for larval fish (Hall et

al. 1994a,b). Two other LC50 values of 13,000 and >16,000 μg/L for sheepshead minnow was derived

from the flow-through concentration measured test by Machado (1994b) and Ward and Ballantine

(1985). However, because the former LC50 values were from a more sensitive life-stage, an SMAV of

4,208 μg/L has been calculated for this species.

Saltwater GMAVs (Table 3) were identical to the SMAVs in all cases with the exception of

Acartia where the two species tested had different SMAVs. Three of the four most sensitive saltwater

genera to atrazine are crustaceans. The saltwater FAV for atrazine, 1,519 μg/L, was calculated using the

procedure described in the Guidelines and the GMAVs in Table 3. This saltwater FAV is lower than all

available saltwater SMAVs (Figure 2).

CHRONIC TOXICITY TO FRESHWATER ANIMALS

The data concerning the chronic toxicity of atrazine that are usable according to the Guidelines

are available for 6 freshwater species (Table 2a). Eight freshwater tests have been completed with two

invertebrate and four fish species.

The cladoceran, Ceriodaphnia dubia, was exposed to atrazine over its entire life cycle in two 7-

day tests (Oris et al. 1991). The end result was identical in both tests, with chronic limits of 2,500 and

5,000 μg/L, and a calculated chronic value (geometric mean) of 3,536 μg/L. An accompanying acute

toxicity test resulted in an LC50 of >30,000 μg/L (Oris et al. 1991). The resultant acute-chronic ratio

was >8.484 (Table 2b).

In another 7-day life cycle exposure with C. dubia (Jop 1991b), atrazine did not affect survival at

any of the test concentrations (i.e., 290, 600, 1,200, 2,500 or 4,900 μg/L). However, reproduction was

significantly reduced at the two highest treatment levels. An average of 10 young per female were

produced at these two treatments compared to a mean of 23 for the pooled controls. The chronic limits

in this study were 1,200 and 2,500 μg/L, and the chronic value was 1,732 μg/L. An accompanying
11

acute value of >4,900 μg/L (Jop 1991a) resulted in an acute-chronic ratio of >2.829. Therefore, the

species mean acute-chronic ratio is >4.899 (Table 3).

The midge, Chironomus tentans, was continuously exposed to atrazine for two generations in a

life-cycle test (Macek et al. 1976). The test was initiated by exposing first generation eggs through the

various larval instar stages, pupation and emergence. Eggs from first generation adults were then

continuously exposed in a similar fashion. Mean measured concentrations were 110, 230, 420, 780 and

1,330 μg/L. No significant differences between controls and the lowest exposure (110 μg/L) were noted

in hatchability, survival, pupation or emergence in first generation animals. Significant reductions in the

number of adults emerging in the first generation exposure occurred at atrazine concentrations of 230

and 420 μg/L. First generation larvae exposed to higher concentrations experienced high mortality at

the early instar stages. In the second generation, hatchability was reduced at 420 μg/L, while pupation

and emergence were reduced at 230 and 420 μg/L of atrazine. Exposure to 110 μg/L had no effect on

growth or development of the chironomid larvae. Based on these observations, the chronic limits were

110 and 230 μg/L, and the resultant chronic value (geometric mean) was 159.1 μg/L. A corresponding

acute value of 720 μg/L for a test that was fed (Macek et al. 1976) yielded an acute-chronic ratio of

4.525 for C. tentans. 

Rainbow trout (Oncorhynchus mykiss) were exposed to atrazine in an early-life stage test (ELS)

conducted in reconstituted water with a hardness of 50 mg/L as calcium carbonate (Whale et al. 1994). 

The ELS test was divided into 3 main stages: (I) immediately post-fertilization to hatching (30-day

duration), (II) post-hatch to swim up (28-day duration), (III) post-swim up to 3 months old (28-day

duration), for a total exposure of 86 days. Mean measured concentrations (mean ± SD) were <10 (water

control), <10 (solvent control), 36 ± 12, 130 ± 50, 410 ± 170, 1,100 ± 660, and 3,800 ± 2,200 μg/L,

respectively. Significant mortalities (58.8 percent) occurred in the highest atrazine exposure during

stage I and II of the test although no other dose response relationships could be defined. Significant

decrease in fish wet weight was observed in concentrations of 1,100 and 3,800 μg/L compared to the

solvent control, although fry exposed to 1,100 μg/L did show signs of a recovery in wet weight toward

the end of the stage III exposure. Statistical analysis of the dry weights of these same fish samples

showed that a significant decrease in weight occurred only in fish exposed to 3,800 μg/L atrazine. 

Because of the recovery in growth at the 1,100 μg/L atrazine concentration, the chronic limits in this

study were set at 1,100 and 3,800 μg/L, resulting in a chronic value of 2,045 μg/L. An accompanying

acute value is not available for this species, therefore, an acute-chronic ratio cannot be calculated.

Yearling brook trout (Salvelinus fontinalis) and their offspring were continuously exposed to

atrazine for 306 days at mean measured concentrations of 65, 120, 240, 450 and 720 μg/L (Macek et al.
12

1976). At 90 days, significant reductions in weight and total length of first generation fish occurred at

concentrations of 240 μg/L and above. At 306 days, weight and total length of first generation fish were

significantly less than controls at atrazine exposures of 120 μg/L and above. Fish at these exposures

also appeared lethargic in comparison to the controls and fish at 65 μg/L. Spawning activity and

hatchability of second generation fry did not appear to be affected, although considerable variability

between replicates in the observed characteristics of total number of eggs spawned, number of eggs per

female, percent fertilization and hatchability precluded statistical interpretation. High replicate

variability was also observed in morphological development of the embryos. At 30 days of exposure,

fry survival was similar for all treatments, but was significantly reduced at concentrations of 240 μg/L

and above after both 60 and 90 days. As in first generation fry, length and weight of second generation

fry at 90 days were significantly less than controls at atrazine exposures of 240 μg/L and above. Based

on the most sensitive measure, i.e., growth of first generation fish at 306 days, the chronic limits were 65

and 120 μg/L, with a resultant chronic value of 88.32 μg/L. A corresponding acute value of 6,300 μg/L

(Macek et al. 1976) yielded an acute-chronic ratio of 71.33 for brook trout (Table 2b).

A fathead minnow full life-cycle chronic test that extended for 274 days was performed, with

mean measured atrazine concentrations of 0, 150, 250, 460, 990 and 2,000 μg/L (Dionne 1992). At 30

days, first generation larval length was significantly reduced by concentrations $990 μg/L, whereas, at

60 days, length was reduced at concentrations $460 μg/L. At 274 days, survival was significantly

reduced at 990 and 2,000 μg/L of atrazine. There was no effect upon the reproductive characteristics of

number of eggs per spawn, total number of eggs produced, number of spawns per female, or number of

eggs per female at any treatment level. Hatching success was slightly, but significantly, reduced at

concentrations of 250 μg/L and above. Second generation larval growth (length and weight) was

significantly reduced at $460 μg/L of atrazine. The chronic limits were reported to be 250 and 460

μg/L, based upon first and second generation larval hatching and growth. This resulted in a chronic

value of 339.1 μg/L. An accompanying acute value of 20,000 μg/L (Dionne 1992) yielded an acutechronic ratio of 58.98.

Bluegills (Lepomis macrochirus) were continuously exposed to atrazine for 18 months starting

with 7-10 cm long fish, continuing through spawning, and into a second generation for 60 days (Macek

et al. 1976). Mean measured exposure concentrations were 8, 14, 25, 49 and 95 μg/L. Survival and

growth of first generation fish exposed to atrazine for 6 and 18 months were similar to the controls. 

Spawning activity was too sporadic to indicate any adverse effects. Percent hatchability of eggs was

similar to controls at concentrations between 14 and 95 μg/L. Low fry survival in the second generation

controls for the first 30 days precluded observations on survival effects due to atrazine in this time
13

interval. However, between 30 and 90 days, survival was near 100 percent in the controls and all

atrazine treatments. Total length of second generation fish through 90 days was considered to be

unaffected by any of the atrazine exposures. From a lack of any adverse effect at concentrations as high

as 95 μg/L, the chronic limits were set at 95 and >95 μg/L. The resultant chronic value was >95 μg/L. 

A corresponding acute value of >8,000 μg/L (Macek et al. 1976) yielded an acute-chronic ratio of

>84.21.

The acute values for C. tentans, S. fontinalis and L. macrochirus in tests reported by Macek et al.

(1976) were used in calculating acute-chronic ratios even though the acute test concentrations were not

measured. This was because of close agreement between nominal and measured concentrations in the

chronic tests. For six chronic tests, the overall agreement between measured and nominal concentrations

was 94.4 percent. Therefore, it appeared likely that the nominal concentrations presented for acute tests

were also in good agreement with actual concentrations.

CHRONIC TOXICITY TO SALTWATER ANIMALS

The chronic toxicity of atrazine to saltwater species has been determined in three 8-day life

cycle tests with the copepod, Eurytemora affinis, a 28-day life cycle test with the mysid, Americamysis

bahia, and an early life-stage test (28-day) with the sheepshead minnow, Cyprinodon variegatus (Table

2a). Survival was the most sensitive endpoint in the 8-day chronic tests with E. affinis. Tests were

performed at salinity levels of 5, 15 and 25 g/kg. At a salinity of 5 g/kg, survival was significantly

reduced to 37 percent at the 17,500 μg/L concentration, while at the next lower concentration of 12,250

μg/L it was similar to controls at 71 percent (Hall et al. 1995). The chronic value was 14,640 μg/L. At

a salinity of 15 g/kg, the chronic limits were 17,500 and 25,000 μg/L, and the chronic value was 20,920

μg/L. Sensitivity appeared greater at a salinity of 25 g/kg, with chronic limits of 4,200 and 6,000 μg/L,

and a chronic value of 5,020 μg/L. Only at this highest salinity level was the acute value greater than

the chronic value. The resultant Acute-Chronic Ratio of 2.629, determined at a salinity of 25 g/kg

(13,200 μg/L ÷ 5,020 μg/L), was considered to be the correct ratio for this species, and was used in

subsequent calculations involving the Species Mean Acute-Chronic Ratio.

 Survival was the most sensitive endpoint in the mysid test (Ward and Ballantine 1985). Survival

was 60, 30, and 20 percent at 190, 290 and 470 μg/L, respectively. No statistically significant effect was

observed for survival at concentrations #80 μg/L. Reproduction did not occur at 470 μg/L, but no

adverse effects on reproduction were observed at all lower concentrations. The chronic value for

mysids, is 123.3 μg/L based upon no survival effects at 80 μg/L and a 40 percent reduction in survival at
14

190 μg/L. The acute value, as determined by the same authors, is 1,000 μg/L and the resulting acutechronic ratio is 8.110 (Table 2b). 

In the sheepshead minnow test (Ward and Ballantine 1985), juvenile survival was significantly

reduced at 3,400 μg/L, but not at #1,900 μg/L. All fish exposed to 5,700 μg/L died. There was no

effect on either hatching success or growth in any of the concentrations with surviving fish (#5,700

μg/L). The chronic value for sheepshead minnows, based on mortality of juveniles, is 2,542 μg/L. The

acute value for the sheepshead minnow, as determined by the same authors, is a "greater than" value

(>16,000 μg/L). Therefore, the resulting acute-chronic value is >6.294.

The range of definitive species mean acute-chronic ratios (ACRs) for both freshwater and

saltwater differ by more than a factor of 10 (Table 2b - Acute-Chronic Ratios with greater than values

were not used for these calculations), and are not related to rank order of acute sensitivity (Table 3). 

Since the available species mean ACRs do not meet Guideline requirements (Stephan et al. 1985), a

Final Acute-Chronic Ration (FACR) cannot be calculated, nor can a freshwater or saltwater Final

Chronic Value (FCV) based on the available aquatic animal data. 

TOXICITY TO AQUATIC PLANTS

For inclusion in Table 4, according to the Guidelines, exposures with algae must have been for a

minimum of 4 days. With vascular plants, chronic exposures must have been conducted. In both cases,

it is a requirement that the concentrations of atrazine were measured during the tests. A Final Plant

Value can be obtained by selecting the lowest result from a test with an important aquatic species in

which the concentrations of test material were measured and the endpoint was biologically important.

Two species of freshwater green algae were exposed to atrazine in studies in which the exposure

duration was 4 days or longer and the atrazine concentrations were measured (Table 4). 

Chlamydomonas reinhardtii cell numbers were reduced 50 percent after 4 days of exposure to 51 μg/L

(Girling et al. 2000; Schafer et al. 1993), after 7 days of exposure to 21 μg/L, and after 10 days of

exposure to 10.2 μg/L (Schafer et al. 1993). 

Selenastrum capricornutum had a 4-day EC50 of 4 μg/L, based upon cell numbers (University of

Mississippi 1990). The EC50 values for pheophytin-a and chlorophyll-a content were 20 and 150 μg/L,

respectively. The 4-day No-Observed-Effect-Concentration (NOEC) and Lowest-Observed-EffectConcentration (LOEC) values based on cell numbers were 0.5 and 1.0 μg/L, respectively (University of

Mississippi 1990). Using the same species and cell number as an endpoint, Gala and Giesy (1990)

reported a 4-day EC50 of 128.2 μg/L, and Hoberg (1991a) reported a 4-day EC50 of 130 μg/L. Hoberg
15

(1993a) calculated a 5-day EC50 of 55 μg/L. EC10 values at 4 and 5 days were 90 and 26 μg/L,

respectively, whereas, EC90 values at 4 and 5 days were 190 and 120 μg/L, respectively (Hoberg 1991a,

1993a). The 4-day S. capricornutum NOEC and LOEC determined by Hoberg (1991a) were 76 and 130

μg/L atrazine, respectively.

A 7-day exposure of the duckweed, Lemna gibba, to atrazine resulted in an EC50 of 180 μg/L,

based upon frond production (Hoberg 1991b). Two 14-day studies were also conducted with L. gibba

(Hoberg 1993b,c). A major difference in these two studies was that, in the latter study, the effect

concentrations were calculated based upon the atrazine concentrations that were measured on the last

day only. This may have resulted in effect levels that appeared to be lower than in the first study, where

concentrations were measured more often during the test. In the first study (Hoberg 1993b), using frond

number as an endpoint, the EC10, EC50 and EC90 values were 6.2, 37, and 220 μg/L, respectively, after

14 days of exposure. Using frond biomass, the EC10, EC50 and EC90 values were 12, 45 and 170

μg/L, respectively. The NOEC and LOEC for frond number were <3.4 and 3.4 μg/L atrazine,

respectively. In the second study (Hoberg 1993c), the EC10, EC50 and EC90 values were 2.2, 50, and

98 μg/L, respectively, using the frond number endpoint, while the respective values for frond biomass

were 4.2, 22, and 110 μg/L. The authors determined a NOEC of 8.3 μg/L and a LOEC of 18 μg/L based

on frond number (Hoberg 1993c).

Exposure of a different species of duckweed, Lemna minor, to atrazine for 14 days resulted in a

NOEC of 10 μg/L based upon a biomass endpoint (University of Mississippi 1990). In this study, a

LOEC of 100 μg/L was obtained for the biomass endpoint. The EC50, based on biomass, was 8,700

μg/L. Girling et al. (2000) reported a L. minor 28-day growth NOEC of 38 μg/L atrazine, and the LOEC

was 120 μg/L atrazine. In another study using L. minor (Kirby and Sheahan 1994), 10-day exposures to

atrazine yielded EC50 values that were comparable to those found for L. gibba by Hoberg (1993b,c). 

EC50 values of 56, 60 and 62 μg/L were obtained based upon frond number, fresh weight and

chlorophyll content, respectively.

Elodea (Elodea canadensis) was exposed to atrazine for 20 days by Girling et al. (2000), and the

NOEC and LOEC values based on length were 20 and 30 μg/L atrazine, respectively. In a study

conducted by the University of Mississippi (1990), the effects of atrazine were evaluated both in the

absence and presence of sediment. In the absence of sediment, LOEC values of 10 and 100 μg/L were

observed, based upon mature frond production and biomass, respectively. With sediment present, the

biomass LOEC was also 100 μg/L. Biomass EC50 values were 1,200 and 25,400 μg/L when sediment

was absent and present, respectively, in the test systems. 
16

As stated in the Guidelines (Stephan et al. 1985), the Final Plant Value (FPV) is the

lowest result from a test with an important aquatic plant species in which the concentrations of

test material were measured, and the endpoint was biologically important. In this case, the

freshwater FPV would be the geometric mean of the two duckweed species (Lemna gibba and

Lemna minor) species mean chronic values (SMCVs) of 6.44 μg/L (Hoberg 1993b,c) and 46.19

μg/L (University of Mississippi 1990; Girling et al. 2000), or 17.25 μg/L atrazine (Text Table A). 

Using the geometric mean of the two SMCVs for Lemna is consistent with the Guidelines, and is

how all the SMAVs and GMAVs are calculated in the WQC documents.

Text Table A. Selected Freshwater Acute and Chronic Plant Data Taken From Table 4.

Species

Acute

Value

(EC50)

SMAV

(μg/L)

GMAV

(μg/L)

NOEC - LOEC

(μg/L)

Chroni

c Value

(μg/L)

SMCV

(μg/L)

Reference

Green alga,

Chlamydomonas

reinhardtii

51

(4 days)

51 --- --- --- Girling et al.

2000

Green alga,

Chlamydomonas

reinhardtii

51

(4 days)

51 51 --- --- --- Schafer et

al.1993 

Green alga, Selenastrum

capricornutum

4

(4 days)

0.5 - 1.0

(4 days - cell #)

0.7071 Univ. of

Mississippi

1990

Green alga, Selenastrum

capricornutum

130

(4 days)

76 - 130

(4 days - cell #)

99.398 8.384 Hoberg

1991a

Green alga, Selenastrum

capricornutum

128.2

(4 days)

40.55 40.55 --- --- --- Gala and

Giesy 1990

Duckweed,

Lemna gibba

180

(7 days)

<3.4 - 3.4

(14 days - frond #)

3.4 Hoberg

1991b, 1993b

Duckweed,

Lemna gibba

50

(14 days)

94.89 8.3 - 18

(14 days - frond #)

12.2 6.440 Hoberg

1993c

Duckweed,

Lemna minor

56

(10 days)

56 72.89 10 - 100

(14 days - biomass)

31.62 Univ. of

Mississippi

1990

Duckweed,

Lemna minor

-- -- 38 - 120

(28 days - growth)

67.5 46.19 Girling et al. 

2000

Elodea,

Elodea

canadensis

--- --- --- 20 - 30

(20 days - length)

24.49 Girling et al.

2000

Elodea,

Elodea

canadensis

1,200

(10 days)

1,200 1,200 10 - 100

(10 days - biomass)

31.62 27.83 Univ. of

Mississippi

1990
17

Information on the sensitivities of saltwater plants to atrazine is available for five phytoplankton

species and five vascular plant species, representing nine genera (Table 4). Although the phytoplankton

test results do not meet the minimum requirement of a four-day exposure, they are included here to show

that their sensitivity to atrazine is similar to vascular plants. All of the plant effect concentrations were

less than the acute values for aquatic animals. Short-term (two and three day) growth tests with

phytoplankton resulted in EC50 values ranging from 79 to 265 μg/L (Mayer 1987; Walsh 1983); a factor

of only 3.4. Two species of estuarine submerged vascular plants, Potamogeton perfoliatus and

Myriophyllum spicatum, exposed for 28-35 days to various concentrations of atrazine, had IC50 values

for final biomass and photosynthesis between 25 and 117 μg/L, with the biomass endpoint being more

sensitive in both species (Kemp et al. 1982b, 1983, 1985). The sago pondweed, Potamogeton

pectinatus, was tested (Hall et al. 1997) for atrazine toxicity for 28 days at three salinities (1, 6, and 12

g/kg). Dry weight was the most sensitive endpoint with chronic values (calculated as the geometric

mean of the respective NOEC and LOEC values) of 21.2, 21.2 and 10.6 μg/L at salinities of 1, 6, and 12

g/kg salinity, respectively. The wild celery, Vallisneria americana exposed to atrazine for 42 days had

chronic values of 6.19 μg/L for leaf area (Correll and Wu 1982) and 178.9 μg/L for dry weight (Forney

and Davis 1981). Four separate 21-day exposures of the seagrass, Zostera marina, resulted in LC50

values ranging from 100 to 540 μg/L (Delistraty and Hershner 1984). 

For saltwater, the FPV would be the geometric mean of the three Potamogeton pectinatus

(Sago pondweed) measured chronic studies conducted by Hall et al. (1997) at different salinities,

or 16.83 μg/L atrazine (Text Table B). Using the geometric mean of the SMCVs for the three P.

pectinatus tests is consistent with the Guidelines, and is how all the SMAVs and GMAVs are

calculated in the WQC documents.
18

Text Table B. Selected Saltwater Acute and Chronic Plant Data Taken From Table 4.

Species Salinity

(g/kg)

NOEC - LOEC

(μg/L)

Chronic

Value

(μg/L)

SMCV

(μg/L)

Reference

Redheadgrass pondweed,

Potamogeton perfoliatus

9 IC50

(35 days - biomass)

30 30 Kemp at al. 1982b,

1983, 1985

Sago pondweed,

Potamogeton pectinatus 

1 15 - 30

(28 days - dry wt.)

21.2 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

6 15 - 30

(28 days - dry wt.)

21.2 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

12 7.5 - 15

(28 days - dry wt.)

10.6 16.83 Hall et al. 1997

Eurasian water milfoil,

Myriophyllum spicatum

9 IC50

(35 days - biomass)

25 25 Kemp at al. 1982b,

1983, 1985

Wild celery,

Vallisneria americana

5 3.2 - 12

(42 days - leaf area)

6.19 Correll and Wu

1982

Wild celery,

Vallisneria americana

3, 6 100 - 320

(42 days - dry wt.)

178.9 33.28 Forney and Davis

1981

Eelgrass,

Zostera marina

22 LC50

(21 days)

540 Delistraty and

Hershner 1984

Eelgrass,

Zostera marina

20 LC50

(21 days)

100 Delistraty and

Hershner 1984

Eelgrass,

Zostera marina

20 LC50

(21 days)

365 Delistraty and

Hershner 1984

Eelgrass,

Zostera marina

19 LC50

(21 days)

367 291.6 Delistraty and

Hershner 1984

ECOSYSTEM EFFECTS DATA

Several aquatic ecosystem studies, either artificial laboratory microcosms or field mesocosms,

have provided valuable insight into ecosystem structural and functional responses to atrazine (see Other

Data, Table 6). A mixed assemblage of algal species exposed to 10 μg/L of atrazine for periods of time

ranging from 1 day to 3 weeks exhibited reductions in gross productivity between 39 and 78 percent

(Kosinski and Merkle 1984; Kosinski et al. 1985). Exposure of an experimental stream periphyton

community to 1,000 μg/L for 14 days caused severe population density reductions in several species,

and total destruction of the green alga, Cladophora glomerata (Kosinski 1984). The extreme toxicity to

C. glomerata is notable because of the dominant role that it often plays in structuring a benthic

community. Similarly, Moorhead and Kosinski (1986) observed reduced net primary productivity at
19

100 μg/L in an assemblage of mixed stream algal species. By contrast, in a mixed stream community,

no effects were observed upon stream macroinvertebrate community structure, periphyton production or

biomass, or the community photosynthesis/respiration ratio following a 30-day exposure at 25 μg/L

(Lynch et al. 1985).

Malanchuk and Kollig (1985) observed chemical changes in an experimental stream community

consisting of microscopic autotrophs and heterotrophs following the introduction of atrazine at a

nominal concentration of 100 μg/L for a 2-week exposure period, after which time the atrazine was

removed from the ecosystem. They observed decreased diurnal fluctuations in pH and dissolved oxygen

concentrations, as well as lower mean values for these water characteristics while atrazine treatment was

on-going, but nitrate nitrogen levels increased. Following the cessation of atrazine treatment, there was

a rapid recovery for each of these water characteristics back to control levels. 

Biomass reductions were also noted in a stream aufwuchs community exposed to 24 or 134 μg/L

of atrazine for 12 days (Krieger et al. 1988), although a 24-hour exposure of 77.5 μg/L had no effect

upon algal cell numbers or biomass in a natural stream periphyton community (Jurgenson and Hoagland

1990). An exposure of as low as 0.5 μg/L for 6 months resulted in an initial decrease in phytoplankton

species followed by a recovery (Lakshminarayana et al. 1992). Gruessner and Watzin (1996), however,

did not observe any effects of atrazine on a stream community of attached algae and benthic

invertebrates at a concentration of 5 μg/L when exposed for 14 days. Pearson and Crossland (1996)

reported an inhibition of photosynthesis by the periphyton community of an artificial stream following

exposure of 100 μg/L of atrazine for 30 days.

In a static pond microcosm (1 L beaker), Brockway et al. (1984) found that a 7-day exposure to

5.0 μg/L had no effect upon diurnal oxygen production, a measure of photosynthesis, by the various

species of green and blue-green algae present. A 50 μg/L exposure for 12 days resulted in a 25 to 30

percent reduction in diurnal oxygen production, while 7- to 12-day exposures at 100 to 5,000 μg/L

further decreased oxygen production. Berard et al. (1999) observed seasonal and species-dependent

effects in a lake microcosm plankton community after 10 to 21 days of exposure to 10 μg/L atrazine. 

During the experiment, growth was generally stimulated for Chryptophytes and Chrysophytes, but

inhibited in Chlorella vulgaris.

Exposure of a freshwater microcosm to 5.1 μg/L of atrazine for 7 weeks did not affect the

species composition of phytoplankton, zooplankton or benthic macroinvertebrates, but did cause a slight

decrease in photosynthetic activity (Van den Brink et al. 1995). Hamala and Kollig (1985) found an

approximate 75 percent decrease in the productivity/respiration (P/R) ratio in a 14-day exposure to 100

μg/L of a periphyton-dominated microcosm which contained 33 algal taxa. They also observed reduced

algal densities, decreased species diversity, altered species composition and reduced biomass
20

accumulation. In a 21-day recovery period, net community productivity returned to control values

within 16 days, while very little recovery occurred in community structural characteristics. This fairly

rapid recovery in a functional characteristics indicated that the primary effect of atrazine at this exposure

level was algistatic and not algicidal for those species involved in the recovery.

Stay et al. (1985), using a 3.7 L laboratory microcosm consisting of 10 algal species and 5

animal species (one protozoan, one rotifer, and three crustaceans), found that reduction in the ratio of 14C

uptake/chlorophyll-a was the most sensitive measure of atrazine effect. This suggested that the

effectiveness of the photosynthetic system was impaired. The lowest exposure (i.e., 43.8 μg/L over 60

days) resulted in significant reductions (approximately 60 to 90 percent) in the ratio throughout most of

the study. Higher exposures (nominal concentrations of 100 to 500 μg/L) caused further reductions in

this ratio, but not as large a difference as between controls and the lowest exposure.

Peichl et al. (1984) observed changes in the population densities of zooplankton in a pond

mesocosm study after 70 days of exposure to 200 μg/L of atrazine. In a later study (Peichl et al. 1985),

the authors observed changes in the phytoplankton community after 121 days of exposure to only 10

μg/L. Experimental ponds in Kansas that were exposed for several years to single annual applications

of atrazine at nominal concentrations of 20 μg/L or more exhibited reductions in the production and

biomass of phytoplankton, in macrophyte populations and in populations of benthic insect grazers,

bullfrog (Rana catesbeiana) tadpoles, grass carp (Ctenopharyngodon idella) that had been introduced,

and in bluegills (deNoyelles et al. 1982, 1989, 1994). Initial nominal concentrations of 20, 100, 200 and

500 μg/L depressed phytoplankton growth within a few days in the ponds. However, after 3 weeks,

phytoplankton production and biomass were similar to controls. deNoyelles and Kettle (1985) observed

reduced photosynthesis of 40 percent or more in short-term (24-hour) bioassays at these same atrazine

concentrations, but longer-term bioassays (20 days) and the experimental pond studies showed a

recovery from this initial reduction.

Benthic insect community structure was studied in the same experimental ponds used in Kansas

following two single annual treatments at 20, 100 and 500 μg/L (Dewey 1986; Dewey and deNoyelles

1994). Significant reductions of both species richness and total abundance of emerging insects was

observed at the lowest exposure of 20 μg/L. Abundance of the herbivorous, non-predatory insects was

reduced at 20 μg/L, but not abundances of the predatory species. This indicated that the observed loss

of total insects was a secondary effect due to feeding habit and loss of plant life, rather than a direct

toxic effect. Loss of insect habitat, particularly in the form of macrophytes, also likely had some effect

upon the insect community. These effects tended to destabilize the ecosystem (Dewey and deNoyelles

1994).
21

Species composition of macrophytes was altered in a pond mesocosm community following an

8-week exposure to 50 μg/L of atrazine (Fairchild et al. 1994a). However, functional characteristics

were unaffected, indicating functioning redundancy within the ecosystem. Juttner et al. (1995) did not

observe any effects upon the plankton community of a pond mesocosm following a 2-month exposure to

5 μg/L, but did observe decreased oxygen production, pH and conductivity at 10 μg/L, and decreased

phytoplankton populations at 182 μg/L. At 318 μg/L, reproduction was affected in Daphnia longispina

and a population of rotifers, Polyarthra sp., was eliminated.

In a laboratory microcosm using a naturally derived microorganism community, Pratt et al.

(1988) observed that a 21-day exposure to a mean measured concentration of 10 μg/L of atrazine did not

affect the dissolved oxygen, a measure of photosynthetic function, but that a concentration of 32.0 μg/L

caused significant reductions in this characteristics. This resulted in a calculated maximum acceptable

toxicant concentration (MATC) of 17.9 μg/L based upon this functional endpoint. Several other

endpoints, such as protozoan colonization, biomass protein, chlorophyll-a and potassium levels, were

less sensitive than dissolved oxygen, and had a calculated MATC of 193 μg/L.

Stay et al. (1989) studied atrazine effects in 1 L laboratory microcosms containing mixed phytoand zooplankton cultured from three Oregon lakes and one pond. A 42-day exposure of approximately

15 μg/L atrazine did not affect net primary productivity, the P/R ratio, or pH, but these characteristics

were significantly reduced from controls at a mean measured concentration of approximately 84 μg/L.

Larsen et al. (1986) measured photosynthetic 14C uptake in a 3 L Taub microcosm community at

different time intervals for up to 373 days after treatment with atrazine. EC50 values ranged from 24

μg/L at 177 days to 131 μg/L at 43 days after atrazine treatment.

A 50 m2

 pond community exposed to atrazine for 4 months at a concentration between 60 and

120 μg/L eliminated a population of duckweed, Lemna minor, within 27 days (Gunkel 1983). Gunkel

also observed a rapid succession of algal species and a reduced rate of reproduction in Daphnia

pulicaria. Treatments of a pond mesocosm community for 2 years with 20, 100 and 300 μg/L of

atrazine caused decreases in cell numbers of green algae and of cladoceran populations, but increased

numbers of cryptomonads (Neugebauer et al. 1990).

In experimental ponds treated in May and June with 20 μg/L of atrazine for two years, there was

decreased abundance of Endochironomus nigricans in June and of total macroinvertebrates in both May

and June, followed by recovery in July (Huggins et al. 1994). Epiphytes, detritovores and generalists

also exhibited initial decreases in populations, followed by a recovery. A short-term exposure (>3 hour)

of pond algae to 10 μg/L of atrazine was observed to increase the rate of fluorescence for photosystem II

(Ruth 1996). 
22

In two reports of studies conducted at the same site, a lake community was enclosed with a

limnocorral (5 m x 5 m x 5 m deep) to which atrazine was added. Both studies focused on the

periphyton community. In the first study (Herman et al. 1986), the limnocorrals received two nominal

atrazine applications of 100 μg/L, one on day 0 and another on day 35. After 34 days of exposure to

measured concentrations ranging between 80 and 140 μg/L, a reduction in periphyton ash-free dry

weight was observed. Over a 9-week period with two atrazine applications 6 weeks apart, which

resulted in measured concentrations of approximately 80 to 140 μg/L after the first application and 110

to 190 μg/L after the second application, reductions occurred in chlorophyll-a, organic matter and total

periphyton algal biomass. In the second study (Hamilton et al. 1987), a 230-day exposure to a mean

measured atrazine concentration of 80 μg/L caused approximate reductions of 60 percent in biomass, 22

percent in cell numbers and 32 percent in number of species. The results were more pronounced in

exposures to mean measured atrazine concentrations of 140 and 1,560 μg/L. A shift in community

structure occurred from a chlorophyte-dominated community to a diatom-dominated community.

Aquatic enclosures exposed to a nominal atrazine application of 100 μg/L on June 1 followed by

a second application of the same concentration 35 days later, exhibited a gradual die-off of the

phytoplankton, a long period of recovery for the green algal community, and a distinct shift in the

taxonomic composition of algae (Hamilton et al. 1988). Thirteen days after the first application,

significant declines occurred in populations of the green algal species Elakatothrix gelatinosa, Tetraedon

minimum, Sphaerocystis schroeteri, and Oocystis lacustris, and of the dinoflagellate, Gymnodinium spp. 

Seventy-seven days after the second application, phytoplankton communities were still distinctly

different, and total fresh weight biomass was reduced. By 323 days after the first application, the

phytoplankton assemblages were again similar between control and treated enclosures. From day 1 to

day 114, control enclosures had an average of five more taxa than the atrazine-treated enclosures. 

During the period between days 49 and 77, the green algal (Chlorophyta) biomass represented <7

percent of that found in the controls. By the following spring (day 323), the biomass had returned to

control levels. The herbicide treatment did not affect the rotifer or crustacean communities. In the same

exposures, Hamilton et al. (1989) observed that the atrazine-treated enclosures became clearer with

increased Secchi disc readings, while readings of dissolved oxygen, chlorophyll, dissolved organic

carbon, and particulate organic carbon decreased.

Using 1.70 m2

 enclosures in a moderately eutrophic lake, Lampert et al. (1989) observed

decreased photosynthesis and decreased populations of certain zooplankters at atrazine concentrations of

0.1 and 1.0 μg/L. At 0.1 μg/L, populations of Daphnia sp. were severely reduced within 15 days, and

oxygen concentrations were reduced after 10 days. At 1.0 μg/L, concentrations of chlorophyll-a and

oxygen were reduced after 18 days as were populations of Daphnia, Cyclops, and Bosmina species, and
23

nauplii larvae. At 0.1 μg/L, there was an apparent recovery after about 25 days. The authors noted,

however, that the effects of atrazine observed in their experimental plastic bag enclosures may have

been exaggerated, because gas exchange and re-colonization from the surrounding medium were

limited. Likewise, the enclosures may have accentuated trophic feeding dynamics of primary

consumers, as fish and larger zooplankton (predators) were excluded. Genoni (1992) observed a

decreased algal population density and a decreased "scope for change in ascendency" in a microcosm

community exposed to 250 μg/L. The scope for change in ascendency is a biological system response

endpoint, considered to be analogous to the scope for growth endpoint for individual organisms.

Gustavson and Wangberg (1995) observed some minor changes in species composition of the

phytoplankton community in a lake mesocosm community after a 20-day exposure to 20 μg/L. EC50

values were 58 and 52 μg/L for the phytoplankton community, and 52 and 54 μg/L for the periphyton

community. Brown and Lean (1995) found that a short-term exposure (3 hours) of lake phytoplankton

to atrazine resulted in a much lower EC50 based upon photosynthetic carbon assimilation (i.e., 100

μg/L), than when based upon phosphate or ammonium assimilation (14,000 and >33,000 μg/L,

respectively). A stream periphyton community exhibited a significant reduction in chlorophyll-a

following a brief exposure (<4 hours) to 109 μg/L of atrazine (Day 1993). Caux and Kent (1995)

observed a reduction in green algae in Quebec streams following the spring atrazine runoff pulse, with a

maximum stream concentration of approximately 40 μg/L. Detenbeck et al. (1996) observed a decrease

in the gross productivity of a wetland mesocosm community after 9 to 27 days of exposure at an atrazine

concentration of 15 μg/L. There also was an increase in the concentrations of dissolved nutrients in the

water.

In the range of 10 to 100 μg/L, it appears that atrazine changes planktonic community structure

and composition (Berard et al. 1999, Peichel et al. 1984), which may recover in functional

characteristics after cessation of treatment, e.g., productivity, pH, dissolved oxygen production -

deNoyelles et al. 1982, 1989, 1994; Malanchuk and Kollig 1985), but not necessarily structure (Hamala

and Kollig 1985). Planktonic community structure effects are seasonal and species-dependent (Berard et

al. 1999), with the diatom community generally less sensitive than green algae (Lakshminarayana et al.

1992). 

Changes in habitat and loss of certain plant species at 20 μg/L can lead to secondary effects

higher in the food web (Dewey and DeNoyelles 1994), but even at this initial exposure level, structure

and functional integrity of aquatic insect communities are generally maintained, as indicated by only

very small changes in species diversity and evenness indices (Dewey 1986). Concentrations above 50

μg/L, on the other hand, cause more severe reductions in productivity, plant biomass, and community

structure, as well as indirect effects on herbivorous invertebrates and fish. Changes in species
24

composition without loss of functionality at 50 μg/L atrazine, however, indicates a great deal of

functional redundancy within some systems (Fairchild et al. 1994a). 

Rotifer and crustacean communities are generally less sensitive to direct atrazine toxicity with

an LOEC of about 200 μg/L (Peichl et al. 1984). Other benthic macroinvertebrate species can be

affected at as low as 20 μg/L, but the effects (mostly abundance) are seasonal (Huggins et al. 1994). 

Studies by Berard et al. (1999), Kosinski and Merkle (1984), Kosinski et al. (1985),

Lakshminarayana et al. (1992), Lampert et al. (1989), and Peichl et al. (1984, 1985) have observed

effects at lower concentrations. The lowest recorded effects of atrazine occurred in experimental

enclosures with natural communities (Lampert et al. 1989). 

In summary, aquatic ecosystem structural and functional parameters have most frequently been

observed to be adversely affected by atrazine concentrations exceeding 10 μg/L. The lowest

concentrations of atrazine that have resulted in temporary negative effects upon abundance of aquatic

plants (primary effect) and animals (secondary effect) have generally occurred at 15-20 μg/L and above. 

It appears that for effects at concentrations up to 15 μg/L, the communities can recover quite rapidly

following dissipation of the atrazine concentration. In a review of microcosm and mesocosm studies

with atrazine, Giddings and Biever (1994) concluded that concentrations of 20 μg/L or less typically

caused minor effects, if any, on primary production and plant community composition, and recovery

occurred quickly, even if atrazine remained in the system. 

IMPACTS TO PLANT COMMUNITY STRUCTURE AND FUNCTION

Impacts to Plant Community Structure and Function 

The Guidelines and the CWA expect that the Agency will establish a sound scientific basis for

all of its water quality criteria for the protection of aquatic life. In light of this expectation and because

of the unique use and chemical characteristics of atrazine, the Agency has selected an approach to

deriving the chronic criterion for the protection of freshwater aquatic life as described below.

In summary, threshold concentrations were determined from realistic and complex time variable

atrazine exposure profiles (chemographs) for modeled aquatic community structure changes. Methods

were developed to estimate ecological community responses for monitoring data sets of interest based

on their relationship to micro- and mesocosm study results, and thus to determine whether a certain

exposure profile at a site may have exceeded a level-of-concern.
25

This required a two step process: (1) Determine the magnitude and duration of exposure of

aquatic plants to atrazine that constitute LOC(s) for aquatic communities and/or ecosystems, and (2)

Determine the best available method(s) to interpret monitoring data relative to these LOC(s).

Endpoints

The initial assessment endpoint was chosen based on the reported results from 77 micro- and

mesocosm studies for which atrazine was tested: change in aquatic community structure and function of

primary producers. This endpoint appeared to be the most sensitive of the effect endpoints affecting

aquatic plants. Further, the effect of atrazine on aquatic plants, whether direct or indirect, appeared to be

more sensitive than effects on other organisms in the aquatic ecosystem, e.g., aquatic invertebrates, fish.

Thus, by focusing on aquatic plant community structural changes, we would be in effect, protecting

against adverse effects on the rest of the aquatic community. The measurement endpoints reported in

available studies which tested atrazine were: laboratory – growth (rate) and biomass; microcosms,

mesocosms and models - reduction in primary production and changes in structure of primary producer

communities.

Community Level Studies

Ecological responses of aquatic communities to atrazine exposures can be assessed using

community level studies, such as micro- and mesocosms. The subgroup reviewed 25 different studies

with 77 reported effects/no effects on aquatic plants (See Appendix 1). Twenty-four results were from

tests on ponds or lakes; 20 on artificial streams; and, 33 were microcosm tests. Eight results were on

macrophytes, 29 on periphyton, and 40 on phytoplankton. However, only a limited number of exposure

profiles could be tested in these studies. Typically, one to three concentrations of atrazine were tested in

these studies each with a single application to the test system at initiation. Atrazine concentrations were

often kept constant for a variable duration period before the concentrations slowly decrease with time.

Unfortunately, the variable quality of these studies and the many different study designs did not always

allow a reliable association of exposure magnitude and duration to a certain community level effect, and

in many cases the duration of the studies was too short to document community recovery. 

To better understand the impact of exposure duration and magnitude on aquatic communities,

the effects reported in these studies had to relate to specific exposure durations and magnitudes. First,
26

the 77 study results had to be quantified as to severity of effects of atrazine on the aquatic plant

community. Brock et al 2000 analyzed a majority of the study results and quantified them as follows: 

Effect Scores (Brock et al 2000):

1 = no effect

2 = slight effect

3 = significant effect followed by return to control levels within 56 d

4 = significant effect without return to control levels during an observation period of less than 56 d

5 = significant effect without return to control levels for more than 56 d

Studies not analyzed by Brock but considered in this analysis were scored with the same methods. The

distribution of the scores for the 77 study results were as follows (also see Appendix 1):

Distribution of Effect Scores: 

15 were ranked as 1; 

12 were ranked as 2; 

12 were ranked as3; 

23 were ranked as 4; 

15 were ranked as 5 

Next, the 77 effect scores representing the results from the 25 micro- and mesocosm studies for

atrazine were plotted against the study specific test concentrations and exposure durations in Figure 1.
2

 See http://www.epa.gov/waterscience/models/aquatox/about.html and

http://www.myweb.cableone.net/dickpark/AQTXFacts.htm

27

Figure A. Mesocosm / Microcosm Effects Scores (after Brock et al 2000) versus Atrazine 

Exposure Concentration (ug/L) and Duration (days) 

0.1

10

1000

1 10 100 1000

Duration (days) [Log Scale]

Atrazine concentration (ug/L) [Log Scale] 

Effect Score #1- No Effect

Effect Score #2 - Slight Effect

Effect Score #3 - Signif Effect Recovery

w/in 56-days

Effect Score #4 - Signif Effect No

Recovery <56-days

Effect Score #5 - Signif Effect No

Recovery >56-days

Figure 1: Micro- and mesocosm study effect concentrations scored according to Brock et al 2000 and

plotted against the study specific exposure duration

As expected, based on the mode of action of atrazine that inhibits primary production by

reversibly blocking photosynthesis, the effects observed in micro- and mesocosm studies generally

become more severe with increasing exposure time and magnitude. 

The challenge for step two was to define an appropriate exposure concentration and duration

relationship that properly defines duration specific levels of concern. For that purpose, ecological

modeling was used to simulate a large number of exposure durations and magnitudes for the ecological

response in a generic Midwestern 2nd to 3rd order stream. Two ecological models were initially

considered: (1) the Comprehensive Aquatic Systems Model (CASM) (Bartell et al. 2000, Bartell et al

1999, DeAngelis et al 1989), and (2) AQUATOX2

. The decision to use CASM was made after a

preliminary comparison revealed that CASM could include a larger number of species in the community
28

structure, which appeared to better support our assessment endpoint. In addition, CASM had a relatively

uncomplicated exposure profile for a chemical such as atrazine.

Model Parameterization

A large number of single-species laboratory toxicity test results on atrazine toxicity to aquatic

organisms (See Giddings et al 2000), including aquatic plants (macrophytes, periphyton, and

phytoplankton) were available (Figure 2). A subset of these data (CASM EC50 geometric means) was

selected and used to drive the toxicity of atrazine to aquatic organisms in the CASM simulation model

(See Appendix 2). The modeled toxicity profile included twenty-six producer species (10 plankton, 10

periphyton, 6 macrophytes), and 17 consumer species. Three toxicity scenarios were modeled: 10th

centile, geometric mean, and 90th centile for species with more than one toxicity study. The geometric

mean scenario (toxicity scenario 1) was chosen for the reported model results. 
29

SSD Using Adjusted Mean Slope = 3.42

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1.00 10.00 100.00 1000.00 10000.00

ECx (ug/L) - Log Scale

Cumulative % of Species

EC10

EC50

EC90

CASM EC50

Log. (EC10)

Log. (EC50)

Log. (EC90)

Log. (CASM EC50)

Figure B: Plant Species Sensitivity Distribution for EC10, EC50, and EC90 values overlaid with the

Plant Species Sensitivity Distribution (EC50 geometric mean) used to parameterize CASM.
30

∑ ∑

∑

= =

=

+

= n

k k

n

k k

n

k k k

a a

Min a a S

1 2, 1 1,

1 1, 2, 2* ( , )

CASM Model Simulations

CASM is an ecological food chain model. It was set-up to run simulations for exposure

durations from 1 to 260 days, and concentrations from 20 to 220 :g/L atrazine. The scenarios were

designed to simulate a generic 2nd or 3rd order Midwestern stream, typical for the majority of atrazine

use on corn and sorghum. The CASM model provides the following results: production – modeled as

biomass production (g Carbon m-2) for 1 m2

 surface area) (Appendix 3a), and community structure

(similarity) – species population size derived from species daily biomass (Appendix 3b). Thus, the

model integrates direct and indirect effects to indicate changes in community structure. The endpoint

selected for the model results was percent (%) change in aquatic community structure (as determined by

Steinhaus Similarity coefficient) of primary producers (phytoplankton, periphyton, macrophytes). 

CASM Steinhaus Similarity Analysis 

Coefficients of similarity are used to determine whether the composition of two communities is

similar. The Steinhaus coefficient or similarity index is based on the species abundances (in this case

indicated by the species specific daily biomass) common to two communities. The index is described in

the following equation:

Where ai,k : abundances of species k in sample I

The similarity indices for each possible pair of samples per day are calculated and this results in

a matrix of between (different treatments) similarities as in Figure 3.
31

 1d1 1d2 1d3 etc. Xd260

1d1 B B B B 

1d2 B B B 

1d3 B B 

etc. B B

Xd260 B

Figure C. Example of a matrix of similarities resulting 

from Similarity Index calculations.

Similarity indices were calculated for primary producers, consumers, and fish over exposure

periods from 1 to 20 days (See Appendix 3b). The results show that the changes in percent (%) change

in aquatic community structure of primary producers is a more sensitive (conservative) measurement

endpoint than the same for consumers or fish. 

Determining the LOC - CASM Steinhaus similarity vs. the effects of Atrazine exposure in microand mesocosm studies 

A wide range of single pulses of different duration and magnitude were simulated and used to

calculate community structure changes. Community structure changes were expressed as percent (%)

change in the Steinhaus similarity index that was calculated based on the simulated daily biomass for

each individual species and plotted over time.
32

Table 1: A) Maximum daily percent changea in community structure (Steinhaus

similarity) of primary producers for a modeled generic 2nd-3rd order Midwestern

stream. 

Atrazine

conc. [:g/L]

Pulse duration [d]b

1 3 5 10 20 60 130 260

20 0.1c 0.2 0.7 0.9 1 1.2 1.2 2.3

25 0.8 1.9 2.9 5 7.8 11.7 13 15.5

30 0.8 1.9 2.9 5 7.8 11.7 13 15.8

40 1.1 2.3 3.2 5.2 8 11.7 13.1 16.6

50 1.1 2.3 3.1 5.2 7.9 11.6 13.1 17.5

70 3.7 8 10.7 13.8 16.1 17.3 18.1 22.5

90 4.4 9.4 12.6 15.9 18.2 18.2 18.3 23.5

130 4.5 9.6 12.7 15.8 17.8 17.8 17.8 20.1

170 5.6 13.1 18.1 24.1 29.7 56.3 67.1 72.4

220 5.7 13.2 18.2 24 29.7 56.3 67.1 72.3

B) Year end percent changea in community structure (Steinhaus similarity) of

primary producers for a modeled generic 2nd-3rd order Midwestern stream. 

Atrazine

conc. [:g/L]

Pulse duration [d]b

1 3 5 10 20 60 130 260

20 0 c 0 0 0.2 0.2 0.2 0.2 2.3

25 0.7 1.7 2.7 4.7 7.3 10.9 12.1 15.5

30 0.7 1.7 2.7 4.6 7.2 10.8 12.1 15.8

40 0.7 1.9 3 4.9 7.5 11 12.4 16.6

50 0.7 1.9 2.9 4.9 7.5 10.9 12.9 17.5

70 1.5 3.7 5.2 7.9 10.9 14.6 17.6 22.5

90 1.7 4.1 5.7 8.5 11.6 15.5 18.3 23.5

130 1.7 4 5.7 8.4 11.5 15.3 16.4 20.1

170 2 5.4 8.1 15.5 27.9 51.7 61.2 71.5

220 2 5.3 8.1 15.4 27.8 51.6 61.1 71.1

C) Average percent changea in community structure (Steinhaus similarity) of

primary producers for a modeled generic 2nd-3rd order Midwestern stream. 

Atrazine

conc. [:g/L]

Pulse duration [d]b

1 3 5 10 20 60 130 260

20 0 c 0 0.1 0.4 0.4 0.5 0.5 0.7

25 0.5 1.2 1.9 3.4 5.1 7.4 8.2 8.5

30 0.4 1.2 2 3.5 5.2 7.6 8.4 8.7

40 0.8 1.8 2.6 4.1 5.8 8.3 9.3 9.7

50 0.8 1.8 2.6 4.2 6 8.9 10.1 10.7

70 2.2 4.8 6.4 9.1 11.6 14.9 16.9 17.5

90 2.6 5.6 7.4 10.2 12.8 15.8 17.5 18

130 2.6 5.6 7.4 10.2 12.7 15.4 16.3 16.4

170 2.9 6.8 9.8 16.3 25.5 40.6 46.3 48.4

220 2.9 6.8 9.8 16.4 25.5 40.6 46.3 48.4

aBased on the mean values of 100 Monte Carlo simulations using the Comprehensive Aquatic Systems

Model (CASM)

bConsecutive days of constant exposure beginning on model day 105 (April 15)
33

For further evaluation, the maximum daily percent (Table1 A), year-end percent, i.e. at day 260

post application (Table 1 B), and the average percent change in community structure in the primary

producer community (Table 1 C) were calculated. Maximum daily deviations indicate the short-term

(temporary) maximum change in community structure. The average community structure change

integrates short-term changes and long-term recovery of the communities. A comparison of short- and

long-term %-impact shows that for concentrations >20 :g/L, short-term changes are always between 1-

to 2-fold the average response. For example, an average 5% community structure change may cause a

less than or equal to 10% short-term (temporary) change in primary producer community structure. The

average percent change in community structure was chosen for the reported results since it captures the

short-term changes as well as recovery.

The modeling results in Table 1C were used to help define duration-specific levels of concern.

Two approaches were used. First, the simulated response (or effect) had to be set in context to the microand mesocosm data. A similarity index value was estimated for each micro- and mesocosm test result by

finding the average model similarity deviations (%) of a simulated exposure profile closest to the

conditions used in each study (test concentration and exposure duration) (See Appendix 1 for assigned

index values for each of the 77 test results). Next, the index values were plotted against the Brock et al

effect scores for each micro- and mesocosm test results for comparison (See Figure 4). 

There is a lot of scatter that is reflective of the diversity of this data; however, there is a clear,

strong correlation of the scores with the index. An index value of 5 (vertical red line on the figure)

conservatively separates the 3/4/5 from the 1-2 scores. That means that a 5% change in community

structure (Steinhaus similarity) of the CASM simulations compares to a large majority of the micro- and

mesocosm studies with no to slight effects (leaving only 8% potential false negatives and false positives,

i.e., false negatives - 6 out of 77 studies above the effects score 3 line and to the left of the 5% line; false

positives - 6 out of 77 studies blow the effects score 3 line and to the right of the 5% line). 
34

0

1

2

3

4

5

6

0.10 1.00 10.00 100

Severity Index based on CASM Max % Comm Struct Change

Brock et al 2000 Effects Scores

Potential False Negatives ~8%

Potential False Positives ~8%

Figure D. Correlation between the Similarity Index [CASM AVG % change in community structure for 77 atrazine

micro- and mesocosm studies] and the Brock et al 2000 effect scores.

For the second approach, the CASM simulation results in Table 1C were interpolated to develop

a set of concentration / duration pairs equivalent to 5% effect from CASM. The interpolated results

follow:

Time (days) Concentration (:g/L)

1.1 220

1.6 130

3 75

5 63

10 53

20 24.8

60 23.3

130 22.9

260 22.7
35

0.1

10

1000

1 10 100 1000

Duration (days) [Log Scale]

Atrazine concentration (ug/L) [Log Scale] 

Effect Score #1- No Effect

Effect Score #2 - Slight Effect

Effect Score #3 - Signif Effect

Recovery w/in 56-days

Effect Score #4 - Signif Effect No

Recovery <56-days

Effect Score #5 - Signif Effect No

Recovery >56-days

Interpolated EC5 values

For times greater than 3 days, a linear interpolation was performed across the different

concentrations at each time. For times from 60 to 260 days, the abrupt shift in response between 20 and

25:g/L made interpolation tenuous, but the best estimate would seem to be in the mid-part of the range

and this did not involve much uncertainty given the narrow range. For times less than 3 days, the

response did not reach 5%, but the additional points seem to be points needed at high concentrations.

Thus, interpolations were performed across times at a fixed concentration instead of across

concentrations at a fixed time.

Next, these concentration-duration pairs, representing the 5% index points based on

interpolation, were plotted with lines connecting each point on Figure 1 (See Figure 5 below).

Figure E. Micro- and mesocosm study effect concentrations scored according to Brock et al 2000 and plotted

against the study specific exposure duration. Interpolated 5% CASM Similarity Index points plotted. 

The plot of the interpolated 5% Similarity index points, like Figure 4, conservatively separates the 3/4/5

from the 1-2 scores. Based on both approaches, an index of 5%, meaning a 5% change in community

structure of primary producers, is a reasonable LOC for atrazine exposures in freshwater environments. 
36

Discussion of Uncertainty in Selection of Data, Methods, and Decisions

Since the potential risk of atrazine to aquatic communities will be based on a set of micro- and

mesocosm tests, the critical decision is which tests to include or exclude. The large set of available

studies for atrazine included in this analysis (Appendix 1) have various strengths and weaknesses and

use many different testing designs and methods. The key point here is that there are a large number of

such studies and the subgroup decided to be relatively inclusive, rather than excluding data for various

limited uncertainties or ambiguities. This approach provides a better data set for weight-of-evidence and

allows for addressing "false-negatives" and "false-positives" in light of the overall frequency/magnitude

of the wide range of possible exposure situations. It would not be prudent to rely on any one or two of

these studies.

Quantification of Results of Micro- and Mesocosm Tests

The effect scores in Brock et al (2000) were used to quantify the results of the micro- and

mesocosm tests. The subgroup reached general agreement that the scores assigned to the 77 results were

reasonable, and that scores of 2 (‘slight’ effect) do not constitute a level-of-concern, while scores of 3 (a

pronounced ‘slight effect’) do. Brock et al further characterized a score of 2 as “effects reported in terms

of ‘slight’; ‘transient’, and short-term and/or quantitatively restricted response of sensitive endpoints, and

effects only observed at individual samplings.” Scores of 3 were characterized as a “clear response of

sensitive endpoints, but total recovery within 8 weeks after the last application, and effects reported as

‘temporary effects on several sensitive species’; ‘temporary elimination of sensitive species’; ‘temporary

effects on less sensitive species / endpoints’, and effects observed at some subsequent samplings.” This last

decision is perhaps the most critical risk decision here, because these scores define the actual level of

protection being sought. Therefore, Appendix 1 is arranged by decreasing effects score and shows the

range and nature of effects represented by the different scores. 

Another aspect of quantification is the exposure duration that any score and concentration relate

to. This might not seem to be an issue because the exposure duration is fixed and specified in any test,

but for long exposures in which severe effects occur early, might not these effects be better related to a

shorter duration? For example, the significant effects (scored as a 5 and described as a decrease in

macrophyte coverage in the pond by 95%) in the Kettle et al. (1987) study were related to a full year's

exposure (actually 300 days). However, the study also reported that there was ~60% decrease in

coverage after 60 days. It was decided to stay with the 300 day test duration because (1) the exposures in

the study were constant over the whole time period, (2) Brock et al as well as other authors reported the
37

test duration as ~1 year, and (3) the most dramatic effect without testing for recovery did occur after the

~year long exposure duration. Yet, some could argue that 60% decrease in macrophyte coverage is

significant and should also be scored as a 5 and included. However, the uncertainty resulting from this

observation for the calculation of the time specific LOC(s) in this document is very small because, as

shown in Figure 5, the concentrations causing community structure changes do not further decrease for

constant exposure periods longer than 20 to 30 days, i.e. longer exposure periods do not significantly

change the effect threshold. The Kettle et al study was conducted at the borderline of this threshold

concentration (ca. 20 :g/L). In the weight-of-evidence approach applied here, it constitutes only one of

the large numbers of such studies that also measured less severe impact at the comparable

concentrations and exposure durations. 

Extrapolation of Micro- and Mesocosm Tests to Different Exposure Time Series

Another critical decision was to use an aquatic ecological community model as the extrapolation

tool. It is important to emphasize that EPA is not claiming that the model accurately predicts the effects

in any particular community, but rather that it is a useful means for integrating the kinetics of various

processes (toxic effects on photosynthesis, plant growth dynamics, interactions among plant species

across a growing season) and describing the RELATIVE effects of different exposure time series on the

overall response. 

Parameterization of Model 

The critical data here are the plant laboratory toxicity data assigned to each species in CASM.

These data are the key factor determining the concentration at which CASM predicts significant effects

(slightly above 20 :g/L) and describing the "step-wise" nature of the effects versus concentration.

Because of the concern about effect levels that reflect the more sensitive organisms, Figure 2 and

Appendix 2 show that the decision to use the geometric mean toxicity values (EC50s) for CASM

appears to adequately represent plant species sensitivity distribution. However, one consequence of the

limited number of possible species in the model is that only a few species represent sensitivities below

the 10th centile and above the 90th centile. Additional analyses using the 10th and the 90th centile of the

EC50 instead of geometric means was conducted to test for the potential impact of the species sensitivity

on the CASM results (Appendix 5). For the majority of the simulations, the lower toxicity profiles

(scenario 2) did not cause significantly higher responses than the geometric mean scenario. It was also

observed that the higher and lower toxicity scenarios did not necessarily bracket the geometric mean

scenario. This can partly be explained by the complex nature of the food-chain interactions in the
38

ecological model. The impact of slightly different species sensitivity distributions used to parameterize

the model is therefore probably low, when compared to relative importance of the species composition

in the food-chain model.

EPA recognizes that different species have different relative importance in CASM results and

this varies seasonally. Even if each CASM species is linked to the most relevant laboratory species, the

original selection of CASM species and the assignment of the laboratory data represent a major

uncertainty and further evaluation using model parameterizations representing different generic aquatic

communities are recommended. 

Selection of Model Variable to Relate to Micro- and Mesocosm Results 

The selection of this endpoint is a critical decision, even if model results are calibrated to the

micro- and mesocosm data, because different endpoints have different time-dependencies. These

differences will affect the relative level of concern for different exposure series. While EPA believes that

the average similarity index is a reasonable choice, we also recognize that its meaning is somewhat

uncertain. The critical point is the time trajectory of the index when the effect on the average community

structure is less than that at the end of the year. EPA recognizes that the recommended average index

combines direct toxic effects and consequent shifts in later seasonal plant succession. However, it is

important to note that this index can have different time dependence than an endpoint such as overall

primary productivity, and thus is a key decision. 
39

ENDOCRINE DISRUPTION EFFECTS DATA

Atrazine has been reported in a number of studies as an endocrine disruptor. Researchers at the

University of California at Berkeley (Hayes et al. 2002) have reported that frogs (Xenopus laevis)

exposed to atrazine in the water at concentrations #1 μg/L suffered abnormalities in gonadal

development, including feminization and hermaphroditism, which could render male frogs sterile. In

addition, these same exposures resulted in a reduction in the size of the laryngeal muscle in male frogs,

an important muscle used for the mating call of the frog. Studies conducted by Carr et al. (2003) and

Carr and Solomon (2003) designed to replicate the Hayes et al. (2002) experiments observed these same

effects at approximately 20-21 μg/L atrazine. A third study conducted by Sullivan et al. (2003) with

Xenopus laevis looking at the same end-points yielded an effect level of 20 μg/L atrazine (the lowest

concentration tested). Although the atrazine concentrations reported in this latter study were nominal,

measurements of actual atrazine levels in a more recent experiment by the same authors (unpublished

study) of the same design and methodology showed good agreement between nominal and measured

concentrations. As stated by Sullivan et al. (2003), “these results allow us to confidently indicate actual

atrazine concentrations are likely to have occurred in this study.” 

Until this issue is resolved, justification and defense of a freshwater chronic criterion based on

the endocrine disrupting effects of atrazine on amphibians is difficult. A recently convened Scientific

Advisory Panel (SAP) reviewed EPA’s (2003) evaluation of 17 laboratory and field studies concerning

the potential developmental effects of atrazine on amphibians. The SAP agreed with EPA’s conclusion

that additional studies are warranted to reduce the scientific uncertainty regarding whether atrazine

causes replicable effects on amphibians (Scientific Advisory Panel 2003). Substantial additional

research to resolve this issue is currently underway, or planned for the immediate future. Once

additional data are available that conclusively demonstrate a significant reproductive effect (or other

endpoint that significantly impairs the populations ability to survive long term) to aquatic species, then

derivation of the freshwater chronic criterion will be reexamined.
40

Text Table C. Summary of Endocrine Disruption Effects of Atrazine to Freshwater Organisms

Species Methoda Chemical

Exposure

Medium

Effect

(metamorphosis completed)

Effect

Level

(μg/L)b References

African clawed frog

(larval),

Xenopus laevis

R,M - 10%

Holtfreter’s

solution

abnormalities in gonadal

development, including

feminization and

hermaphroditism

#1 Hayes et al.

2002a,b

African clawed frog

(larval),

Xenopus laevis

R,M - 10%

Holtfreter’s

solution

reduction in the size of the

laryngeal muscle in male

frogs

1 Hayes et al.

2002a,b

African clawed frog

(larval),

Xenopus laevis

R,M 98.6% FETAX 

solution

increased incidence of

intersex animals (based on

assessment of gonadal

morphology)

21.3 Carr et al.

2003

African clawed frog

(larval),

Xenopus laevis

R,M 98.6% FETAX

solution

reduction in the size of the

laryngeal muscle in male

frogs

>21.3 Carr et al.

2003

African clawed frog

(9-11 days old),

Xenopus laevis

R,U 99% Moderately

Hard

Reconstituted

Laboratory

Water

mean weight at

metamorphosis

20 Sullivan and

Spence 2003

a

 S = static; R = renewal; F = flow-through; M = measured; U = unmeasured.

b

 Results are expressed as atrazine, not as the chemical.

BIOACCUMULATION

The data available according to the Guidelines concerning the bioaccumulation of atrazine are

included in Table 5. Only freshwater data are available. Macek et al. (1976) analyzed muscle tissue or

the eviscerated carcasses of fish at the end of extended exposure periods. Brook trout exposed to

atrazine at 740 μg/L for 308 days contained less than 200 μg/kg of atrazine in muscle tissue, resulting in

a bioconcentration factor (BCF) of <0.27. Fathead minnows exposed to atrazine at 210 μg/L for 301

days had less than 1,700 μg/kg of atrazine in pooled samples of eviscerated carcasses, for a BCF of
41

<8.1. Bluegills exposed to 94 μg/L for 546 days also contained less than 200 μg/kg in their muscle

tissue, for a BCF of <2.1.

Dionne (1992) exposed fathead minnows to atrazine for up to 274 days using 14C-labeled

atrazine and measuring the radiolabel in fish tissue. The values obtained represent maximum possible

BCFs. Regardless of the life-stage or exposure duration, maximum BCFs were less than or equal to 8.5

in all cases.

There is no U.S. Food and Drug Administration action level or any other established maximum

allowable concentration of chemical residues in tissue available for atrazine. Therefore, a Final Residue

Value cannot be determined.

OTHER DATA

Many tests with atrazine and various freshwater or saltwater organisms have been conducted

either for a different duration or by different protocols than those specified in the Guidelines for

inclusion in Tables 1, 2, 4 and 5. These test results are presented in Table 6. For example, plant tests

were included in Table 6 rather than Table 4 if the test duration was less than 4 days or the exposure

concentrations were not measured (an exception was the saltwater species phytoplankton data that was

included in Table 4 for comparison purposes). Tests with animals were included in Table 6 for a

number of reasons, including considerations of test duration, type of test, and test endpoints other than

those of toxicity or bioaccumulation. Below is a summary of their results.

At the lowest levels of biological organization, mixed nitrifying bacteria were unaffected

regarding ammonium oxidation at 28-day exposures up to 2,000 μg/L of atrazine (Gadkari 1988), and

cell growth in the bacterium, Pseudomonas putida, was not inhibited following a 16-hour exposure at

10,000 μg/L (Bringmann and Kuhn 1976, 1977). Progressing phylogenetically, Rohwer and Fluckiger

(1979) obtained a 14-day growth LOEC of 2,160 μg/L for Anabaena cylindrica, while Stratton (1984)

obtained a 12 to 14-day EC50 of 1,200 μg/L in terms of cell number. The latter EC50 value was

approximately 5 to 7 times higher than the 24-hour EC50 values based on 14C uptake of 253, 178 and

182 μg/L as reported by Larsen et al. (1986) for this same species (Table 6). The other species of

cyanobacteria tested by Stratton (1984), Anabaena inaequalis and Anabaena variabilis, had highly

different EC50 values of 30 and 4,000 μg/L after 14 days. A. inaequalis and Pseudoanabaena sp.

exhibited reduced photosynthetic uptake of 14C in the amounts of 65 and 91 percent, respectively,

following a 22-hour exposure to 2,667 μg/L of atrazine (Peterson et al. 1994).

A number of tests have been performed with the cyanobacterium, Anabaena flos-aquae. Hughes

(1986) and Hughes et al. (1986, 1988) reported an EC50 based on cell number of 230 μg/L following a
42

5-day exposure. A concentration of 40 μg/L non-radiolabeled atrazine reduced 14C uptake by

approximately 50 percent after 1 to 3 days of exposure, after which the reduction was less (Abou-Waly

et al. 1991a). At this concentration of atrazine, chlorophyll-a content was initially reduced but

recovered with time. Using this characteristic, the 3-day EC50 was 58 μg/L, while the 7-day EC50 was

766 μg/L (Abou-Waly 1991b). A. flos-aquae had a 4-day EC50 based on chlorophyll-a that exceeded

3,000 μg/L in a study by Fairchild et al. (1998).

The cyanobacterium Microcystis aeruginosa exhibited the onset of cell growth inhibition at a

concentration of 3 μg/L in an 8-day exposure (Bringmann and Kuhn 1976, 1978a,b). After 5 days of

exposure, cell numbers were significantly reduced at 108 μg/L, and the minimum algistatic

concentration was 440 μg/L (Parrish 1978). Kallqvist and Romstad (1994) obtained a 6-day EC50 of

630 μg/L with M. aeruginosa, while Peterson et al. (1994) reported that photosynthetic 14C uptake was

highly reduced (84-96 percent) in M. aeruginosa following a 22-hour exposure to 2,667 μg/L of

atrazine. A 4-day EC50 of 90 μg/L was reported for an unidentified species of Microcystis based on

biomass (Fairchild et al. 1998).

Toxicity studies of atrazine toward several other species of cyanobacteria have been reported. 

Peterson et al. (1994) found that Aphanizomenon flos-aquae and Oscillatoria sp. exhibited highly

reduced photosynthetic uptake of 14C (97 and 87 percent, respectively) from a 22-hour exposure to 2,667

μg/L of atrazine. The latter is consistent with the lowest complete inhibition of growth reported for

Oscillatoria cf. chalybea after 6 days of exposure to 2,160 μg/L atrazine (Schrader et al. 1997). A 31-

day exposure of Plectonema boryanum to 10,000 μg/L of atrazine resulted in a 69 percent decrease in

cell numbers (Mallison and Cannon 1984), whereas, 5-day exposures of Synechococcus leopolensis

yielded an EC50 of 130 μg/L (Kallqvist and Romstad 1994).

The green alga, Ankistrodesmus braunii, had an 11-day EC50 of 60 μg/L (Burrell et al. 1985). 

Similarly, 14C uptake EC50 values of 72 and 61 μg/L resulted from 24-hour exposures of

Ankistrodesmus sp. to atrazine (Larsen et al. 1986). The green alga, Chlamydomonas geitleri Ettl, had a

slightly higher EC50 of 311 μg/L based on CO2 fixation after a 1-hour exposure (Francois and Robinson

1990). Similarly, a growth-based EC50 of 330 μg/L was obtained for Chlamydomonas noctigama after 3

days of atrazine exposure (Kallqvist and Romstad 1994).

The green alga, Chlamydomonas reinhardtii, appears more sensitive to atrazine, exhibiting

approximately a 32 percent inhibition of photosynthesis in an 8-hour exposure to 10 μg/L (Valentine and

Bingham 1976), and EC50 values based on reduction in photosynthetic activity (14C uptake) in 24-hour

exposures of 19 to 48 μg/L of atrazine (Larsen et al. 1986). Atrazine-sensitive and atrazine-resistant

strains of C. reinhardtii responded to 2-minute exposures by a difference of approximately an order of

magnitude in their respective EC50 values of 45 and 484 μg/L (Hersh and Crumpton 1989). A 65-hour
43

exposure to 49.6 μg/L resulted in a 13 percent reduction of chlorophyll (Hiranpradit and Foy 1992), and

Fairchild et al. (1998) obtained a 96-hour chlorophyll-based EC50 of 176 μg/L for this same species.

Foy and Hiranpradit (1977) exposed an unknown Chlamydomonas sp. to various concentrations

of atrazine for 72 to 96 hours. Concentrations of 50 to 52 μg/L inhibited growth by 84.9 percent and

reduced chlorophyll by 12.8 percent. Slight additional increases in growth inhibition were observed

with increased atrazine concentrations up to 832 μg/L. Fairchild et al. (1994a) obtained a 4-day EC50

based on biomass of 176 μg/L to a different species of Chlamydomonas.

Chlorella fusca cell reproduction was reduced and an EC50 of 26 μg/L was calculated following

a 24-hour exposure to atrazine (Altenburger et al. 1990). Similarly, Faust et al. (1993) obtained a 24-

hour EC50 of 15 μg/L for this species, and Kotrikla et al. (1997) report 14-day EC50 values based on

growth inhibition of 53.91 (exponential growth phase) and 75.73 μg/L (stationary growth phase). In

contrast, Chlorella kessleri exhibited 30 percent growth inhibition following a 72-hour exposure at a

concentration of 1,078 μg/L (El-Sheekh et al. 1994), while Chlorella pyrenoidosa had 70 to 95 percent

reduced growth following 2-week exposures to atrazine concentrations ranging from 500 to 10,000 μg/L

(Virmani et al. 1975). Photosynthesis in this species was inhibited by approximately 64 percent

following an 8-hour exposure to 100 μg/L atrazine (Valentine and Bingham 1976). Stratton (1984)

obtained an EC50 of 300 μg/L following a 12- to 14-day exposure. A 30 percent reduction in growth

and 40 percent reduction in chlorophyll-a was observed in a 10-day exposure to 53.9 μg/L (GonzalezMurua et al. 1985), while a 110-hour exposure to 49.6 μg/L reduced chlorophyll by 39 percent

(Hiranpradit and Foy 1992). Photosynthetic CO2 uptake was inhibited by more than 80 percent in C.

pyrenoidosa following a less than 50-minute exposure to 125 μg/L (Hannan 1995).

The green alga, Chlorella vulgaris, had 24-hour EC50 values of 325, 305 and 293 μg/L in three

separate tests based upon 14C uptake (Larsen et al. 1986). Similarly, a 30-minute EC50 value of 305

μg/L based on decreased oxygen evolution was obtained for the same species by Van der Heever and

Grobbelaar (1997). Following 7 days of exposure to 250 to 5,000 μg/L (only 2.3 to 4.7 percent

remained on day 7), dry weights of C. vulgaris were reduced from 31 to 62 percent (Veber et al. 1981). 

This same species had an EC50 of 94 μg/L based upon chlorophyll concentration after a 96-hour

exposure (Fairchild et al. 1998). Reduced growth was initially observed for C. vulgaris exposed for 12

days to 10 μg/L, although signs of recovery were evident by the end of the exposure (Berard et al.

1999).

In an undefined species of Chlorella, a 72- to 96-hour atrazine exposure at 52 μg/L resulted in a

31 percent inhibition of growth and a 39 percent reduction in chlorophyll (Foy and Hiranpradit 1977). 

In that same study, higher exposures generally resulted in greater adverse effects. More recently, a 2- to

3-day atrazine exposure of 21.6 μg/L reduced the growth rate of one Chlorella sp. by 55 percent (Hersh
44

and Crumpton 1987), and another study using Chlorella sp. exhibited very rapid responses to atrazine

with EC50 values of 35 to 41 μg/L based upon photosynthetic oxygen evolution following a 2-minute

atrazine exposure (Hersh and Crumpton 1989). Fairchild et al. (1994a) reported a 4-day biomass-based

EC50 of 92 μg/L in yet another study using an unidentified species of the genus Chlorella.

Virmani et al. (1975) observed 75 and 92 percent reductions in growth of a much less sensitive

species of green algae, Chlorococcum hypnosporum, following 2-week exposures to 5,000 and 10,000

μg/L atrazine, respectively. Similarly, a high test concentration (2,157 μg/L) was necessary to inhibit

calcification in Gloetaenium loitlesbergarianum in a 96-hour test (Prasad and Chowdary 1981). Short

exposures (2 minutes) to Franceia sp. yielded EC50 values between 430 and 774 μg/L, measured as

photosynthetic oxygen evolution (Hersh and Crumpton 1989).

In three tests with the green alga, Scenedesmus obliquus, the 24-hour EC50 values for 14C uptake

were between 38 and 57 μg/L (Larsen et al. 1986). The green alga, Scenedesmus quadricauda, exhibited

photosynthesis inhibition of approximately 42 percent after 8 hours at an atrazine exposure of 10 μg/L

(Valentine and Bingham 1976). Bringmann and Kuhn (1977, 1978a,b) found that 30 μg/L caused the

onset of cell multiplication inhibition after 8 days of atrazine exposure to this species. S. quadricauda

exhibited a 12- to 14-day EC50 of 100 μg/L based on cell number (Stratton 1984). Bogacka et al.

(1990) studied photosynthesis reductions in S. quadricauda at various concentrations after 8 days of

atrazine exposure. These authors observed a gradation from 4.5 percent reduction at 4 μg/L to a 99.3

percent reduction at 337 μg/L. Similarly, photosynthetic 14C uptake was highly inhibited (96 percent)

after 22 hours at 2,667 μg/L of atrazine (Peterson et al. 1994). This species had a 96-hour EC50 of 169

μg/L, based upon chlorophyll concentration (Fairchild et al. 1998).

In this same genera of algae, Scenedesmus subspicatus had a 4-day EC50 of 110 μg/L (Geyer et

al. 1985), and Schafer et al. (1994) found that 37 μg/L of atrazine inhibited the effective photosynthetic

rate of this species by 57.4 percent within 24 hours. This latter apparent effect concentration was

corroborated by Kirby and Sheahan (1994) who reported a 2-day EC50 of 21 μg/L based on cell

numbers, as well as Zagorc-Koncan (1996) who reported a 24-hour EC50 value of 25 μg/L based on net

assimilation and inhibition. Reinhold et al. (1994) observed a 50 percent reduction in dry mass at 21.5

μg/L within 24 hours, and Behra et al. (1999) reported a 60-day NOEC based on growth and

photosynthetic oxygen evolution for this species of 20 μg/L.

Exposure of an unidentified species of Scenedesmus for 72 to 96 hours at 50 μg/L resulted in

60.2 percent growth inhibition (Foy and Hiranpradit 1977), and increased concentrations resulted in

increased growth inhibition. Fairchild et al. (1994a) obtained a 4-day EC50 based on biomass of 169

μg/L.
45

The green alga, Selenastrum capricornutum, exhibited a significant reduction in cell numbers

following a 5-day exposure to 54 μg/L of atrazine (Parrish 1978). In this study, chlorophyll-a reduction

increased as concentrations increased from 32 and 200 μg/L. The minimum algistatic concentration was

determined to be 200 μg/L. A similar 5-day LOEC for S. capricornutum growth of 220 μg/L was

recently reported by Schrader et al. (1998). Interestingly, a 7-day exposure at 100 μg/L resulted in a

13.8 percent increase in biomass, whereas 1,000 μg/L resulted in decreases (Johnson 1986). The lowest

complete inhibition concentration of growth after a 6-day exposure was 2,160 μg/L (Schrader et al.

1997). 

There are a number of additional EC50 values from exposures of S. capricornutum to atrazine

(Table 6). Larsen et al. (1986) obtained 24-hour EC50 values of 53, 34 and 42 μg/L based upon 14C

uptake. In a couple of 21-day exposures (Turbak et al. 1986), biomass-based EC50 values of 58.7 and

410 μg/L were obtained using algal assay media and creek water for test media, respectively. Likewise,

EC50 values were 69.7 and 854 μg/L, respectively, using these two media in 24-hour tests that measured

photosynthetic oxygen evolution. Roberts et al. (1990) reported 5-day EC50 values of 100 and 95 μg/L

based on cell numbers, and an EC50 of 50 μg/L based on cell numbers was reported in a 4-day exposure

by Versteeg (1990). Similarly, El Jay et al. (1997) found the 4-day IC50 values based on chlorophyll-a

content to be 80 μg/L. Reductions in chlorophyll content and in 14C uptake occurred at 130 μg/L in 1- to

7-day exposures (Abou-Waly et al. 1991a). EC50 values were 283, 218 and 214 μg/L for chlorophyll-a

content at 3, 5, and 7 days, respectively (Abou-Waly et al. 1991b). Fairchild et al. (1994a, 1998)

reported a 4-day EC50 of 117 μg/L for chlorophyll content, while Kallqvist and Romstad (1994)

obtained 3-day growth-based EC50 values of 200 and 110 μg/L. Photosynthetic 14C uptake was almost

completely inhibited (99 percent) within 22 hours at an exposure of 2,667 μg/L (Peterson et al. 1994). A

96-hour EC50 of 147 μg/L was reported by Gaggi et al. (1995) for chlorophyll-a content. Additional

cell number-based EC50 values reported for 72- to 96-hour exposures include 118.2 μg/L (Radetski et

al. 1995), 359 μg/L (Van der Heever and Grobbelaar 1996), 200 and 220 μg/L (Abdel-Hamid 1996), and

26 μg/L (Caux et al. 1996). Van der Heever and Grobbelaar (1997, 1998) expanded on their 1996 study

and reported a 30-minute EC50 value based on decreased oxygen evolution of 222 μg/L (1997) and a 4-

hour EC50 value based on chlorophyll-a fluorescence of 232 μg/L (1998). Benhra et al. (1997) reported

an EC50 of 164.3 μg/L based on growth inhibition and Fairchild et al. (1997) reported a biomass-based

EC50 of 235 μg/L.

Two tests with Stigeoclonium tenue yielded 24-hour EC50 values based on 14C uptake of 127 and

224 μg/L, while a test with Ulothrix subconstricta yielded an EC50 of only 88 μg/L (Larsen et al. 1986). 

Several diatom species have been tested for their sensitivities to atrazine. Chlorophyll-a content

in the benthic diatom, Craticula cuspidata, was significantly reduced after 12 days exposure to 83 μg/L
46

atrazine immediately following 67 days in 1 μg/L atrazine (Nelson et al. 1999). Cyclotella

meneghiniana yielded 7-minute EC50 values based upon photosynthesis between 99 and 243 μg/L

(Millie and Hersh 1987), while a 22-hour exposure to 2,667 μg/L of atrazine inhibited photosynthetic

14C uptake by 97 percent (Peterson et al. 1994). A 6-day growth-based EC50 of 430 μg/L was obtained

for an unidentified species of Cyclotella by Kallqvist and Romstad (1994). Hughes (1986) and Hughes

et al. (1986, 1988) determined several endpoints in 5-day exposures of Navicula pelliculosa to atrazine,

including a 5-day EC50 of 60 μg/L based on cell numbers. Using a 9-day recovery period following the

5-day exposure, they determined algistatic and algicidal concentrations of 1,710 and >3,200 μg/L,

respectively. Likewise, photosynthesis was almost completely inhibited (99 percent) in Nitzschia sp. by

a 22-hour exposure to 2,667 μg/L of atrazine (Peterson et al. 1994). The cryptomonad, Cryptomonas

pyrinoidifera, which also appears to be somewhat less sensitive to atrazine, had a 6-day EC50 based on

growth of 500 μg/L (Kallqvist and Romstad 1994).

The duckweed, Lemna minor, when exposed to 20 μg/L of atrazine for 20 days, did not exhibit

any adverse effects, but reduced growth occurred at concentrations of 50 to 250 μg/L (Beaumont et al.

1976,a,b, 1978). Peterson et al. (1994), on the other hand, observed that growth was inhibited 95

percent by a 7-day exposure to 2,667 μg/L. Four-day EC50 values for L. minor based on biomass and

frond production were 153 and 92 μg/L, respectively (Fairchild et al. 1997, 1998). Biochemical and

ultrastructural changes in the chloroplasts of Lemna minor were observed in 15-day exposures of 100

and 1000 μg/L of atrazine (Grenier et al. 1979) as well as an exposure of 248 μg/L (Grenier et al. 1987,

1989; Simard et al. 1990) for 15, 10 and 2 days, respectively. This is very close to the EC50 of 170

μg/L for frond production obtained when Hughes (1986) and Hughes et al. (1986, 1988) exposed a

different species of duckweed, Lemna gibba, to atrazine for 5 days. Using a 9-day recovery period, the

phytostatic and phytocidal concentrations were 1,720 and >3,200 μg/L, respectively.

Exposure of wild rice, Zizania aquatica, to 50 μg/L of atrazine for 83 days resulted in a visible

state of senescence and a 75 percent reduction in chlorophyll-a in the leaves (Detenbeck et al. 1996). 

Wild celery, Vallisneria americana, exhibited reduced leaf growth and whole plant biomass at an

exposure of 8 μg/L and reduced over-wintering success of tubers at 4 μg/L (Cohn 1985). A 42-day test

using this species resulted in an EC50 based on total leaf length of 163 μg/L (Davis 1981; Forney and

Davis 1981). A 14-day EC50 based on wet weight of 22 μg/L was reported for coontail, Ceratophyllum

sp. (Fairchild et al. 1998), and reduced stem elongation occurred within 6 to 8 days at 50 μg/L

(Detenbeck et al. 1996). These authors also found that cattails, Typha latifolia, were unaffected at 25

μg/L atrazine after 19 days. The Eurasian watermilfoil, Myriophyllum heterophyllum, had a 14-day wet

weight-based EC50 of 132 μg/L (Fairchild et al. 1998) while Myriophyllum spicatum had a 28-day EC50

based on length of 1,104 μg/L (Davis 1981; Forney and Davis 1981). This species also exhibited a 50
47

percent reduction in branch number at 3,700 μg/L after 5 days (Bird 1993). Sago pondweed,

Potamogeton pectinatus, on the other hand, had reduced biomass after 28 days at 100 μg/L (Fleming et

al. 1991), and bushy pondweed, Najas sp., had a 14-day wet weight-based EC50 of 24 μg/L (Fairchild et

al. 1998). A 14-day biomass-based EC50 of <38 μg/L was reported for Egeria sp. (Fairchild et al.

1994a). 

The exposure of Elodea canadensis to atrazine for 21 and 28 days resulted in EC50 values based

on length of 109 and 80 μg/L, respectively (Davis 1981; Forney and Davis 1981), and Detenbeck et al.

(1996) reported that growth was unaffected after 19 days at 75 μg/L. Fairchild et al. (1998) reported a

14-day EC50 of 21 μg/L for E. canadensis based upon wet weight.

Three species of water moss (Fontinalis antipyretica, Fontinalis hypnoides and Fontinalis

squamosa) were tested by Hoffman and Winkler (1990). While F. squamosa and F. antipyretica were

affected in their photosynthetic production at 10 μg/L after 24 hours and 20 days, respectively, F.

hypnoides exhibited a much greater reduction (90 percent) in net photosynthesis within 24-hours at an

exposure of only 2 μg/L. Conversely, Johnson (1986) found that 10 μg/L stimulated growth of mixed

macrophytes, Ceratophyllum sp. and Elodea sp., but that 100 and 1,000 μg/L decreased plant biomass

after 30 days.

The protozoan, Acanthamoeba castellanii, had population decreases of from 5 to 40 percent

when exposed for 6 days to atrazine at concentrations from 100 to 10,000 μg/L (Prescott et al. 1977). 

Photosynthesis was inhibited by about 11 percent in Euglena gracilis at 10 μg/L after 8 hours, and

exhibited increasingly greater inhibition at higher concentrations (Valentine and Bingham 1976). Two

species of protozoans, Colpidium campylum and Tetrahymena pyriformis, had 24-hour EC50 values of

>50,000 (Roberts et al. 1990) and 118,500 μg/L (Huber et al. 1991), respectively. Schafer et al. (1994)

reported a 48-hour EC50 of 96,000 μg/L for T. pyriformis. 

Relatively high concentrations were required to produce notably adverse responses in

representatives from higher animal phyla. A concentration of 5,000 μg/L reduced the budding rate in

Hydra viridis after 21 days (Benson and Boush 1983). The rotifer, Brachionus calyciflorus, had a 24-

hour LC50 of 7,840 μg/L (Crisinel et al. 1994). Two species of leeches, Glossiphonia complanata and

Helobdella stagnalis, had LC50 values of 6,300 and 9,900 μg/L, respectively, after a 27- to 28-day

exposure (Streit and Peter 1978). After 21 weeks, snail (Lymnaea palustris) growth, fecundity and tissue

glycogen content were unaffected at concentrations up to 125 μg/L (Baturo et al. 1995), but the

activities of benzo[a]pyrene and glutathione-s-transferase enzymes were inhibited at 5 μg/L (Baturo and

Lagadic 1996). The 24- and 48-hour LC50 values were greater than 60,000 μg/L for both larval and

juvenile mussels, Anadonta imbecilis (Johnson et al. 1993).
48

The anostracan crustacean, Streptocephalus texanus, had a 24-hour LC50 of >30,000 μg/L

(Crisinel et al. 1994). The cladoceran, Ceriodaphnia dubia, exhibited maximum acceptable toxicant

concentrations (MATCs) of 7,100 and 14,100 μg/L in two 4-day tests (Oris et al. 1991). A 26-hour

LC50 of 3,600 μg/L was reported for Daphnia magna (Frear and Boyd 1967). In 48-hour exposures of

Daphnia magna to a nominal atrazine concentration of 10 μg/L, whole body residues were only 4.4 and

2.2 times greater than the nominal concentration in water (Ellgehausen et al. 1980). Young production

was reduced in D. magna after 21 days at 2,000 μg/L (Kaushik et al. 1985). After 96 hours of exposure,

Bogacka et al. (1990) observed a 30 percent mortality in D. magna at 16,900 μg/L, and a 60 percent

mortality at 48,300 μg/L. Johnson et al. (1993) reported a 48-hour LC50 of 9,400 μg/L, but the animals

were fed at 24 hours. Crisinel et al. (1994) obtained a 24-hour EC50 of >30,000 μg/L, while Detenbeck

et al. (1996) observed a significant decrease in the survival of these invertebrates after 48 hours of

exposure at 25 μg/L, but not at 50 μg/L. Nishiuchi and Hashimoto (1967, 1969) found the 3-hour LC50

to be greater than 40,000 μg/L for Daphnia pulex. Exposures of D. pulex for 28 to approximately 70

days resulted in decreased survival and reproduction at concentrations ranging from 1,000 and 20,000

μg/L atrazine, with reproduction affected more than survival (Schober and Lampert 1977). Food

consumption was reduced by 10 percent at 350 μg/L and by 50 percent at 1,600 μg/L after 10 minutes

(Pott 1980). Bowman et al. (1981) reported an 18-hour LC50 for D. pulex of approximately 700 μg/L. 

Conversely, the 3-hour LC50 was in excess of 40,000 μg/L for the cladoceran, Moina macrocopa

(Nishiuchi and Hashimoto 1967, 1969), and a concentration of 1,000 μg/L was shown to cause 40

percent mortality and reduced population growth after 4 to 6 weeks (Shcherban 1972a,b).

The amphipod, Gammarus fasciatus, had a 48-hour LC50 of 5,700 μg/L (Macek et al. 1976). 

Similarly, exposure of Hyalella azteca for 18 hours resulted in an LC50 of 2,000 μg/L (Bowman et al.

1981). For the midge, Chironomus riparius, a 10-day exposure to atrazine yielded an LC50 of 18,900

μg/L (Taylor et al. 1991), while a 96-hour exposure of C. tentans in a fed test had less than 50 percent

mortality at the high concentration of 28,000 μg/L (McNamara 1991b). Macek et al. (1976) reported a

LC50 of 720 μg/L for a 48-hour C. tentans midge test initiated with first instar animals, which did not

adhere to the 2nd or 3rd instar life stages requirement specified by the Guidelines. Pape-Lindstrom and

Lydy (1997) and Jin-Clark et al (2002) likewise used 4th instar larvae to initiate C. tentans acute tests that

yielded LC50 values of >20,000 and >1,000 μg/L atrazine, respectively. The 18-hour LC50 for the

white dotted mosquito, Culex restuans, is considerably higher at approximately 60,000 μg/L (Bowman

et al. 1981).

Rainbow trout, Oncorhynchus mykiss, embryos and sac fry exposed continuously for 23

(embryos at hatching) and 27 (sac fry, 4 days post-hatch) days had LC50 values between 696 and 888

μg/L (Birge et al. 1979). Water hardness did not have any appreciable effect. A concentration of 4,020
49

μg/L was required to produce over 60 percent teratic larvae. Pluta (1989) reported a 48-hour LC50 of

5,660 μg/L. Changes in the ultrastructure of trout renal corpuscles and tubules were observed following

28-day exposures to 5 to 10 μg/L of atrazine (Fischer-Scherl et al. 1991). Similarly, 28-day exposures

resulted in slight ultrastructural changes in trout renal corpuscles at 5 μg/L, slight histopathological

changes in the liver and increased ultrastructural changes in renal corpuscles at 10 μg/L, and in further

changes in renal corpuscles and liver cells at 20 μg/L (Schwaiger et al. 1991). A 14-day exposure to 10

μg/L of atrazine did not affect survival, body weight, liver weight or liver enzyme activity (Egaas et al.

1993). Exposure to concentrations of 3.0 and 50 μg/L for 10 days were reported to reduce plasma

protein in rainbow trout, but no effects were observed at 10 μg/L (Davies et al. 1994b). Oulmi et al.

(1995) observed kidney changes at the cellular level within 5 weeks in O. mykiss in the proximal tubules

at 12.4 μg/L, and in both the proximal and distal tubules at 24.0 μg/L. 

The 48-hour LC50 for the goldfish, Carassius auratus, was >10,000 μg/L (Nishiuchi and

Hashimoto 1967, 1969), although Saglio and Trijasse (1998) observed reduced burst swimming

performance in goldfish after a 24-hour exposure to 50 μg/L. The 48-hour LC50 for the common carp,

Cyprinus carpio, was also >10,000 μg/L (Nishiuchi and Hashimoto 1967, 1969). Short-term exposures

of from 4 to 24 hours to lesser concentrations between 100 and 500 μg/L resulted in increased serum

cortisol and serum glucose (Hanke et al. 1983). Serum acetylcholinesterase first increased and then

decreased with time of exposure. Changes were also noted in gill ATPase activity. Longer exposures of

72-hour duration to 1,000 μg/L and 100 μg/L of atrazine also yielded decreased liver glycogen (Hanke

et al. 1983), and decreased liver and muscle glycogen as well as serum protein and cholesterol (Gluth

and Hanke 1984, 1985), respectively. Juvenile carp yielded a 48-hour LC50 of 16,100 μg/L (Pluta

1989), and a 96-hour LC50, in which the fish were fed, of 18,800 μg/L (Neskovic et al. 1993). It was

noted in the latter study that biochemical changes in the serum, heart, liver and kidneys of carp were

observed after 14 days of exposure to 1,500 μg/L, as well as hyperplasia of gill epithelial cells

(Neskovic et al. 1993). Conversely, no effects on gill, liver, and histopathology were observed at this

same concentration (1,500 μg/L) in a study by Poleksic et al. (1997).

Jop (1991c) reported the "no observed effect concentration" (NOEC) to be in excess of 4,900

μg/L for fathead minnows, P. promelas, exposed to atrazine for 7 days. Also, survival and growth were

shown to be unaffected in fathead minnows exposed to 75 μg/L for 13 days (Detenbeck et al. 1996). On

the other hand, channel catfish (Ictalurus punctatus) embryos and sac fry had LC50 values between 176

and 272 μg/L after exposures of either 4.5 (embryos at hatch) or 8.5 (sac fry, 4 days post-hatch) days

(Birge et al. 1979). Concentrations of approximately 340 μg/L caused an incidence of 13 to 16 percent

teratic larvae, while concentrations of approximately 3,850 μg/L resulted in 47 to 69 percent teratic

larvae.
50

Mosquitofish (Gambusia affinis) survival was unaffected in a 48-hour exposure to 10,000 μg/L

(Darwazeh and Mulla 1974), and LC50 values as high as 38,200 and 31,600 μg/L were reported for the

guppy (Poecilia reticulata) after exposures of 48 and 72 hours, respectively (Tscheu-Schluter 1976). 

These data are consistent with results reported by Bogacka et al. (1990), in which the authors reported

mortalities of 40 and 53.2 percent after exposing guppies for 96 hours to 28,600 and 37,200 μg/L,

respectively. 

Exposure of the Mozambique tilapia, Tilapia mossambica, to 1,100 μg/L of atrazine for 30 to 90

days affected blood composition, oxygen consumption, water content, and the biochemistry of the brain

and liver (Prasad et al. 1991a,b; Srinivas et al. 1991). A 90-day exposure also resulted in increased

serum sodium and potassium, and decreased serum calcium, magnesium and bicarbonate (Prasad and

Reddy 1994).

The embryo and larval stages of several amphibian species were exposed to atrazine (Birge et al.

1980), the results of which are quite different between species (Table 6). LC50 values for continuous

exposure of embryos and larvae through 4 days post-hatch were 410 μg/L for the bullfrog (Rana

catesbeiana), 7,680 μg/L for the leopard frog (Rana pipiens), 17,960 μg/L for the pickerel frog (Rana

palustris), and >48,000 μg/L for the American toad (Bufo americanus). In most of these species,

concentrations of atrazine in excess of 5,000 μg/L were required to cause an incidence of teratic larvae

in excess of 7 percent. Survival and growth of R. pipiens tadpoles were unaffected after 41 days of

exposure to 25 μg/L (Detenbeck et al. 1996). A 96-hour exposure of the African clawed frog (Xenopus

laevis) embryos to 8,000 μg/L resulted in 100 percent abnormal embryos (Morgan et al. 1996). The

lowest observed effect concentration (LOEC; teratogenesis) in the study was 1,100 μg/L. This

concentration is more than an order of magnitude higher than that which delayed development and

retarded the growth in the tiger salamander, Ambystoma tigrinum, after 86 days of exposure (Larson et

al. 1998).

In summary, cyanobacteria had EC50 values for various exposure durations of 30 μg/L or

greater, while EC50 values for green algae, diatoms and cryptomonads were $15 μg/L. Among

macrophytes, duckweed had a minimal 4-day EC50 of 92 μg/L. Wild rice was affected at 50 μg/L, and

wild celery had reduced growth at 8 μg/L. Several rooted vascular plants (i.e., coontail, bushy

pondweed, egeria, and elodea) had 14-day EC50 values between 21 and <38 μg/L, while that for a water

milfoil was 132 μg/L. Two species of water moss (Fontinalis sp.) exhibited reduced photosynthetic

activity at 10 μg/L, and one species was affected at 2 μg/L. EC50/LC50 values for protozoans,

coelenterates, annelids, molluscs and rotifers were $6,300 μg/L. Various crustaceans had LC50 values

$5,700 μg/L. The most sensitive endpoints among fish were rainbow trout plasma protein and kidney

ultrastructural changes at atrazine exposures of 3 and 3.5 μg/L, respectively. The lowest LC50 values in
51

fish were 176-272 μg/L for 4.5 to 8.5-day exposures with early life-stages of channel catfish. Frog

embryo and tadpole life-stages had LC50 values $410 μg/L. As noted in the ecosystem effects data

section in this document, most reductions in algal or vascular plant biomass were observed at

concentrations $15 μg/L. This commonly resulted in the reduction of herbivore populations, as well. 

One exception reported effects at much lower concentrations (as low as 0.1 μg/L). From these

freshwater Other Data, most of the effect levels of possible biological significance appear to be $15

μg/L. This concentration is greater than the freshwater Final Chronic Value based on ecosystem effects

data (10 μg/L), and therefore does not determine the Criterion Continuous Concentration. 

Additional data are available for saltwater algae, kelp, submerged vascular plants, emergent

vascular plants, and aquatic animals (Table 6). EC50 values based on differing endpoints (e.g., oxygen

evolution or growth) for various green algal species ranged from 37 μg/L to 600 μg/L (Gaggi et al.

1995; Hollister and Walsh 1973; Hughes 1986; Hughes et al. 1986, 1988; Samson and Popovic 1988;

Walsh 1972). A 48-hour exposure of the green alga, Dunaliella bioculata, to 216 μg/L of atrazine

resulted in a growth reduction of approximately 35 percent (Felix et al. 1988). Seven-day growth tests

with the green alga, Nannochloris oculata, at concentrations of 50 and 100 μg/L suggested that atrazine

toxicity was dependent on light and temperature (Karlander et al. 1983; Mayasich et al. 1986), although

the effect was not dramatic. A concentration of 15 μg/L changed the doubling time in N. oculata

(Mayasich et al. 1987). 

Diatom species were similar to green algae in terms of their sensitivities to atrazine. EC50

values for exposures of various durations were generally between 20 and 460 μg/L (Hollister and Walsh

1973; Walsh 1972; Walsh et al. 1988). Plumley and Davis (1980) observed reduced photosynthesis in

Nitzschia sigma and reduced chlorophyll in Thalassiosira fluviatilis in 7-day exposures to 220 μg/L. 

Mayasich et al. (1987) reported a limited effect on doubling time to Phaeodactylum tricornutum in a 7-

day exposure to 50 μg/L of atrazine.

The red alga, Porphyridium cruentum, had an EC50 based on oxygen evolution of 79 μg/L when

exposed for 90 minutes (Hollister and Walsh 1973), and the kelp, Laminaria hyperborea, had a 24-hour

LOEC value for respiration of >1,000 μg/L (Hopkins and Kain 1971). The 28-day LOEC for this

species based on growth of new sporophytes was 10 μg/L. It was shown in another species of kelp,

Laminaria saccharina, that a 2-day exposure to $72.2 μg/L of atrazine was sufficient to significantly

reduce sexual reproduction, but no effect was detected at 33.2 μg/L (Thursby and Tagliabue 1990). 

Inhibition concentrations of 77 to 120 μg/L for a 50 percent effect on photosynthesis by vascular

plants in short-term (2- to 4-hour) exposures to atrazine (Jones and Winchell 1984; Jones et al. 1986)

were similar to the effects upon growth and photosynthesis in longer exposures with several other

species (Table 4). Studies involving Vallisneria americana at low salinities for 42 to 47 days resulted in
52

reduced leaf production in terms of length, leaf area, and dry weight for concentrations ranging from 12

to 320 μg/L of atrazine (Correll and Wu 1982; Forney 1980; Forney and Davis 1981). Eelgrass, Zostera

marina, had reduced oxygen evolution at 100 μg/L, and complete inhibition of photosynthesis and

growth at 1,000 (Kemp et al. 1982a) and 1,900 μg/L of atrazine (Schwarzschild et al. 1994). Walsh et

al. (1982) report a 40-hour EC50 of 320 μg/L for the turtlegrass, Thalassia testudinum. The emergent

salt-marsh rush, Juncus roemerianus, exhibited effects indicative of stress after a 35-day exposure to 30

μg/L, while the salt-marsh grass, Spartina alterniflora, only exhibited enhanced peroxidase activity at a

concentration as high as 3,100 μg/L for the same length of time (Lytle and Lytle 1998).

The three LC50 values for the copepod, Acartia tonsa, at 24, 48 and 72 hours showed that the

sensitivity to atrazine increased with increasing duration of exposure (McNamara 1991b; also see Table

1). The 96-hour EC50 in the juvenile Eastern oyster, Crassostrea virginica, as well as the 48-hour LC50

for the juvenile spot, Leiostomas santhurus, were both $1,000 μg/L, while the brown shrimp, Penaeus

aztecus, had a 48-hour EC50 of 1,000 μg/L (Butler 1964; Mayer 1987). Adult fiddler crabs, Uca

pugnax, were not very sensitive to one-time applications of atrazine either in field or laboratory

exposures (Plumley et al. 1980). However, there was a seasonal effect on the sensitivity of this species

even when the laboratory conditions were the same. Animals collected in the summer were more

sensitive to atrazine than those collected in either the spring or fall. Two other species of crabs, Sesarma

cinereum and Panopeus sp., were also insensitive to very high levels of atrazine (Plumley et al. 1980).

The acute and chronic effects of atrazine on an estuarine microbial community were recently

examined by DeLorenzo et al. (1999a,b). Exposure for 9 days to 40 μg/L of atrazine in dilute seawater

(7-25 g/kg) inhibited the phototrophic component - chlorophyll-a, carbon assimilation, biovolume, and

caused changes in species composition (DeLorenzo et al. 1999a). The same effects were observed in

full strength seawater at an atrazine concentration of 47 μg/L, but within 24 hours (DeLorenzo et al.

1999b). 

UNUSED DATA

Data from some studies were not used in this document, as they did not meet the criteria for

inclusion as specified in the Guidelines (Stephan et al. 1985). The reader is referred to the Guidelines

for further information regarding these criteria.
53

Studies Were Conducted with Species That Are Not Resident in North America

Alazemi et al. (1996)

Biagianti-Risbourg and Bastide (1995) 

Diaz et al. (1998)

Forget et al. (1998)

Görge and Nagel 1990

Gunkel and Kausch (1976)

Gzhetotskii et al. (1977)

Hussein et al. (1996)

Juhnke and Luedemann (1978)

Kirby et al. (1998)

Lewis et al. (1993

L'Haridon et al. (1993)

Nagel (1992)

Pantani et al. (1997)

Portmann (1972)

Prasad et al. (1990, 1995)

Ralph (2000)

Steinberg et al. (1995)

Results were not used if the duration of the exposure was not specified or was unclear (e.g.,

Hopkins and Kain 1968; Portmann 1972; Rojickova-Padrtova and Marsalek 1999; Tellenbach et al.

1983), or if the procedures or test materials were not adequately described or translated (e.g. Braginskii

and Migal 1973; Delistraty 1999; Kross et al. 1992; Moore and Lower 2001; Moore and Waring 1998;

Shcherban 1973; Tang et al. 1998a,b; Wenzel et al. 1997).

Acute toxicity data were not used if an insufficient number of test organisms (Bathe et al. 1973,

1975), or exposure concentrations were used (Allran et al. 2000; Bouilly et al. 2003). Data were also not

used if there was a lack of a dose response (Bester et al. 1995; Britson and Threlkeld 2000). High

control moralities occurred in tests reported by Dodson et al. (1999), as well as in chronic studies with

Daphnia magna, Gammarus fasciatus and fathead minnows (Macek et al. 1976). Studies published only

as abstracts of presentations were not used (e.g., Fairchild et al. 1994b; Palmstrom and Krieger 1983;

Zora and Paladino 1986). Secondary observations reported in a review were not used (e.g., Giddings

and Hall 1998; Hurlbert 1975; Hutchinson et al. 1998; Lange et al. 1998; Mercurio 1998). Similarly,

papers by Birge et al. (1983), Fairchild et al. (Manuscript), Mark and Solbe (1998), and Pratt et al.

(1993, 1997) were not used, as the data they contained had been previously published. A study by

Butler et al. (1975) was not used since data from several algal taxa were grouped in the reporting of

results. Stratton and Giles (1990) expressed toxicity on the basis of cell numbers.

Atrazine Was a Formulation or Emulsifiable Concentrate (and comprised <80% of its weight)

Antychowicz et al. (1979)

Carder and Hoagland (1998)

Clements et al. (1997)

deNoyelles et al. (1982)

Hartman and Martin (1985) 

Hiltibran (1967)

Hofmann and Winkler (1990)

Howe et al. (1998)

Lin et al. (1999)

Kettle et al. (1987)

Pavlov (1976)

Rojickova-Padrtova & Marsalek 1999

Semov and Iosifov (1973)

Sreenivas and Rana (1991, 1994)

Torres and O'Flaherty (1976)

Walker (1964)
54

Atrazine Was a Component of a Drilling Mud, Effluent, Mixture, Sediment or Sludge

Berard et al. 1999

Britson and Threlkeld (1998) 

Crain et al. (1998) 

Goodbred et al. 1997

Guasch and Sabater (1998)

Guasch et al. (1997, 1998)

Hartgers et al. (1998)

Lowcock et al. (1997)

Ort et al. (1994)

Pollehne et al. (1999)

Putt (2003)

Reeder et al. (1998)

Vanderpoorten (1999)

Toxicity data from laboratory tests were generally not used if atrazine was dosed in the diet (e.g.,

Cossarini-Dunier et al. 1988), or if the concentration of solvent used in atrazine stock preparation

exceeded 0.5 ml/L (e.g., Cheney et al. 1997; Crain et al. 1997, 1999; Messaad et al. 2000; Pennington

and Scott 2001; Schafer et al. 1994; Tang et al. 1997); the latter representing a value below which

neither acetone nor ethanol are toxic to algae (e.g., El Jay 1996; Stratton and Corke 1981), but where

DMSO and atrazine may interact additively (El Jay 1996). 

The results from Langan and Hoagland (1996) were not used because the tests were conducted

in distilled water without addition of the appropriate salts. Toxicity tests by Schmitz et al. (1994) and

Tubbing et al. (1993) were not used because the tests were performed in river water which was likely

contaminated with various other chemicals. Similarly, a cytopathological study of fish exposed to a spill

of atrazine plus other pesticides was not used (e.g., Spazier et al. 1992). Effects data were not used if the

atrazine exposure was part of a soil mixture (e.g., Johnson et al. 1999; Jones and Estes 1984; Lytle and

Lytle 1998; Miller and Doxtader 1995; Ruth 1997). McBride and Richards (1975) exposed excised

tissue, and Petit et al. (1997) exposed cell cultures.

A study of atrazine accumulation by Bohm and Muller (1976) was not used due to expression of

results on a volume basis rather than a weight basis. A bioconcentration study by Walsh and Ribelin

(1973) was not used due to the use of nominal atrazine concentrations in the exposure water rather than

measured concentrations. Data were not used if the exposure was to radiolabeled atrazine (e.g., Davis et

al. 1979; Jones et al. 1982; McEnerney and Davis 1979; Neumann et al. 1987; Nikkila et al. 2001; Pillai

et al. 1977, 1979; Weete et al. 1980), or atrazine was not detected in tissue (e.g., Harris et al. 1998). 

Uptake and accumulation from exposures in flasks or microcosms were not used if 14C only was

measured and not atrazine itself (e.g., Huckins et al. 1986; Isensee 1976, 1987; Kearney et al. 1977;

Mailhot 1987).

Biochemical studies of resistant strains of mutated algae (e.g., Boura-Halfon et al. 1997; Forster

et al. 1997; Ottmeier et al. 1991) and results from in vitro genotoxicity and mutagenicity tests (e.g., Ruiz

and Marzin 1997) were not used. A study of atrazine effects upon promutagen activation by
55

Selenastrum capricornutum (e.g., Sauser and Klaine 1990) and alteration in allele and genotype

frequencies of the oyster, Crassostrea gigas (e.g., Moraga and Tanguy 2000) were also not used.

SUMMARY

Atrazine is not highly toxic to aquatic animals on an acute basis. SMAVs for eight freshwater

invertebrate species ranged from 3,000 μg/L for a hydra, Hydra sp., to 49,000 for Daphnia magna. 

SMAVs for nine fish species ranged from 5,300 μg/L for the rainbow trout, Oncorhynchus mykiss, to

60,000 μg/L for the goldfish, Carassius auratus (Figure 1). The three amphibian species evaluated each

has a LC50 value of >20,000 μg/L atrazine. GMAVs for atrazine are available for nine genera of

saltwater animals and range from 2,324 to >30,000 μg/L; a factor of approximately 12.9 (Figure 2). 

GMAVs for the four most sensitive genera (three species of crustaceans and one fish) differed by a

factor of approximately 2.5.

Chronic effects of atrazine exposure to aquatic animals have been studied with six freshwater

species, two of which are invertebrates and four of which are fish (Figure 3). In three tests with

Ceriodaphnia dubia, chronic values were 3,536, 3,536, and 1,732 μg/L. The growth of a midge,

Chironomus tentans, was retarded at 230 μg/L of atrazine, but not at 110 μg/L. A chronic value of 159.1

μg/L was calculated, and a corresponding acute-chronic ratio of 4.525 was derived.

Brook trout, Salvelinus fontinalis, had reduced growth at 120 μg/L, but not at 65 μg/L, in a

chronic exposure. A chronic value of 88.32 μg/L and an acute-chronic ratio of 71.33 were calculated. 

In a life-cycle test with the fathead minnow, Pimephales promelas, the chronic limits were set at 250 and

460 μg/L, based upon growth of larval fish, resulting in a chronic value of 339.1 μg/L and an acutechronic ratio of 58.98. Bluegills, Lepomis macrochirus, were unaffected in a chronic exposure to 95

μg/L, thereby setting the chronic limits at 95 and >95 μg/L, with a chronic value of >95 μg/L. Since the

acute value was a "greater than" value, the acute-chronic ratio was >84.21.

Chronic values are available for three species of saltwater organisms. The chronic values for

Eurytemora affinis ranged from 5,020 to 20,920 μg/L, based on survival. The chronic value for

Americamysis bahia was 123.3 μg/L, also based on survival. The chronic value for Cyprinodon

variegatus was 2,542 μg/L, based on mortality of juveniles. The resultant acute-chronic ratio for E.

affinis was 2.629, while the acute-chronic ratios for A. bahia and C. variegatus were 8.110 and >6.294,

respectively.

Effect concentrations for freshwater and saltwater plants are lower than the acute and chronic

values for aquatic animals (Figures 4 and 5). Atrazine toxicity to aquatic plants, both algae and

macrophytes, commonly occurs at concentrations of 10 μg/L and above, with several reports of toxicity
56

to specific plant taxa at concentrations below 10 μg/L (primarily freshwater plant species). Effects are

thought to be algistatic rather than algicidal at these lower concentrations, with recovery occurring once

the atrazine is removed. The lowest EC50 values for freshwater green algae with exposure durations of

4 days or longer were 10.2 and 4 μg/L for Chlamydomonas reinhardtii and Selenastrum capricornutum,

respectively. Mean EC50 values for these species would be considerably higher. The lowest reported

EC50 value for a freshwater vascular plant species, Lemna gibba, was 37 μg/L in a 14-day exposure,

using wet weight as an endpoint (Figure 4). As stated in the Guidelines (Stephen et al. 1985), the Final

Plant Value (FPV) is the lowest result from a test with an important aquatic plant species in which the

concentrations of test material were measured, and the endpoint was biologically important. In this case,

the freshwater FPV is 17.25 μg/L atrazine, which is the geometric mean of the two duckweed species

(Lemna gibba and Lemna minor) species mean chronic values (SMCVs) of 6.44 μg/L (Hoberg 1993b,c)

and 46.19 μg/L (Text Table A: University of Mississippi 1990; Girling et al. 2000). Using the

geometric mean of the two SMCVs for Lemna is consistent with the Guidelines, and is how all the

SMAVs and GMAVs are calculated in the WQC documents.

Conversely, the lowest EC50 based on growth for a saltwater green algae species, Neochloris

sp., was 82 μg/L, while the equivalent value for a saltwater vascular plant species, Myriophyllum

spicatum, was 25 μg/L. For saltwater, the FPV would be the geometric mean of the three Potamogeton

pectinatus (Sago pondweed) measured chronic studies conducted by Hall et al. (1997) at different

salinities, or 16.83 μg/L atrazine (Text Table B). Using the geometric mean of the SMCVs for the three

Potamogeton pectinatus tests is consistent with the Guidelines, and is how all the SMAVs and GMAVs

are calculated in the WQC documents.

Aquatic ecosystem structural and functional parameters have most frequently been observed to

be adversely affected by atrazine concentrations of 10 μg/L and above (Figures 4 and 5). Ecosystem

effects have been shown to occur at atrazine concentrations less than 5-10 μg/L, but data are limited. 

Several microcosm and mesocosm studies ranging from 7 days to 2 months report no effect of atrazine

on community structure, composition and functionality at atrazine as low as 5 μg/L (Gruessner and

Watzin 1996, Brockway et al. 1984, Van den Brink 1995, Juttner et al. 1995). The ecosystem effects

that do occur below 5 μg/L are generally transient and not well established. Recovery is quite rapid and

functionality is generally not compromised until much higher concentrations are reached. It appears that

for effects at concentrations up to 15 μg/L, the communities can recover quite rapidly following

dissipation of the atrazine concentration. The median LOEC from 65 community studies using multiple

endpoints, excluding those studies where recovery was known to occur, is 60 μg/L, and the 5th percentile

LOEC is 10 μg/L (Figure 6). The observed effects have been on both the plant and animal communities,

with the effects upon the animal community being secondary in nature, mainly a result of decreased
57

availability of shelter and plant matter for food. Thus, permanent ecosystem effects should only occur at

atrazine concentrations greater than 10 μg/L. 

Atrazine has been reported in a number of studies as an endocrine disruptor. Laboratory

exposures of 1 μg/L atrazine have been reported to cause abnormalities in frog (Xenopus laevis) gonadal

development (feminization and hermaphroditism - which could render male frogs sterile) and reduction

in the size of the laryngeal muscle in male frogs, an important muscle used for the mating call of the

frog (Hayes et al. 2002; Text Table C). However, studies conducted by Carr et al. (2003) and Carr and

Salomon (2003) designed to replicate the Hayes et al. (2002) experiments observed these same gonadal

development effects at approximately 20-21 μg/L atrazine. A third study conducted by Sullivan et al.

(2003) with Xenopus laevis looking at the same end-points yielded an effect level of 20 μg/L atrazine

(the lowest concentration tested). Until this issue is resolved, justification and defense of a freshwater

chronic criterion based on the endocrine disrupting effects of atrazine on amphibians is not possible. A

recently convened Scientific Advisory Panel agreed with EPA’s conclusion that additional studies are

warranted to reduce the scientific uncertainty regarding whether atrazine causes replicable effects on

amphibians (Scientific Advisory Panel 2003). Substantial additional research to resolve this issue is

currently underway, or planned for the immediate future. Once additional data are available that

conclusively demonstrate a significant reproductive effect (or other endpoint that significantly impairs

the populations ability to survive long term) to aquatic species, then derivation of the freshwater chronic

criterion will be reevaluated.

Atrazine has a limited tendency to accumulate in tissues of aquatic animals. BCFs ranged from

<0.27 to a maximum of 8.5 in three species of freshwater fish. There are no BCFs available for

saltwater species.

 The national criteria are determined on the basis of atrazine toxicity to aquatic animals (acute

criteria), ecosystem effects (freshwater chronic criterion), and toxicity to plants (saltwater chronic

criterion). The Criterion Maximum Concentrations (CMC) for fresh water (1,511 μg/L) and salt water

(759.5 μg/L) are one-half of the respective Final Acute Values (3,021 and 1,519 μg/L, respectively). 

These values are based on Table 1 acute toxicity values for all invertebrate and vertebrate species. The

Criterion Continuous Concentration (CCC) for freshwater is based on the ecosystem effects of atrazine

to aquatic plants. The saltwater CCC of 16.83 μg/L is based on the Final Plant Value determined for the

Sago pondweed. 
3

CASM is an aquatic ecological food chain model, specifically, the Comprehensive Aquatic Systems Model

(Bartell et al. 2000, Bartell et al 1999, DeAngelis et al 1989).

Bartell, S.M., K.R. Campbell, C.M. Lovelock, S.K. Nair, and J.L. Shaw. 2000. Characterizing aquatic ecological

risk from pesticides using a diquat dibromide case study III. Ecological Process Models. Environ. Toxicol. Chem.

19(5):1441-1453. 

Bartell, S.M., G. Lefebvre, G. aminski, M. Carreau, and K.R. Campbell. 1999. An ecosystem model for assessing

ecological risks in Quebec rivers, lakes, and reservoirs. Ecol. Model. 124:43-67. 

58

NATIONAL CRITERIA

The procedures described in the Guidelines indicate that, except possibly where a locally

important species is very sensitive, freshwater aquatic life and their uses should not be directly affected

unacceptably if the Average Primary Producer Steinhaus Similarity deviation for a site is less than 5%

(as determined using Comprehensive Aquatic Systems Model (CASM)3

 or other appropriate model and

index) and is not exceeded more than once every three years (or other appropriate return frequency

sufficient to allow system recovery) and if the one-hour average concentration does not exceed 1,500

ug/L more than once every three years on the average. The 5% index for the protection of aquatic plant

community should also be protective of most freshwater animals.

The procedures described in the Guidelines indicate that, except possibly where a locally

important species is very sensitive, saltwater aquatic organisms and their uses should not be affected

unacceptably if the thirty-day average concentration of atrazine does not exceed 17 μg/L more than once

every three years on the average, and if the one-hour average concentration does not exceed 760 μg/L

more than once every three years on the average. 

IMPLEMENTATION

As discussed in the Water Quality Standards Regulation (U.S. EPA 1983a) and the Foreword to

this document, a water quality criterion for aquatic life has regulatory impact only when it has been

adopted in a State water quality standard. Such a standard specifies a criterion for a pollutant that is

consistent with a particular designated use. With the concurrence of the U.S. EPA, States designate one

or more uses for each body of water, or segment thereof, and adopt criteria that are consistent with the

use(s) (U.S. EPA 1983a,b, 1987, 1994). Water quality criteria adopted in State water quality standards

could have the same numerical values as criteria developed under Section 304, of the Clean Water Act. 

However, in many situations States might want to adjust water quality criteria developed under Section

304 to reflect local environmental conditions and human exposure patterns. Alternatively, States may

use different data and assumptions than the U.S. EPA in deriving numeric criteria that are scientifically
59

defensible and protective of designated uses. State water quality standards include both numeric and

narrative criteria. A State may adopt a numeric criterion within its water quality standards and apply it

either state-wide to all waters for the use the criterion is designed to protect or to a specific site. A State

may use an indicator characteristic or the national criterion, supplemented with other relevant

information, to interpret its narrative criteria within its water quality standards when developing NPDES

effluent limitations under 40 CRF 122.44(d)(1)(vi).2.

Site-specific criteria may include not only site-specific criterion concentrations (U.S. EPA

1994), but also site-specific, and possibly pollutant-specific, durations of averaging periods and

frequencies of allowed excursions (U.S. EPA 1991). The averaging periods of "one hour" and "four

days" were selected by the U.S. EPA on the basis of data concerning how rapidly some aquatic species

react to increases in the concentrations of some aquatic pollutants, and "three years" is the Agency's best

scientific judgment of the average amount of time aquatic ecosystems should be provided between

excursions (Stephan et al. 1985; U.S. EPA 1991). However, various species and ecosystems react and

recover at greatly differing rates. Therefore, if adequate justification is provided, site-specific and/or

pollutant-specific concentrations, durations, and frequencies may be higher or lower than those given in

national water quality criteria for aquatic life.

Use of criteria, which have been adopted in State water quality standards, for developing water

quality-based permit limits and for designing waste treatment facilities requires selection of an

appropriate wasteload allocation model. Although dynamic models are preferred for the application of

these criteria (U.S. EPA 1991), limited data or other considerations might require the use of a steadystate model (U.S. EPA 1986). Guidance on mixing zones and the design of monitoring programs is also

available (U.S. EPA 1987, 1991).
60

0.0 0.2 0.4 0.6 0.8 1.0

% Rank GMAVs

100

1000

104

105

Atrazine Effect Concenration (μg/L)

Ranked Summary of Atrazine GMAVs

Freshwater

 Invertebrates

 Fish

Freshwater Final Acute Value = 3,021 μg/L Atrazine

Criterion Maximum Concentration = 1,500 μg/L Atrazine

 Amphibians

Figure 1. Ranked Summary of Atrazine GMAVs - Freshwater.
61

0.00 0.15 0.30 0.45 0.60 0.75 0.90

% Rank GMAVs

10

100

1000

104

105

Atrazine Effect Concentration ( μg/L)

Ranked Summary of Atrazine GMAVs

Saltwater

Saltwater Final Acute Value = 1519 μg/L Atrazine

Criterion Maximum Concentration = 760 μg/l Atrazine

 Invertebrates

 Fish

Figure 2. Ranked Summary of Atrazine GMAVs - Saltwater.
62

0.0 0.2 0.4 0.6 0.8 1.0

% Rank Genus Mean Chronic Value

1

10

100

1000

104

105

Atrazine Chronic Value (μg/L)

Chronic Toxicity of Atrazine to Aquatic Animals

Saltwater Final Chronic Value = 17 μg/L Atrazine

Freshwater Final Chronic Value = 10 μg/L Atrazine

 Freshwater Invertebrates

 Freshwater Fish

 Saltwater Invertebrates

 Saltwater Fish

Figure 3. Chronic Toxicity of Atrazine to Aquatic Animals.
63

0 20 40 60 80 100

% Rank Individual Test Values

0.1

1

10

100

1000

104

105

Atrazine Effect Concentration (μg/L)

Ranked Summary of Test Values for Freshwater Plants

Chlamydomonas reinhardtii

Selenastrum capricornutum

Lemna gibba

Lemna minor

Elodea canadensis

Freshwater Final Acute Value = 3,021 μg/L

Freshwater Final Chronic Value = 10 μg/L

Typical Range of

Atrazine Effect

Levels in Microcosm,

Mesocosm and

Community Studies

(10 μg/L - 5,000 μg/L)

Algistatic to 0.1 μg/L

Figure 4. Ranked Summary of Test Values for Freshwater Plants.
64

0 20 40 60 80 100

% Rank Individual Test Values

0.1

1

10

100

1000

104

105

Atrazine Effect Concentration (μg/L)

Ranked Summary of Test Values for Saltwater Plants

Skeletonema costatum

Chlorella sp.

Platymonas sp.

Porphyridium cruentum

Potamogeton pectinatus

Saltwater Final Acute Value = 1519 μg/L

Algistatic to 0.12 μg/L?

Neochloris sp. Potamogeton perfoliatus

Myriophyllum spicatum

Zostera marina

Typical Range of

Atrazine Effect

Levels in Microcosm,

Mesocosm and

Community Studies

(5.8 μg/L - 47 μg/L) Saltwater Final Chronic Value = 17 μg/L

Figure 5. Ranked Summary of Test Values for Saltwater Plants
65

LOEC NOEC

Effect Type

1

10

100

1000

Atrazine Concentration (μg/L)

Median

25-75%

10-90%

N = 65 N = 29

Figure 6. Range of Reported Atrazine Lowest Observed Effect Concentrations (LOECs) and

No Observed Effect Concentrations (NOECs) Excluding Those LOECs Where

Recovery Was Reported to Occur. 
66

Table 1. Acute Toxicity of Atrazine to Aquatic Animals

Species Methoda Chemical

Hardness

(mg/L as 

 CaCO3) 

LC50 

or EC50

 (μg/L)b

Species Mean

Acute Value

 (μg/L) References

FRESHWATER SPECIES

Hydra,

Hydra sp.

R,M $98.5% 48.9 3,000 3,000 Brooke 1990

Annelid,

Lumbriculus variegatus

F,M $98.5% 67.3 >37,100 >37,100 Brooke 1990

Snail,

Physa acuta

S,M - - >20,000 >20,000 Rosés et al. 1999

Snail (adult),

Physa sp.

R,M $98.5% 48.9 >34,100 >34,100 Brooke 1990

Cladoceran (<24 hr),

Ceriodaphnia dubia

S,M 97% 52 >4,900 - Jop 1991a

Cladoceran (<12 hr), 

Ceriodaphnia dubia

S,M >99% 57.1 >30,000 >12,120 Oris et al. 1991

Cladoceran (<24 hr),

Daphnia magna

S,U 94% - 6,900 - Macek et al. 1976

Cladoceran (<24 hr),

Daphnia magna

S,U $96% 250 >39,000 - Marchini et al. 1988

Cladoceran,

Daphnia magna

F,M 79.6% 170 49,000 49,000 Putt 1991

Amphipod (14-21 d),

Hyalella azteca

S,M $98% - >10,000 - Anderson and Lydy 2002

Amphipod,

Hyalella azteca

F,M $98.5% 67.4 14,700 14,700 Brooke 1990

Stonefly (nymph),

Acroneuria sp.

F,M $98.5% 67.4 6,700 6,700 Brooke 1990

Coho salmon (yearling),

Oncorhynchus kisutch

R,M $80% 101 >18,000 >18,000 Lorz et al. 1979

Rainbow trout

(juvenile),

Oncorhynchus mykiss

S,U 98.8% 43 5,300 5,300 Beliles and Scott 1965

Brown trout,

Salmo trutta

R,U - 11 27,000 27,000 Grande et al. 1994

Brook trout (juvenile),

Salvelinus fontinalis

F,U 94% - 6,300 6,300 Macek et al. 1976

Goldfish (juvenile),

Carassius auratus

S,U 98.8% 43 60,000 60,000 Beliles and Scott 1965

Fathead minnow

Pimephales promelas

R,U 94% - 15,000 - Macek et al. 1976

Fathead minnow

(juvenile),

Pimephales promelas

S,M 97% 52 >4,900 - Jop 1991d

FRESHWATER SPECIES
Table 1 (Continued)

Species Methoda Chemical

Hardness

(mg/L as 

 CaCO3) 

LC50 

or EC50

 (μg/L)b

Species Mean

Acute Value

 (μg/L) References

67

Fathead minnow,

Pimephales promelas

F,M 97.1% 20-40 20,000 20,000 Dionne 1992

Channel catfish 

(sac fry),

Ictalurus punctatus

S,U 80% 78 >10,000 >10,000 Jones 1962

Bluegill (juvenile),

Lepomis macrochirus

S,U 98.8% 43 24,000 - Beliles and Scott 1965

Bluegill (juvenile),

Lepomis macrochirus

F,U 94% - >8,000 >13,856 Macek et al. 1976

Largemouth bass (fry),

Micropterus salmoides

S,U 80% 78 >10,000 >10,000 Jones 1962

Leopard frog, 

Rana pipiens

R,M 99% 290 >20,000 >20,000 Allran and Karasov 2001

Wood frog, 

Rana sylvatica

R,M 99% 290 >20,000 >20,000 Allran and Karasov 2001

American toad, 

Bufo americanus

R,M 99% 290 >20,000 >20,000 Allran and Karasov 2001

Species Methoda Chemical

Salinity

 (g/kg) 

LC50 

or EC50

 (μg/L)b

Species Mean

Acute Value

 (μg/L) References

SALTWATER SPECIES

Eastern oyster

(embryo/larval),

Crassostrea virginica

S,U 97.4% 16 >30,000 >30,000 Ward and Ballantine 1985

Copepod (nauplius),

Eurytemora affinis

S,M 97.1% 5 500 - Hall et al. 1994a,b

Copepod (nauplius),

Eurytemora affinis

S,M 97.1% 15 2,600 - Hall et al. 1994a,b

Copepod (nauplius),

Eurytemora affinis

S,M 97.1% 25 13,200 2,579 Hall et al. 1994a,b

Copepod (adult),

Acartia clausii

R,U 70% 6 7,925 7,925 Thursby et al. 1990

Copepod,

Acartia tonsac

S,U 97.4% 20 94 - Ward and Ballantine 1985

Copepod (adult),

Acartia tonsa

R,M 70% 31-32 210.1 - Thursby et al. 1990

Copepod (adult),

Acartia tonsa

R,M 70% 31 91.73 - Thursby et al. 1990

Copepod (adult),

Acartia tonsa

F,M 97.1% 30-34 4,300 4,300 McNamara 1991a

SALTWATER SPECIES
Table 1 (Continued)

Species Methoda Chemical

Salinity

 (g/kg) 

LC50 

or EC50

 (μg/L)b

Species Mean

Acute Value

 (μg/L) References

68

Mysid,

Americamysis bahia

F,M 97.4% 20 1,000 - Ward and Ballantine 1985

Mysid,

Americamysis bahia

F,M 97.1% 32 5,400 2,324 Machado 1994

Pink shrimp,

Penaeus duorarumc

S,U 97.4% 26 6,900 6,900 Ward and Ballantine 1985

Grass shrimp,

Palaemonetes pugioc

S,U 97.4% 26 9,000 9,000 Ward and Ballantine 1985

Fiddler crab,

Uca pugilatorc

S,U 97.4% 26 >29,000 >29,000 Ward and Ballantine 1985

Sheepshead minnow

(larva),

Cyprinodon variegatus

S,M 97.1% 5 16,200 - Hall et al. 1994a,b

Sheepshead minnow

(larva),

Cyprinodon variegatus

S,M 97.1% 15 2,300 - Hall et al. 1994a,b

Sheepshead minnow

(larva),

Cyprinodon variegatus

S,M 97.1% 25 2,000 4,208 Hall et al. 1994a,b

Sheepshead minnow,

Cyprinodon variegatus

F,M 97.4% 13 >16,000d - Ward and Ballantine 1985

Sheepshead minnow,

Cyprinodon variegatus

F,M 97.1% 32 13,000d - Machado 1994b

Spot,

Leiostomus xanthurusc

S,U 97.4% 12 8,500 8,500 Ward and Ballantine 1985 

a

 S = static; R = renewal; F = flow-through; M = measured; U = unmeasured. b

 Results are expressed as atrazine, not as the chemical. Each Species Mean Acute Value was calculated from the associated underlined

 number(s) in the preceding column.

c

 Test organisms collected from the field.

d

 Not used in calculations because data are available for a more sensitive life stage.
69

Table 2a. Chronic Toxicity of Atrazine to Aquatic Animals

Species Testa Chemical

Hardness

(mg/L as 

 CaCO3) 

Chronic 

Limits

(μg/L)b 

Chronic Value

 (μg/L) References

FRESHWATER SPECIES

Cladoceran,

Ceriodaphnia dubia

LC >99% 57.1 2,500-5,000 3,536 Oris et al. 1991

Cladoceran,

Ceriodaphnia dubia

LC >99% 57.1 2,500-5,000 3,536 Oris et al. 1991

Cladoceran,

Ceriodaphnia dubia

LC 97% 52 1,200-2,500 1,732 Jop 1991b

Midge,

Chironomus tentans

LC 94% 43.0 110-230 159.1 Macek et al. 1976

Rainbow trout

Oncorhynchus mykiss

ELS Technical 50.0 1,100-3,800 2,045 Whale et al. 1994

Brook trout,

Salvelinus fontinalis

LC 94% 35.7 65-120 88.32 Macek et al. 1976

Fathead minnow,

Pimephales promelas

LC 97.1% 24-36 250-460 339.1 Dionne 1992

Bluegill,

Lepomis macrochirus

LC 94% 33.9 95->95 >95 Macek et al. 1976

Species Testa Chemical

Salinity

 (g/kg) 

Chronic

Limits

(μg/L)b

 

Chronic Value

 (μg/L) References

SALTWATER SPECIES

Copepod,

Eurytemora affinis

LC 97.1% 5 12,250-17,500 14,640 Hall et al. 1995

Copepod,

Eurytemora affinis

LC 97.1% 15 17,500-25,000 20,920 Hall et al. 1995

Copepod,

Eurytemora affinis

LC 97.1% 25 4,200-6,000 5,020 Hall et al. 1995

Mysid,

Americamysis bahia

LC 97.4% 20 80-190 123.3 Ward and Ballantine 1985

Sheepshead minnow,

Cyprinodon

variegatus

ELS 97.4% 13 1,900-3,400 2,542 Ward and Ballantine 1985

a

 LC = Life-cycle or partial life-cycle; ELS = early life-stage.

b

 Results are based on measured concentrations of atrazine.
70

Table 2b. Acute-Chronic Ratios

Species

Hardness

(mg/L as

CaCO3)

Acute Value

(μg/L)a

Chronic Value

(μg/L) Ratio Reference

Cladoceran,

Ceriodaphnia dubia

57.1 >30,000 3,536 >8.484 Oris et al. 1991

Cladoceran,

Ceriodaphnia dubia

52 >4,900 1,732 >2.829 Jop 1991a,b

Midge,

Chironomus tentans

43.0 720b 159.1 4.525 Macek et al. 1976

Brook trout,

Salvelinus fontinalis

35.7 6,300 88.32 71.33 Macek et al. 1976

Fathead minnow,

Pimephales promelas

24-36 20,000 339.1 58.98 Dionne 1992

Bluegill,

Lepomis macrochirus

33.9 >8,000 >95 >84.21 Macek et al. 1976

Copepod,

Eurytemora affinis

5c 500 14,640 0.0342 Hall et al. 1994a,b; 1995

Copepod,

Eurytemora affinis

15c 2,600 20,920 0.1243 Hall et al. 1994a,b; 1995

Copepod,

Eurytemora affinis

25c 13,200 5,020 2.629 Hall et al. 1994a,b; 1995

Mysid,

Americamysis bahia

20c 1,000 123.3 8.110 Ward and Ballantine 1985

Sheepshead minnow,

Cyprinodon

variegatus

13c >16,000 2,542 >6.294 Ward and Ballantine 1985

 a From Table 1.

 b

 From Table 6. c Salinity expressed as g/kg.
71

Table 3. Ranked Genus Mean Acute Values with Species Mean Acute-Chronic Ratios

Ranka

Genus Mean

Acute Value

 (μg/L) Species

Species Mean

Acute Value

 (μg/L)b 

Species Mean

Acute-Chronic

 Ratioc

 

FRESHWATER SPECIES

17 60,000 Goldfish,

Carassius auratus

60,000 -

16 49,000 Cladoceran,

Daphnia magna

49,000 -

15 >37,100 Annelid,

Lumbriculus variegatus

>37,100 -

14 27,000 Brown trout,

Salmo trutta

27,000 -

13 >26,115 Snail,

Physa acuta

>20,000 -

- Snail,

Physa sp.

>34,100 -

12 >20,000 Leopard frog, 

Rana pipiens

>20,000 -

- Wood frog, 

Rana sylvatica

>20,000 -

11 >20,000 American toad, 

Bufo americanus

>20,000 -

10 20,000 Fathead minnow,

Pimephales promelas

20,000 58.98

9 14,700 Amphipod,

Hyalella azteca

14,700 -

8 >13,856 Bluegill,

Lepomis macrochirus

>13, 856 >84.21

7 >12,120 Cladoceran

Ceriodaphnia dubia

>12,120 >4.899

6 >10,000 Channel catfish,

Ictalurus punctatus

>10,000 -

5 >10,000 Largemouth bass,

Micropterus salmoides

>10,000 -

4 9,767 Coho salmon,

Oncorhynchus kisutch

>18,000 -

- Rainbow Trout,

Oncorhynchus mykiss

5,300 -

3 6,700 Stonefly,

Acroneuria sp.

6,700 -

2 6,300 Brook trout,

Salvelinus fontinalis

6,300 71.33

1 3,000 Hydra,

Hydra sp.

3,000 -
Table 3 (continued)

Ranka

Genus Mean

Acute Value

 (μg/L) Species

Species Mean

Acute Value

 (μg/L)b 

Species Mean

Acute-Chronic

 Ratioc 

72

SALTWATER SPECIES

9 >30,000 Eastern oyster,

Crassostrea virginica

>30,000 -

8 >29,000 Fiddler crab,

Uca pugilator

>29,000 -

7 9,000 Grass shrimp,

Palaemonetes pugio

9,000 -

6 8,500 Spot,

Leiostomus xanthurus

8,500 -

5 6,900 Pink shrimp,

Penaeus duorarum

6,900 -

4 5,838 Copepod,

Acartia clausii

7,925 -

- Copepod,

Acartia tonsa

4,300 -

3 4,208 Sheepshead minnow,

Cyprinodon variegatus

4,208 >6.294

2 2,579 Copepod,

Eurytemora affinis

2,579 2.629

1 2,324 Mysid,

Americamysis bahia

2,324 8.110

a Ranked from most resistant to most sensitive based on Genus Mean Acute Value. Inclusion of "greater than" value does not necessarily imply a

true ranking, but does allow use of all genera for which data are available so that the Final Acute Value is not unnecessarily lowered. b

 From Table 1.

c From Table 2b.
Table 3 (continued)

73

Freshwater

Final Acute Value = 3,021 μg/L

Criterion Maximum Concentration = (3,021 :g/L)/2 = 1,511 μg/L

Final Chronic Value = (ecosystem effects - see text)

Saltwater

Final Acute Value = 1,519 μg/L

Criterion Maximum Concentration = (1,519 μg/L)/2 = 759.5 μg/L 

Final Chronic Value = 16.83 μg/L (Final Plant Value - see text)
74

Table 4. Toxicity of Atrazine to Aquatic Plants

Species Chemical

Hardness

(mg/L as

 CaCO3) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

FRESHWATER SPECIES

Green alga,

Chlamydomonas reinhardtii

- - 4 EC50

(cell number)

51 Schafer et al. 1993

Green alga,

Chlamydomonas reinhardtii

- - 4 EC50

(cell number)

51 Girling et al. 2000

Green alga,

Chlamydomonas reinhardtii

- - 7 EC50

(cell number)

21 Schafer et al. 1993

Green alga,

Chlamydomonas reinhardtii

- - 10 EC50

(cell number)

10.2 Schafer et al. 1993

Green alga,

Chlamydomonas reinhardtii

- - 4 NOEC

(growth inhibition)

3.4 Schafer et al. 1994

Green alga,

Chlamydomonas reinhardtii

- - 7 NOEC

(growth inhibition)

5.1 Schafer et al. 1994

Green alga,

Chlamydomonas reinhardtii

- - 10 NOEC

(growth inhibition)

3.7 Schafer et al. 1994

Green alga,

Selenastrum capricornutum

- - 4 NOEC

(cell number, biomass)

0.5 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

- - 4 NOEC

(chlorophyll-a, 

phaeophytin-a)

10 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

- - 4 LOEC

(cell density, biomass)

1.0 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

- - 4 LOEC

(chlorophyll, 

phaeophytin-a)

100 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

- - 4 EC50

(cell number)

4 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

- - 4 EC50

(phaeophytin-a)

20 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

- - 4 EC50

(chlorophyll-a)

150 Univ. of Mississippi

1990

Green alga,

Selenastrum capricornutum

99.1% - 4 EC50

(cell number)

128.2 Gala and Giesy

1990

Green alga,

Selenastrum capricornutum

97.0% - 4 NOEC

(cell number)

76 Hoberg 1991a

Green alga,

Selenastrum capricornutum

97.0% - 4 LOEC

(cell number)

130 Hoberg 1991a

Green alga,

Selenastrum capricornutum

97.0% - 4 EC10

(cell number)

90 Hoberg 1991a

FRESHWATER SPECIES
Table 4 (Continued)

Species Chemical

Hardness

(mg/L as

 CaCO3) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

75

Green alga,

Selenastrum capricornutum

97.0% - 4 EC50

(cell number)

130 Hoberg 1991a

Green alga,

Selenastrum capricornutum

97.0% - 4 EC90

(cell number)

190 Hoberg 1991a

Green alga,

Selenastrum capricornutum

97.1% - 5 NOEC

(cell number)

16 Hoberg 1993a

Green alga,

Selenastrum capricornutum

97.1% - 5 EC10

(cell number)

26 Hoberg 1993a

Green alga,

Selenastrum capricornutum

97.1% - 5 LOEC

(cell number)

31 Hoberg 1993a

Green alga,

Selenastrum capricornutum

97.1% - 5 EC50

(cell number)

55 Hoberg 1993a

Green alga,

Selenastrum capricornutum

97.1% - 5 EC90

(cell number)

120 Hoberg 1993a

Duckweed,

Lemna gibba

97% - 7 EC50

(frond production)

180 Hoberg 1991b

Duckweed,

Lemna gibba

97.1% - 14 NOEC

(frond number)

<3.4 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 LOEC

(frond number)

3.4 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 EC10

(frond number)

6.2 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 NOEC

(frond biomass)

7.7 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 EC10

(frond biomass)

12 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 LOEC

(frond biomass)

17 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 EC50

(frond number)

37 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 EC50

(frond biomass)

45 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 EC90

(frond biomass)

170 Hoberg 1993b

Duckweed,

Lemna gibba

97.1% - 14 EC90

(frond number)

220 Hoberg 1993b

Duckweed,

Lemna gibba

97.4% - 14 EC10

(frond number)

2.2b Hoberg 1993c

FRESHWATER SPECIES
Table 4 (Continued)

Species Chemical

Hardness

(mg/L as

 CaCO3) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

76

Duckweed,

Lemna gibba

97.4% - 14 EC10

(frond biomass)

4.2b Hoberg 1993c

Duckweed,

Lemna gibba

97.4% - 14 NOEC

(frond number &

biomass)

8.3b Hoberg 1993c

Duckweed,

Lemna gibba

97.4% - 14 LOEC

(frond number &

biomass)

18b Hoberg 1993c

Duckweed,

Lemna gibba

97.4% - 14 LOEC

(frond biomass)

22b Hoberg 1993c

Duckweed,

Lemna gibba

97.4% - 14 EC50

(frond number)

50b Hoberg 1993c

Duckweed,

Lemna gibba

97.4% - 14 EC90

(frond number)

98b Hoberg 1993c

Duckweed,

Lemna gibba

97.4% - 14 EC90

(frond biomass)

110b Hoberg 1993c

Duckweed,

Lemna minor

- - 14 NOEC

(biomass)

10 Univ. of 

Mississippi 1990

Duckweed,

Lemna minor

- - 14 LOEC

(mature frond

production)

10 Univ. of 

Mississippi 1990

Duckweed,

Lemna minor

- - 14 LOEC

(biomass)

100 Univ. of 

Mississippi 1990

Duckweed,

Lemna minor

- - 14 EC50

(biomass)

8,700 Univ. of 

Mississippi 1990

Duckweed,

Lemna minor

98% - 10 EC50

(frond number)

56 Kirby and Sheahan

1994

Duckweed,

Lemna minor

98% - 10 EC50

(fresh weight)

60 Kirby and Sheahan

1994

Duckweed,

Lemna minor

98% - 10 EC50

(chlorophyll)

62 Kirby and Sheahan

1994

Duckweed,

Lemna minor

- - 28 NOEC (growth) 38 Girling et al. 2000

Duckweed,

Lemna minor

- - 28 LOEC (growth) 120 Girling et al. 2000

Elodea,

Elodea canadensis

- - 10 NOEC

(biomass)

10c Univ. of 

Mississippi 1990

Elodea,

Elodea canadensis

- - 10 LOEC

(biomass)

100c Univ. of 

Mississippi 1990

FRESHWATER SPECIES
Table 4 (Continued)

Species Chemical

Hardness

(mg/L as

 CaCO3) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

77

Elodea,

Elodea canadensis

- - 10 LOEC

(mature frond

production)

10c Univ. of 

Mississippi 1990

Elodea,

Elodea canadensis

- - 10 EC50

(biomass)

1,200c Univ. of 

Mississippi 1990

Elodea,

Elodea canadensis

- - 10 LOEC

(biomass)

100d Univ. of 

Mississippi 1990

Elodea,

Elodea canadensis

- - 10 EC50

(biomass)

25,400d Univ. of 

Mississippi 1990

Elodea,

Elodea canadensis

- - 20 NOEC (length) 20 Girling et al. 2000

Elodea,

Elodea canadensis

- - 20 LOEC (length) 30 Girling et al. 2000

Species Chemical

Salinity

 (g/kg) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

SALTWATER SPECIES

Diatom,

Skeletonema costatum

- 30 2 EC50 

(growth)

265 Walsh 1983

Green alga,

Chlorella sp.

99.7% 30 3 EC50 

(growth)

140 Mayer 1987

Green alga,

Neochloris sp.

99.7% 30 3 EC50 

(growth)

82 Mayer 1987

Green alga,

Platymonas sp.

99.7% 30 3 EC50 

(growth)

100 Mayer 1987

Red alga,

Porphyridium cruentum

99.7% 30 3 EC50 

(growth)

79 Mayer 1987

Redheadgrass pondweed,

Potamogeton perfoliatus

96.4% 9 28 IC50 (photosynthesis) 55 Kemp et al. 1982b,

1983; Kemp et al.

1985

Redheadgrass pondweed,

Potamogeton perfoliatus

96.4% 9 35 IC50 

(final biomass)

30 Kemp et al. 1982b,

1983; Kemp et al.

1985

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 NOEC

(dry weight)

15 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 NOEC 

(wet weight)

15 Hall et al. 1997

SALTWATER SPECIES
Table 4 (Continued)

Species Chemical

Salinity

 (g/kg) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

78

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 NOEC 

(rhizome tip mass)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 LOEC

(dry weight)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 LOEC

(wet weight)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 LOEC

(rhizome tip mass)

300 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 Chronic value

(dry weight)

21.2 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 Chronic value

(wet weight)

21.1 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1 28 Chronic value

(rhizome tip mass)

94.9 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 NOEC

(dry weight)

15 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 NOEC

(wet weight)

15 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 NOEC

(rhizome tip

mass)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 LOEC

(dry weight)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 LOEC

(wet weight)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 LOEC

(rhizome tip mass)

300 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 Chronic value

(dry weight)

21.2 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 Chronic value

(wet weight)

21.2 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 6 28 Chronic value

(rhizome tip mass)

94.9 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 NOEC

(dry weight)

7.5 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 NOEC

(wet weight)

15 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 NOEC

(rhizome tip mass)

30 Hall et al. 1997

SALTWATER SPECIES
Table 4 (Continued)

Species Chemical

Salinity

 (g/kg) 

Duration

 (days) Effect

Concentration

 (μg/L)a Reference

79

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 LOEC

(dry weight)

15 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 LOEC

(wet weight)

30 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 LOEC

(rhizome tip mass)

300 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 Chronic value

(dry weight)

10.6 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 Chronic value

(wet weight)

21.2 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 12 28 Chronic value

(rhizome tip mass)

94.9 Hall et al. 1997

Sago pondweed,

Potamogeton pectinatus

97.1% 1-12 28 Chronic value

(dry weight)

5.3 Hall et al. 1997

Eurasian water milfoil,

Myriophyllum spicatum

96.4% 9 28 IC50 (photosynthesis) 117 Kemp et al. 1982b,

1983; Kemp et al.

1985

Eurasian water milfoil,

Myriophyllum spicatum

96.4% 9 35 IC50

(final biomass)

25 Kemp et al. 1982b,

1983; Kemp et al.

1985

Wild celery,

Vallisneria americana

- 3 & 6 42 NOEC (dry weight) 100 Forney and Davis

1981

Wild celery,

Vallisneria americana

- 3 & 6 42 LOEC (dry weight) 320 Forney and Davis

1981

Wild celery,

Vallisneria americana

- 5 42 NOEC (leaf area) 3.2 Correll and Wu

1982

Wild celery,

Vallisneria americana

- 5 42 LOEC (leaf area) 12 Correll and Wu

1982

Eelgrass,

Zostera marina

- 22 21 LC50 540 Delistraty and

Hershner 1984

Eelgrass,

Zostera marina

- 20 21 LC50 100 Delistraty and

Hershner, 1984

Eelgrass,

Zostera marina

- 20 21 LC50 365 Delistraty and

Hershner, 1984

Eelgrass,

Zostera marina

- 19 21 LC50 367 Delistraty and

Hershner, 1984

a

 Effect concentrations are based upon measured concentrations of atrazine during the exposure period. b

 Effect concentration is based upon measured concentration of atrazine on the last day of exposure only. c

 No sediment present.

d

 Sediment present.
80

Table 5. Bioaccumulation of Atrazine by Aquatic Organisms

Species Chemical

Hardness

(mg/L as

 (CaCo3)

Concentration

in Water

 (μg/L) 

Duration

 (days) Tissue

BCF

or

 BAF Reference

FRESHWATER SPECIES

Brook trout,

Salvelinus fontinalis

94% 35.7 740 308 Muscle <0.27 Macek et al. 1976

Bluegill,

Lepomis macrochirus

94% 33.9 94 546 Muscle <2.1 Macek et al. 1976

Fathead minnow,

Pimephales promelas

94% 36.2 210 301 Eviscerated

carcass

<8.1 Macek et al. 1976

Fathead minnow 

(Fo larvae),

Pimphales promelas

97.1% 24-36 2,000 60 Whole body 6.5a Dionne 1992

Fathead minnow 

(adult males),

Pimephales promelas

97.1% 24-36 2,000 274 Whole body 8.5a Dionne 1992

Fathead minnow 

(adult females),

Pimephales promelas

97.1% 24-36 2,000 274 Whole body 8.5a Dionne 1992

Fathead minnow 

(F1 embryos),

Pimephales promelas

97.1% 24-36 2,000 3 Whole body

composite

sample

4.6a Dionne 1992

Fathead minnow 

(14-day old larvae),

Pimephales promelas

97.1% 24-36 2,000 14 Whole body 3.3a Dionne 1992

Fathead minnow 

(30-day old larvae),

Pimephales promelas

97.1% 24-36 2,000 30 Whole body 6.0a Dionne 1992

a

 Based on 14C measurements, and therefore, represents a maximum possible bioconcentration factor.
81

Table 6. Other Data on Effects of Atrazine on Aquatic Organisms

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

Mixed nitrifying

bacteria

- - 28 days Increased

nitrite

oxidation; ammonium

oxidation

unaffected

1,000 Gadkari 1988

Mixed nitrifying

bacteria

- - 28 days Ammonium

oxidation

unaffected

2,000 Gadkari 1988

Bacterium,

Pseudomonas putida

- 214 16 hr Incipient

inhibition

>10,000 Bringmann and Kuhn

1976, 1977

Cyanobacterium,

Anabaena cylindrica

- - 14 days LOEC 

(growth)

2,160 Rohwer and Fluckiger

1979

Cyanobacterium,

Anabaena cylindrica

- - 19 hr LOEC 

(nitrogenase activity)

2,160 Rohwer and Fluckiger

1979

Cyanobacterium,

Anabaena cylindrica

- - 1 hr LOEC 

(O2 production)

21,600 Rohwer and Fluckiger

1979

Cyanobacterium,

Anabaena cylindrica

>95% - 12-14 days EC50

(cell number)

1,200 Stratton 1984

Cyanobacterium,

Anabaena cylindrica

- - 24 hr EC50

(

14C uptake)

253a Larsen et al. 1986

Cyanobacterium,

Anabaena cylindrica

- - 24 hr EC50

(

14C uptake)

178a Larsen et al. 1986

Cyanobacterium,

Anabaena cylindrica

- - 24 hr EC50

(

14C uptake)

182b Larsen et al. 1986

Cyanobacterium,

Anabaena flos-aquae

97% - 5 days EC50

(cell number)

230 Hughes 1986; Hughes et

al. 1986, 1988

Cyanobacterium,

Anabaena flos-aquae

97% - 5 day

exposure,

9 day

recovery

NOEC

(cell number)

<100 Hughes 1986; Hughes et

al. 1986, 1988

Cyanobacterium,

Anabaena flos-aquae

97% - 5 day

exposure,

9 day

recovery

Algistatic concentration 4,970 Hughes 1986; Hughes et

al. 1986, 1988

Cyanobacterium,

Anabaena flos-aquae

97% - 5 day

exposure,

9 day

recovery

Algicidal

concentration

>3,200 Hughes 1986; Hughes et

al. 1986, 1988

Cyanobacterium,

Anabaena flos-aquae

99.9% - 1 day 56.2% reduction

in 14C uptake

40 Abou-Waly et al. 1991a

Cyanobacterium,

Anabaena flos-aquae

99.9% - 3 days 50.0% reduction

in 14C uptake

40 Abou-Waly et al. 1991a
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

82

Cyanobacterium,

Anabaena flos-aquae

99.9% - 5 days 9.5% reduction

in 14C uptake

40 Abou-Waly et al. 1991a

Cyanobacterium,

Anabaena flos-aquae

99.9% - 1 day 49.0% reduction

in chlorophyll

100 Abou-Waly et al. 1991a

Cyanobacterium,

Anabaena flos-aquae

99.9% - 3 days 2.0% reduction

in chlorophyll

100 Abou-Waly et al. 1991a

Cyanobacterium,

Anabaena flos-aquae

99.9% - 5 days 21.8% reduction

in chlorophyll

100 Abou-Waly et al. 1991a

Cyanobacterium,

Anabaena flos-aquae

99.9% - 7 days 29.9% reduction

in chlorophyll

100 Abou-Waly et al. 1991a

Cyanobacterium,

Anabaena flos-aquae

99.9% - 3 days EC50

(chlorophyll-a)

58 Abou-Waly et al. 1991b

Cyanobacterium,

Anabaena flos-aquae

99.9% - 5 days EC50

(chlorophyll-a)

469 Abou-Waly et al. 1991b

Cyanobacterium,

Anabaena flos-aquae

99.9% - 7 days EC50

(chlorophyll-a)

766 Abou-Waly et al. 1991b

Cyanobacterium,

Anabaena flos-aquae

92.2% - 4 days EC50

(chlorophyll-a)

>3,000 Fairchild et al. 1998

Cyanobacterium,

Anabaena inaequalis

>95% - 12-14 days EC50

(cell number)

30 Stratton 1984

Cyanobacterium,

Anabaena inaequalis

Technical

or 

analytical

- 22 hr 65% inhibition of

photosynthesis 

(

14C uptake)

2,667 Peterson et al. 1994

Cyanobacterium,

Anabaena variabilis

>95% - 12-14 days EC50

(cell number)

4,000 Stratton 1984

Cyanobacterium,

Aphanizomenon 

flos-aquae

Technical

or

analytical

- 22 hr 97% inhibition of 

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994

Cyanobacterium,

Microcystis aeruginosa

- 214 8 days Incipient

inhibition

3 Bringmann and Kuhn

1976, 1978a,b

Cyanobacterium,

Microcystis aeruginosa

97.4% - 5 days Reduced cell 

numbers

108 Parrish 1978

Cyanobacterium,

Microcystis aeruginosa

97.4% - 5 days Minimum algistatic concentration440 Parrish 1978

Cyanobacterium,

Microcystis aeruginosa

- - 6 days EC50

(growth)

630 Kallqvist and Romstad

1994

Cyanobacterium,

Microcystis aeruginosa

- - 6 days EC50

(microplate method)

630 Kallqvist and Romstad

1994
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

83

Cyanobacterium,

Microcystis aeruginosa

Technical

or 

analytical

- 22 hr 96% inhibition of 

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994

Cyanobacterium,

Microcystis aeruginosa

Technical

or 

analytical

- 22 hr 84% inhibition of 

photosynthesis 

(

14 C uptake)

2,667 Peterson et al. 1994

Cyanobacterium,

Microcystis sp.

Technical

or 

analytical

- 4 days EC50

(biomass)

90 Fairchild et al. 1998

Cyanobacterium,

Oscillatoria cf. chalybea

99.7% - 6 days Lowest complete 

inhibition conc.

2160 Schrader et al. 1997

Cyanobacterium,

Oscillatoria cf. chalybea

99.7% - 5 days LOEC 

(growth)

220 Schrader at al 1998

Cyanobacterium,

Oscillatoria sp.

Technical

or

analytical

- 22 hr 87% inhibition of 

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994

Cyanobacterium,

Plectonema boryanum

- - 31 days 69% decrease

in cell number

10,000 Mallison and Cannon

1984

Cyanobacterium,

Pseudoanabaena sp.

Technical

or

analytical

- 22 hr 91% inhibition of 

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994

Cyanobacterium,

Synechococcus leopolensis

- - 5 days EC50

(growth)

130 Kallqvist and Romstad

1994

Cyanobacterium,

Synechococcus leopolensis

- - 5 days EC50

(microplate method)

130 Kallqvist and Romstad

1994

Green alga,

Ankistrodesmus braunii

99.9% - 11 days EC50

(cell number)

60 Burrell et al. 1985

Green alga,

Ankistrodesmus sp.

- - 24 hr EC50

(

14C uptake)

72a Larsen et al. 1986

Green alga,

Ankistrodesmus sp.

- - 24 hr EC50

(

14C uptake)

61a Larsen et al. 1986

Green alga,

Chlamydomonas geitleri

Ettl

96.4% - 1 hr EC50

(CO2 fixation)

311 Francois and Robinson

1990

Green alga,

Chlamydomonas geitleri

Ettl

96.4% - 1 hr EC50

(CO2 fixation)

194c Francois and Robinson

1990

Green alga,

Chlamydomonas moewssi

95% - 14 days EC50

(growth inhibition)

1384

(exponential

growth phase)

Kotrikla et al. 1997
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

84

Green alga,

Chlamydomonas moewssi

95% - 14 days EC50

(growth inhibition)

1181

(stationary

growth phase)

Kotrikla et al. 1997

Green alga,

Chlamydomonas

noctigama

- - 72 hr EC50

(growth)

330 Kallqvist and Romstad

1994

Green alga,

Chlamydomonas

reinhardtii

- - 8 hr 32% inhibition

of photosynthesis

10 Valentine and Bingham

1976

Green alga,

Chlamydomonas

reinhardtii

- - 8 hr 74% inhibition

of photosynthesis

100 Valentine and Bingham

1976

Green alga,

Chlamydomonas

reinhardtii

- - 8 hr 97% inhibition

of photosynthesis

1,000 Valentine and Bingham

1976

Green alga,

Chlamydomonas

reinhardtii

- - 24 hr EC50

(

14C uptake)

48a Larsen et al. 1986

Green alga,

Chlamydomonas

reinhardtii

- - 24 hr EC50

(

14C uptake)

19a Larsen et al. 1986

Green alga,

Chlamydomonas

reinhardtii

- - 24 hr EC50

(

14C uptake)

44a Larsen et al. 1986

Green alga,

Chlamydomonas

reinhardtiid

- - 1-2 days Growth rate

reduced by 100%

216 Hersh and Crumpton

1987

Green alga,

Chlamydomonas

reinhardtiie

- - 1-2 days Growth rate

reduced by 13%

21.6 Hersh and Crumpton

1987

Green alga,

Chlamydononas

reinhardtiid

94% - 2 min EC50

(photosynthetic oxygen

evolution)

45 Hersh and Crumpton

1989

Green alga,

Chlamydomonas

reinhardtiie

94% - 2 min EC50

(photosynthetic oxygen

evolution)

484 Hersh and Crumpton

1989

Green alga,

Chlamydomonas

reinhardtii

- - 65 hr 13% reduction in

chlorophyll

49.6 Hiranpradit and Foy 1992

Green alga,

Chlamydomonas

reinhardtii

92.2% - 96 hr EC50

(chlorophyll)

176 Fairchild et al. 1998
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

85

Green alga,

Chlamydomonas sp.

- - 72-96 hr 36.2%f and 84.9%g

growth inhibition;

12.8% reduction in

chlorophyll

50-52 Foy and Hiranpradit 1977

Green alga,

Chlamydomonas sp.

- - 72-96 hr 64.1%f

 and 93.3%g

growth inhibition;

32.4% reduction in

chlorophyll

100-104 Foy and Hiranpradit 1977

Green alga,

Chlamydomonas sp.

- - 72-96 hr 77.5%f

 and 96.6%g

growth inhibition;

49.9% reduction in

chlorophyll

200-208 Foy and Hiranpradit 1977

Green alga,

Chlamydomonas sp.

- - 72-96 hr 76.6%f

 and 100%g

growth inhibition;

84.2% reduction in

chlorophyll

400-416 Foy and Hiranpradit 1977

Green alga,

Chlamydomonas sp.

- - 72-96 hr 78.6% growth

inhibitionf

; 90.5%

reduction in

chlorophyll

832 Foy and Hiranpradit 1977

Green alga,

Chlamydomonas sp.

- - 4 days EC50

(biomass)

176 Fairchild et al. 1994a

Green alga,

Chlorella fusca

99% - 15 min EC50

(photosynthesis)

141 Altenburger et al. 1990

Green alga,

Chlorella fusca

99% - 14 hr EC50

(cell volume growth)

36 Altenburger et al. 1990

Green alga,

Chlorella fusca

99% - 24 hr EC50

(cell reproduction)

26 Altenburger et al. 1990

Green alga,

Chlorella fusca

$98% - 24 hr EC50

(cell number)

15 Faust et al. 1993

Green alga,

Chlorella fusca

95% - 14 days EC50

(growth inhibition)

53.91

(exponential

growth phase)

Kotrikla et al. 1997

Green alga,

Chlorella fusca

95% - 14 days EC50

(growth inhibition)

75.73

(stationary

growth phase)

Kotrikla et al. 1997

Green alga,

Chlorella kessleri

- - 72 hr 30% growth inhibition

and photosynthetic O2

evolution; 6.7%

reduction in protein

synthesis; effects upon

lipids

1,078 El-Sheekh et al. 1994
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

86

Green alga,

Chlorella pyrenoidosa

- - 2 wk 70% reduced

growth

500 Virmani et al. 1975

Green alga,

Chlorella pyrenoidosa

- - 2 wk 95% reduced

growth

2,500 Virmani et al. 1975

Green alga,

Chlorella pyrenoidosa

- - 2 wk 92% reduced

growth

10,000 Virmani et al. 1975

Green alga,

Chlorella pyrenoidosa

- - 8 hr 64% inhibition

of photosynthesis

100 Valentine and Bingham

1976

Green alga,

Chlorella pyrenoidosa

- - 8 hr 96% inhibition of

photosynthesis

1,000 Valentine and Bingham

1976

Green alga,

Chlorella pyrenoidosa

>95% - 12-14 EC50

(cell number)

300 Stratton 1984

Green alga,

Chlorella pyrenoidosa

- - 10 days 30% growth

inhibition; 40%

reduction in

chlorophyll-a

53.9 Gonzalez-Murua et al.

1985

Green alga,

Chlorella pyrenoidosa

- - 10 days 65% growth

inhibition; 70%

reduction in

chlorophyll-a

107.8 Gonzalez-Murua et al.

1985

Green alga,

Chlorella pyrenoidosa

- - 110 hr 39% reduction

in chlorophyll

49.6 Hiranpradit and Foy 1992

Green alga,

Chlorella pyrenoidosa

Analytical - <50 min >80% inhibition of

photosynthetic CO2

uptake

125 Hannan 1995

Green alga,

Chlorella pyrenoidosa

Analytical - <50 min 100% inhibition of

photosynthetic CO2

uptake

1,250 Hannan 1995

Green alga,

Chlorella vulgaris

- - 7 days 31.0% reduction in dry

wt.

250h Veber et al. 1981

Green alga,

Chlorella vulgaris

- - 7 days 43.6% reduction in dry

wt.

500h Veber et al. 1981

Green alga,

Chlorella vulgaris

- - 7 days 56.4% reduction in dry

wt.

2,500h Veber et al. 1981

Green alga,

Chlorella vulgaris

- - 7 days 61.8% reduction in dry

wt.

5,000h Veber et al. 1981

Green alga,

Chlorella vulgaris

- - 24 hr EC50

(

14C uptake)

325a Larsen et al. 1986

Green alga,

Chlorella vulgaris

- - 24 hr EC50

(

14C uptake)

305a Larsen et al. 1986
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

87

Green alga,

Chlorella vulgaris

- - 24 hr EC50

(

14C uptake)

293b Larsen et al. 1986

Green alga,

Chlorella vulgaris

- - 30 min EC50 

(Decrease in oxygen

evolution)

305 Van der Heever and

Grobbelaar 1997

Green alga,

Chlorella vulgaris

92.2% - 96 hr EC50 

(chlorophyll)

94 Fairchild et al. 1998

Green alga,

Chlorella vulgaris

98% - 12 days Reduced growth, but

showed signs of

recovery

10 Berard et al 1999

Green alga,

Chlorella vulgaris

98% - 96 hr EC50 172 Seguin et al 2000

Green alga,

Chlorella sp.

- - 72-96 hr 31.0% growth

inhibitionf

;

38.8% reduction in

chlorophyll

52 Foy and 

Hiranpradit 1977

Green alga,

Chlorella sp.

- - 72-96 hr 45.3% growth

inhibitionf

;

30.3% reduction in

chlorophyll

104 Foy and Hiranpradit 1977

Green alga,

Chlorella sp.

- - 72-96 hr 52.3% growth

inhibitionf

;

83.7% reduction in

chlorophyll

208 Foy and 

Hiranpradit 1977

Green alga,

Chlorella sp.

- - 72-96 hr 59.2% growth

inhibitionf

;

93.5% reduction in

chlorophyll

416 Foy and 

Hiranpradit 1977

Green alga,

Chlorella sp.

- - 72-96 hr 53.7% growth

inhibitionf

;

95.4% reduction in

chlorophyll

832 Foy and 

Hiranpradit 1977

Green alga,

Chlorella sp.

- - 1-2 days Growth rate

reduced by 86%

216 Hersh and 

Crumpton 1987

Green alga,

Chlorella sp.

- - 2-3 days Growth rate

reduced by 55%

21.6 Hersh and Crumpton

1987

Green alga,

Chlorella sp.

94% - 2 min EC50

(photosynthetic oxygen

evolution)

36 Hersh and Crumpton

1989

Green alga,

Chlorella sp.e

94% - 2 min EC50

(photosynthetic oxygen

evolution)

41 Hersh and Crumpton

1989
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

88

Green alga,

Clorella sp.e

94% - 2 min EC50

(photosynthetic oxygen

evolution)

35 Hersh and Crumpton

1989

Green alga,

Chlorella sp.

- - 4 days EC50

(biomass)

92 Fairchild et al. 1994a

Green alga,

Chlorococcum

hypnosporum

- - 2 wk 75% reduced growth 5,000 Virmani et al. 1975

Green alga,

Chlorococcum

hypnosporum

- - 2 wk 92% reduced

growth

10,000 Vermani et al. 1975

Green alga,

Franceia sp.f

94% - 2 min EC50

(photosynthetic oxygen

evolution)

466 Hersh and Crumpton

1989

Green alga,

Franceia sp.

94% - 2 min EC50

(photosynthetic oxygen

evolution)

774 Hersh and Crumpton

1989

Green alga,

Franceia sp.

94% - 2 min EC50

(photosynthetic oxygen

evolution)

710 Hersh and Crumpton

1989

Green alga,

Franceia sp.

94% - 2 min EC50

(photosynthetic oxygen

evolution)

430 Hersh and Crumpton

1989

Green alga,

Franceia sp.

94% - 2 min EC50

(photosynthetic oxygen

evolution)

720 Hersh and Crumpton

1989

Green alga,

Gloetaenium

loitlesbergarianum

- - 96 hr inhibition

of calcification

2,157 Prasad and Chowdary

1981

Green alga,

Pseudokirchnierella

subcapitata

98% - 96 hr EC50 118 Seguin et al. 2001

Green alga,

Scenedesmus acutus

98% - 96 hr EC50 45 Seguin et al. 2001

Green alga,

Scenedesmus obliquus

- - 24 hr EC50

(

14C uptake)

38 Larsen et al. 1986

Green alga,

Scenedesmus obliquus

- - 24 hr EC50

(

14C uptake)

57 Larsen et al. 1986

Green alga,

Scenedesmus obliquus

- - 24 hr EC50

(

14C uptake)

49 Larsen et al. 1986
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

89

Green alga,

Scenedesmus quadricauda

- - 8 hr 42% inhibition

of photosynthesis

10 Valentine and Bingham

1976

Green alga,

Scenedesmus quadricauda

- - 8 hr 84% inhibition

of photosynthesis

100 Valentine and Bingham

1976

Green alga,

Scenedesmus quadricauda

- - 8 hr 98% inhibition

of photosynthesis

1,000 Valentine and Bingham

1976

Green alga,

Scenedesmus quadricauda

- 214 8 days Incipient

inhibition

30 Bringmann and Kuhn

1977, 1978a,b

Green alga,

Scenedesmus quadricauda

>95% - 12-14 days EC50

(cell number)

100 Stratton 1984

Green alga,

Scenedesmus quadricauda

- - 8 days 4.5% reduction in

photosynthesis

4 Bogacka et al. 1990

Green alga,

Scenedesmus quadricauda

- - 8 days 9.9% reduction in

photosynthesis

9 Bogacka et al. 1990

Green alga,

Scenedesmus quadricauda

- - 8 days 18.5% reduction in

photosynthesis

30 Bogacka et al. 1990

Green alga,

Scenedesmus quadricauda

- - 8 days 68.1% reduction in

photosynthesis

100 Bogacka et al. 1990

Green alga,

Scenedesmus quadricauda

- - 8 days 99.3% reduction in

photosynthesis

337 Bogacka et al. 1990

Green alga,

Scenedesmus quadricauda

Technical

or

analytical

- 22 hr 96% inhibition of

photosynthesis 

(

14C uptake)

2,667 Peterson et al. 1994

Green alga,

Scenedesmus quadricauda

92.2% - 96 hr EC50

(chlorophyll)

169 Fairchild et al. 1998

Green alga,

Scenedesmus subspicatus

99.0% - 4 days EC50

(cell number)

110 Geyer et al. 1985

Green alga,

Scenedesmus subspicatus

- - 24 hr 24.8% inhibition of

effective photosynthesis

rate

12.3 Schafer et al. 1994

Green alga,

Scenedesmus subspicatus

- - 24 hr 57.4% inhibition of

effective photosynthesis

rate

37 Schafer et al. 1994

Green alga,

Scenedesmus subspicatus

- - 24 hr 93.4% inhibition of

effective photosynthesis

rate

111.1 Schafer et al. 1994

Green alga,

Scenedesmus subspicatus

- - 24 hr 100.0% inhibition of

effective photosynthesis

rate 

333.3 Schafer et al. 1994
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

90

Green alga,

Scenedesmus subspicatus

98% - 2 days EC50

(cell numbers)

21 Kirby and Sheahan 1994

Green alga,

Scenedesmus subspicatus

- - 24 hr 50% reduction in dry

mass

21.5 Reinold et al. 1994

Green alga,

Scenedesmus subspicatus

- - 24 hr EC50 

(net assimilation

inhibition)

25 Zagorc-Koncan 1996

Green alga,

Scenedesmus subspicatus

- - 72 hr EC50

(growth inhibition)

200 Zagorc-Koncan 1996

Green alga,

Scenedesmus subspicatus

99% - 60 days NOEC

(growth and

photosynthetic oxygen

evolution)

20 Behra et al. 1999

Green alga,

Scenedesmus sp.

- - 72-96 hr 60.2% growth

inhibitiong

50 Foy and Hiranpradit 1977

Green alga,

Scenedesmus sp.

- - 72-96 hr 72.4% growth

inhibitiong

100 Foy and Hiranpradit 1977

Green alga,

Scenedesmus sp.

- - 72-96 hr 81.6% growth

inhibitiong

200 Foy and Hiranpradit 1977

Green alga,

Scenedesmus sp.

- - 72-96 hr 84.7% growth

inhibitiong

400 Foy and Hiranpradit 1977

Green alga,

Scenedesmus sp.

- - 72-96 hr 83.7% growth

inhibitiong

800 Foy and Hiranpradit 1977

Green alga,

Scenedesmus sp.

- - 4 days EC50

(biomass)

169 Fairchild et al. 1994a

Green alga,

Selenastrum

capricornutum

97.4% - 5 days Significantly reduced

cell numbers

54 Parrish 1978

Green alga,

Selenastrum

capricornutum

97.4% - 5 days Minimum algistatic

concentration

200 Parrish 1978

Green alga,

Selenastrum

capricornutum

97.4% - 5 days 12% chlorophyll-a

reduction

32 Parrish 1978

Green alga,

Selenastrum

capricornutum

97.4% - 5 days 42% chlorophyll-a

reduction

54 Parrish 1978

Green alga,

Selenastrum

capricornutum

97.4% - 5 days 76% chlorophyll-a

reduction

90 Parrish 1978
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

91

Green alga,

Selenastrum

capricornutum

97.4% - 5 days 92% chlorophyll-a

reduction

150 Parrish 1978

Green alga,

Selenastrum

capricornutum

97.4% - 5 days 96% chlorophyll-a

reduction

200 Parrish 1978

Green alga,

Selenastrum

capricornutum

85.5% 47 7 days 13.8% increased

biomass

100i Johnson 1986

Green alga,

Selenastrum

capricornutum

85.5% 47 7 days 36.2% decreased

biomass

1,000i Johnson 1986

Green alga,

Selenastrum

capricornutum

85.5% 47 7 days 75.9% decreased

biomass

1,000j Johnson 1986

Green alga,

Selenastrum

capricornutum

- - 24 hr EC50

(

14C uptake)

53a Larsen et al. 1986

Green alga,

Selenastrum

capricornutum

- - 24 hr EC50

(

14C uptake)

34a Larsen et al. 1986

Green alga,

Selenastrum

capricornutum

- - 24 hr EC50

(

14C uptake)

42b Larsen et al. 1986

Green alga,

Selenastrum

capricornutum

80% - 21 days EC50

(biomass)

58.7a Turbak et al. 1986

Green alga,

Selenastrum

capricornutum

80% - 21 days EC50

(biomass)

410b Turbak et al. 1986

Green alga,

Selenastrum

capricornutum

80% - 24 hr EC50

(02 evolution)

69.7k Turbak et al. 1986

Green alga,

Selenastrum

capricornutum

80% - 24 hr EC50

(02 evolution)

854l Turbak et al. 1986

Green alga,

Selenastrum

capricornutum

- - 5 days EC50

(cell number)

100 Roberts et al. 1990

Green alga,

Selenastrum

capricornutum

- - 5 days EC50

(cell number) 

95 Roberts et al. 1990
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

92

Green alga,

Selenastrum

capricornutum

Reagent

grade

171 30 min EC50

(CO2 fixation)

100 Versteeg 1990

Green alga,

Selenastrum

capricornutum

Reagent

grade

171 30 min EC50

(O2 generation)

380 Versteeg 1990

Green alga,

Selenastrum

capricornutum

Reagent

grade

171 4 days EC50

(cell number)

50 Versteeg 1990

Green alga,

Selenastrum

capricornutum

99.9% - 1 day 22.0% reduction in

chlorophyll; 69.3%

reduction in 14C uptake

130 Abou-Waly et al. 1991a

Green alga,

Selenastrum

capricornutum

99.9% - 3 days 53.2% reduction in

chlorophyll; 42.4%

reduction in 14C uptake

130 Abou-Waly et al. 1991a

Green alga,

Selenastrum

capricornutum

99.9% - 5 days 24.5% reduction in

chlorophyll; 60.6%

reduction in 14C uptake

130 Abou-Waly et al. 1991a

Green alga,

Selenastrum

capricornutum

99.9% - 7 days 11.6% reduction in

chlorophyll; 31.5%

reduction in 14C uptake

130 Abou-Waly et al. 1991a

Green alga,

Selenastrum

capricornutum

99.9% - 3 days EC50

(chlorophyll-a)

283 Abou-Waly et al. 1991b

Green alga,

Selenastrum

capricornutum

99.9% - 5 days EC50

(chlorophyll-a)

218 Abou-Waly et al. 1991b

Green alga,

Selenastrum

capricornutum

99.9% - 7 days EC50

(chlorophyll-a)

214 Abou-Waly et al. 1991b

Green alga,

Selenastrum capricornutum

92.2% - 4 days EC50

(chlorophyll)

117 Fairchild et al. 1994a,

1998

Green alga,

Selenastrum capricornutum

- - 72 hr EC50

(growth)

200 Kallqvist and Romstad

1994

Green alga,

Selenastrum capricornutum

- - 72 hr EC50

(growth)

110 Kallqvist and Romstad

1994

Green alga,

Selenastrum

capricornutum

Technical

or

analytical

- 22 hr 99% inhibition of

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

93

Green alga,

Selenastrum

capricornutum

- 100 96 hr EC50

(chlorophyll-a)

147 Gaggi et al. 1995

Green alga,

Selenastrum

capricornutum

- - 72 hr EC50 118.2 Radetski et al. 1995

Green alga,

Selenastrum

capricornutum

- - 72 hr EC50

(cell numbers)

359 Van der Heever and

Grobbelaar 1996

Green alga,

Selenastrum

capricornutum

- - 72 hr EC50

(chlorophyll-a;

spectrophotometric

measurement)

902 Van der Heever and

Grobbelaar 1996

Green alga,

Selenastrum

capricornutum

- - 72 hr EC50

(chlorophyll-a;

fluorometric

measurement)

960 Van der Heever and

Grobbelaar 1996

Green alga,

Selenastrum

capricornutum

- - 96 hr EC50

(cell number;

free culture)

200 Abdel-Hamid 1996

Green alga,

Selenastrum

capricornutum

- - 96 hr EC50

(cell number;

immobilized culture)

220 Abdel-Hamid 1996

Green alga,

Selenastrum

capricornutum

- - 96 hr LC50 26 Caux et al. 1996

Green alga,

Selenastrum

capricornutum

- - 96 hr EC50

(cell numbers)

26 Caux et al. 1996

Green alga,

Selenastrum

capricornutum

- - 30 min EC50 

(decrease in oxygen

evolution)

222 Van der Heever and

Grobbelaar 1997

Green alga,

Selenastrum

capricornutum

- - 72 hr EC50

(growth inhibition)

164.3 Benhra et al. 1997

Green alga,

Selenastrum

capricornutum

- - 72 hr EC50

(growth inhibition)

92.9

(Cryoalgotox)

Benhra et al. 1997

Green alga,

Selenastrum

capricornutum

- - 4 days I50

(chlorophyll-a)

80 El Jay et al. 1997
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

94

Green alga,

Selenastrum

capricornutum

Technical

grade

- 96 hr NOEC

(biomass)

75 Fairchild et al. 1997

Green alga,

Selenastrum

capricornutum

Technical

grade

- 96 hr LOEC

(biomass)

150 Fairchild et al. 1997

Green alga,

Selenastrum

capricornutum

Technical

grade

- 96 hr EC50

(biomass)

235 Fairchild et al. 1997

Green alga,

Selenastrum

capricornutum

99.7% - 6 days Lowest Complete

Inhibition Concentration

(growth)

2160 Schrader et al. 1997

Green alga,

Selenastrum

capricornutum

- - 4 hr EC50

(chlorophyll-a

fluorescence)

232 Van der Heever and

Grobbelaar 1998

Green alga,

Selenastrum

capricornutum

ACS - $3 days EC50

(growth)

164 Mayer et al. 1998

Green alga,

Selenastrum

capricornutum

99.7% - 5 days LOEC

(growth)

220 Schrader et al 1998

Green alga,

Stigeoclonium tenue

- - 24 hr EC50

(

14C uptake)

127a Larsen et al. 1986

Green alga,

Stigeoclonium tenue

- - 24 hr EC50

(

14C uptake)

224a Larsen et al. 1986

Green alga,

Ulothrix subconstricta

- - 24 hr EC50

(

14C uptake)

88a Larsen et al. 1986

Benthic diatom,

Craticula cuspidata

98% - 67 days

chronic, 12

days acute

LOEC 

(chlorophyll-a)

83 Nelson et al. 1999

Diatom,

Asterionella formosa

98% - 96 hr EC50 261 Seguin et al. 2001

Diatom,

Cyclotella meneghiniana

(Arizona race)

- - 7 min EC50

(photosynthesis)

99 Millie and Hersh 1987

Diatom,

Cyclotella meneghiniana

(Iowa race)

- - 7 min EC50

(photosynthesis)

105 Millie and Hersh 1987

Diatom,

Cyclotella meneghiniana

(Minnesota race)

- - 7 min EC50

(photosynthesis)

243 Millie and Hersh 1987
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

95

Diatom,

Cyclotella meneghiniana

Technical

or

analytical

- 22 hr 97% inhibition of

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994

Diatom,

Cyclotella sp.

- - 6 days EC50

(growth)

430 Kallqvist and Romstad

1994

Diatom,

Navicula accomuda

98% - 96 hr EC50 164 Seguin et al. 2001

Diatom,

Navicula pelliculosa

97% - 5 days EC50

(cell number)

60 Hughes 1986; Hughes et

al. 1986, 1988

Diatom,

Navicula pelliculosa

97% - 5 day

exposure, 9

day

recovery

NOEC <100 Hughes 1986; Hughes et

al. 1986, 1988

Diatom,

Navicula pelliculosa

97% - 5 day

exposure,

9 day

recovery

Algistatic concentration 1,710 Hughes 1986; Hughes et

al. 1986, 1988

Diatom,

Navicula pelliculosa

97% - 5 day

exposure,

9 day

recovery

Algicidal concentration >3,200 Hughes 1986; Hughes et

al. 1986, 1988

Diatom,

Nitzschia sp.

98% - 96 hr EC50 412 Seguin et al. 2001

Diatom,

Nitzschia sp.

Technical

or

analytical

- 22 hr 99% inhibition of

photosynthesis

(

14C uptake)

2,667 Peterson et al. 1994

Mixed algal assemblage 98% - 21 days Shift in dominant algal

abundance

30 Seguin et al. 2001

Algal assemblage - - 28 days LOEC (biomass) 11 Girling et al. 2001

Cryptomonad,

Cryptomonas

pyrinoidifera

- - 6 days EC50

(growth)

500 Kallqvist and Romstad

1994

Duckweed,

Lemna gibba

97% - 5 days EC50

(frond production)

170 Hughes 1986; Hughes et

al. 1986, 1988

Duckweed,

Lemna gibba

97% - 5 day

exposure

9 day

recovery

NOEC

(frond production)

<100 Hughes 1986; Hughes et

al. 1986, 1988

Duckweed,

Lemna gibba

97% - 5 day

exposure

9 day

recovery

Phytostatic

concentration

1,720 Hughes 1986; Hughes et

al. 1986, 1988
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

96

Duckweed,

Lemna gibba

97% - 5 day

exposure

9 day

recovery

Phytocidal concentration >3,200 Hughes 1986; Hughes et

al. 1986, 1988

Duckweed,

Lemna minor

- - 20 days No effect upon

growth; increased

soluble protein content;

increased

photosynthesis and

respiration

20 Beaumont et al. 1976a,b

Duckweed,

Lemna minor

- - 20 days 12% reduced growth;

increased water and

soluble protein content;

increased photosynthesis

and respiration

50 Beaumont et al. 1976a,b,

1978

Duckweed,

Lemna minor

- - 20 days 23% reduced growth;

increased water and

soluble protein content;

increased photosynthesis

and respiration

100 Beaumont et al. 1976a,b,

1978

Duckweed,

Lemna minor

- - 20 days 74% reduced growth;

increased water,

chlorophyll, and soluble

protein content;

increased photosynthesis

and respiration

250 Beaumont et al. 1976a,b

Duckweed,

Lemna minor

- - 15 days Increased total fatty acid

and -linolenic acid

content; increased

monogalatosyldia-cylglycerol percentage

100 Grenier et al. 1979

Duckweed,

Lemna minor

- - 15 days Increased total fatty acid

and -linolenic acid

content; decreased

linoleic acid content;

increased monogalactosyldiacyl-glycerol

percentage

1,000 Grenier et al. 1979

Duckweed,

Lemna minor

- - 15 days Increased amounts of

polar lipids in

chlorophyll-protein

complexes of

chloroplasts

248 Grenier et al. 1987

Duckweed,

Lemna minor

- - 10 days Increased [14C]- acetate

incorporation into

chloroplast lipids

248 Grenier et al. 1989
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

97

Duckweed,

Lemna minor

- - 2 days Changes in chloroplast

ultrastructure; increased

chlorophyll content

248 Simard et al. 1990

Duckweed,

Lemna minor

Technical

or

analytical

- 7 days 95% inhibition of

growth

2,667 Peterson et al. 1994

Duckweed,

Lemna minor

Technical - 96 hr NOEC

(biomass)

75 Fairchild et al. 1997

Duckweed,

Lemna minor

Technical - 96 hr LOEC

(biomass)

150 Fairchild et al. 1997

Duckweed,

Lemna minor

Technical - 96 hr EC50

(biomass)

153 Fairchild et al. 1997

Duckweed,

Lemna minor

92.2% - 4 days EC50

(frond production)

92 Fairchild et al. 1998

Wild rice,

Zizania aquatica

85% - 83 days Visibly senescent; 75%

reduction in chlorophylla in leaves

50 Detenbeck et al. 1996

Wild celery,

Vallisneria americana

- - 42 days EC50

(total leaf length)

163 Davis 1981;

Forney and Davis 1981

Wild celery,

Vallisneria americana

- - - Reduced leaf growth

and whole plant biomass

8 Cohn 1985

Wild celery,

Vallisneria americana

- - - Reduced tuber overwintering success4 Cohn 1985

Coontail,

Ceratophyllum dermersum

85% - 6-8 days Reduced stem

elongation

50 Detenbeck et al. 1996

Coontail,

Ceratophyllum sp.

92.2% - 14 days EC50

(wet weight)

22 Fairchild et al. 1998

Cattail,

Typha latifolia

85% - 19 days No effect upon growth 25 Detenbeck et al. 1996

Watermilfoil,

Myriophyllum

heterophyllum

92.2% - 14 days EC50

(wet weight)

132 Fairchild et al. 1998

Watermilfoil,

Myriophyllum spicatum

- - 28 days EC50

(length)

1,104 Davis 1981;

Forney and Davis 1981

Watermilfoil,

Myriophyllum spicatum

- - 24 hr 30% increase in net

photosynthetic rate

10 Hoffmann and Winkler

1990

Watermilfoil,

Myriophyllum spicatum

- - 5 days 50% reduction in branch

number

3,700 Bird 1993

Sago pondweed,

Potamogeton pectinatus

- - 28 days Reduced

biomass

100 Fleming et al. 1991
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

98

Bushy pondweed,

Najas sp.

92.2% - 14 days EC50

(wet weight)

24 Fairchild et al. 1998

Egeria,

Egeria sp.

- - 14 days EC50

(biomass)

<38 Fairchild et al. 1994a

Elodea,

Elodea canadensis

- - 28 days EC50

(length)

80 Davis 1981;

Forney and Davis 1981

Elodea,

Elodea canadensis

- - 21 days EC50

(length)

109 Davis 1981;

Forney and Davis 1981

Elodea,

Elodea canadensis

- - 20 days Dark respiration rate

exceeded net

photosynthesis rate

10 Hoffmann and Winkler

1990

Elodea,

Elodea canadensis

85% - 19 days No effect upon growth 75 Detenbeck et al. 1996

Elodea,

Elodea canadensis

92.2% - 14 days EC50 

(wet weight)

21 Fairchild et al. 1998

Water moss,

Fontinalis antipyretica

- - 20 days Dark respiration rate

exceeded net

photosynthesis rate

10 Hoffmann and Winkler

1990

Water moss,

Fontinalis hypnoides

- - 24 hr 90% reduction in net

photosynthesis

2 Hoffmann and Winkler

1990

Water moss,

Fontinalis squamosa

- - 24 hr 20% reduction in net

photosynthesis

10 Hoffmann and Winkler

1990

Mixed macrophytes,

Ceratophyllum sp.

and Elodea sp.

85.5% 47 30 days 18.3% increased

biomass

10 Johnson 1986

Mixed macrophytes,

Ceratophyllum sp.

and Elodea sp.

85.5% 47 30 days 11.6% decreased

biomass

100 Johnson 1986

Mixed macrophytes,

Ceratophyllum sp.

and Elodea sp.

85.5% 47 30 days 47.6% decreased

biomass

1,000 Johnson 1986

Protozoa,

Acanthamoeba castellanii

- - 6 days 5% population decrease 100 Prescott et al. 1977

Protozoa,

Acanthamoeba castellanii

- - 6 days 14% population

decrease

1,000 Prescott et al. 1977

Protozoa,

Acanthamoeba castellanii

- - 6 days 15% population

decrease

4,000 Prescott et al. 1977

Protozoa,

Acanthamoeba castellanii

- - 6 days 40% population

decrease

10,000 Prescott et al. 1977
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

99

Protozoa,

Colpidium campylum

- - 24 hr EC50

(cell number)

>50,000 Roberts et al. 1990

Protozoa,

Euglena gracilis

- - 8 hr 11% inhibition of

photosynthesis

10 Valentine and Bingham

1976

Protozoa,

Euglena gracilis

- - 8 hr 28% inhibition of

photosynthesis

100 Valentine and Bingham

1976

Protozoa,

Euglena gracilis

- - 8 hr 83% inhibition of

photosynthesis

1,000 Valentine and Bingham

1976

Protozoa,

Tetrahymena pyriformis

- - 24 hr EC50 118,500 Huber et al. 1991

Protozoa,

Tetrahymena pyriformis

- - 48 hr EC50

(cell number)

96,000 Schafer et al. 1994

Hydra,

Hydra viridis

- - 21 days Reduced budding rate 5,000 Benson and Boush 1983

Rotifer,

Brachionus calyciflorus

- - 24 hr LC50 7,840 Crisinel et al. 1994

Leech,

Glossiphonia complanata

99.2% - 27-28 days LC50 6,300 Streit and Peter 1978

Leech,

Helobdella stagnalis

99.2% - 27-28 days LC50 9,900 Streit and Peter 1978

Snail,

Lymnaea palustris

97.8% - 12 wk No effect upon growth,

fecundity or glycogen

metabolism

125 Baturo et al. 1995

Snail,

Lymnaea palustris

97.8% - 12 wk Inhibited BaPH and

GST enzyme activities

5 Baturo and Lagadic 1996

Snail,

Physa acuta

- - 18 days Increased grazing

searching velocity and

movement patterns

15 Roses et al. 1999

Mussel (glochidia larva),

Anadonta imbecilis

97.3% 40-50 24 hr LC50 >60,000 Johnson et al. 1993

Mussel (1-2 d old juvenile),

Anadonta imbecilis

97.3% 40-50 48 hr LC50 >60,000 Johnson et al. 1993

Mussel (7-10 d old

juvenile),

Anadonta imbecilis

97.3% 40-50 48 hr LC50 >60,000 Johnson et al. 1993

Anostracan,

Streptocephalus texanus

- - 24 hr LC50 >30,000 Crisinel et al. 1994

Cladoceran,

Ceriodaphnia dubia

>99% 57.1 4 days MATC 7,100 Oris et al. 1991
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

100

Cladoceran,

Ceriodaphnia dubia

>99% 57.1 4 days MATC 14,100 Oris et al. 1991

Cladoceran,

Daphnia magna

- - 26 hr LC50 3,600 Frear and Boyd 1967

Cladoceran,

Daphnia magna

- 100 48 hr BCF = 4.4 10 Ellgehausen et al. 1980

Cladoceran,

Daphnia magna

- 100 48 hr BCF = 2.2 10 Ellgehausen et al. 1980

Cladoceran,

Daphnia magna

- - 21 days Reduced young

production

2,000 Kaushik et al. 1985

Cladoceran,

Daphnia magna

- - 48 hr 10% mortality 22,000 Bogacka et al. 1990

Cladoceran,

Daphnia magna

- - 96 hr 30% mortality 16,900 Bogacka et al. 1990

Cladoceran,

Daphnia magna

- - 96 hr 60% mortality 48,300 Bogacka et al. 1990

Cladoceran,

Daphnia magna

97.3% 40-50 48 hr LC50 9,400m Johnson et al. 1993

Cladoceran,

Daphnia magna

- - 24 hr EC50 >30,000 Crisinel et al. 1994

Cladoceran,

Daphnia magna

- - 48 hr EC50 >30,000 Crisinel et al. 1994

Cladoceran,

Daphnia magna

85% - 48 hr Significantly decreased

survival

25 Detenbeck et al. 1996

Cladoceran,

Daphnia magna

85% - 48 hr No effect upon survival 50 Detenbeck et al. 1996

Cladoceran,

Daphnia pulex

- - 3 hr LC50 >40,000 Nishiuchi and Hashimoto

1967, 1969

Cladoceran,

Daphnia pulex

99.2% - 28 days 11.7% decreased

survival and 28.2%

decreased reproduction

1,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 28 days 4.2% decreased survival

and 26.8% decreased

reproduction

2,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - ~70 days 41.7% decreased

reproduction

2,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 28 days 20.2% decreased

survival and 45.5%

decreased reproduction

3,000 Schober and Lampert

1977
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

101

Cladoceran,

Daphnia pulex

99.2% - 28 days 9.6% decreased survival

and 48.3% decreased

reproduction

4,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 28 days 42% decreased

reproduction

5,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 70 days 48.2% decreased

reproduction

5,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 28 days 14.9% decreased

survival; 53.9%

decreased reproduction

10,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 70 days 62.6% decreased

reproduction

10,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

99.2% - 28 days 96.5% decreased

reproduction

20,000 Schober and Lampert

1977

Cladoceran,

Daphnia pulex

- - 10 min 10% reduction in food

consumption

350 Pott 1980

Cladoceran,

Daphnia pulex

- - 10 min 50% reduction in food

consumption

1,600 Pott 1980

Cladoceran,

Daphnia pulex

98% - 18 hr LC50 700 Bowman et al 1981

Cladoceran (adult),

Moina macrocopa

- - 3 hr LC50 >40,000 Nishiuchi and Hashimoto

1967, 1969

Cladoceran,

Moina macrocopa

- - 4-6 wk 40% mortality; 10%

increase in potential

production; reduced

actual population growth

1,000 Shcherban 1972a,b

Amphipod (1st instar),

Gammarus fasciatus

94% - 48 hr LC50 5,700 Macek et al. 1976

Amphipod (approx 2nd

instar),

Hyalella azteca

98% - 18 hr LC50 2,000 Bowman et al. 1981

White dotted mosquito,

Culex restuans

98% - 18 hr LC50 60,000 Bowman et al. 1981

Midge (2nd instar),

Chironomus riparius

- 151 10 days LC50 18,900 Taylor et al. 1991

Midge (~10 d),

Chironomus tentans

97.1% 42-44 96 hr

(fed)

LC50 >28,000 McNamara 1991b

Midge (4th instar),

Chironomus tentans

99% 80-100 48 hr LC50 >20,000 Pape-Lindstrom and Lydy

1997
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

102

Midge (1st instar),

Chironomus tentans

94% - 48 hr LC50 720 Macek et al. 1976

Midge (4th instar),

Chironomus tentans

99% - 48 hr LC50 >1,000 Jin-Clark et al. 2002

Midge (3rd instar),

Chironomus tentans

98.5% 40-52 48 hr LC50 (fed) >24,000 Springborn Smithers 2002

Midge (3rd instar),

Chironomus tentans

98.5% 40-52 10 days LC50 >24,000 Springborn Smithers 2002

Midge (3rd instar),

Chironomus tentans

98.5% 40-52 10 days EC50 (growth) 8,300 Springborn Smithers 2002

Midge (3rd instar),

Chironomus tentans

98.5% 40-52 10 days NOEC (survival) 16,000 Springborn Smithers 2002

Midge (3rd instar),

Chironomus tentans

98.5% 40-52 10 days NOEC (growth) 5,400 Springborn Smithers 2002

Rainbow trout (embryo),

Oncorhynchus mykiss

80% 50 23 days

(at hatching)

LC50 736 Birge et al. 1979

Rainbow trout (embryo),

Oncorhynchus mykiss

80% 200 23 days

(at

hatching)

LC50 888 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 50 27 days

(4 days

post-hatch)

LC50 696 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 200 27 days

(4 days

post-hatch)

LC50 864 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 50 27 days

(4 days

post-hatch)

LC1 23.2 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 200 27 days

(4 days

post-hatch)

LC1 61.8 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 50 27 days

(4 days

post-hatch)

3% teratic larvae 43.2 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 50 27 days

(4 days

post-hatch)

6% teratic larvae 432 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchuls mykiss

80% 50 27 days

(4 days

post-hatch)

62% teratic larvae 4,020 Birge et al. 1979
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

103

Rainbow trout (sac fry),

Oncorhynchuls mykiss

80% 200 27 days

(4 days

post-hatch)

2% teratic larvae 13.6 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 200 27 days

(4 days

post-hatch)

3% teratic larvae 48.0 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 200 27 days

(4 days

post-hatch)

4% teratic larvae 416 Birge et al. 1979

Rainbow trout (sac fry),

Oncorhynchus mykiss

80% 200 27 days

(4 days

post-hatch)

65% teratic larvae 4,020 Birge et al. 1979

Rainbow trout (juvenile),

Oncorhynchus mykiss

99.3% - 48 hr LC50 5,660 Pluta 1989

Rainbow trout (juvenile),

Oncorhynchus mykiss

- - 28 days Changes in renal

corpuscle ultrastructure

5 Fischer-Scherl et al. 1991

Rainbow trout (juvenile),

Oncorhynchus mykiss

- - 28 days Changes in renal

corpuscle and tubule

ultrastructure

10 Fischer-Scherl et al. 1991

Rainbow trout,

Oncorhynchus mykiss

- - 28 days Slight ultrastructural

changes in renal

corpuscles

5 Schwaiger et al. 1991

Rainbow trout,

Oncorhynchus mykiss

- - 28 days Slight histopathological

changes in liver;

increased ultrastructural

changes in renal

corpuscles

10 Schwaiger et al. 1991

Rainbow trout,

Oncorhynchus mykiss

- - 28 days Ultrastructural changes

in renal corpuscles and

histopathological

changes in liver

20 Schwaiger et al. 1991

Rainbow trout (juvenile),

Oncorhynchus mykiss

93.7% - 14 days No effect upon survival,

body weight, liver

weight, or liver

xenobiotic-metabolizing

enzyme activities

10 Egaas et al. 1993

Rainbow trout (juvenile),

Oncorhynchus mykiss

$98% - 10 days Reduced plasma protein 3.0 Davies et al. 1994b

Rainbow trout (juvenile),

Oncorhynchus mykiss

$98% - 10 days Reduced plasma protein 50 Davies et al. 1994b

Rainbow trout (juvenile),

Oncorhynchus mykiss

99% 380 5 wk Ultrastructural

alterations in kidney

proximal tubules

12.4 Oulmi et al. 1995
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

104

Rainbow trout (juvenile),

Oncorhynchus mykiss

99% 380 5 wk Ultrastructural

alterations in kidney

proximal and distal

tubules

24.0 Oulmi et al. 1995

Atlantic salmon (parr),

Salmo salar

- - 30 min Reduced olfactory

response to female

pheromone

2.0 Moore and Waring 1998

Goldfish,

Carassius auratus

- - 48 hr LC50 >10,000 Nishiuchi and Hashimoto

1967, 1969

Goldfish (6-9 g),

Carassius auratus

97.9% - 24 hr 

(10 min

flowing)

Burst swimming 0.5 

(0.1 test

dripping)

Saglio and Trijasse 1998

Common carp,

Cyprinus carpio

- - 48 hr LC50 >10,000 Nishiuchi and Hashimoto

1967, 1969

Common carp (30-50 g),

Cyprinus carpio

- - 12 hr 125% increased serum

cortisol

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 24 hr 300% increased serum

cortisol

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 6 hr 40% increased serum

cortisol

500 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 12 hr 60% increased serum

cortisol

500 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 24 hr 250% increased serum

cortisol

500 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 12 hr 60% increased serum

glucose

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 24 hr 35% increased serum

glucose

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 6 hr 15% increased serum

glucose

500 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 12 hr 40% increased serum

glucose

500 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 24 hr 70% increased serum

glucose

500 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 72 hr 180% increased serum

glucose; 40%

decreased liver glycogen

1,000 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 4 hr 25% increase in gill

total ATPase activity;

20% increase in gill

Na-K dependent ATPase

100 Hanke et al. 1983
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

105

Common carp (30-50 g),

Cyprinus carpio

- - 6 hr 10% increase in gill

total ATPase; 30%

decrease in gill Na-K

dependent ATPase

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 12 hr 40% decrease in gill

total ATPase;

30%decrease in gill

Na-K dependent ATPase

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 24 hr 5% decrease in gill

total ATPase; 25%

decrease in gill Na-K

dependent ATPase

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 4 hr 60% increase in serum

AChE

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 6 hr 15% increase in serum

AChE

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 12 hr 35% increase in serum

AChE

100 Hanke et al. 1983

Common carp (30-50 g),

Cyprinus carpio

- - 24 hr 25% decrease in serum

AChE

100 Hanke et al. 1983

Common carp,

Cyprinus carpio

- - 72 hr Increased serum glucose

and cortisol; decreased

liver and muscle

glycogen; decreased

serum protein and

cholesterol

100 Gluth and Hanke 1984,

1985

Common carp (juvenile),

Cyprinus carpio

99.3% - 48 hr LC50 16,100 Pluta 1989

Common carp (juvenile),

Cyprinus carpio

93.7% 141-223 96 hr

(fed)

LC50 18,800 Neskovic et al. 1993

Common carp (juvenile),

Cyprinus carpio

93.7% 141-223 14 days Increased serum alkaline

phosphatase; decreased

alkaline phosphatase in

heart, liver and kidneys;

increased GPT in liver

and kidneys; hyperplasia

of some gill epithelial

cells

1,500 Neskovic et al. 1993

Common carp (50-60 g),

Cyprinus carpio

94% - 14 days NOEC 

(gill, liver, and kidney

histopathology)

1,500 Poleksic et al. 1997

Fathead minnow (#24h),

Pimephales promelas

97 60 7 days NOEC

(biomass)

$4,900 Jop 1991b
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

106

Fathead minnow (larvae),

Pimephales promelas

85% - 7 No effect upon survival 75 Detenbeck et al. 1996

Fathead minnow (juvenile),

Pimephales promelas

85% - 13 days No effect upon survival

or growth

75 Detenbeck et al. 1996

Channel catfish (embryo),

Ictalurus punctatus

80% 50 4.5 days

(at

hatching)

LC50 272 Birge et al. 1979

Channel catfish (embryo),

Ictalurus punctatus

80% 200 4.5 days

(at

hatching)

LC50 248 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 50 8.5 days

(4 days

post-hatch)

LC50 176 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 200 8.5 days

(4 days

post-hatch)

LC50 192 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 50 8.5 days

(4 days

post-hatch)

1% teratic larvae 22.4 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 50 8.5 days

(4 days

post-hatch)

4% teratic larvae 47.2 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 50 8.5 days

(4 days

post-hatch)

13% teratic larvae 344 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 50 8.5 days

(4 days

post-hatch)

69% teratic larvae 3,864 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 50 8.5 days

(4 days

post-hatch)

100% teratic larvae 37,360 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 200 8.5 days

(4 days

post-hatch)

1% teratic larvae 26.4 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 200 8.5 days

(4 days

post-hatch)

4% teratic larvae 43.2 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 200 8.5 days

(4 days

post-hatch)

16% teratic larvae 336 Birge et al. 1979
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

107

Channel catfish (sac fry),

Ictalurus punctatus

80% 200 8.5 days

(4 days

post-hatch)

47% teratic larvae 3,848 Birge et al. 1979

Channel catfish (sac fry),

Ictalurus punctatus

80% 200 8.5 days

(4 days

post-hatch)

86% teratic larvae 37,360 Birge et al. 1979

Mosquitofish,

Gambusia affinis

Technical - 48 hr No mortality 10,000 Darwazeh and Mulla 

1974

Guppy,

Poecilia reticulata

- - 48 hr LC50 38,200 Tscheu-Schluter 1976

Guppy,

Poecilia reticulata

- - 72 hr LC50 31,600 Tscheu-Schluter 1976

Guppy,

Poecilia reticulata

- - 96 hr 40%

mortality

28,600 Bogacka et al. 1990

Guppy,

Poecilia reticulata

- - 96 hr 53.2%

mortality

37,200 Bogacka et al. 1990

Mozambique tilapia,

Tilapia mossambica

- - 90 days Decreased red and white

blood cell counts,

hemoglobin, packed cell

volume, mean

corpuscular hemoglobin;

decreased whole animal

oxygen consumption;

increased mean cell

volume, blood volume

and blood water content

1,100 Prasad et al. 1991a

Mozambique tilapia,

Tilapia mossambica

- - 30 days Changed enzyme

activity and levels of

amino acids, proteins,

ammonia, and urea in

brain and liver

1,100 Prasad et al. 1991b

Mozambique tilapia,

Tilapia mossambica

- - 30 days Increased lipase activity,

free fatty acids,

acetoacetate

concentration, and total

cholesterol in liver and

muscle; decreased total

lipids, glycerol and

phospholipids in liver

and muscle.

1,100 Srinivas et al. 1991

Mozambique tilapia,

Tilapia mossambicus

- - 90 days Increased body weight,

percent water, serum

Na+

 and serum K+;

decreased serum Ca++, 

Mg++ and HCO3

-

1,100 Prasad and Reddy 1994
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

108

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 8 days

(4 days

post-hatch)

LC1 7.4 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 8 days

(4 days

post-hatch)

LC10 44.9 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 8 days

(4 days

post-hatch)

LC50 410 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 4 days

(to hatch)

1% teratic surviving

larvae

51 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 4 days

(to hatch)

3% teratic surviving

larvae

410 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 4 days

(to hatch)

7% teratic surviving

larvae

6,330 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 4 days

(to hatch)

22% teratic surviving

larvae

14,800 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 4 days

(to hatch)

47% teratic surviving

larvae

26,400 Birge et al. 1980

Bullfrog (embryo and

tadpole),

Rana catesbeiana

80% 113 4 days

(to hatch)

100% teratic surviving

larvae

45,800 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 9 days

(4 days

post-hatch)

LC1 32.6 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 9 days

(4 days

post-hatch)

LC10 378.9 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 9 days

(4 days

post-hatch)

LC50 7,680 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 5 days

(to hatch)

2% teratic

surviving larvae

110 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 5 days

(to hatch)

2% teratic

surviving larvae

210 Birge et al. 1980
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

109

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 5 days

(to hatch)

5% teratic

surviving larvae

1,113 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 5 days

(to hatch)

9% teratic 

surviving larvae

6,540 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 5 days

(to hatch)

13% teratic surviving

larvae

13,200 Birge et al. 1980

Leopard frog (embryo and

tadpole),

Rana pipiens

80% 115 5 days

(to hatch)

46% teratic surviving

larvae

48,700 Birge et al. 1980

Leopard frog (tadpole),

Rana pipiens

85% - 41 days No effect upon growth

or survival

25 Detenbeck et al. 1996

Pickerel frog (embryo and

tadpole),

Rana palustris

80% 103 8 days

(4 days

post-hatch)

LC50 17,960 Birge et al. 1980

Pickerel frog (embryo and

tadpole),

Rana palustris

80% 103 4 days

(to hatch)

2% teratic

surviving larvae

10,400 Birge et al. 1980

Pickerel frog (embryo and

tadpole),

Rana palustris

80% 103 4 days

(to hatch)

5% teratic surviving

larvae

20,600 Birge et al. 1980

Pickerel frog (embryo and

tadpole),

Rana palustris

80% 103 4 days

(to hatch)

18% teratic surviving

larvae

33,900 Birge et al. 1980

American toad (embryo

and tadpole),

Bufo americanus

80% - 7 days

(4 days

post-hatch)

LC50 >48,000 Birge et al. 1980

American toad (embryo

and tadpole),

Bufo americanus

80% - 3 days

(to hatch)

2% teratic surviving

larvae

490 Birge et al. 1980

American toad (embryo

and tadpole),

Bufo americanus

80% - 3 days

(to hatch)

2% teratic surviving

larvae

5,560 Birge et al. 1980

American toad (embryo

and tadpole),

Bufo americanus

80% - 3 days

(to hatch)

3% teratic surviving

larvae

10,800 Birge et al. 1980

American toad (embryo

and tadpole),

Bufo americanus

80% - 3 days

(to hatch)

6% teratic surviving

larvae

24,800 Birge et al. 1980
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

110

American toad (embryo

and tadpole),

Bufo americanus

80% - 3 days

(to hatch)

17% teratic surviving

larvae

48,200 Birge et al. 1980

African clawed frog

(embryo),

Xenopus laevis

40.8% - 96 hr 100% abnormal

embryos

8,000 Morgan et al. 1996

African clawed frog

(embryo),

Xenopus laevis

40.8% - 96 hr LC50 126,000 Morgan et al. 1996

African clawed frog

(embryo),

Xenopus laevis

40.8% - 96 hr LOEC

(teratogenesis)

1,100 Morgan et al. 1996

Tiger salamander,

Ambystoma tigrinum

- 333 86 days Stimulated plasma

thyroxine; delayed

development - retarded

growth

82 Larson et al. 1998

American alligator,

Alligator mississippiensis

99% - 15 min 50% inhibition of (3

H)

17-estradiol binding

4,465 Vonier et al. 1996

Stream mixed

algal species

80% - 1 day to 3

wk

39-78% reduction in

gross productivity

10 Kosinski et al. 1985;

Kosinski and Merkle

1984

Stream mixed

algal species

80% - 3 days Reduced net primary

productivity

100 Moorhead and Kosinski

1986

Experimental stream

periphyton community

80% - 14 days Severe population

density reductions in

several species; total

destruction of

Cladophora glomerata

1,000 Kosinski 1984

Stream mixed 

community

Technical 164-202 30 days No effect upon

macroinvertebrate

community structure,

periphyton production or

biomass, and

community P/R ratio

25 Lynch et al. 1985

Experimental laboratory

stream community

96.5 - 2 wk Decreased diurnal

fluctuation and mean

values for pH and

dissolved oxygen;

increased nitrate

nitrogen; parameters

rapidly returned to

control levels when

treatment ended

100 Malanchuk and Kollig

1985

Stream aufwuchs

community

- - 12 days 4% biomass reduction at

10°C

24 Krieger et al. 1988
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

111

Stream aufwuchs

community

- - 12 days 24% biomass reduction;

30% chlorophyll-a

reduction at 25°C

24 Krieger et al. 1988

Stream aufwuchs

community

- - 12 days 47% biomass reduction;

40% chlorophyll-a

reduction at 10°C

134 Krieger et al. 1988

Stream aufwuchs

community

- - 12 days 31% biomass reduction;

44% chlorophyll-a

reduction at 25°C

134 Krieger et al. 1988

Natural stream 

periphyton community

98% - 24 hr No effect upon algal cell

numbers or biomass

77.5 Jurgenson and Hoagland

1990

Natural stream 

plankton community

Commercial

product

- 6 mo Initial decrease in

phytoplankton species (6

wks) followed by a

recovery

0.5 Lakshminarayana et al.

1992

Stream algal and benthic

invertebrate community

90% - 14 days No effect upon attached

algal chlorophyll-a

concentrations or

benthic invertebrate

populations

5 Gruessner and Watzin

1996

Artificial stream 

periphyton community

- - 30 days Community

photosynthesis inhibited

100 Pearson and Crossland

1996

Pond microcosm,

(static system)

98.2% - 7 days No effect upon diurnal

oxygen production

5.0 Brockway et al. 1984

Pond microcosm,

(static system)

98.2% - 12 days 25-30% decreased

oxygen production

50 Brockway et al. 1984

Pond microcosm,

(static system)

98.2% - 7 days 40-50% decreased

diurnal oxygen

production

100 Brockway et al. 1984

Pond microcosm,

(static system)

98.2% - 12 days 90% decreased diurnal

oxygen production

500 Brockway et al. 1984

Pond microcosm,

(static system)

98.2% - 12 days 100% inhibition of

diurnal oxygen

production

5,000 Brockway et al. 1984

Pond microcosm,

(static system)

Technical - 40 days NOEC (chlorophyll-a) 2,000 Diana et al. 2000

Pond microcosm,

(static system)

Technical - 40 days NOEC 

(macrophyte biomass)

20 Diana et al. 2000

Pond microcosm,

(static system)

Technical - 40 days NOEC (gray tree frog,

Hyla versicolor growth)

20 Diana et al. 2000
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

112

Lake microcosm 

plankton community

98% - 10-21 days Seasonal and speciesdependent effects;

growth generally

stimulated for

Chryptophytes and

Chrysophytes, but

inhibited in Chlorella

vulgaris

10 Berard et al. 1999

Freshwater microcosm - - 7 wk No effects upon species

composition of

phytoplankton,

zooplankton or benthic

macroinvertebrates;

slight decrease in

photosynthetic activity

5.1 Van den Brink 1995

Periphyton-dominated 

microcosm

96.5% - 1 day 77% decrease in daily

net productivity

100 Hamala and Kollig 1985

Periphyton-dominated 

microcosm

96.5% - 14 days 75% decrease in P/R

ratio

100 Hamala and Kollig 1985

Phytoplankton,

zooplankton and benthos

microcosm

- - 60 days Reduced 14C

uptake/chlorophyll-a

ratio

43.8 Stay et al. 1985

Phytoplankton,

zooplankton and benthos

microcosm

- - 25 days Reduced net primary

productivity 

50 Stay et al. 1985

Pond mesocosm 

community

- - 70 days Changed population

densities of zooplankton

(rotifers, crustaceans and

insect larvae)

200 Peichl et al. 1984

Pond mesocosm 

community

- - 121 days Changed phytoplankton

community

composition; increased

rotifer population

10 Peichl et al. 1985

Pond mesocosm

community

41% - 805 days Reduced phytoplankton

production and biomass,

macrophyte,

populations, and

populations of benthic

insect grazers, Rana

catesbiana tadpoles,

grass carp and bluegills

20 deNoyelles et al. 1982,

1989, 1994

Pond mesocosm

community

41% - 4 yr single

annual

application

Reduced photosynthesis

in 24 hr bioassays,

followed by recovery in

20-day bioassays and

long-term pond studies

20-500 deNoyelles and Kettle

1985
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

113

Pond mesocosm

community

97% - 9-112 days Significant reductions of

herbivorous benthic

insect species richness,

abundance, and total

insect emergence (89%),

shift to earlier

emergence for some

herbivorous species;

destabilization of

ecosystem

20n Dewey 1986; Dewey and

deNoyelles 1994 

Pond mesocosm

community

97% - 9-112 days Significant reductions of

herbivorous benthic

insect species richness,

abundance, and total

insect emergence (95%),

shift to earlier

emergence for some

herbivorous species;

reduced species

evenness; destabilization

of ecosystem

100n Dewey 1986; Dewey and

deNoyelles 1994 

Pond mesocosm

community

97% - 9-112 days Significant reductions of

herbivorous benthic

insect species richness,

abundance, and total

insect emergence (85%),

shift to earlier

emergence for some

herbivourous species;

reduced species

evenness; destabilization

of ecosystem

500n Dewey 1986; Dewey and

de Noyelles 1994

Pond mesocosm

community

40.8% - 8 wk Altered macrophyte

community species

composition; no effects

upon primary

productivity, total plant

biomass, zooplankton or

fish

50 Fairchild et al. 1994a

Pond mesocosm 

plankton community

- - 2 mo No effect 5 Juttner et al. 1995

Pond mesocosm 

plankton community

- - 2 mo Decreased O2, pH and

conductivity

10 Juttner et al. 1995

Pond mesocosm 

plankton community

- - 2 mo Decreased

phytoplankton

populations

182 Juttner et al. 1995
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

114

Pond mesocosm 

plankton community

- - 2 mo Reduced peak egg ratios

in Daphnia longispina

and elimination of

Polyarthra sp. rotifers

318 Juttner et al. 1995

Pond microbial microcosm

community

98.6% 70 21 days NOEC for

concentrations of Mg,

Ca and dissolved

oxygen

10 Pratt et al. 1988

Pond microbial microcosm

community 

98.6% 70 21 days MATC for

concentrations of Mg,

Ca and dissolved

oxygen

17.9 Pratt et al. 1988

Pond microbial microcosm

community 

98.6% 70 21 days LOEC for

concentrations of Mg,

Ca and dissolved

oxygen

32.0 Pratt et al. 1988

Pond microbial microcosm

community

98.6% 70 21 days NOEC for protozoan

colonization, biomass

protein, chlorophyll-a,

and potassium

concentration

110 Pratt et al. 1988

Pond microbial microcosm

community

98.6% 70 21 days MATC for protozoan

colonization, biomass

protein, chlorophyll-a,

and potassium

concentration

193 Pratt et al. 1988

Pond microbial microcosm

community

98.6% 70 21 days LOEC

for protozoan

colonization, biomass

protein, chlorophyll-a

and potassium

concentration

337 Pratt et al. 1988

Phyto- and zooplankton

microcosm community

- - 42 days No or little effect upon

net primary

productivity, P/R ratio,

and pH

15 Stay et al. 1989

Phyto- and zooplankton

microcosm community

- - 42 days Reduced net primary

productivity, P/R ratio,

and pH

84 Stay et al. 1989

Experimental pond

community

- - 39 days

after

treatment

EC50 

(

14C uptake)

96 Larsen et al. 1986

Experimental pond

community

- - 43 days

after

treatment

EC50

(

14C uptake)

131 Larsen et al. 1986
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

115

Experimental pond

community

- - 101 days

after

treatment

EC50

(

14C uptake)

109 Larsen et al. 1986

Experimental pond

community

- - 177 days

after

treatment 

EC50

(

14C uptake)

24 Larsen et al. 1986

Experimental pond

community

- - 249 days

after

treatment

EC50

(

14C uptake)

27 Larsen et al. 1986

Experimental pond

community

- - 259 days

after

treatment

EC50

(

14C uptake)

37 Larsen et al. 1986

Experimental pond

community

- - 373 days

after

treatment

EC50 

(

14C uptake)

100 Larsen et al. 1986

Mixed pond 

community

99.2% - 4 mo Elimination of Lemna

minor population

60-120 Gunkel 1983

Mixed pond 

community

99.2% - 4 mo Rapid succession of

algal species; reduced

reproduction rate in

Daphnia pulicaria

60-120 Gunkel 1983

Pond mesocosm

community

99% - 2 yr Decreased green algal

species, cell numbers

and cladoceran

populations; increased

cryptomonad cell

numbers

20 Neugebauer et al. 1990

Pond mesocosm

community

99% - 2 yr Decreased green algal

species, cell numbers

and cladoceran

populations; increased

cryptomonad cell

numbers

100 Neugebauer et al. 1990

Pond mesocosm

community

99% - 2 yr Decreased green algal

species, cell numbers

and cladoceran

populations; increased

cryptomonad cell

numbers

300 Neugebauer et al. 1990
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

116

Pond mesocosm

community

Reagent

grade

- 2 yr Atrazine applied in May

and June each year:

decreased abundance of

Endochironomus

nigricans in June and of

total macroinvertebrates in both May and

June, followed by

recovery in July;

epiphytes decreased in

abundance in June,

followed by recovery in

July; detritovore

abundance decreased in

May, followed by

recovery in June; 

generalists decreased in

May and June, followed

by recovery in July

20 Huggins et al. 1994

Pond mesocosm

community

Reagent

grade

- 2 yr Results similar to those

at 20 μg/L in May and

June; Caenis sp.

significantly increased

in July; also increased

abundance of Caenis

sp., total macroinvertebrates, detritovores and

generalists in late July

100 Huggins et al. 1994

Pond mesocosm

community

Reagent

grade

- 2 yr Results similar to those

at 20 and 100 :g/L in

May and June: Caenis

sp. were significantly

reduced in abundance in

early July but not in late

July; the abundance of

epiphytes decreased,

while the abundance of

total macroinvertebrates and generalists

increased in late July

500 Huggins et al. 1994

Mixed algae 

from pond

- - >3 hr Increased fluorescence

rate for photosystem II

10 Ruth 1996

Lake limnocorral

community

80% - 34 days Reduced periphyton ashfree dry weight80-140 Herman et al. 1986

Lake limnocorral

community

80% - 9 wk 

(2

applications

6 weeks

apart)

36-67% reduction in

chlorophyll-a, organic

matter, and total periphyton algal biomass

80-140

(first

application);

110-190

(second

application)

Herman et al. 1986
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

117

Lake limnocorral

periphyton community

80% - 50 days 50% reduction in ashfree dry weight80 Hamilton et al. 1987

Lake limnocorral

periphyton community

80% - 230 days Reductions of 60% in

biomass, 22% in cell

numbers, and 32% in

number of species

80 Hamilton et al. 1987

Lake limnocorral

periphyton community

80% - 56 days Reductions of 50% in

chlorophyll-a, 32% in

biomass, 14% in cell

numbers, and 33% in

number of species

140 Hamilton et al. 1987

Lake limnocorral

periphyton community

80% - 56 days Reductions of 55% in

chlorophyll-a, 68% in

biomass, 19% in cell

numbers, and 48% in

number of species

1,560 Hamilton et al. 1987

Lake limnocorral

community

80% - Two

exposures

35 days

apart

Different phytoplankton

species assemblages for

up to 114 days after

second application;

increased Secchi disc

readings and decreased

levels of dissolved

oxygen, chlorophyll, and

organic carbon; phytoplankton communities

were similar by day 323.

100 

(1st applic.) 155 

(2nd applic.)

Hamilton et al. 1988,

1989

Lake mesocosm plankton

community

- - 18 days Decreased chlorophyl-a,

dissolved oxygen,

nauplii, Daphnia,

Cyclops; increased

particulate organic

carbon 

1 Lampert et al. 1989

Lake mesocosm plankton

community

- - 10 dayso Decreased algal

photosynthetic

production, dissolved

oxygen and Daphnia

population; apparent

recoveries after about 25

days

0.1 Lampert et al. 1989

Lake bacterial and algal

species in microcosm study

- - - Decreased algal

population density and

decreased "scope for

change in ascendance"

of community

250 Genoni 1992
Table 6 (Continued)

Species Chemical

Hardness

(mg/L as 

 CaCO3) Duration Effect

Concentration

 (μg/L) Reference 

FRESHWATER SPECIES

118

Lake mesocosm 

community

- - 20 days No effect upon tolerance

to atrazine by

phytoplankton and

periphyton communities

or upon length of

Cladocera; minor

changes in species

composition, POC/PON

ratio and chlorophyll

concentration

20 Gustavson and Wangberg

1995

Lake mesocosm 

phytoplankton community

- - 20 days EC50 58 Gustavson and Wangberg

1995

Lake mesocosm 

phytoplankton community

- - 20 days EC50 52 Gustavson and Wangberg

1995

Lake mesocosm 

periphyton community

- - 20 days EC50 52 Gustavson and Wangberg

1995

Lake mesocosm 

periphyton community

- - 20 days EC50 54 Gustavson and Wangberg

1995

Lake phytoplankton - - 3 hr EC50

(carbon assimilation)

100 Brown and Lean 1995

Lake phytoplankton - - 3 hr EC50

(phosphate assimilation)

14,000 Brown and Lean 1995

Lake phytoplankton - - 3 hr EC50

(ammonium

assimilation)

>33,000 Brown and Lean 1995

Stream 

periphyton community

85.5% - <4 hr LOEC

(chlorophyll-a)

109 Day 1993

Stream 

phytoplankton community

- - Spring

season

Reduction in

populations of green

algae

40.4

maximum

Caux and Kent 1995

Wetland 

mesocosm community

85% - 9-27 days Decreased periphyton

gross productivity;

increased dissolved

nutrients

15 Detenbeck et al. 1996
119

Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

Green alga,

Chlamydomonas sp.

- 30 90 min EC50

(oxygen evolution)

60 Hollister and Walsh 1973

Green alga,

Chlorella sp.

- 30 90 min EC50 

(oxygen evolution

143 Hollister and Walsh 1973

Green alga,

Chlorococcum sp.

Technical 30 90 min EC50

(oxygen evolution)

100 Walsh 1972

Green alga,

Chlorococcum sp.

80.0% 30 90 min EC50

(oxygen evolution)

400 Walsh 1972

Green alga,

Chlorococcum sp.

Technical 30 90 min EC100

(oxygen evolution)

400 Walsh 1972

Green alga,

Chlorococcum sp.

80.0% 30 90 min EC100

(oxygen evolution)

800 Walsh 1972

Green alga,

Chlorococcum sp.

Technical 30 10 days EC50

(growth)

100 Walsh 1972

Green alga,

Chlorococcum sp.

80.0 30 10 days EC50

(growth)

100 Walsh 1972

Green alga,

Chlorococcum sp.

Technical 30 10 days EC100

(growth)

500 Walsh 1972

Green alga,

Chlorococcum sp.

80.0% 30 10 days EC100

(growth)

500 Walsh 1972

Green alga,

Chlorococcum sp.

- 30 90 min EC50

(oxygen evolution)

80 Hollister and Walsh 1973

Green alga,

Dunaliella tertiolecta

Technical 30 90 min EC50

(oxygen evolution)

300 Walsh 1972

Green alga,

Dunaliella tertiolecta

80.0% 30 90 min EC50

(oxygen evolution)

600 Walsh 1972

Green alga,

Dunaliella tertiolecta

Technical 30 90 min EC100

(oxygen evolution)

700 Walsh 1972

Green alga,

Dunaliella tertiolecta

80.0% 30 90 min EC100

(oxygen evolution)

1,000 Walsh 1972

Green alga,

Dunaliella tertiolecta

Technical 30 10 days EC50

(growth)

300 Walsh 1972

Green alga,

Dunaliella tertiolecta

80.0% 30 10 days EC50

(growth)

400 Walsh 1972

Green alga,

Dunaliella tertiolecta

Technical 30 10 days EC100

(growth)

1,200 Walsh 1972

Green alga,

Dunaliella tertiolecta

80.0% 30 10 days EC100

(growth)

1,500 Walsh 1972

Green alga,

Dunaliella tertiolecta

- 30 90 min EC50

(oxygen evolution)

159 Hollister and Walsh 1973
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

120

Green alga,

Dunaliella tertiolecta

97% - 5 days EC50

(cell number)

170 Hughes 1986; Hughes et 

al. 1986, 1988

Green alga,

Dunaliella tertiolecta

97% - 5 day

exposure,

9 day

recovery

NOEC

(cell numbers)

< 100 Hughes 1986; Hughes et 

al. 1986, 1988

Green alga,

Dunaliella tertiolecta

97% - 5 day

exposure,

9 day

recovery

Algistatic concentration 1,450 Hughes 1986; Hughes et 

al. 1986, 1988

Green alga,

Dunaliella tertiolecta

97% - 5 day

exposure,

9 day

recovery

Algicidal concentration >3,200 Hughes 1986; Hughes et 

al. 1986, 1988

Green alga,

Dunaliella tertiolecta

- - 15 min EC50

(oxygen evolution)

270 Samson and Popovic

1988

Green alga,

Dunaliella tertiolecta

- - 15 min EC50

(complementary area)

37 Samson and Popovic

1988

Green alga,

Dunaliella tertiolecta

- - 96 hr EC50

(cell number)

132 Gaggi et al. 1995

Green alga,

Dunaliella bioculata

Technical - 48 hr 35% reduction in growth 216 Felix et al. 1988

Green alga,

Dunaliella bioculata

Technical - 48 hr 85% reduction in growth 3,240 Felix et al. 1988

Green alga,

Dunaliella bioculata

Technical - 48 hr 100% growth inhibition 21,570 Felix et al. 1988

Green alga,

Nannochloris oculata

- 15 7 days 21% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 11% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 12% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 34% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 35% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 33% change in doubling

time

50 Karlander et al. 1983;

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 42% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 35% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

121

Green alga,

Nannochloris oculata

- 15 7 days 28% change in doubling

time

50 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 46% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 35% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 21% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 59% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 52% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 47% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 57% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 56% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days 54% change in doubling

time

100 Karlander et al. 1983; 

Mayasich et al. 1986

Green alga,

Nannochloris oculata

- 15 7 days change in doubling time 15 Mayasich et al. 1987

Green alga,

Neochloris sp.

- 30 90 min EC50

(oxygen evolution)

82 Hollister and Walsh 1973

Green alga,

Platymonas sp.

- 30 90 min EC50

(oxygen evolution)

102 Hollister and Walsh 1973

Diatom,

Achnanthes brevipes

- 30 90 min EC50

(oxygen evolution)

93 Hollister and Walsh 1973

Diatom,

Amphora exigua

- 30 90 min EC50

(oxygen evolution)

300 Hollister and Walsh 1973

Diatom,

Cyclotella nanna

- 30 90 min EC50

(oxygen evolution)

84 Hollister and Walsh 1973

Diatom,

Isochrysis galbana

Technical 30 90 min EC50

(oxygen evolution)

100 Walsh 1972

Diatom,

Isochrysis galbana

80.0% 30 90 min EC50

(oxygen evolution)

200 Walsh 1972

Diatom,

Isochrysis galbana

Technical 30 90 min EC100

(oxygen evolution)

200 Walsh 1972

Diatom,

Isochrysis galbana

80.0% 30 90 min EC100

(oxygen evolution)

500 Walsh 1972
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

122

Diatom,

Isochrysis galbana

Technical 30 10 days EC50

(growth)

100 Walsh 1972

Diatom,

Isochrysis galbana

80.0% 30 10 days EC50

(growth)

100 Walsh 1972

Diatom,

Isochrysis galbana

Technical 30 10 days EC100

(growth)

200 Walsh 1972

Diatom,

Isochrysis galbana

80.0% 30 10 days EC100

(growth)

200 Walsh 1972

Diatom,

Isochrysis galbana

- 30 90 min EC50

(oxygen evolution)

100 Hollister and Walsh 1973

Diatom,

Minutocellus polymorphus

- - 72 hr EC50

(cell numbers)

50 Walsh et al. 1988

Diatom,

Monochrysis lutheri

- 30 90 min EC50

(oxygen evolution)

77 Hollister and Walsh 1973

Diatom,

Navicula inserta

- 30 90 min EC50

(oxygen evolution)

460 Hollister and Walsh 1973

Diatom,

Nitzschia closterium

- 30 90 min EC50

(oxygen evolution)

287 Hollister and Walsh 1973

Diatom,

Nitzschia (Ind. 684)

- 30 90 min EC50

(oxygen evolution)

434 Hollister and Walsh 1973

Diatom,

Nitzschia sigma

- 20 7 days Reduced photosynthesis 220 Plumley and Davis 1980

Diatom,

Nitzschia sigma

- 20 7 days Reduced chlorophyll

and cell number

2,200 Plumley and Davis 1980

Diatom,

Phaeodactylum

tricornutum

Technical 30 90 min EC50

(oxygen evolution)

100 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

80.0% 30 90 min EC50

(oxygen evolution)

200 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

Technical 30 90 min EC100

(oxygen evolution)

200 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

80.0% 30 90 min EC100

(oxygen evolution)

600 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

Technical 30 10 days EC50

(growth)

200 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

80.0% 30 10 days EC50

(growth)

200 Walsh 1972
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

123

Diatom,

Phaeodactylum

tricornutum

Technical 30 10 days EC100

(growth)

500 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

80.0% 30 10 days EC100

(growth)

500 Walsh 1972

Diatom,

Phaeodactylum

tricornutum

- 30 90 min EC50

(oxygen evolution)

100 Hollister and Walsh 1973

Diatom,

Phaeodactylum

tricornutum

- - 7 days Limited effect on

doubling time

50 Mayasich et al. 1987

Diatom,

Skeletonema costatum

- - 48 hr EC50

(cell numbers)

20 Walsh et al. 1988

Diatom,

Stauroneis amphoroides

- 30 90 min EC50

(oxygen evolution)

348 Hollister and Walsh 1973

Diatom,

Thalassiosira fluviatilis

- 20 7 days Reduced chlorophyll 220 Plumley and Davis 1980

Diatom,

Thalassiosira fluviatilis

- 20 7 days Reduced cell number

and photosynthesis

2,200 Plumley and Davis 1980

Diatom,

Thalassiosira fluviatilis

- 30 90 min EC50

(oxygen evolution)

110 Hollister and Walsh 1973

Red alga,

Porphyridium cruentum

- 30 90 min EC50

(oxygen evolution)

79 Hollister and Walsh 1973

Kelp,

Laminaria hyperborea

- - 28 days LOEC

(growth of new

sporophytes)

10 Hopkins and Kain 1971

Kelp,

Laminaria hyperborea

- - 24 hr LOEC

(respiration)

>1,000 Hopkins and Kain 1971

Kelp,

Laminaria saccharina

70% 30 2 days No effect on sexual

reproduction

33.2 Thursby and Tagliabue

1990

Kelp,

Laminaria saccharina

70% 30 2 days 66% reduction in

fertilization

72.2 Thursby and Tagliabue

1990

Redheadgrass pondweed,

Potamogeton perfoliatus

- 8-12 2 hr IC50 (photosynthesis) 77 Jones and Winchell 1984

Redheadgrass pondweed,

Potamogeton perfoliatus

99.7% 10 4 hr IC50 (photosynthesis) 80 Jones et al. 1986

Euraisian watermilfoil,

Myriophyllum spicatum

- 8-12 2 hr IC50 (photosynthesis) 104 Jones and Winchell 1984

Aquatic vascular plant,

Zannichellia palustris

- 8-12 2 hr IC50 (photosynthesis) 91 Jones and Winchell 1984
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

124

Widgeon grass,

Ruppia maritima

- 8-12 2 hr IC50 (photosynthesis) 120 Jones and Winchell 1984

Vallisneria,

Vallisneria americana

- 3 42 days 47% decrease in growth

as length, and 48%

decrease as dry weight

100 Forney 1980; Forney and 

Davis 1981

Vallisneria,

Vallisneria americana

- 6 42 days 27% decrease in growth

as length, and 30%

decrease as dry weight

100 Forney 1980; Forney and 

Davis 1981

Vallisneria,

Vallisneria americana

- 3 42 days 27% decreased in

growth as length, and

41% decrease as dry

weight

320 Forney 1980; Forney and 

Davis 1981

Vallisneria,

Vallisneria americana

- 6 42 days 32% decrease in growth

as length, and 29%

decrease as dry weight

320 Forney 1980; Forney and 

Davis 1981

Vallisneria,

Vallisneria americana

- 5 47 days 67% reduction in leaf

production & 76%

reduction in leaf area

12 Correll and Wu 1982

Eelgrass,

Zostera marina

- - 24 hr Reduced net oxygen

evolution

100 Kemp et al. 1982a

Eelgrass,

Zostera marina

- - 24 hr No net oxygen evolution 1,000 Kemp et al. 1982a

Eelgrass,

Zostera marina

97.2% 14 10 days 100% growth inhibition 1,900 Schwarzchild et al. 1994

Turtlegrass,

Thalassia testudinum

Technical

99.7%

30 40 hr EC50 (photosynthesis) 320 Walsh et al. 1982

Salt-marsh grass,

Spartina alterniflora

97.1% - 35 days Increased peroxidase

activity

30 Lytle and Lytle 1998

Salt-march grass,

Spartina alterniflora

97.1% - 35 days No effect upon shoot

growth, lipid

peroxidation products or

chlorophyll production;

enhanced peroxidase

activity

3,100 Lytle and Lytle 1988

Salt-marsh rush,

Juncus roemerianus

97.1% - 35 days Reduced chlorophyl-a;

Increased peroxidase

activity and lipid

peroxidation products

30 Lytle and Lytle 1998

Salt-marsh rush,

Juncus roemerianus

97.1% - 35 days Reduced shoot growth,

chlorophyll-a,

chlorophyll-a; increased

lipid peroxidation

products

3,800 Lytle and Lytle 1998
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

125

Eastern oyster (juvenile),

Crassostrea virginica

Technical

99.7%

28 96 hr EC50

(shell growth) 

>1,000 Butler 1964; Mayer 1987

Copepod,

Acartia tonsa

97.1% 30-34 72 hr LC50 6,100 McNamara 1991b

Copepod,

Acartia tonsa

97.1% 30-34 48 hr LC50 8,400 McNamara 1991b

Copepod,

Acartia tonsa

97.1% 30-34 24 hr LC50 15,000 McNamara 1991b

Brown shrimp (juvenile),

Penaeus aztecus

Technical

99.7%

30 48 hr EC50 1,000 Mayer 1987

Brown shrimp,

Penaeus aztecus

- - 24 hr 20% mortality 1,000 Butler 1964

Brown shrimp,

Penaeus aztecus

- - 48 hr 30% mortality 1,000 Butler 1964

Mud crab (field),

Panopeus sp.

80% - 70 days No effect on number per

m2

 after a single

application

10,000,000 Plumley et al. 1980

Drift line crab (field),

Sesarma cinereum

80% - 70 days No effect on number per

m2

 after a single

application

10,000,000 Plumley et al. 1980

Fiddler crab (field),

Uca pugnax

80% - 70 days No effect on number per

m2

 after a single

application

1,000,000 Plumley et al. 1980

Fiddler crab (field),

Uca pugnax

80% - 70 days 94% reduction in

number per m2

 relative

to control after a single

application

10,000,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August)

80% 20 8 days 25% mortality of large

males; 

100% mortality of large

females;

100% mortality of small

males;

75% mortality of small

females

100,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1977)

80% 20 8 days 50% mortality of large

males;

100% mortality of large

females;

75% mortality of small

males,

50% mortality of small

females

1,000,000 Plumley et al. 1980
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

126

Fiddler crab,

Uca pugnax

(animals collected in

November)

80% 20 30 days No effect on survival of

small males

1,000,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

March)

80% 20 9 days No effect on survival of

small males

1,000,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1978)

80% 20 9 days 60% mortality 100,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1978)

80% 20 9 days 90% mortality 180,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1978)

80% 20 9 days 80% mortality 320,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1978)

80% 20 9 days 90% mortality 560,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1978)

80% 20 9 days 90% mortality 1,000,000 Plumley et al. 1980

Fiddler crab,

Uca pugnax

(animals collected in

August 1978)

80% 20 9 days 100% mortality 10,000,000 Plumley et al. 1980

Spot (juvenile),

Leiostomas santhurus

Technical

99.7%

29 48 hr LC50 >1,000 Butler 1964; Mayer 1987

Estuarine microbial 

community

- 7-25 9 days Effects on phototrophic

component: chlorophylla, carbon assimilation,

biovolume, and changes

in species composition

40 DeLorenzo et al. 1999a
Table 6 (continued)

Species Chemical

Salinity

 (g/kg) Duration Effect

Concentration

 (μg/L) Reference 

SALTWATER SPECIES

127

Estuarine microbial 

community

97% - 24 hr Effects on phototrophic

component: 

chlorophyll-a, carbon

assimilation, and

biovolume

47 DeLorenzo et al. 1999b

Mesocosm,

Mixed marine

phytoplankton

Residue

grade

- 15 days Reduced pH, particulate

carbohydrates,

chlorophyll,

photosynthesis, primary

production; increased

dissolved organic

phosphorus, dissolved

organic nitrogen, and

dissolved amino acids

0.12 Bester et al. 1995

Mesocosm,

Mixed marine

phytoplankton

Residue

grade

- 15 days Reduced pH, particulate

carbohydrates,

chlorophyll,

photosynthesis, primary

production; increased

dissolved organic

phosphorus, dissolved

organic nitrogen, and

dissolved amino acids

0.56 Bester et al. 1995

Mesocosm,

Mixed marine

phytoplankton

Residue

grade

- 15 days Reduced pH, particulate

carbohydrates,

chlorophyll,

photosynthesis, primary

production; increased

dissolved organic

phosphorus, dissolved

organic nitrogen, and

dissolved amino acids

5.80 Bester et al. 1995

a

 Test was run using a Taub and Dollar (1964) medium.

b

 Test was run using an algal assay medium (U.S. EPA 1971).

c

 Algae were pre-conditioned for 4 days with 531 :g/L of atrazine. d

 Test performed with an atrazine-sensitive strain. e

 Test performed with an atrazine-resistant strain

f

 Nephelometric determination.

g

 Colorimetric determination.

h

 Only 2.3 to 4.7 percent of this concentration remained on day 7.

i

 Test performed with water from microcosm 30 days after atrazine had been introduced. j

 Test performed directly with atrazine in water without a microcosm exposure. k

 EC50 obtained using an algal assay medium.

l

 EC50 obtained using creek water as the test medium.

m Animals were fed at 24 hr.

n

 Two single annual applications at nominal concentration indicated. o

 Atrazine concentrations were below detection after 10 days; however, the study continued for 42 days.
DRAFT

129

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