1

Appendix B: Supporting Ecological Toxicity Data 

(94 pages) 

A.1 Toxicity to Birds / Reptiles ....................................................................................................... 4

A.1 Toxicity to Birds / Reptiles ....................................................................................................... 4

A.1.1 Birds: Acute Oral Studies ........................................................................................... 4

A.1.2 Birds: Subacute Dietary Studies ................................................................................. 5

A.1.3 Birds: Chronic Studies ........................................................................................................ 6

A.1.4 Birds/Reptiles: Open Literature .................................................................................. 7

 A.1.4a Birds: Open Literature Data .................................................................................. 7

 A.1.4b Reptiles: Open Literature Data ............................................................................. 7

A.2 Toxicity to Freshwater Animals .............................................................................................. 13

A.2.1 Freshwater Fish, Acute .............................................................................................. 13

 A.2.2 Freshwater Fish, Chronic .......................................................................................... 16

 A.2.3 Sublethal Effects, Freshwater Fish (Open Literature) .............................................. 17

A.2.3 Sublethal Effects, Freshwater Fish (Open Literature) ...................................................... 18

A.2.4a Sublethal Effects: Freshwater Fish: ............................................................................ 18

A.2.4c Amphibians: ................................................................................................................. 22

A.2.5 Freshwater Invertebrates, Acute ....................................................................................... 22

 A.2.6 Freshwater Invertebrate, Chronic .............................................................................. 25

A.2.8b Freshwater Field Studies (New Open Literature Data) ............................................... 28

A.3 Toxicity to Estuarine and Marine Animals ............................................................................. 29

 A.3.1 Estuarine and Marine Fish, Acute ............................................................................. 29

 A.3.2 Estuarine and Marine Fish, Acute (Open Literature 2006 Review) ......................... 30

 A.3.2 Estuarine and Marine Fish, Chronic ......................................................................... 30

 A.3.3a Sublethal Effects: Estuarine/Marine Fish ........................................................... 31

 A.3.4 Estuarine and Marine Invertebrates, Acute ............................................................... 32

452083-03 & ................................................................................................................................... 32

452277-11 ....................................................................................................................................... 32

Hall, Ziegenfuss, Anderson, Spittler & Leichtweis 1994 ............................................................... 32

 A.3.5 Estuarine and Marine Invertebrate, Chronic ............................................................. 34

A.3.7a Estuarine and Marine Field Studies (2003 IRED Data) ......................................... 36

A.3.7b Estuarine and Marine Field Studies (New Open Literature Data) .............................. 40

A.4 Toxicity to Plants .................................................................................................................... 42

 A.4.1 Terrestrial Plants ....................................................................................................... 42

A.4.2 Aquatic Plants ................................................................................................................... 44

A.5 Toxicity to Terrestrial Invertebrates ....................................................................................... 55

A.6 Effects of Environmental Factors and Life-Stage on Aquatic Atrazine Toxicity ................... 56

 A.6.1 Interaction Effects on Atrazine Toxicity to Plants .................................................... 57

 A.6.2 Interaction Effects on Atrazine Toxicity to Aquatic Animals ................................. 58

A.7 Pesticide Toxicity Interactions ................................................................................................ 59

A.7.1 Plants .............................................................................................................................. 59

A.7.2 Animals .......................................................................................................................... 61
2

A.8. References .............................................................................................................................. 65

 
3

This appendix presents available submitted and open literature studies available on atrazine. 

Studies that are submitted to the Agency in support of pesticide registration or re-registration are 

categorized as either acceptable, supplemental, or invalid. Acceptable means that all essential 

information was reported, the data are scientifically valid, and the study was performed according 

to recommended protocols. Studies in the “acceptable” category fulfill the corresponding data 

requirement in 40 CFR Part 158 and are appropriate for use in risk assessment. Supplemental 

studies are also scientifically valid; however, they were either performed under conditions that 

deviate from recommended guideline protocols or certain data necessary for complete verification 

are missing. Supplemental studies may be used quantitatively in the risk assessment and can, at 

the Agency’s discretion, fulfill the corresponding data requirement in 40 CFR Part 158. Invalid 

studies are not scientifically valid, or deviate substantially from recommended protocols such that 

they are not useful for risk assessment. Invalid studies do not fulfill the corresponding data 

requirement in 40 CFR Part 158. 

With respect to the open literature, studies may be classified as either qualitative, quantitative, or 

invalid. The degree to which open literature data are quantitatively or qualitatively characterized 

is dependent on whether the information is relevant to the assessment endpoints (i.e., maintenance 

of the survival, reproduction, and growth of the assessed listed species) identified in the problem 

formulation. Open literature studies classified as qualitative are not appropriate for quantitative 

use but are of good quality, address issues of concern to the risk assessement, and, when 

appropriate, are discussed qualitatively in the risk characterization discussion. Those open 

literature studies that are classified as quantitative are appropriate for quantitative use in the risk 

assessment including calculation of RQs. It should be noted that this appendix includes all 

relevant data taken from the 2003 IRED atrazine effects appendix. In addition, ECOTOX 

information was obtained on October 16, 2011. The May 2007 ECOTOX search included all 

open literature data for atrazine (i.e., pre- and post-IRED). Data that pass the ECOTOX screen 

described in Section 4.1 of the assessement are evaluated along with the registrant-submitted data, 

and may be incorporated qualitatively or quantitatively into this endangered species assessment. 

In general, effects data in the open literature that are more conservative than the registrantsubmitted data are considered for quantitative use. 

Citations for all open literature not considered as part of this assessment because it was either 

rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g., the endpoint is less 

sensitive and/or not appropriate for use in this assessment) is included in Appendix G. Appendix 

G also includes a rationale for rejection of those studies that did not pass the ECOTOX screen and 

those that were not evaluated as part of this endangered species assessment. Further detail on the 

ECOTOX exclusion categories is provided in the Agency’s Guidance of the Evaluation Criteria 

for Ecological Toxicity Data in the Open Literature (U.S. EPA, 2004). 
4

A.1 Toxicity to Birds / Reptiles 

Given limited ecotoxicity data for reptiles, avian acute oral, subacute dietary, and chronic 

reproduction data are used as a surrogate for sea turtles. In addition, open literature data are 

available for a limited number of reptiles including turtles (red-eared slider [Trachemys scripta 

elegans] and snapping turtles [Chelydra serpentine]) and American alligators (Alligator 

mississippiensis). Ecotoxicity data for birds and reptiles are discussed in Sections A.1.1 through 

A.1.4. 

A.1.1 Birds: Acute Oral Studies 

An acute oral toxicity study using the technical grade of the active ingredient (TGAI) is required 

to establish the toxicity of atrazine to birds. The preferred test species is either mallard duck 

(Anas platyrhynchos; a waterfowl) or bobwhite quail (Colinus virginianus; an upland gamebird). 

Results of these studies are summarized below in Table A-1. 

Table A-1. Avian Acute Oral Toxicity: Technical Grade and Formulations

Surrogate Species % ai

LD50 (mg/kg) 

Probit Slope Toxicity Category

MRID No. 

Author/Year

Study 

Classification1

Northern bobwhite quail 

(Colinus virginianus) 

14-day old chicks; 8-day test

Tech. 783 

slope 3.836

Slightly toxic 000247-21 

Fink 1976

Acceptable 

Mallard Duck 

(Anas platyrhynchos) 

6-months old; 14-day test

76 % 

80 WP

> 2,000 

slope none

Practically non-toxic 001600-00 

Hudson, Tucker & 

Haegle 1984

Supplemental 

(only 3 birds) 

(formulation)

Ring-necked Pheasant 

(Phasianus colchicus) 

3-months old; 14-day test

76 % 

80 WP

> 2,000 

slope none

Practically non-toxic 001600-00 

Hudson, Tucker & 

Haegle 1984

Supplemental 

(only 3 birds) 

(formulation)

Japanese Quail 

(Coturnix c. japonica) 

50-60 days old; 14-day test

Tech. 4,237 

slope > 6 

Practically non-toxic 000247-22 

Sachsse and Ullman 

1974

Supplemental 

(species not 

native)

Degradates: Minor atrazine degradates include deethylatrazine (DEA), deisopropylatrazine 

(DIA) and diaminochlorotriazine. Acute mammalian LD50 values available for deethylatrazine 

and deisopropylatrazine are both more sensitive than the parent atrazine. Therefore, a special (70-

1) acute oral toxicity test with the upland gamebird (preferably northern bobwhite) are required to 

address the concern for these degradates. Acute avian LD50 data for the atrazine degrdates, 

deethylatrazine (DEA) and deisopropylatrazine(DIA), and hydroxyatrazine (HA) are summarized 

in Table A-2. 
5

Table A-2. Avian Acute Oral Toxicity: Degradates

Surrogate Species

Degradate 

% ai

LD50 (mg/kgbw) 

Probit Slope

Toxicity Category

MRID No. 

Author/Year

Study 

Classification1

Northern bobwhite quail 

(Colinus virginianus) 

18-week old chicks; 14-day test

Deisopropyl

atrazine 

(DIA) 

96%

> 2,000 

slope none

Practically non-toxic 465000-07 

Stafford, 2005a

Acceptable 

Northern bobwhite quail 

(Colinus virginianus) 

17-week old chicks; 14-day test

Hyrdroxy 

atrazine 

(HA) 

97.1% 

> 2,000 

slope none

Practically non-toxic 465000-08 

Stafford, 2005b

Acceptable

Northern bobwhite quail 

(Colinus virginianus) 

16-week old chicks; 14-day test 

Desethyl 

Atrazine 

(DEA) 

96% 

768 

Slope = 6.21 

(95% CI = 

3.19 – 9.27) 

Slightly toxic 465000-09 

Stafford, 2005c

Acceptable

A.1.2 Birds: Subacute Dietary Studies 

Two subacute dietary studies using the TGAI are required to establish the toxicity of atrazine to 

birds. The preferred test species are mallard duck and bobwhite quail. Results of these tests are 

tabulated below in Table A-3. 

Table A-3. Avian Subacute Dietary Toxicity

Surrogate Species % ai

5-Day LC50

(ppm)1

Toxicity Category MRID No. 

Author/Year

Study 

Classification

Northern bobwhite 

(Colinus virginianus) 

9-days old chicks

 99.0 > 5,000 

(no mortality)

Practically non-toxic 000229-23 

Hill et al. 1975

Supplemental 

(no control 

raw data)

Northern bobwhite 

(Colinus virginianus) 

young adults

Tech. > 10,000 Practically non-toxic unknown - Gulf South 

Gough & Shellenberger 

1972

Supplemental 

(Adult birds & 

no raw data)

Ring-necked pheasant 

(Phasianus colchicus) 

10-days old chicks

 99.0 > 5,000 

(no mortality)

Practically non-toxic 000229-23 

Hill et al. 1975

Supplemental 

(no control 

raw data)

Japanese Quail 

(Coturnix. japonica) 

7-days old chicks

 99.0 > 5,000 

(7 % mortality 

 at 5,000 ppm)

Practically non-toxic 000229-23 

Hill et al. 1975

Supplemental 

(no control 

raw data; 

species not 

native)

Mallard duck 

(Anas platyrhynchos) 

10-days old ducklings

 99.0 > 5,000 

(30 % mortality 

 at 5,000 ppm)

Practically non-toxic 000229-23 

Hill et al. 1975

Supplemental 

(no control 

raw data)

 

1

 Test organisms observed an additional three days while on untreated feed. 
6

Subacute dietary studies using a typical end-use product (TEP) may be required on a case-by-case 

basis to establish the toxicity of atrazine formulations to birds. The preferred test species are 

mallard duck and bobwhite quail. Results of these tests are summarized below in Table A-4. 

Table A-4. Formulation Avian Subacute Dietary Toxicity

Surrogate Species

% ai 

Form

5-Day LC50 (ppm ai)1

Probit Slope

Toxicity Category MRID No. 

Author/Year

Study 

Classification

Northern bobwhite 

(Colinus virginianus) 

(6-weeks old)

76 

80 WP

 5,760 

slope 3.252

Practically non-toxic 000592-14 

Beliles & Scott 1965

Supplemental 

(birds too old)

Mallard duck 

(Anas platyrhynchos)

76 

80 WP

19,560 

slope 1.807

Practically non-toxic 000592-14 

Beliles & Scott 1965

Acceptable for 

80W 

formulation

 

1

 Test organisms observed an additional three days while on untreated feed.

A.1.3 Birds: Chronic Studies 

Avian reproduction studies using the TGAI are required for atrazine, because the following 

conditions are met: (1) birds may be subject to repeated or continuous exposure to the pesticide, 

especially preceding or during the breeding season, (2) the pesticide is stable in the environment 

to the extent that potentially toxic amounts may persist in animal feed, (3) the pesticide is stored 

or accumulated in plant or animal tissues, and/or, (4) information derived from mammalian 

reproduction studies indicates reproduction in terrestrial vertebrates may be adversely affected by 

the anticipated use of the product. The preferred test species are mallard duck and bobwhite 

quail. Results of these tests are provided below in Table A-5.

Table A-5. Avian Reproduction 

Surrogate Species/ 

Study Duration % ai

NOAEC/ 

LOAEC (ppm ai)

MRID No. 

Author/Year

Study 

Classification

Northern bobwhite 

(Colinus virginianus) 

20 weeks

97.1 NOAEC 225 

LOAEC 675 

(based on egg production and embryo viability)

425471-02 

Pedersen & 

DuCharme 1992

Acceptable 

Mallard duck 

(Anas platyrhynchos) 

20 weeks

97.1 NOAEC <75 

LOAEC 75

(based on egg production and hatchability, adult food 

consumption and male wt; hatchling wt at 75 ppm), 

425471-01 

Pedersen & 

DuCharme 

1992

Acceptable

Japanese quail 

(Coturnix. japonica) 

8 days 

Tech Reduced food consumption and body wt; sescation of 

egg production; LC50 >10000 ppm 

00024723 

Sachsse and Ullman 

1975 

Supplemental 

(not chronic 

exposure) 

 
7

A.1.4 Birds/Reptiles: Open Literature 

 A.1.4a Birds: Open Literature Data 

Three studies were located in the open literature that evaluated the potential for atrazine to affect 

endpoints including growth, sexual maturity, liver effects, and endocrine effects in birds 

(summarized in Table A-6). 

Table A-6. Avian Reproduction/Growth Effects Tests from Open Literature (2007 Review)

Study type/ 

Test material

Test Organism 

(Common and 

Scientific Name) and 

Age and/or Size

Test 

Design

Endpoint Concentration Citation 

(EcoRef. #) 

Rationale for Use in Risk 

Assessment

Reproduction 

dietary studies in 

birds / Atrazine 

technical 99.9% ai 

Male Japanese quail Seven separate studies were conducted. 

Dietary concentrations ranged from 10 to 

1000 ppm. Animals were approximately 

6-week old males. Endpoints evaluated 

included growth, liver effects, sexual 

maturation, and anti-estrogenic effects. 

Exposure duration was up to 4 weeks. 

In addition, studies using SC 

administration and silastic implants were 

also conducted that evaluated endpoints 

including growth, liver effects, testes 

weight, and circulating LH levels. Doses 

up to 10 mg/kg-bw were tested. 

At 1000 ppm, there was a 

reduction in growth rate and food 

intake and an elevation in 

testosterone levels, although the 

reduction in testosterone leves 

was not consistently observed 

across studies. Other statistically 

significant observations were 

considered spurious and not 

related to atrazine treatment. 

Wilhelms et 

al., 2005 

(80632) 

Qual: 42547101 produced a 

more sensitive LOAEC 

Reproduction 

maturation in birds 

/ Atrazine 

technical, 99.9% ai 

Female Japanese 

quail 

Birds were exposed to dietary 

concentrations that ranged from 1 ppm to 

1000 ppm. The following endpoints were 

evaluated: growth, food intake, liver, 

ovary, and oviduct weight, and plasma 

luteinizing hormone and estradiol levels. 

Exposure was up to 4 weeks.

Growth, food intake, liver 

weight, and circulating estradiol 

levels were significantly 

(p<0.05) reduced in birds 

exposed to atrazine at 1000 ppm, 

but not at lower levels. 

Wilhelms et 

al., 2006a 

(82035) 

Qual: 42547101 produced a 

more sensitive LOAEC. 

Reproduction 

toxicity study in 

birds 

Japanese quail Birds were exposed to atrazine in the diet 

at concentrations that ranged from 0.001 

ppm to 1000 ppm.. No effects on body 

weight, food intake, mortality, circulating 

corticosterone levels, or weights of liver, 

ovaries, or oviducts. 

NOAEC: 1000 ppm Wilhelms et 

al., 2006b 

(85511) 

QUAL. No effects were 

observed in the study. 

Subchronic 

toxicity study in 

birds 

Japanese quail Male birds orally dosed at concentrations 

of 10-500 mg/kg-bw for 45 days. Feed 

consumption reduced at 100-500 ppm 

and reduced body weight at 25-500 ppm; 

at ≥50 ppm decrease in leukocyte 

counts

NOAEC: 10 ppm (based on body 

wt) 

Hussain et al. 

2011 

(153875_ 

Qual: Formulation used, 

uncertain if registered in U.S.; 

 A.1.4b Reptiles: Open Literature Data 

Open literature studies for reptiles exposed to atrazine are summarized below in Table A-7. 
8

 Table A-7. Reptilian Toxicity Tests from Open Literature (2007 Review)

Study type/ 

Test material

Test Organism (Common 

and Scientific Name) and 

Age and/or Size

Test 

Design

Endpoint 

Concentration 

in ppm

Citation 

(EcoRef. #) 

Rationale for Use in 

Risk Assessment

Chronic lab (117 

days) / 

Atrazine 480 

formulation 

(atrazine content = 

481 g/L and 

unspecified 

triazines of 29 

g/L) 

Snapping turtle (Chelydra 

serpentine) eggs - Eggs incubated in soil 

treated w/atrazine at 1.32 lb 

ai/A (measured conc = 0.64 

ppm) and 13.2 lb ai/A 

(measured conc = 8.1 ppm) 

and control. 

- 3 replicates (with 23-24 

eggs/replication)/treatment 

group. 

- Incubator temp = 25o

(+1o

C) to produce males. 

- Endpoints: gonadal 

development (hatching 

success, gonadal 

morphology, and thyroid 

activity) 

NOAEC = 13.2 lb ai/A 

(0.81 ppm) 

Some males w/testicular 

oocytes and females 

produced in atrazinetreated groups (3.3 – 

3.7%); however, no 

significant differences 

between atrazine 

treatments and controls 

were observed. 

Thyroids from each 

treatment and control 

displayed similar levels 

of activity. 

De Solla et al., 

2005 

(82032) 

QUAL: 

3 PAHs detected at nontoxic levels in control 

soil, but not analyzed 

for in the atrazine 

treatment groups 

- low incidence of 

intersex or females 

precluded ability to 

differentiate between a 

low incidence caused 

by atrazine exposure 

and random sampling 

error 

Chronic lab 

(duration NR) / 

Atrazine (99 % ai) 

American alligator 

(Alligator mississippiensis) 

eggs at stage 21 in 

embryonic development, 

just prior to onset of 

gonadal differentiation 

- Eggs were treated 

w/atrazine at 0, 0.014, 0.14, 

1.4, and 14 ppm via topical 

application to the eggshell 

in 50 μl of 95% ethanol. 

- 5 eggs/treatment were 

incubated at temperatures 

to produce either 100% 

males (33 o

C) or 100% 

females (30 o

C). 

- Endpoints: gonadal 

histology and hepatic 

steroidogenic activity 

NOAEC = 14 ppm 

All atrazine treated eggs 

incubated at female- and 

male-determining temps 

produced female and 

male hatchlings, 

respectively. No 

differences in gonadal 

histology (Mullerian 

duct epithelial cell 

height and medullary 

regression) and hepatic 

aromatase activity was 

noted between atrazine 

treated groups and 

controls. 

Crain et al., 1999 

(70208) 

QUAL: No treatmentrelated effects occurred 

in the study (study did 

not provide a sensitive 

endpoint for use in risk 

assessment). 

Relevance of exposure 

pathway (direct 

application to eggs) to 

the current assessment 

is questionable. 

10 day study / 

Atrazine 97% 

American alligator 

(Alligator mississippiensis) 

and red-eared slider turtle 

(Trachemys scripta elegans 

Eggs 

-eggs placed in nests 

treated w/0, 10, 50, 100 

and 500 ppb via nest 

saturation of solution for 

10 days 

-Incubated at 27.3 and 

32.8° for turtles and 

alligators, respectively 

-Endpoints:hatchability, 

embryo mortality and 

sexual differentiation 

NOAEC=500 ppb 

No adverse effects 

found; no atrazine 

detected in embryonic 

fluids 

Gross 2001 (MRID 

45545302 and 03) 

QUAL: No treatmentrelated effects occurred 

in the study (study did 

not provide a sensitive 

endpoint for use in risk 

assessment). 

Subchronic (10 

day) / atrazine (% 

NS) 

Caiman (Caiman latirostris) 

Stage 20 

- 0.2 ppm atrazine (ethanol 

used as solvent) topically 

applied to eggs once; 

-Incubated at 33°C (male 

temp) for 10 days 

-Endpoints: histopathology 

and testosterone analysis 

NOAEC <0.2 ppm 

Altered 

histoarchitecture of the 

testis

Rey et al. 2009 

(153844) 

QUAL: 

Relevance of exposure 

pathway (direct 

application to eggs) to 

the current assessment 

is questionable. 
9

 Table A-7. Reptilian Toxicity Tests from Open Literature (2007 Review)

Study type/ 

Test material

Test Organism (Common 

and Scientific Name) and 

Age and/or Size

Test 

Design

Endpoint 

Concentration 

in ppm

Citation 

(EcoRef. #) 

Rationale for Use in 

Risk Assessment

Subchronic (10 

day) / atrazine (% 

NS) 

Caiman (Caiman latirostris) 

Stage 20 

- 0.2 ppm atrazine (ethanol 

used as solvent) topically 

applied to eggs once; 

-Incubated at 30°C (female 

temp) or 33°C (male temp) 

for 10 days 

-Endpoints: sex 

determination, 

histopathology and 

hormone analysis 

NOAEC <0.2 ppm 

Changes in Type III 

germ cells in ovaries; 

decrease testosterone 

compared to control in 

females 

Rey et al. 2009 

(153844) 

QUAL: 

Relevance of exposure 

pathway (direct 

application to eggs) to 

the current assessment 

is questionable. 

Chronic (11 

months) / Atrazine 

(>99%) 

Map turtles (Graptemys 

ouachitensis and G. 

pseudogeographica)/ 

eggs

-Incubated ggs exposed to 

sand containing 0, 0.1, 1.0 

and 100 ppb atrazine 

applied once and sand 

rehydrated sand with 

control water 

-Reared subset of neonates 

for 11 months under 

control conditions. 

-Endpoints: hatching 

success, incubation 

time, external 

morphological 

abnormalities, gonadal 

sex, three measures of 

body size, righting time, 

and swimming time for 

all turtles; subset- nest 

escape behavior, time to 

first foraging event, 

time to capture prey, 

growth, and survival -

NOAEC = not dose 

responsive. 

At hatch, no significant 

effects but abnormalities 

decreased with 

increasing conc. 

however, % still lower 

than control 

For subset, turtles at 0.1 

ppb had inhibited nest

escape behavior and 

reduced post hatch 

survival 

Neuman-Lee & 

Janzen 2011 

(153816) 

Qual: no raw data,; 

negative control not 

used; results for both 

species presented as one 

dataset 

NR = Not reported. 

A. 1.5. Toxicity to Mammals 

Acute Exposure (Mortality) Studies 

Acute oral toxicity data are summarized in Table A.8. 
10

Table A-8. Summary of Acute Toxicity of Atrazine and its Degradates of Concern 

Chemical Acute Mammal LD50 

(mg/kg-bw) 

Atrazine 1869 (MRID 00024709) 

HA Not available 

DEA 1240 (MRID 43013201) 

DIA 1111 (MRID 43013202) 

DACT Not available 

Reproduction Toxicity 

A 2-generation reproduction study with parent atrazine is available. Reproduction studies are not 

available on the degradates of concern. However, the degradates have been tested in prenatal 

developmental studies in rodents. These studies are summarized below. Results for atrazine from 

the same guideline study are also presented for comparison. Additional reproduction toxicity data 

is available for amphibians and will be evaluated for possible inclusion in the risk assessment. 

Table A-.9. Toxicity Reference Values for Atrazine and Degradates of Concern in Guideline 

Prenatal Developmental Toxicity Studies and the 2-generation Reproduction study for 

Parent Atrazine 

Chemical Study type/Data 

Source 

Study Summary 

 2-generation 

reduction study in 

rate / 40431306 

LOAEL = 500 mg/kg-diet (39 mg/kg/day in males, 43 mg/kg/day in 

females) based on decreased body weights, body weight gains, and 

food consumption. NOAEL = 50 ppm (3.8 mg/kg/day in males, 3.7 

mg/kg/day in females). 

Atrazine Prenatal developmental in 

rodents / 40566302 

Maternal NOAEL = 10 mg/kg/day. 

Maternal LOAEL = 70 mg/kg/day, based on reduced body weight 

gain 

Developmental NOAEL = 10 mg/kg/day 

Developmental LOAEL = 70 mg/kg/day based on delayed or no 

ossification at several sites 

MRID 41065201 Maternal NOAEL = 25 mg/kg/day. 

Maternal LOAEL = 100 mg/kg/day based on reduced body weight 

gain and food consumption. 

Developmental NOAEL = 25 mg/kg/day. 

Developmental LOAEL = 100 mg/kg/day based on increased 

incidence of delayed ossification of skull bones. 

HA Prenatal developmental in 

rodents / MRID 41065202 

Maternal NOAEL = 25 mg/kg/day 

Maternal LOAEL = 125 mg/kg/day based on decreased food 

consumption during the dosing period and enlarged and mottled 

kidneys. 

Developmental NOAEL = 25 mg/kg/day. 
11

Developmental LOAEL = 125 mg/kg/day based on increased 

incidence of partially ossified interparietal and hyoid bones and 

decreased fetal body weight. 

DIA Prenatal developmental in 

rodents / MRID 43013209 

Maternal NOAEL = 5 mg/kg/day 

Maternal LOAEL = 25 mg/kg/day based 

decreased food consumption, body weight/weight gain and food 

consumption 

Developmental NOAEL = 25 mg/kg/day 

Developmental LOAEL = 100 mg/kg/day based on increased fetal 

and litter incidences of fused sternebrae 1 and 2 and increased fetal 

incidence of poor ossification of the proximal phalanx of posterior 

digit 5 (a skeletal variation) 

DEA Prenatal developmental in 

rodents / MRID 43013208 

Maternal NOAEL= 5 mg/kg/day 

Matenal LOAEL= 25 mg/kg/day based on decreased body weight 

gain and food consumption 

Developmental NOAEL= 5 mg/kg/day 

Developmental LOAEL 25 mg/kg/day based on . increased fetal and 

litter incidences of fused sternebrae 1 and 2 

DACT Prenatal developmental 

toxicity in rodents / 

MRID 41392402 

Maternal NOAEL = 25 mg/kg/day 

Maternal LOAEL = 75 mg/kg/day, based on decreased body weight 

gain during dosing. 

Developmental NOAEL is 2.5 mg/kg/day. 

Developmental LOAEL = 25 mg/kg/day, based on increases in 

incidences of incompletely ossified parietals, interparietals and 

unossified hyoids. 

Metabolism in Mammals 

Metabolism data are summarized in Table A-10. 

Table A.10. Summary of Available Metabolism Data for Atrazine in Rodents 

Guideline No./ 

Study Type 

MRID No. (year) /Doses Results 

870.7485 

Metabolism and 

pharmacokinetics 

40431304 (1987) 

 0, 1, and 100 mg/kg for a 

single dose given through oral 

gavage. 1.0 mg/kg/day for 15 

days by oral gavage. 

Distribution, accumulation

Distribution was dose-dependent and independent of sex. 

Distribution appeared to follow first-order kinetics and the 

half-life in the tissues was 31.3 hours. 

Excretion

Approximately 95% of the atrazine excreted within 7 days 

of dosing. Urinary route accouted for about 75% of the 

excretion feces accounted for 20%. Route of excretion did 

not seem to vary among sexes or with dose. 

870.7485 MRID 40431305 (1987) Distribution, accumulation
12

Guideline No./ 

Study Type 

MRID No. (year) /Doses Results 

Metabolism and 

pharmacokinetics 

The animals were dosed daily 

for 10 days through a stomach 

tube with dose levels of 0, 1, 

3, 7, 10, 50 or 100 mg/kg/day. 

Distribution was highest in the red blood cell, followed by 

the liver, ovary and kidney. When the dose increased the 

amount distributed in the tissues increased. The distribution 

appeared to follow first-order kinetics and the tissue halflife was 38.6 hours. This indicates that atrazine, with 

possible exception of the red blood cell, does not 

bioaccumulate. 

870.7485 

Metabolism and 

pharmacokinetics 

MRID 40431306 (1987) 

Rats were given test 100 

mg/kg article was given 

through the stomach tube in a 

single oral dose. 

Other rats were given 16.18 

and 19.64 mg/kg and urine 

was collected over a 24 hr 

period. The urine was 

analyzed for metabolites. 

Excretion

In the rats given 100 mg/kg greater than 100% of the 

administered radioactivity was recovered within 3 days of 

dosing. Urine was found to contain 47.3% of the 

radioactivity and the feces 49.3%. The tissues contained 

5.75% and 1.4% was found in the blood. 

Metabolism

Metabolites indicate that dechlorination of the triazine ring 

and N-dealkylation are the major metabolic pathways for 

atrazine in rats. Oxidation of the alky substituents of 

atrazine appears to be of minor metabolic importance. 

870.7485 

Metabolism and 

pharmacokinetics 

MRID 42165503 (1993) 

Fecal and urinary samples 

from rats exposed in a seprate 

metabolism study (MRID 

40431304) were obtained and 

analyzed to determine 

metabolism profiles. 

Metabolic profile

No sex differences in metabolic profiles were evident. The 

major fecal metabolite was DACT which accounted for 

40% of the total fecal radioactivity. 

870.7485 

Metabolism and 

pharmacokinetics 

MRID 44713802 (1993) 

single oral dose of 1 or 100 

mg/kg through oral gavage 

Distribution, accumulation

Time to maximum blood concentration (tcmax) was 2 hours 

and 24 hours for the low and high dose groups, respectively. 

With exception of red blood cells, whole blood, and skeletal 

muscle, tissue burden for any specific tissue or organ 

represented less than 1% of the administered dose by 14 

days post dosing 

Excretion

Urinary excretion was 64.72% of the total administered low 

dose over a 48-hour period and 66.16% of the total 

administered high dose over a 168-hour period. Within 48 

hours urinary excretion was 100% and 94% complete for 

the low-dose and high-dose group, respectively. 

Fecal elimination accounted for 10.80% and 19.69% of the 

total dose for the low and high dose groups, respectively. 
13

A.2 Toxicity to Freshwater Animals 

 

 A.2.1 Freshwater Fish, Acute 

Two freshwater fish toxicity studies using the TGAI are required to establish the toxicity of 

atrazine to fish. The preferred test species are rainbow trout (Oncorhynchus mykiss; a coldwater 

fish) and bluegill sunfish (Lepomis macrochirus; a warmwater fish). Toxcity data for TGAI are 

summarized below in Table A-8. 

Table A-8. Freshwater Fish Acute Toxicity (TGAI)

Surrogate Species/ 

Static or 

Flow-through test % a.i.

96-hour LC50 (ppb) 

(measured/nominal) 

Probit Slope Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Rainbow trout 

(Oncorhynchus mykiss) 

Static test 

 98.8 5,300 

 (nominal) 

slope - 2.723

moderately toxic 000247-16 

Beliles & Scott 1965

Acceptable; water 

quality other than 

temp not reported 

Brook trout 

(Salvelinus tontinalis) 

Flow-through test

94 6,300 

4,900 (8-day test) 

not specified

moderately toxic 000243-77 

Macek et al. 1976

Supplemental 

(52-gram fish & 

no raw data)

Fish from the Nile River 

Chrysichthyes auratus

Static-renewal - daily 

150 mg/L CaCO3; 22ΕC

96 6,370 

(not specified)

moderately toxic 452029-11 

Hussein, El-Nasser 

& Ahmed 1996

Supplemental 

(non-native sp.; 

26-gram fish; 

no raw data)

Bluegill sunfish 

(Lepomis macrochirus) 

Flow-through test

94 > 8,000 

6,700 (7-day test) 

 (not specified)

moderately toxic 000243-77 

Macek et al. 1976

Supplemental 

(6.5-gram fish & 

no raw data)

Tilapia 38 grams 

(Oreochromis niloticus) 

Static-renewal - daily 

150 mg/L CaCO3: 22ΕC

96 9,370 

(not specified)

moderately toxic 452029-11 

Hussein, El-Nasser & 

Ahmed 1996

Supplemental 

(non-native sp.; 

38-gram fish; 

no raw data)

Silver catfish (2-4 g) 

 (Rhamdia quelen) 

Static, 

Form 

(250 g/L 

both ais) 

10,200 (atrazine only) 

10,500 (atrazine & 

simizine) 

(Nominal) 

moderately toxic E11938 

Kreutz et al. 2008 

Supplemental (nonnative sp., no raw 

data, unknown 

formulation used) 

Fathead minnow 

(Pimephales promelas) 

24-Hour renewal test

94 15,000 

(nominal) 

15,000 (5-day test)

slightly toxic 000243-77 

Macek et al. 1976

Supplemental 

(no raw data)

Carp 

(Cyprinus carpio) 

Semi-static test

93.7 18,800 

(nominal) 

slope not reported

slightly toxic 452029-13 

Neskovic et al. 1993

Supplemental 

(no raw data)

Fathead minnow juvenile 

(Pimephales promelas) 

Flow-through test; 

52 mg/L CaCO3

97.1 20,000 

(measured) 

Slope - 6.889

slightly toxic 425471-03 

Dionne 1992

Acceptable 

Bluegill sunfish 

(Lepomis macrochirus) 

Static test

98.8 24,000 

(nominal) 

no slope 

slightly toxic 000247-17 

Beliles & Scott 1965

Acceptable 

Brown trout 

(Salmo trutta) 1.9 gr. 

Static-Renewal - daily 

pH 6; 10ΕC; 

11 mg/L CaCO3

NR 27,000 

(nominal) 

slightly toxic 452029-09 

Grande, Anderson & 

Berge 1994

Supplemental 

(no raw data; 

slight aeration & 

purity unknown)
14

Table A-8. Freshwater Fish Acute Toxicity (TGAI)

Surrogate Species/ 

Static or 

Flow-through test % a.i.

96-hour LC50 (ppb) 

(measured/nominal) 

Probit Slope Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Zebrafish 

(Brachydanio rerio)

NR 37,000 

(NR) 

slightly toxic

MRID # NR 

Korte & Greim 1981 Supplemental 

(article 

unavailable)

Bluegill sunfish 

(Lepomis macrochirus) 

Static test

100 57,000 

(nominal)

slightly toxic 001471-25 

Buccafusco 1976

Acceptable 

Goldfish 

(Carassius auratus) 

Static test

98.8 60,000 

(nominal) 

Slope - 2.695

slightly toxic 000247-18 

Beliles & Scott 1965

Supplemental 

(not an acceptable 

species)

Table A-9 presents fish and amphibian toxicity data for formulated products. 

Table A-9. Freshwater Fish Acute Toxicity (Formulated Products)

Surrogate Species/ 

Flow-through or Static

% ai 

formul.

96-hour LC50 (ppb) 

(measured/nominal) Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Black Bass - fry 

(Micropterus salmoides) 

Static test; 20ΕC 

78 mg/L hardness 

80 

80 W

12,600 

(nominal) 

slope - 5.86

slightly toxic 452277-17 

R. O. Jones 1962

Supplemental 

(48-hours; 

 limited raw data)

Channel Catfish yolk sac 

(Ictalurus punctatus) 

Static test; 23.3-25.8ΕC 

78 mg/L hardness

80 

80 W

16,000 

(nominal) 

slope - 3.36

 sightly toxic 452277-17 

R. O. Jones 1962

Supplemental 

(limited raw data)

Bluegill Sunfish fry 

(Lepomis macrochirus) 

Static test; 25-27ΕC 

78 mg/L hardness

80 

80 W

20,000 

(nominal) 

no slope

slightly toxic 452277-17 

R. O. Jones 1962

Supplemental 

(limited raw data)

Coho Salmon 

(Oncorhynchus kisutch) 

Renewal daily; 144 hr

 40.8* 

AAtrex

Liquid

> 18,000 

25 % mortality 

(measured)

slightly toxic 452051-07 

Lorz et al. 1979

Supplemental 

(no LC50 value & 

12-17 months old)

Rainbow trout 

(Onchorhynchus mykiss) 

Flow-through test

40.8 

4L

20,500 

(nominal)

slightly toxic 452029-10 

Howe et al. 1998

Supplemental 

(no raw data)

Channel Catfish 

(Ictalurus punctatus) 

Flow-through test

40.8 

4L

23,800 

(nominal)

slightly toxic 452029-10 

Howe et al. 1998

Supplemental 

(no raw data)

Rainbow trout 

(Oncorhynchus mykiss) 

Static test

 43 

Liquid

 24,000 

(unknown)

slightly toxic 400980-01 

Mayer & Ellersieck 

 1986

Supplemental 

(no raw data)

Bluegill sunfish 

(Lepomis macrochirus) 

Static test 

 43 

Liquid

 42,000 

 (unknown)

slightly toxic 400980-01 

Mayer & Ellersieck 

 1986

Supplemental 

(no raw data)

* Percent a.i. assumed based on description as a liquid formulation, AAtrex.
15

Acute toxicity data that did not produce a more sensitive LC50 value were reported in the 2008 

ECOTOX summary and that data is presented below in Table A-9a. 

Acute Studies identified in 2008 ECOTOX search which have a less sensitive toxicity value than most 

sensitive value in Table A8. 

Endpoint Common Name Toxicity Value Reference (ECOTOX #) 

48- h LC50 Bluegill fish ca. 26 mg/L Beliles et al. 1965 (80976) 

96- h LC50 Brown trout 27 mg/L Grande et al. 1994 (62367) 

48-96 h LC50 Goldfish >56-60 mg/L Beliles et al. 1965 (80976) 

48-96 h LC50 Rainbow trout 

4.5-10 mg/L(same 

study as above for 

000247-16 4.5 study 

authors value but 

recalculation results in 

value above 

Beliles et al. 1965 (80976) 

120 hours post 

fertilization 

Zebrafish 

7.5 uM Muncke et al. 2007 (95954) 

96 hours post 

fertilization LC50 

and EC50 

Zebrafish LC50 = 1255 uM 

EC50 = 440 uM 

Ton et al. 2006 (93401) 

48 and 96 hours post 

fertilization NOAEL 

& LOAEL 

Zebrafish 48 hpf NOAEL = 

500 uM; 

96 NOAEL/LOAEC 

= 200/500 uM 

Ton et al 2006 (93401) 

12-48 hr LOEC 

12-48 h NOEC 

Zebrafish LOEC = 5-40 mg/L 

NOEC = 5-30 mg/L 

Wiegand et al. 2001 (62460) 

96-h NOEC Fathead minnow 4.1 mg/L Jop 1991 (81782) 

72 h Non-lethal Guppy 106.1 mg/L Bogacka et al 1990 (61069) 

96-h 

NOAEL/LOAEL 

Mummichog 0.05/0.5 mg/L Fortin et al. 2008 (103349) 

72-h LOAEL Nile tilapia 0.00610 mg/L De campos et al. 2008 (103350) 

12-h LOAEL Spotted seatrout 0.1 uM Thomas and Sweatman 208 

(103377) 

24-48 LC50 (unsure 

of test substance) 

Harlequin fish, red 

rasbora 

0.55-0.5 mg/L Alabaster 1969 (542) 

Degradates Acute fish testing with bluegill and rainbow trout are required to address degradate 

concerns for hydroxyatrazine (HA). Acute studies in rainbow trout have also been submitted for 

DACT and DIA degradates. Table A-10 presents freshwater fish toxicity data for HA, DIA, and 

DACT. 

Table A-10. Freshwater Fish Acute Toxicity 

Surrogate Species/ 

Flow-through or Static

% ai 

formul.

96-hour LC50 (ppb) 

(measured/nominal) Toxicity Category

MRID No. 

Author/Year

Study 

Classification

HA

Bluegill sunfish 

(Lepomis macrochirus); 

1.15 g 

Static test; 20.8 – 21.6 o

C 

125 mg/L hardness 

98 >3,800 

(measured dissolved) moderately toxic* 

465000-05 

Peither, 2005b 

Acceptable 
16

Table A-10. Freshwater Fish Acute Toxicity 

Surrogate Species/ 

Flow-through or Static

% ai 

formul.

96-hour LC50 (ppb) 

(measured/nominal) Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Rainbow trout 

(Oncorhynchus mykiss); 

0.75 g 

Static test; 13.2 – 14.1 o

C 

125 mg/L hardness 

98 >3,000 

(measured dissolved) moderately toxic* 

465000-04 

Peither, 2005a 

Acceptable 

DIA 

Rainbow trout 

(Oncorhynchus mykiss); 

1.5 grams 

Static test; 14 o

C 

165 mg/L hardness 

Not 

reported 

17,000 

(measured dissolved) Slightly toxic 

47046103 

Vial, 1991a 

Supplemental 

DACT 

Rainbow trout 

(Oncorhynchus mykiss); 

1.5 g 

Static test; 14 o

C 

164 mg/L hardness 

Not 

reported 

>100,000 

(measured dissolved) Practically non-toxic 

47046104 

Vial, 1991b 

Supplemental 

* Biological results for both studies were based on the mean-measured concentration of dissolved Hydroxyatrazine, 

which remained constant at the limit of its water solubility throughout the duration of the tests. Therefore, 

hydroxyatrazine is not acutely toxic to bluegill sunfish and rainbow trout at the limit of its water solubility. 

 A.2.2 Freshwater Fish, Chronic 

A freshwater fish early life-stage test using the TGAI is required for atrazine because the end-use 

product is expected to be transported to water from the intended use site, and the following 

conditions are met: the pesticide is intended for use such that its presence in water is likely to be 

continuous and recurrent; the pesticide is persistent in water (i.e., half-life greater than 4 days). 

Table A-11 presents the chronic toxicity data for freshwater fish. 

Table A-11. Freshwater Fish Early Life Stage Toxicity

Surrogate Species/ 

Study Duration/ 

Flow-through or 

Static Renewal % ai

NOAEC/LOAEC 

 ug/L (ppb) 

(measured or 

nominal)

Statistically sign. (p=0.05) 

Endpoints Affected

MRID No. 

Author/Year

Study 

Classification

Rainbow trout 

(Oncorhynchus mykiss) 

86 days, flow-through 

50 mg/L CaCO3

Tech. NOAEC 410 

LOAEC 1,100 

 (measured)

sign. delays in hatching @ 

1,100 and 3,800 μg/L 

sign. red. wet wt. at 30 & 58 

 days @ 1,100 & 3,800 μg/L 

sign. red. dry wt. @ 3,800 μg/L 

58.8 % mortality @ 3,800 μg/L 

 at swim-up

452083-04 

Whale et al. 

1994

Supplemental 

(DMSO used as 

solvent, no raw 

data for statistical 

analyses)

Rainbow trout 

embryo-larvae 

(Oncorhynchus mykiss) 

27 days; flow-through

80 

WP

Hardness 50 mg/L: 

LC50 660 

LC01 29 

Slope 1.2 

Hardness 200 mg/L: 

LC50 810 

LC01 77 

Slope 1.38

% normal survival 50/200 mg/L 

 19 μg/L - 94 98 

 54 - 88 90 

 54 ** - 68 74 

 5,020 ** - 10 9 

50,900 ** - 0 0

452029-02 

Birge, Black 

& Bruser 

1979

Supplemental 

(short test; 

no raw data for 

statistical 

analyses)
17

Table A-11. Freshwater Fish Early Life Stage Toxicity

Surrogate Species/ 

Study Duration/ 

Flow-through or 

Static Renewal % ai

NOAEC/LOAEC 

 ug/L (ppb) 

(measured or 

nominal)

Statistically sign. (p=0.05) 

Endpoints Affected

MRID No. 

Author/Year

Study 

Classification

Channel catfish 

embryo-larvae 

(Ictalurus punctatus) 

8 days; flow-through

80 

WP

Hardness 50 mg/L: 

LC50 220 

Slope 0.977 

 Hardness 200 mg/L: 

LC50 230 

Slope 0.84 

highly teratogenic in all tests; 

no results for soft water 

 420 μg/L - 16% terata 

 830 μg/L - 47 % terata 

46,700 μg/L - 86 % terata 

452029-02 

Birge, Black 

& 

Bruser 1979

Supplemental 

(short test; 

no raw data for 

statistical 

analyses)

Zebrafish 

(Brachydanio rerio) 

35 Days; pH 8; 27+1ΕC 

Flow-through test 

Hardness 24 mg/L

98 NOAEC 300 

LOAEC 1,300 

(measured) 

35-Day LC50 890 

 Slope 1.25

2 - 3 % sign. incr. in edema 

45-62 % mortality

452029-08 

Gorge & 

Nagel 1990

Supplemental 

(no raw data for 

statistical 

analyses)

A freshwater fish life-cycle test using the TGAI is required for atrazine because the end-use 

product is expected to be transported to water from the intended use site and studies of other 

organisms indicate that the reproductive physiology of fish may be affected. Results of four fish 

life-cycle tests are tabulated below in Table A-12. 

Table A-12. Freshwater Fish Life-Cycle Toxicity

Surrogate Species/ 

Study Duration/ 

Flow-through or 

Static Renewal % 

ai

NOAEC/LOAEC 

 μg/L (ppb) 

(measured or 

 nominal)

Statistically sign. (p<0.05) 

Endpoints Affected

MRID No. 

Author/Year

Study 

Classification

Brook trout 

(Salvelinus frontinalis) 

44 weeks, flow-through

94 NOAEC 65 

LOAEC 120 

(measured)

 7.2 % red. mean length 

16 % red. mean body weight

00024377 

Macek et al. 1976

Supplemental 

(used DMSO, 

treated fish for 

disease after 

allocation to 

tanks, no SC) 

Bluegill sunfish 

(Lepomis macrochirus) 

6-18 months, flow-through

94 NOAEC 95 

LOAEC 500 

(measured)

LOAEC based on loss of 

equilibrium in a 28-day test 

conducted at the same lab.

00024377 

Macek et al. 1976 

Supplemental 

(Low survival for 

fry (F1) in the 

controls)

Fathead minnow 

(Pimephales promelas) 

39 weeks; flow-through

97.1 NOAEC < 150 

LOAEC 150 

(measured)

6.7 % red. in F1 length 

22 % red. in F1 body wt. 

(sign. diff. from neg. control)

42547103 

Dionne 1992

Supplemental 

(Failed to identify 

a NOAEC)

Fathead minnow 

(Pimephales promelas) 

43 weeks, static-renewal

94 NOAEC 210 

LOAEC 870 

(measured)

LOAEC based on 25% 

mortality in a 96-hour test 

conducted at the same lab.

00024377 

Macek et al. 1976

Supplemental 

(High mortality in 

control adults)
18

 A.2.3 Sublethal Effects, Freshwater Fish (Open Literature) 

A.2.4a Sublethal Effects: Freshwater Fish:

A number of open literature studies were reviewed as part of the 2003 IRED. Additional studies 

were reviewed for the California Red-legged frog assessment and results from the 2007 are 

presented. A number of studies were also located in the October, 2008 ecotox search that 

evaluated effects to fish. Most studies located in the open literature search reported endpoints that 

were not more sensitive than the currently available data. Additional studies, evaluating 

biochemical or molecular endpoints, were identified in the 2011 ECOTOX query and the studies 

are presented below. 

Table A-15. Freshwater Fish Sublethal Effects Tests (from 2003 IRED and 2007 ECOTOX Review)

Study type/ 

Test material

Test Organism 

(Common and 

Scientific Name) 

and Age and/or 

Size

Test 

Design

Endpoint Concentration 

in ppb

Citation 

(MRID/ 

EcoRef. #) 

Classification

Hormone evaluation Adult largemouth 

bass (Micropterus 

salmoides) 

Fish exposed to 0, 25, 35, 

50, 75,and 100 ppb for 20 

days 

↑ plasma estradiol (sign) and 

↑ vitellogenin (37x) in 

female bass at 100 ppb 

formulation; sign. ↓ plasma 

11-ketotestosterone in male 

fish at 100 ppb form; plasma 

11-ketotestosterone sign ↓ in 

fish at >35 ppb 

Wieser and 

Gross 2002 

(MRID 

45622304) 

Supplemental (high 

variability) 

Behavior (refuge) Zebrafish 

(Brachydanio 

rerio) 

Fish exposed to 5 to 3125 

ppb for 4 week 

Exposed fish showed a sign. 

preference for dark part of 

aquaria at 5-3125 ppb but no 

difference between atrazine 

treatments; after 4 weeks 15-

24% more fish preferred dark 

habitats 

Steinberg et al 

1995 (MRID 

45204910) 

Supplemental 

Behavior (grouping, 

surfacing, swimming) 

Goldfish Fish exposed to 0.5, 5 and 

50 ppb for 24 hours 

Skin extract added to tanks 

Significant reduction in 

groups at 5 and 50 ppb; other 

significant behaviors 

observed but not doseresponsive – surfacing at 5 

ppb, burst swimming at 0.5 

and 50 ppb, reduced 

sheltering and groups at 5 ppb 

after skin extract added 

Saglio and 

Trijase 1998 

(MRID 

45202914) 

Supplemental 

Kidney function Rainbow trout 28 day exposure to 5, 10 

and 20, 40 and 80 ppb; 

96 hour exposures 

Chronic exposure at 5 ppb 

and higher altered kidney 

structure 

Fischer-Scherl 

et al 1991 

(45202907) 

Supplemental 

Growth and 

properties of various 

tissues 

Rainbow trout; 

Galaxias maculates

and Pseudaphritis 

urvillii

Fish exposed to 0.9, 3.0, 10, 

50 and 340 ppb for 10 days

Consistent significant effects 

observed at 10 ppb for G. 

maculates (↑ muscle 

RNA/DNA); Glutathione in 

liver significantly reduced at 

50 ppb in P. urvillii; 

Reduction in muscle protein 

significant in rainbow trout; 

other effects (not consistent) 

observed at 0.9 and 3.0 ppb 

Davies et al 

1994 (MRID 

45202904) 
19

Gill physiology Gnathonemus 

petersii 

Fish exposed to 500 and 

5000 ppb for 6 hours 

Breaks in gill epithelium at 

500 ppb with deep pits at 

5000 ppb 

Alazemi et al 

1996 (MRID 

45202901) 

Supplemental 

Behavior (breathing, 

swimming, feeding, 

equilibrium) and 

survival 

Nile river fish 

Oreochromis 

niloticus and 

Chrysichthyes 

auratus

Fish exposed to 3000 and 

6000 ppb for 28 days. 

Significant decrease in red 

blood cells, hemoglobin and 

hematocrit 

Significant changes in 

corpuscular endpoints and 

AChE levels 

Clinical signs such as rapid 

respiration and increase gill 

cover movement, slower 

reflexes and swimming, 

reduced feeding, equilibrium 

and death (more pronounced 

in C. auratus) reported 

Hussein et al 

1996 (MRID 

45202911) 

Supplemental – not all 

endpoints could be confirmed 

with data presented 

Enzyme activity Carp Fish exposed to 1500, 3000 

and 6000 ppb 

Serum alkaline phosphatase 

level sign. higher at all 

atrazine levels; effects on 

glutamic-oxaloacetic in liver 

and kidney; histopathological 

effects to gills, liver, kidney 

and intestine at 6000ppb 

Neskovic et al 

1993 (MRID 

45202913) 

Supplemental 

Olfactory function Atlantic salmon 

 (Salmo slar) 

Adult male fish exposed to 

0.5, 5, 10, 20 ppb 

(measured 0.04,3.6,,6.0, and 

14 ppb) 

Effects on olfactory function 

at 0.5-20 ppb 

Moore and 

Waring 1998 

(MRID 

45204906) 

Supplemental (uncertainty in 

measured conc due to possible

degredation) 

Gill physiology and 

survival after transfer 

to full salinity 

seawater. 

 Salmon smolts Fish were exposed to 

atrazine for 7 days at 

atrazine concentrations of 1 

– 23 ug/L under flow 

through conditions. 

Endpoints evaluated 

included gill physiology 

and survival after transfer to 

full salinity sea water. 

Temp: 10-12.5 deg. C 

pH: 7.6 

Solvent: Industrial 

methylated spirits 

Effects on gill physiology 

were observed in at least one 

experiment at 2 ug/L and 

higher. Effects included 

altered Na K ATPase activity, 

increased sodium levels, and 

increased potassium levels. 

Transfer of fish exposed to 

atrazine in freshwater at 1 

ug/L and higher into atrazinefree full salinity seawater 

resulted in mortality; 43% 

mortality was observed at 5 

ug/L and higher after 24 

hours. 

Waring and 

Moore 2004 

(72625) 

Qual: Relevance of 

environmental conditions 

used in this study to the 

assessed species is 

questionable because the 

assessed fish species do not 

enter full salinity seawater; an 

unacceptable solvent was 

used (industrial methylated 

spirits) 

Olfactory detection of

female priming 

pheromone, 

protogandin F2α in FW 

fish 

30 min exposure 

Simazine, Atrazine, 

and Simazine/ 

Atrazine mixtures (% 

a.i. NR) 

Mature male 

Atlantic salmon 

(Salmo salar L.) 

parr; length = 140 

mm; weight = 34.2 

g) 

source: 

Environment 

Agency, Cynrig 

hatchery, Wales 

Skin and cartilage removed 

to expose olfactory rosettes

Olfactory epithelium 

perfused with control water 

for 30 min, then to atrazinetreated water at nominal 

concentrations of 0.1, 0.5, 

and 2.0 ug/l for 30 min 

[results from 0.1 ug/L not 

reported presumably due to 

lack of atrazine detection at 

this concentration]. 

Significant reduction in the 

priming response of male 

salmon to PGF2α (increased 

levels of expressible milt not 

present following exposure to 

PGF) was observed at 0.5 

ug/L. 

Moore, A., and 

N. Lower, 

2001 

(67727) 

Qual: A solvent control, but 

no negative control, was used; 

therefore, potential solvent 

effects cannot be evaluated; 

Study conducted on olfactory 

epithelium; therefore it is 

unclear whether response to 

chemical stimuli would 

impair similar responses in 

intact fish. 

Relationship between the 

magnitude of effects on the 

endpoints evaluated and 

reproduction or survival has 

not been established. 
20

Developmental study; 

Atrazine technical 

unspecified purity 

Rainbow trout Eggs were exposed for 24 

days then hatchlings were 

exposed for 4 days at 

atrazine concentrations of 

28 to 4800 ug/L under flow 

through conditions. 

Incidence of “gross 

debilitating” anomalies was 

evaluated. 

Temp: 12-14 DegC 

pH: 7 – 7.8 

LC50 (combined mortality + 

terata incidences) in rainbow 

trout was 870 ug/L. 

Birge et al., 

1983. , 

(19124) 

Qual: No control responses 

were reported; limited water 

quality parameters were 

provided; use of a solvent is 

uncertain; Reported toxicity 

value is less sensitive than the 

available life-cycle NOAEC 

of 65 ppb. LC50s were based 

on combination of 

abnormalities and mortality. 

Olfactory-mediated 

behavioral and 

neurophysiological 

response in FW fish 

30 min exposure 

Atrazine (97.4% ai) 

Juvenile rainbow 

trout (mass = 32.7 

+1.2 g, length = 

14.7 + 0.18 cm) 

Source: Sun 

Valley Trout Farm 

(Mission BC) 

Fish statically exposed to 1, 

10, and 100 ug/L atrazine (6 

per treatment level) and 

acetone control. 

Preference/avoidance to 10-7 

L-histidine was measured. 

Electro-olfactograms 

(EOGs) of olfactory rosettes 

were measured (EOGs 

measure electrical responses 

of olfactory neurons) 

N = 6 fish/treatment level 

and solvent control 

Filtered, dechlorinated 

municipal water used. 

pH = 6.8 

Hardness = 6.12 CaCO3 

Oxygen = > 90% sat. 

Light/Dark = 12:12 h 

Food: salmon pellets ad 

libitum 

Temp: 12o

C 

Exposure to 10 ppb atrazine 

resulted in L-histidine 

avoidance 

Hyperactivity observed at 

atrazine concentrations of 1 

and 10 ppb. 

L-histidine evoked EOGs 

were significantly reduced at 

10 ppb 

Tierney et al., 

2007 

(89625) 

Qual: A solvent control, but 

no negative control, was used; 

therefore, potential solvent 

effects cannot be evaluated. 

Study conducted on olfactory 

epithelium; therefore it is 

unclear whether response 

would impair similar 

responses in intact fish. 

Relationship between the 

magnitude of effects on the 

endpoints evaluated and 

reproduction, survival, or 

growth has not been 

established. 

Studies from 2008 ECOTOX 

Endpoint Common name Toxicity Value Ref# 

Reference 

7-21 d 

LOEC/NOAEC 

Goldfish 0.859 mg/L/0.19-0.9 

mg/L 

Spano et al. 2004 (73297) 

8-8.5 d nonlethal 

4.5 d nonlethal 

Channel catfish 4.5, 8-8.5 d: 46.7 

mg/L 

Birge et al. 1979 (563) 

23 d non-lethal Rainbow trout 50 mg/L Birge et al 1979 (563) 

12-h 

NOAEL/LOAEC 

Atlantic 

croaker 

1-10 uM Thomas and Sweatman 2008 (103377) 

81-d NOAEL 

5-d NOAEL 

Atlantic 

salmon 

81-d: 0.0005/0.005 

mg/L 

5-d: 0.000495 mg/L 

Moore et al. 2007 (103267) 

10-21-d 

NOAEL/LOAEL 

Atlantic 

salmon 

0.0085-0.084 / 0.084 Nieves-Puigdoller et al. 2007 (93473) 

10-d LC50 Blennie 

Common 

jollytail 

Rainbow trout 

>0.34 mg/L Davies et al. 1994 (4442) 

10-d 

NOEC/LOEC 

Blennie 0.003-0.01 mg/L Davies et al. 1994 (4442) 

10-d NOEC/ 

LOEC 

Rainbow trout 0.05- >0.34/ 0.34 

mg/L 

Davies et al. 1994 (4442) 
21

8-d 

NOAEL/LOAEL 

Red drum 0.06-0.08 / 0.033 -

0.037 mg/L 

McCarthy and Fuiman 2008 (103059) 

27-d LC01 Channel catfish 0.029-0.0772 mg/L Birge et al. 1979 (563) 

Studies from 2011 ECOTOX 

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Gonads of Juvenile Goldfish (Carassius auratus L.).  Ecotoxicology17(6): 464‐470.  E111569.

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Cericato L;Neto JGM;Fagundes M;Kreutz LC;Quevedo RM;Finco J;Da Rosa JGS;Koakoski G;Centenaro L;Pottker E;Anziliero D;Barcellos LJG. 2008

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Responsiveness of the Interrenal Tissue of Jundia (Rhamdia quelen) to an In Vivo ACTH Test Following Acute Exposure to Sublethal

Concentrations of Agrichemicals Comp. Biochem. Physiol. C Pharmacol. Toxicol. Endocrinol.149:363‐367. E112903

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Liedtke A;Muncke J;Rufenacht K;Eggen RIL. 2008.  Molecular Multi‐Effect Screening of Environmental Pollutants Using the MolDarT.  Environ.

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Raldua D;Babin PJ. 2009.  Simple, Rapid Zebrafish Larva Bioassay for Assessing the Potential of Chemical Pollutants and Drugs to Disrupt Thyroid

Gland Function

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Suzawa M;Ingraham HA. 2008. The Herbicide Atrazine Activates Endocrine Gene Networks via Non‐Steroidal NR5A Nuclear Receptors in Fish and

Mammalian Cells

PLoS One3(5): 11 p. E119818

Dong X;Zhu L;Wang J;Xie H;Hou X;Jia W. 2009. Effects of Atrazine on Cytochrome P450 Enzymes of Zebrafish (Danio rerio) Chemosphere77(3):

404‐412. E150207

Jin Y;Zhang X;Shu L;Chen L;Sun L;Qian H;Liu W;Fu Z. 2010.  Oxidative Stress Response and Gene Expression with Atrazine Exposure in Adult

Female Zebrafish (Danio rerio)

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Xing H;Wang J;Li J;Fan Z;Wang M;Xu S.  Effects of Atrazine and Chlorpyrifos on Acetylcholinesterase and Carboxylesterase in Brain and Muscle of

Common Carp

Environ. Toxicol. Pharmacol.30:26‐30.  E150334

Reimschuessel R;Evans E;Andersen WC;Turnipseed SB;Karbiwnyk CM;Mayer TD;Nochetto C;Rummel NG;Gieseker CM.  2010.   Residue Depletion

of Melamine and Cyanuric Acid in Catfish and Rainbow Trout Following Oral Administration J. Vet. Pharmacol. Ther.33(2): 172‐182. E152274

Reimschuessel R;Gieseker CM;Miller RA;Ward J;Boehmer J;Rummel N;Heller DN;Nochetto C;De Alwis GK;Bataller N;Andersen WC;Turnipseed

SB;Karbiwnyk CM;Satzger RD;Crowe JB;Wilber NR;Reinhard MK;Roberts JF;Witkowski MR. 2008.  Evaluation of the Renal Effects of Experimental

Feeding of Melamine and Cyanuric Acid to Fish and Pigs

Am. J. Vet. Res.69(9): 1217‐1228.  E152942

Kreutz LC;Barcellos LJG;Marteninghe A;Davi dos Santos E;Zanatta R. 2010.  Exposure to Sublethal Concentration of Glyphosate or Atrazine‐Based

Herbicides Alters the Phagocytic Function and Increases the Susceptibility of Silver Catfish Fingerlings (Rhamdia quelen) to Aeromonas hydrophila

Challenge Fish Shellfish Immunol.29(4): 694‐697   

Ramesh M;Srinivasan R;Saravanan M. 2009.   Effect of Atrazine (Herbicide) on Blood Parameters of Common Carp Cyprinus carpio

(Actinopterygii: Cypriniformes)

Afr. J. Environ. Sci. Technol.3(12): 453‐458. E153798

Nwani CD;Lakra WS;Nagpure NS;Kumar R;Kushwaha B;Srivastava SK.  2010.   Toxicity of the Herbicide Atrazine: Effects on Lipid Peroxidation and

Activities of Antioxidant Enzymes in the Freshwater Fish Channa punctatus (Bloch)  Int. J. Environ. Res. Public Health7(8): 3298‐3312.  E153817

Yan X;Zha J;Shi B;Wang D;Wang Z;Tang H. 2010.  In Vivo Toxicity of Nano‐C60 Aggregates Complex with Atrazine to Aquatic Organisms.  Chin. Sci.

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Matsumoto J;Hosmer AJ;Van Der Kraak G.  2010.  Survival and Iono‐Regulatory Performance in Atlantic Salmon Smolts is not Affected by Atrazine

Exposure

Comp. Biochem. Physiol. C Pharmacol. Toxicol. Endocrinol.152(3): 379‐384. E153822

Xing H;Han Y;Li S;Wang J;Wang X;Xu S.  2010.  Alterations in mRNA Expression of Acetylcholinesterase in Brain and Muscle of Common Carp

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Ecotoxicol. Environ. Saf.73(7): 1666‐1670.  E153823

Yang L;Zha J;Zhang X;Li W;Li Z;Wang Z. 2010.   Alterations in mRNA Expression of Steroid Receptors and Heat Shock Proteins in the Liver of Rare

Minnow (Grobiocypris rarus) Exposed to Atrazine and p,p'‐DDE Aquat. Toxicol.98(4): 381‐387. E153830

Nwani CD;Nagpure NS;Kumar R;Kushwaha B;Kumar P;Lakra WS. 2011. Mutagenic and Genotoxic Assessment of Atrazine‐Based Herbicide to

Freshwater Fish Channa punctatus (Bloch) Using Micronucleus Test and Single Cell Gel Electrophoresis  Environ. Toxicol. Pharmacol.31(2): 314‐

322.  E153833

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Atrazine to Freshwater Air Breathing Fish Channa punctatus (Bloch) Int. Aquat. Res.2(2): 105‐111. E153834

Zhu L;Zhu LS;Shao B;Song Y;Xie H;Wang J;Wang JH;Liu W;Hou XX.  2011. DNA Damage and Effects on Antioxidative Enzymes in Zebra Fish (Danio

rerio) Induced by Atrazine.  Toxicol. Mech. Methods21(1): 31‐36. E153842

Cavas T. 2011.  In Vivo Genotoxicity Evaluation of Atrazine and Atrazine‐Based Herbicide on Fish Carassius auratus Using the Micronucleus Test

and the Comet Assay.  Food Chem. Toxicol.49(6): 1431‐1435.  E153855

Wang X;Xing H;Li X;Xu S;Wang X. 2011.   Effects of Atrazine and Chlorpyrifos on the mRNA Levels of IL‐1 and IFN‐[Gamma]2b in Immune Organs

of Common Carp  Fish Shellfish Immunol.31(1): 126‐133.  E153872.

 

 

A.2.4c Amphibians:

Toxicity Data for amphibians in presented in Appendix C. 

A.2.5 Freshwater Invertebrates, Acute 

A freshwater aquatic invertebrate toxicity test using the TGAI is required to establish the toxicity 

of atrazine to aquatic invertebrates. Results of this test and others are summarized below in Table 

A-18. 

Table A-18. Freshwater Invertebrate Acute Toxicity

Surrogate Species/ 

Static or 

Flow-through % ai

48 or 96-hour LC50/EC50 

μg/L (ppb) 

(measured/nominal) 

Toxicity 

Category

MRID No. or 

ECOTOX No. 

Author/Year

Study Classification

Midge 

(Chironomus tentans) 

Static test

94 720 

(nominal)

highly toxic 000243-77 

Macek et al. 1976

Supplemental 

(48-hour LC50 & 

raw data are missing)

Midge 

(Chironomus riparius)

85.5 1,000 

(unknown)

highly toxic 450874-13 

Johnson 1986

Supplemental 

(raw data are missing)

Scud ≤ 7-d old 

(Hyalella azteca) 

Static renewal 

98 

1,500 

(measured, unknown if 

used in calc) 

Moderately 

toxic 

E 118745 

Ralston-Hooper 2009 

Qualitative (raw data 

missing) 

Waterflea 

(Daphnia magna)

85.5 3,500 

(unknown)

moderately 

toxic

450874-13 

Johnson 1986

Supplemental 

(raw data are missing)
23

Table A-18. Freshwater Invertebrate Acute Toxicity

Waterflea < 24-hours old 

(Daphnia magna) 

26-Hour static test

?? 3,600 

(unknown)

at least 

moderately 

toxic

000028-75 

Frear & Boyd 1967

Supplemental 

(unknown ai, 26-hour test 

& no raw data)

 

Scud 

(Gammarus fasciatus) 

Static test

94 5,700 

(nominal)

moderately 

toxic

000243-77 

Macek et al. 1976

Supplemental 

(48-hour LC50 & 

raw data are missing)

Stonefly (nymph) 

(Acroneuria sp.) 

Flow-through test 

67.4 mg/L CaCO3

98.5 6,700 

(measured)

moderately 

toxic

Brooke 1991 Supplemental 

(raw data are missing) 

Waterflea 

(Daphnia magna) 

Static test

94 6,900 

(nominal)

moderately 

toxic

000243-77 

Macek et al. 1976

Supplemental 

(raw data are missing)

Shrimp (1-1.5 cm) 

(Paratya australiensis) 

Static-renewal-48 hr 

97 9,700-9,900 (water only) 

6,500-6,800 (water & 

sediment) 

(measured-initial) 

Moderately 

toxic 

E76267 

Phyu et al. 2005 

Qualitative (raw data 

missing, non-native spp., 

Scud juvenile 

(Hyalella azteca) 

Flow-through test 

67.4 mg/L Ca CO3

98.5 14,700 

(measured)

slightly toxic Brooke 1991 Supplemental 

(raw data are missing)

Scud juvenile 

(Gammarus pulex) 

Static-renewal - daily

?? 14,900 

(measured) 

4.4 @ 10 days

slightly toxic 452029-17 

Taylor, Maund & 

Pascoe 1991

Supplemental 

(raw data are missing)

Cladoceran 

(Pseudosida ramosa) 

static 

99 17,100 (mean of 20 trials) 

(nominal) 

Slightly 

toxic 

E153837 

Freitas et al 2011 

Qualitative (raw data 

missing) 

Waterflea 

(Daphnia carinata) 

Static 

 22,400-24,600 (water 

only) 

25,300-26,700 (water & 

sediment) 

(measured –initial) 

Slightly 

toxic 

E74233 

Phyu et al 2004 

Qualitative (raw data 

missing) 

 

Scud adult 

(Diporeia spp.) 

Static renewal 

98 

>3,000 

(measured unknown if 

used in calc) 

unknown 

Ralston-Hooper et al. 

2009 

E118745 

Qualitative (raw data 

missing) 

Waterflea 

(Ceriodaphnia dubia) 

48-Hour static test

97 > 4,900 

(measured) 

Slope - no mortality

unknown 452083-09 

Jop 1991

Supplemental 

( EC50 value not 

determined)

Leech 

(Glossiphonia 

complanata) 

Static-renewal weekly

99.2 > 16,000 

(measured) 

6,300 μg/L @ 28 days

slightly toxic 452029-16 

Streit & Peter 1978

Supplemental 

(raw data are missing)

Leech 

(Helobdella stagnalis) 

Static-renewal weekly

99.2 > 16,000 

(measured) 

9,900 μg/L @ 27 days

slightly toxic 452029-16 

Streit & Peter 1978

Supplemental 

(raw data are missing)

Snail 

(Ancylus fluviatilis) 

Static-renewal weekly

99.2 >16,000 

(measured) 

> 16, 000 μg/L @ 

40 days 

(35 % mortality)

slightly toxic 452083-05 

Oris, Winner & 

Moore 1991

Supplemental 

(raw data are missing)

Waterflea <12 hr old 

(Ceriodaphnia dubia) 

Static 48-hour test 

57 mg/L CaCO3

> 99 > 30,000 

(measured) 

Slope - no data

slightly toxic 452029-17 

Taylor, Maund & 

Pascoe 1991

Supplemental 

(raw data are missing)
24

Table A-18. Freshwater Invertebrate Acute Toxicity

Mussel (glochidia and 

juveniles) 

(Lampsilis siliquoidea) 

static 

98 >30,000 (both life stages) 

(measured, results based 

on nominal) 

unknown E99469 

Bringolf et al. 2007 

Qualitative (raw data 

missing) 

Freshwater mussel 

A. imbecillis juvenile and 

mature organisms 

97 >60,000 in both juvenile 

and mature A. imbecillis. 

Unknown Johnson et al. 1993 

(50679) 

Qualitative (no raw data, 

uncertain about reported 

high concentrations) 

Midge

(Chironomus riparius) 

Static-renewal - daily 

10-Day test

?? > 33,000 

(measured) 

18,900 μg/L @ 10 days

slightly toxic 000272-04 

Drake 1976

Supplemental 

(raw data are missing) 

(EC50 115 ppm exceeds 

water solubility (33 ppm)

Midge

(Chironomus tentans) 

Flow-through 

10-Day test; water-spiked 

exposure

98.5 Mortality: 

LC50 > 24,000 

(measured) 

(37% mortality) 

NOAEC = 16,000 

LOAEC = 24,000 

Growth (dry weight): 

EC50 = 8,300 (measured) 

NOAEC <3,200 

LOAEC = 3,200 

slightly toxic 459040-01 

Putt, 2002

Supplemental 

(does not fulfill any 

currently-approved U.S. 

EPA SEP guideline) 

Midge

(Chironomus temtans) 

Static-renewal – to 

maintain water quality 

10-Day test; sedimentspiked exposures

98.5 

Mortality (measured conc):

SED NOAEC = 130,000 

SED LOAEC = 270,000 

Pore Water (PW) NOAEC 

= 26,000 

PW LOAEC = 29,000 

(14% mortality) 

PW LC50 >30,000 

Growth: Dry Weight 

(measured conc):

SED NOAEC = 24,000 

SED LOAEC = 60,000 

PW NOAEC = 4,000 

PW LOAEC = 21,500 

slightly toxic 459040-02 

Putt, 2003

Supplemental 

(does not fulfill any 

currently-approved U.S. 

EPA SEP guideline) 

Formulations % ai 

Product

 

Waterflea 

(Daphnia magna) 

Flow-through test

79.6 

80 WP

>31,000 

(higher concs. than 31,000 

υg/L were cloudy; 40% 

immobilization at 31 ppm) 

(measured) 

slope 2.433

slightly toxic 420414-01 

Putt 1991 

Supplemental 

for formulation 

(EC50 was not identified 

due to insolubility)

Waterflea 

(Daphnia pulex) 

Static test; 15ΕC 

282 mg/L hardness 

With & without sediment

40.8 

4 L

36,500 

(nominal) 

46,500 

(with sediment)

slightly toxic 452277-12 

Hartman & Martin 

1985

Supplemental 

for formulation 

(EC50 exceeds water 

solublity and low temp.)

Mussel (glochidia and 

juveniles) 

(Lampsilis siliquoidea) 

static 

40.8 

4L 

>30,000 (both life stages) 

(measured, results based 

on nominal) 

unknown E99469 

Bringolf et al. 2007 

Qualitative (raw data 

missing) 

Freshwater mussel 

Utterbackia imbecillis

Glochidia 

static 

40.8 

4L 

LC50 = 241,000 Practically 

non-toxic 

Conners and Black, 

2004 

(74236) 

Qual: Study tested a 

formulated product at 

concentrations 

considerably higher than 

the solubility limit of 

atrazine of 33 mg/L. 
25

Degradates: Table A-19 presents freshwater invertebrate toxicity data for four degradates. 

Table A-19. Freshwater Invertebrate Acute Toxicity 

Surrogate Species/ 

Flow-through or Static

% ai 

formul.

48-hour EC50 (ppb) 

(measured/nominal) Toxicity Category

MRID No. 

Author/Year

Study 

Classification

HA 

Waterflea 

(Daphnia magna); 1st

instar (6-24 h old) 

Static test 

98 >4,100 

(measured dissolved) moderately toxic* 

465000-01 

Peither, 2005c 

Acceptable 

DIA 

Waterflea 

(Daphnia magna); 1st

instar (6-24 h old) 

Static test 

Not 

reported 

>100,000 

 (measured dissolved) Practically non-toxic 

47046101 

Vial, 1991c 

Supplemental 

Amphipod 

(Hyalella azteca) 

98 96-hr LC50 7,200 

(measured unknown if 

used in calc) 

Moderately toxic Ralson-Hooper et al 

2009 

E118745 

Qualitative – no 

raw data, 

Amphipod 

(Diporeia spp) 

98 96-hr LC50 >3,000 

(measured unknown if 

used in calc) 

Moderately toxic Ralson-Hooper et al 

2009 

E118745 

Qualitative – no 

raw data, 

DACT 

Waterflea 

(Daphnia magna); 1st

instar (6-24 h old) 

Static test 

Not 

reported 

>100,000 

(measured dissolved) Practically non-toxic 

47046102 

Vial, 1991d 

Supplemental 

DEA 

Amphipod 

(Hyalella azteca) 

98 96-hr LC50 7,200 

(measured unknown if 

used in calc) 

Moderately toxic Ralson-Hooper et al 

2009 

E118745 

Qualitative – no 

raw data, 

Amphipod 

(Diporeia spp) 

98 96-hr LC50 >3,000 

(measured unknown if 

used in calc) 

Moderately toxic Ralson-Hooper et al 

2009 

E118745 

Qualitative – no 

raw data, 

* Biological results for the study were based on the mean-measured concentration of dissolved Hydroxyatrazine, 

which remained constant at the limit of its water solubility throughout the duration of the test. Therefore, 

hydroxyatrazine is not acutely toxic to Daphnia magna at the limit of its water solubility. 

Although the freshwater invertebrate EC50 value (>4,100 ppb) for the degradate, hydroxyatrazine, 

is within the range classifying it as moderately toxic, the biological results for the study were 

based on dissolved (filtered) mean-measured concentrations of hydroxyatrazine, which remained 

constant at the limit of its water solubility (3-4 ppm ai) throughout the duration of the test (MRID 

465000-01). Therefore, the potential toxicity of hydroxyatrazine appears to be limited by its 

solubility. 

 A.2.6 Freshwater Invertebrate, Chronic 

A freshwater aquatic invertebrate life-cycle test using the TGAI is required for atrazine since the 

end-use product is expected to be transported to water from the intended use site and the 

following conditions are met: the pesticide is intended for use such that its presence in water is 

likely to be continuous; an aquatic acute LC50 is less than 1 mg/L; and the pesticide is persistent 
26

in water (i.e., half-life greater than 4 days). The preferred test species is Daphnia magna. Results 

of these tests are summarized below in Table A-20. 

Table A-20. Freshwater Aquatic Invertebrate Life-Cycle Toxicity

Surrogate Species/ 

Study Duration/ 

Flow-through or 

Static Renewal % ai

NOAEC/LOAEC 

 μg/L (ppb) 

(measured or 

nominal)

Statistically sign. (p=0.05) 

Endpoints Affected

MRID No. 

Author/Year

Study 

Classification

Scud 

(Gammarus fasciatus) 

30 days / flow-through 

94 NOAEC 60 

LOAEC 140 

(measured)

Based on reduced development of 

F1 to seventh instar.

000243-77 

Macek et al. 

1976

Supplemental 

(used DMSO, 

no SC, 64-74% 

control 

survival, 

reproduction in 

1 of 2 reps in 

control) 

Midge 

(Chironomus tentans) 

38 days / flow-through

94 NOAEC 110 

LOAEC 230 

(measured)

Based on reduced adult emergence

000243-77 

Macek et al. 

1976

Supplemental 

(used DMSO, 

no SC) 

Waterflea 

(Daphnia magna) 

21 days / flow-through

94 NOAEC 140 

LOAEC 250 

(measured)

Based on reduced production of 

young/female in F0 generation

000243-77 

Macek et al. 

1976

Supplemental 

(used DMSO, 

no SC, control 

survival 61%) 

Waterflea 

(Daphnia pulex) 

28-Day static-renewal 

 

70-Day static-renewal test

99.2 NOAEC 1,000 

LOAEC 2,000 

(nominal)

Based on reduction in 

young/female

452029-15 

Schober & 

Lampert 1977

Supplemental 

(no raw data for 

statistical 

analyses)

Waterflea - 6 generations 

(Daphnia magna) 

Static-renewal test 

NR Cups: 

NOAEC 200 

LOAEC 2,000 

(unknown) 

4 L aquarium: 

NOAEC ?? 

LOAEC ?? 

(water from 

treated corrals)

Based on reduction in # of young 

in generations 4, 5, & 6. 

Kaushik, 

Solomon, 

Stephenson and 

Day 1985

Supplemental 

(methods and 

raw data are not 

reported)

Leech 

(Helobdella stagnalis) 

40 Days 

Static-Renewal weekly

99.2 NOAEC <1,000 

LOAEC 1,000 

(measured)

Based on reduced % hatch

452029-16 

Streit & Peter 

1978

Supplemental 

(no raw data for 

statistical 

analyses)

Waterflea < 12 hr. old 

(Ceriodaphnia dubia) 

Two 7-Day static-renewal 

tests; Renewed M, W, & F 

57 CaCO3; Temp. 25ΕC

> 99 NOAEC 2,500 

LOAEC 5,000 

NOAEC 2,500 

LOAEC 5,000 

(measured)

Based on reduction in mean total 

number of young per living female 

(3 broods)

452083-05 

Oris, Winner and 

Moore 1991

Supplemental 

(no raw data for 

analyses)

Green hydra (normal) 

(Chlorohydra viridissima) 

21-Day Static test

NR NOAEC <5,000 

LOAEC 5,000 

(nominal)

Based on reduction in budding 

rates

452029-01 

Benson & Boush 

1983

Supplemental 

(no raw data for 

analyses)

Waterflea 3-day old adult 

(Ceriodaphnia dubia) 

Two 4-Day static-renewal 

tests; Renewed M & W 

57 CaCO3; Temp. 25ΕC

> 99 NOAEC 5,000 

LOAEC 10,000 

NOAEC 10,000 

LOAEC 20,000 

(measured)

Based on reduction in mean total 

number of young per living female 

(3 broods)

452083-05 

Oris, Winner and 

Moore 1991

Supplemental 

(no raw data for 

analyses)
27

Table A-20. Freshwater Aquatic Invertebrate Life-Cycle Toxicity

Freshwater Snail 

(Ancylus fluviatilis) 

40 Days 

Static-Renewal weekly

99.2 1,000 

 4,000 

16,000 

 (measured)

38-39% red. in egg capsules & 

 eggs in April/May 

56-57% red. in eggs in April/May 

15-16% red. in eggs in July/Aug. 

68-73% red. in eggs in April/May 

65-71% red. in eggs in July/Aug.

452029-16 

Streit & Peter 

1978

Supplemental 

(no raw data for 

statistical 

analyses)

Leech 

(Glossiphonia complanata) 

27-Days 

Static-Renewal weekly

99.2 1,000 

 4,000 

16,000 

 (measured)

no reduction in egg production 

17 % higher mortality 

33 % higher mortality 

67 % higher mortality

452029-16 

Streit & Peter 

1978

Supplemental 

(no raw data for 

statistical 

analyses)

Ancylus fluviatilis (river 

limpet), Glossiphonia 

complanata (leech), 

Helobdella stagnalis (leech) 

40-Day lab 

99.2 Effects observed 

at all 

concentrations 

(1000, 4000 and 

16000 ) 

Evaluated for food ingestion, 

growth, and egg production. 

Streit and Peter, 

1978 

QUAL. 

NOAEC was 

not achieved; 

no information 

was reported on 

experimental 

conditions (e.g., 

temperature, 

pH, DO); 

limited 

information on 

study design 

parameters 

such as no. of 

replicates, no. 

of animals 

treated per 

concentration, 

etc.) was 

reported. 

Numerous invertebrates 

including annelids, 

arthropods, and mollusks. 

8 wks

NS No effects were 

observed at any 

concentration. 

NOAEC = 670 

ppb 

evaluated for abundance of various 

taxa 

EG&G, 1979 Invalid: 

Possible control 

contamination;; 

unacceptable 

solvent; a 

solvent control, 

but no negative 

control was 

used 

Lymnaea palustris 

12-week mesocosm study 

97.8 No effects 

occurred at any 

concentration for 

any of the 

parameters 

evaluated..The 

NOAEC was 125 

ug/L (nominal). 

Endpoints evaluated included 

mortality, growth, fecundity, and 

biochemical parameters (glycogen 

content, polysaccharide hydrolysis 

Baturo et a. 

(1995) 

QUAL. 

Replicate 

mesocosms 

were not used 

per 

concentration; 

atrazine 

concentrations 

were not 

analytically 

confirmed; no 

water/sediment 

quality data 

were provided. 

Mussel (1.475 mm) 

(Lampsilis siliquoidea) 

21 –d static renewal (95% 

every 48 or 72 hours) 

98 

and 

40.8 

Tech 21-d EC50 = 

10,100 

Form 21-d EC50 

= 3,100 

(measured based 

on 

Based on immobility of organisms; 

no effect on growth 

E99469 

Bringolf et al 

2007 

Qualitative: no 

raw data 

reported water 

quality and 

control 

mortality was 

provided 
28

 

A.2.8b Freshwater Field Studies (New Open Literature Data) 

Based on the results of the 2003 IRED for atrazine, potential adverse effects on sensitive aquatic 

plants and non-target aquatic organisms including their populations and communities, are likely 

to be greatest when atrazine concentrations in water equal or exceed approximately 10 to 20 μg/L 

on a recurrent basis or over a prolonged period of time. Given the large amount of 

microcosm/mesocosm and field data for atrazine, only effects data that are less than or more 

conservative than the 10 μg/L aquatic-community effect level were considered. In addition, data 

for taxa that are directly relavent to the endangered species evaluated as part of this assessment 

were also considered. Field study data for amphibians, including frogs and salamanders are 

included in Section D.2.3. Based on the selection criteria for review of new open literature, all 

of the available studies show effects levels to freshwater fish and invertebrates at concentrations 

greater than 10 μg/L. 

One open literature artifical stream mesocosm study was reviewed because it provides data on 

freshwater snails, which may be used as surrogate for endangered mussels. The results of this 

study, which are summarized as part of Table A-25, show potential indirect effects to grazing 

behavior (i.e., increased searching velocity and movement patterns) at 15 μg/L atrazine, due to a 

decrease in periphyton biomass (Roses et al., 1999; Ecotox Reference # 60860). No significant 

effects were observed in rates of snail mortality and biomass. An increase in snail activity may 

represent a change in resource quantity, resulting in increased searching speed when the biomass 

of periphyton decreases. However, it is not possible to make a quantitative link between 

increased searching velocity in snails and the assessment endpoints of survival, fecundity or 

growth; therefore, data from this study is not used to derive RQs in the risk assessment. 

 Table A-25. Freshwater Mesocosm Study from Open Literature (2007 Review)

Study type/ 

Test material

Test Organism (Common 

and Scientific Name) and 

Age and/or Size

Test 

Design

Endpoint 

Concentration 

in ppm

Citation 

(EcoRef. #) 

Rationale for Use in 

Risk Assessment(1)

Artifical stream 

18 day exposure 

Atrazine (% ai 

NR) 

Freshwater snails (Physa 

acuta and Ancylus 

fluviatilis) 

- U-shaped artifical streams 

(170 cm L x 20 cm W x 20 

cm deep); water velocity = 

1 cm/sec; depth = 1.9 – 2.2 

cm; photoperiod: 8:16 h 

light/dark; channel bottoms 

contained surfaces for 

algae attachment. 

- Atrazine injected 

continuously at 15 ppb in 3 

ponds, 3 ponds = control 

- Endpoints: snail 

mortality, biomass, and 

activity; chlorophyll a

concentration 

LOAEC = 15 ppb 

Sign. changes in grazer 

behavior, increased 

searching velocity, and 

different movement 

patterns at 15 ppb. No 

sign. effects on snail 

mortality or biomass 

Roses, et al., 1999 

(60860) 

QUAL: 

- no raw data provided 

- only one atrazine 

concentration tested 

- relevance of increased 

searching velocity in 

snails to survival, 

growth and 

reproductive success is 

uncertain 
29

(1) QUAL = The paper is not appropriate for quantitative use but is of good quality, addresses issues of concern to the risk 

assessment and is used in the risk characterization discussion. 

NR = Not reported. 

A.3 Toxicity to Estuarine and Marine Animals 

 A.3.1 Estuarine and Marine Fish, Acute 

Acute toxicity testing with estuarine/marine fish using the TGAI is required for atrazine because 

the end-use product is expected to reach this environment due to its use in coastal counties. The 

preferred test species is sheepshead minnow. Results of these tests are summarized in Table A26 

Table A-26. Estuarine/Marine Fish Acute Toxicity

Surrogate Species/ 

Static or Flow-through/ 

Salinity & Temperature % ai

96-hour LC50 (ppb) 

(measured/nominal) 

Probit Slope Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Sheepshead Minnow 

larvae < 48-hours old 

(Cyprinodon variegatus) 

Static test, T - 20ΕC 

Salinity 25, 15, 5 g/L;

97.1 Sal. 25 g/L 2,000

Sal. 15 g/L 2,300 

Sal. 5 g/L 16,200 

(measured) 

Slope - no data

moderately toxic 452083-03 & 

452277-11 

Hall, Jr., Ziegenfuss, 

Anderson, Spittler & 

Leichtweis 1994

Supplemental 

(no raw data 

on mortalities; 

fed fish during 

study)

Spot 

(Leiostomus xanthurus) 

Static test 

Salinity - 12 g/L; T - 22+1ΕC

97.4 8,500 

(nominal) 

Slope - no data

moderately toxic 452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data)

Sheepshead minnow 

(Cyprinodon variegatus) 

Flow-through test 

Salinity - 31 g/L; T - 22-23ΕC

97.1 13,400 

(measured) 

Slope 4.377

slightly toxic 433449-01 

Machado 1994

Acceptable 

Spot (juvenile) 

(Leiostomus xanthurus) 

Flow-through test 

Salinity - 29 g/L; T - 28ΕC

99.7 > 1,000 

(nominal) 

Slope - none

unknown 402284-01 

Mayer 1986

Supplement 

(48-hour test)

Sheepshead minnow 

(Cyprinodon variegatus) 

Flow-through test

97.4 > 16,000 

(30 % mortlity) 

(measured) 

Slope - none

unknown 452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data)

Since the LC50 values are in the range of 1,000 – 10,000 ppb, atrazine is categorized as 

moderately toxic to estuarine/marine fish on an acute exposure basis. Toxicity data on 

sheepshead minnow, Cyprinodon variegatus, indicates that atrazine toxicity increases with 

increasing salinity levels. The acute effects endpoint for estuarine/marine fish is based on the 

LC50 value of 2,000 ppb for sheepshead minnow at a salinity of 25 o

/oo (MRID 452083-03 and 

452277-11). 
30

 A.3.2 Estuarine and Marine Fish, Acute (Open Literature 2006 Review) 

A.3.3. Acute Marine/Estuarine Toxicity Data - Degradates

A special acute estuarine fish test (72-3) is required to address concerns for the toxicity of 

atrazine degradates to estuarine fish (preferably sheepshead minnow). Table A-27 presents 

estuarine/marine fish toxicity data for hydroxyatrazine. 

Table A-27. Marine/Estuarine Invertebrate Acute Toxicity (Hydroxyatrazine)

Surrogate Species/ 

Flow-through or Static

% ai 

formul.

96-hour LEC50 (ppb) 

(measured/nominal) Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Sheepshead minnow 

(Cyprinodon variegatus) 

Static test; T = 21-24 o

C 

Salinity = 32‰ 

97.1 >1,900 (no mortality) 

(measured) moderately toxic* 

465000-06 

Sayers, 2005a 

Acceptable 

* Biological results for the study were based on the mean-measured concentrations of Hydroxyatrazine, which 

remained constant at the limit of its water solubility throughout the duration of the tests. Therefore, hydroxyatrazine 

is not acutely toxic to estuarine/marine fish at the limit of its water solubility. 

Although the estuarine/marine fish LC50 value (>1,900 ppb) for the degradate, hydroxyatrazine, 

is within the range classifying it as moderately toxic, the biological results for the study were 

based on mean-measured concentrations of hydroxyatrazine, which remained constant (>90% 

recovery of nominal concentrations) at the limit of its water solubility (~1 ppm ai) throughout the 

duration of the test (MRID 465000-06). Therefore, the solubility of hydroxyatrazine may limit 

its toxicity to marine and estuarine invertebrates. 

 A.3.2 Estuarine and Marine Fish, Chronic 

An estuarine/marine fish early life-stage toxicity test using the TGAI is required for atrazine 

because the end-use product may be applied directly to the estuarine/marine environment or is 

expected to be transported to this environment from the intended use site, and the following 

conditions are met: the pesticide is intended for use such that its presence in water is likely to be 

continuous; an aquatic acute LC50 or EC50 is less than 1 mg/L; and the pesticide is persistent in 

water (i.e., half-life greater than 4 days). The preferred test species is sheepshead minnow. 

Results of this test are summarized below in Table A-28. 
31

Table A-28. Estuarine/Marine Fish Early Life-Stage Toxicity Under Flow-through Conditions

Surrogate Species/ 

Study Duration/ 

Flow-through or Static 

Salinity & Temperature

% ai

NOAEC/LOAEC 

μg/L (ppb) 

(measured or nominal)

Statistically sign. (p=0.05) 

Endpoints Affected

MRID No. 

Author/Year

Study 

Classification

Sheepshead Minnow 

(Cyprinodon variegatus)

Study duration - unknown 

Flow-through test 

Salinity -13g/L; T 30+1ΕC

97.4 NOAEC 1,900 

LOAEC 3,400 

(measured)

89 % red. in juvenile 

 survival

452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data for 

statistical 

analyses)

Sheepshead Minnow 

(Cyprinodon variegatus)

Study duration – 28 days PH 

Flow-through test 

Salinity = 29 – 31 o

/oo

T = 24 – 27 o

C 

97.1 NOAEC = 1,100

LOAEC = 2,200 

(measured 

17% reduction in mean 

length; 46% reduction in 

mean wet weight 

466482-03, 49526-

06, and 469526-04 

Cafarella, 2005a 

Acceptable 

In the 2003 atrazine IRED, chronic estuarine/marine fish data from Ward and Ballentine (1985; 

MRID # 452029-20) were used to evaluate chronic risks to estuarine/marine fish, based on 89% 

reduction in juvenile survival of sheepshead minnow (Cyprinodon variegates). However, the 

results of more recent chronic estuarine/marine fish data from Caferalla, 2005a (MRID # 

466482-03) show that juvenile growth may be a more sensitive endpoint than survival. Although 

no effect on pre- or post-hatch survival was observed at atrazine concentrations ranging from 

1,500 to 2,200 ppb, juvenile length and wet weights were significantly decreased at the 2,200 

ppb treatment level, relative to the control. The NOAEC and LOAEC values, based on growth 

(i.e., larval length and wet weight) are 1,100 and 2,200 ppb, respectively. Because juvenile 

growth appears to be the more sensitive endpoint, chronic risks associated with estuarine/marine 

fish exposure to atrazine are based on respective NOAEC and LOAEC values of 1,100 and 2,200 

ppb (MRID # 466482-03). 

 A.3.3a Sublethal Effects: Estuarine/Marine Fish 

Biagianti-Risbourg and Bastide (1995) exposed juvenile gray mullets (Liza ramada) to 170 μg/L 

atrazine for 9, 20, and 29 days in static tests and for 11 days followed by 18 days of 

decontamination; and then measured the sublethal effects on the liver. At 170 μg/L, 10, 25 and 

60 percent mortality occurred following 9-, 20- and 29-day exposures, respectively; control 

mortality was a constant 10 percent throughout the test. Treated mullets showed normal 

behavior until Day 20 after which they stopped feeding and rapidly died; which is in contrast to 

the 90 percent survival of the treated fish that were transferred to clean water after 11 days of 

exposure. After 3-days exposure, a number of abnormalities were found in the liver (i.e., hepatic 

parenchyma with a few cytologically detectable perturbations and hepatocytes had particularly 

large lipofuscin granules (MRID # 452049-02). 

Alvarez (2005; ECOTOX No. 81672) investigated effects of exposure to atrazine for up to 8 

days on growth, swimming behavior, predator response, and respiration rate in red drum 
32

(Sciaenops ocellatus) larvae. This study reported effects including reduced growth rate at 80 ppb 

and changes in swimming speed and respiration at 40 ppb. However, a negative control was not 

used in the evaluation of these endpoints; therefore, potential solvent effects could not be 

evaluated. Also, mortality in the control and treated groups was high for an exposure study that 

was approximately 1 week (23% mortality, survival for each test group was not reported). Also, 

it is uncertain if any relationship between the respiration and behavioral effects observed in this 

study and reduced survival and reproduction exists. Therefore, these data were not used in 

derivation of risk quotients. 

 A.3.4 Estuarine and Marine Invertebrates, Acute 

Acute toxicity testing with estuarine/marine invertebrates using the TGAI is required for atrazine 

because the end-use product is expected to reach this environment due to its use in coastal 

counties. Results of these tests for the TGAI and formulations of atrazine are provided below in 

Tables A-30 and A-31. 

Table A-30. Estuarine/Marine Invertebrate Acute Toxicity

Surrogate Species/ 

Static or Flow-through/ 

Salinity & Temperature % ai.

96-hour LC50/EC50 

μg/L (ppb) 

(measured/nominal) 

Probit Slope Toxicity 

Category

MRID 

No./ECOTOX No. 

Author/Year

Study 

Classification

Mysid shrimp (Neomysis 

integer)Juvenile 4-7 mm/ 

Static renewal – 48 hrs / 5 psu 

; T15oC 

98-99 48 

(measured) Very highly toxic E103334 / Noppe et al. /2007 

Qualitative (no 

raw data) 

Copepod (Acartia tonsa) 

Static-renewal - daily 

Salinity - 31 g/L; T 22o

C

70 

Tech.

 88.9 

(measured) 

Slope 0.947

very highly toxic 452029-18 

Thursby et al. 

1990 memo

Supplemental 

(12% control 

mortality)

Copepod (Acartia tonsa) 

Static test 

Salinity - 20 g/L; T 20+1 o

C

97.4 94 

(nominal) 

Slope - none

very highly toxic 452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data)

Copepod (Tigriopus 

brevicornis) various life 

stages / static / 35 ppt; T: 20 

99 121-153 

(nominal) 

Slope no data 

Highly toxic E19281 / Forget et 

al. / 1998 

Qualitative (no 

raw data; 

uncertainty in 

CIs 

Copepod (Eurytemora affinis) 

/ static / 2 ppt; T: 18 

 

Tech 125 

(nominal) 

Slope no data 

Highly toxic E80951/ Forget et 

al. / 2005 

Qualitative (no 

raw data) 

Copepod (Acartia tonsa) 

Static-renewal - daily 

Salinity - 31-32 g/L; T 22 o

C 

70 

Tech.

 139 

(measured) 

Slope 0.543

highly toxic 452029-18 

Thursby et al. 

1990 memo

Supplemental 

(20% control 

mortality)

Copepod 

nauplii < 24 hours old 

(Eurytemora affinis) 

Static test; T – 20 o

C 

Salinity - 5, 15 & 25g/L 

97.1 Sal. 5 g/L 500 

Sal. 15 g/L 2,600 

Sal. 25 g/L 13,300 

(measured) 

Slope - no data

highly toxic 

 to 

slightly toxic

452083-03 & 

452277-11 

Hall, Ziegenfuss, 

Anderson, Spittler 

& Leichtweis 1994

Supplemental 

(no raw data on 

mortality)
33

Table A-30. Estuarine/Marine Invertebrate Acute Toxicity

Surrogate Species/ 

Static or Flow-through/ 

Salinity & Temperature % ai.

96-hour LC50/EC50 

μg/L (ppb) 

(measured/nominal) 

Probit Slope Toxicity 

Category

MRID 

No./ECOTOX No. 

Author/Year

Study 

Classification

Mysid Shrimp 

(Americamysis bahia) 

Flow-through test 

Salinity 26 g/L; T 22+1 o

C

 97.4 1,000 

(Measured) 

Slope - none

highly toxic 452029-20 

Ward & Ballantine 

1985

Supplemental 

(no raw data)

Brown Shrimp (juvenile) 

(Penaeus aztecus) 

Flow-through test 

Salinity - 30 g/L; T 27 o

C

 99.7 1,000 

(nominal) 

Slope - none

at least highly 

toxic

402284-01 

Mayer 1986

Supplemental 

(48-hr LC50

& no raw data)

Copepod - 17 days old 

(Acartia tonsa) 

Flow-through test 

Salinity - 31-33 /L, T – 20 o

C

97.1 4,300 

(measured) 

Slope - 2.467

moderately toxic 452083-08 

McNamara 1991

Supplemental 

(cloudy with no 

0.45 μm filter 

of undissolved 

test material)

Mysid Shrimp 

(Americamysis bahia) 

Flow-through test 

Salinity -32 g/L; T 25-26 o

C

 97.1 5,400 

 (measured) 

Slope 4.513

moderately toxic 433449-02 

Machado 1994

Acceptable 

Pink Shrimp 

(Penaeus duorarum) 

Static test 

Salinity 26 g/L; T 22+1 ο

C

97.4 6,900 

(nominal) 

Slope - none

moderately toxic 452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data)

Copepod (Acartia clausii) 

Static-renewal - daily 

Salinity - 31 g/L; T 6-6.2 o

C

70 

Tech.

 7,900 

(nominal) 

Slope 0.958

moderately toxic 452029-18 

Thursby et al. 1990 

memo

Acceptable

Grass Shrimp 

(Palaemonetes pugio) 

Static test 

Salinity - 26 g/L; T 22+1 o

C

97.4 9,000 

(nominal) 

Slope - none

moderately toxic 452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data)

Eastern oyster (juvenile) 

(Crassostrea virginica) 

(Shell deposition) 

Flow-through test 

Salinity - 28 g/L; T – 28 o

C

 99.7 > 1,000 

 no effect 

 (nominal) 

Slope - none

unknown 40228-01 

Mayer 1986

Supplemental 

(EC50 has not 

been identified 

& no raw data)

Eastern oyster (juvenile) 

(Crassostrea virginica) 

(Shell deposition) 

Flow-through test 

Salinity 31-32 g/L; T =20-21 

o

C 

97.1 > 1,7 00 

 no effect 

 (measured) 

Slope - none 

unknown 466482-01 

Caferalla, 2005b 

Acceptable 

Mud Crab 

(Neopanope texana) 

Static test 

Salinity & T - unknown

Tech. > 1,000 

(nominal) 

Slope - none

slightly toxic 000247-19 

Bentley & Macek 

1973

Supplemental 

(LC50 exceeds 

water 

solubility)

Table A-31. Estuarine/Marine Invertebrate Acute Toxicity - Formulations
34

Surrogate Species/ 

Static or 

 Flow-through

% ai. 

Product

96-hour LC50/EC50 

μg/L (ppb) 

(measured/nominal) 

Probit Slope Toxicity 

Category

MRID No. 

Author/Year

Study 

Classification

Eastern Oyster 

(Crassostrea virginica) 

(Shell deposition) 

Flow-through test 

Salinity -11.8 mg/L; T 21ΕC

79.6 

80 WP

> 800 

 no effect 

 (nominal) 

Slope - none

unknown 000247-20 

Wright & Beliles 

1966

Supplemental 

(EC50 has not 

been identified)

Pacific Oyster 

(Crassostrea gigas) 

24-Hour Static-Renewal

?? > 100 

(nominal) 

0.1 - 50% dead at 22 days 

0.2 - 50% dead at 18 days

unknown 452277-22 

Moraga & 

Tanguy 2000

Supplemental 

(no 96-hour 

LC50 value)

European Brown Shrimp 

(Crangon crangon) 

Static test; 15ΕC

?? 

WP

10,000 - 33,000 

(nominal) 

no slope

slightly toxic 452277-28 

Portmann 1972

Supplemental 

(only 48 hours & 

no raw data)

European Cockle 

(Cardium edule) 

Static test; 15ΕC

?? 

WP

> 100,000 

(nominal) 

no slope

practically 

 non-toxic

452277-28 

Portmann 1972

Supplemental 

(only 48 hours; 

LC50 exceeds 

water solubility 

& no raw data)

Fiddler Crab 

(Uca pugilator) 

Static test 

Salinity - 30 g/L; T 19ΕC

79.6 

80 WP

198,000 

(nominal) 

Slope - none

unknown 000243-95 

Union Carbide 

Corp. 1975

Supplemental 

(LC50 exceeds 

water solubility)

Fiddler Crab 

(Uca pugilator) 

Static test 

Salinity - 30 g/L; T 19ΕC

Unknown 

4-1-3-1 

WDL

239,000 

(nominal) 

Slope - none

unknown 000243-95 

Union Carbide 

Corp. 1975

Supplemental 

(LC50 exceeds 

water solubility)

Degradates: Estuarine invertebrate acute tests (72-3) are required to address concerns for the 

toxicity of atrazine degradates to estuarine invertebrates (preferably Americamysis bahia). Table 

A-32 presents estuarine/marine invertebrate toxicity data for hydroxyatrazine. 

Table A-32. Estuarine/Marine Invertebrate Acute Toxicity (Hydroxyatrazine)

Surrogate Species/ 

Flow-through or Static

% ai 

formul.

96-hour LEC50 (ppb) 

(measured/nominal) Toxicity Category

MRID No. 

Author/Year

Study 

Classification

Mysid Shrimp 

(Americamysis bahia) 

Static test 

Salinity +22-25 g/L; T 25-

26 o

C 

97.1 >2,000 (5% mortality 

(measured) moderately toxic* 

465000-03 

Sayers, 2005b 

Acceptable 

* The highest concentration tested in this study approximated the functional water solubility of 

hydroxyatrazine in natural seawater; therefore, hydroxyatrazine is not toxic to mysids on an acute basis at the 

limit of its water solubility. 

 A.3.5 Estuarine and Marine Invertebrate, Chronic 
35

An estuarine/marine invertebrate life-cycle toxicity test using the TGAI is required for atrazine 

because the end-use product may be applied directly to the estuarine/marine environment or is 

expected to be transported to this environment from the intended use site, and the following 

conditions are met: the pesticide is intended for use such that its presence in water is likely to be 

continuous and recurrent; an aquatic acute EC50 is less than 1 mg/L; and the pesticide is 

persistent in water (e.g., half-life greater than 4 days). Results of this test are summarized below 

in Table A-33. 

 

Table A-33. Estuarine/Marine Invertebrate Life-Cycle Toxicity

Species/ 

Duration/ 

Flow-through/ Static-renewal % ai

NOAEC/LOAEC 

 μg/L (ppb) 

(measured/noml)

Statistically sign. (P=0.05) 

Endpoints Affected

MRID No. / 

ECOTOX no. 

Author/Year

Study 

Classification

Copepod (Eurytemora affinis) / 

ca. 21 days / static renewal (every 

3 days) 

Tech A 10-day 

NOAEC 

(survival)= 25 

LOAEC = 49 ; 

30-day LOAEC = 

25 

Delayed metamorphosis E 19281 / Forget 

et al. 2005 

Qualitative 

(no raw data, 

limited data 

on test conc. 

Copepod Amphiascus 

tenuiremis 98 

NOAEC < 2.5 

LOAEC = 2.5 

Decrease in viable offpring 

production 

E73333 / 

Bejarano and 

Chandler / 2003

QUAL. 

Negative 

control was 

not used; 

therefore, 

potential 

solvent 

effects could 

not be 

evaluated

Mysid 

(Americamysis bahia)

Duration of test – unknown 

Flow-though test 

Salinity 20 g/L; T 25+1 o

C

97.4 NOAEC 80 

LOAEC 190 

(measured)

37 % red. In adult survival 452029-20 

Ward & 

Ballantine 1985

Supplemental 

(no raw data 

for statistical 

analyses)

Mysid 

(Americamysis bahia)

Study Duration = 28 days 

Flow-though test 

Salinity 19-21 g/L; T 26+2 o

C 

97.1 NOAEC 260 

LOAEC 500 

(measured) 

9.8% red. In male length 

11% red. In male dry 

weight 

8.5% red. In female dry 

weight 

466482-02, 

469526-01, and 

469526-02 

Cafarella, 2005c 

Acceptable 

Mysid shrimp (Neomysis integer) 

<24 hrs old / ca. 3 weeks / design 

not specified / 

98-99 NOAEC 1 

LOAEC >1 

(measured) 

none E103334 / Noppe 

et al./ 2007 

Supplemental 

(no raw data, 

missing test 

design info) 

 
36

A.3.7a Estuarine and Marine Field Studies (2003 IRED Data) 

 A summary of all the estuarine/marine aquatic microcosm and mesocosm field studies that were 

summarized as part of the 2003 IRED is included in Tables A-35 and A-36, respectively. 

Similar to the freshwater field studies, the estuarine/marine microcosm and mesocosm field 

studies were classified as supplemental in the 2003 IRED because this information is used to 

provide context to the effects data seen in individual organism toxicity tests. Data from nonguideline microcosm/mesocosm tests are typically not used quantitatively to derive RQs in the 

Agency’s ecological risk assessments, but rather to provide qualitatative information regarding 

potential aquatic community-level effects of atrazine. 

Table A-35. Marine/Estuarine Microcosm Tests

Application rate (lb ai/A) 

Nominal/Measured Conc.

Concentration affecting 

endpoint (time to effect) 

o Affected species and life stage

Narrative of Study Trends MRID No. 

Author/Year

Estuarine microcosm: 

Wild celery 

Vallisneria Americana

1 treatment 

Nominal concentrations of 4, 

8,16, 32, and 64 ppb 

NOAEC < 4 ppb 

4 ppb (reproductive season) 

 o sign. 16% reduction in 

tuber formation 

 o 55% reduction in 

biomass 

8 ppb (reproductive season) 

 o 21% reduction in tuber 

formation 

16 ppb (mid season and 

reproductive season) 

 o 60% reduction in tuber 

formation 

 o 27% reduction in tuber 

weight 

 o sign. reduction in leaf 

growth, biomass, and female 

flowers 

64 ppb (reproductive season) 

 o 75% reduction in tubers 

 o reduction in female 

flowers 

Laboratory microcosms were 

used to grow Vallisneria 

americana through entire seasons 

(divided into three periods: early-

, mid-, and reproductive). The 

aquaria were dosed one time at 

nominal concentrations after a 

14-day acclimation period. With 

respect to leaf growth, atrazine 

caused the plants to be shorter 

and more fragile. With respect to 

flowering and rhizome 

production, effects were 

generally first noted at the 16 to 

32 ppb range. Tuber formation 

appeared to be the most sensitive 

endpoint, with production in 

terms of numbers significantly 

reduced at the 4 ppb level. 

450200-01 

Cohn, 1985 

Supplemental 
37

Table A-35. Marine/Estuarine Microcosm Tests

Application rate (lb ai/A) 

Nominal/Measured Conc.

Concentration affecting 

endpoint (time to effect) 

o Affected species and life stage

Narrative of Study Trends MRID No. 

Author/Year

Estuarine lab microcosm: 

7-day exposure 

Nominal concentrations of 22, 

220, and 2200 ppb 

Estuarine field microcosm 

108-days duration 

Single exposure 

Nominal applications of 0.4, 1.4, 

4.5, and 45 lb ai/A 

“NOAEC” = 10 ppb (based on 

author’s use of a 10-fold safety 

factor from the I1 level = 100 

ppb) 

200 ppb (1 week) 

 o significant (0.05 level) 

reduction in cell # of 

Thalassiosira fluviatilis 

 o significant reduction in 

photosynthesis of T. fluviatilis

and Nitzschia sigma

 2200 ppb (1 week) 

 o significant reduction in cell 

#, photosysnthesis, and 

chlorophyll content for both algae 

1.4 lb ai/A (effect up to 5 days) 

 o significant reduction in 

surface chlorophyll and primary 

production (85-89%) 

1.4 lb ai/A (effect up to 8 and 17 

days) 

 o significant reduction in 

carbon fixation (52-73%) 

0.4/4.5 lb ai/A (effect at 16 days, 

but not 26 days) 

 o significant reduction in 

carbon fixation 

45 lb ai/A (42 days) 

 o significant reduction in 

carbon fixation 

 No statistical effects found in 

atrazine treatments on: 

 o periphyton growth 

measured as chlorophyll a levels; 

 chlorophyll a levels 

decreased gradually in all 

 samples (treatments 

& controls) over time, 

 “may have masked 

an effect of atrazine” 

 o indirect effects on function 

or taxonomic 

 composition of benthic 

community structure 

 

Laboratory studies were 

conducted with the salt marsh 

edaphic diatoms Thalassiosira 

fluviatilis and Nitzschia sigma. 

The I50 for both species combined 

was reported to be 939 ppb. The 

I1 was reported to be 100 ppb, 

and by applying a 10-fold safety 

factor, the acceptable level 

(NOAEC) was reported to be 10 

ppb. Subsequently, studies were 

conducted in greenhouse 

microcosms (1.4 lb ai/A) and in 

two field studies (1.4 lb ai/A or 

0.4, 4.5, and 45 lb ai/A) on the 

beach wherein enclosures were 

sunk into the sand and exposed to 

a tidal action. Atrazine treatment 

also appeared to cause a shift to a 

Navicula sp. Dominated system. 

Field results with higher rates of 

atrazine were expected, with 

carbon fixation reduced for up to 

16 days at the 2 lower rates and 

up to 42 days at the highest rate. 

450874-06 

Plumley and Davis, 1980 

Supplemental 
38

Table A-35. Marine/Estuarine Microcosm Tests

Application rate (lb ai/A) 

Nominal/Measured Conc.

Concentration affecting 

endpoint (time to effect) 

o Affected species and life stage

Narrative of Study Trends MRID No. 

Author/Year

Estuarine microcosm: 

5 weeks 

3 weekly applications followed 

by 2 weeks observation. 

Mean-measured concentration at 

approx. mid-point of Spartina

test were 30, 280, and 3100 ppb 

and in the Juncus test were 30, 

250, and 3800 ppb 

30, 280, and 3100 ppb (5 weeks): 

 o sign. (0.05 level) increase 

in peroxidase activity in Spartina 

alterniflora 

30, 250 and 3100 ppb (5 weeks) 

 o sign. (0.05 level) 

reduction in chlorophyll a (Chl-a) 

and Chl- a/Chl-b ration in Juncus 

roemerianus

250 and 3800 ppb (5 weeks) 

 o sign. red. in Chl-b in J. 

roemerianus 

3100 ppb (1 week) 

 o sign. red. in growth of S. 

alterniflora 

3800 ppb (1 week) 

 o sign. red. in growth of J. 

roemerianus

 o sign. increase in oxidized 

lipids in J. roemerianus 

250 ppb (1 year) 

 o partial recovery in J. 

roemerianus 

3800 ppb (1 year) 

 o practically no survival of 

J. roemerianus

Two aquatic estuarine plants 

were exposed to atrazine in 

greenhouse microcosms. The 

plants were exposed to atrazine 

by placing treated sand on the 

surface of the pots three times 

(once a week for the first 3 weeks 

of the study) followed by 2 more 

weeks for a total of 5 weeks. The 

water samples were taken after 

the third application. The pots 

were also tidally-exposed (i.e., 

low tide during the day and high 

tide at night). S. alterniflora

plants demonstrated a doseresponse increase in peroxidase 

activity. In contrast, J. 

roemerianus plants demonstrated 

a dose-responsive reduction in 

chlorophyll and increase in the 

amount of oxidized lipids. The 

authors state that atrazine “should 

pose no significant adverse 

effects on S. alternaiflora. In 

contrast, if chronic levels of 

atrazine persist in the range of 

250 ppb or greater, J. 

roemerianus most likely will 

exhibit die off or decline that may 

lead to loss of this species within 

the habitat. 

450874-05 

Lytle and Lytle, 1998 

Supplemental 

Estuarine microcosm: 

Duration not reported 

Nominal concentrations of 0, 50, 

and 100 ppb 

Both Nannochloris oculata and 

Phaeodactylum tricornutum were 

significantly (mostly at the 0.01 

level) affected by changes in 

light, temperature, and atrazine 

concentration 

A 3x3x3 factorial design 

examined the effect of 

temperature, light, and atrazine 

concentration on two species of 

estuarine algae. N oculata was 

significantly affected by all 

variables, and the three two-way 

and one three-way interactions 

wer also significant. P. 

tricornutum was affected by the 

main variables and the only 

significant interaction was light 

by atrazine 

Mayasich et al., 1986 

Supplemental 

Estuarine microcosm 

Duration not reported 

Nominal concentrations of 0, 15, 

30, and 50 ppb 

The above mentioned algae were 

tested together and this variable 

also caused a significant (0.01 

level) effect on N. oculata growth 

rate. 

An extension of the above 

described study. In addition to 

separate culture, the two estuarine 

algae were cultured together. The 

end result was that P. tricornutum

dominated the cultures due to the 

stress of atrazine N. oculata under 

optimum growth conditions. 

Mayasich et al., 1987 

Supplemental 
39

Table A-35. Marine/Estuarine Microcosm Tests

Application rate (lb ai/A) 

Nominal/Measured Conc.

Concentration affecting 

endpoint (time to effect) 

o Affected species and life stage

Narrative of Study Trends MRID No. 

Author/Year

Estuarine microcosm: 

4 weeks 

Mean-measured concentrations in 

water were 130 ppb for the “low” 

treatment and 1200 ppb for the 

“high” treatment over a 4 week 

period 

130 ppb (Week 1): 

 o no photosynthesis 

130 ppb (Weeks 2-4) 

 o sign. reduction in plant 

total biomass, no change in 

biomass for 3 weeks 

130 ppb (Weeks 1-4) 

 o sign.; averaged 50% 

reduction in photosysnthesis of 

Potamogeton perfoliatus during 

the test; steady recovery after 

first week, but not fully recovered

1200 ppb (Weeks 1-4) 

 o sign. 100% red. in 

photosynthesis throughout the 

test 

1200 ppb (Weeks 2-4) 

 o sign. plant biomass 

steadily reduced

1200 ppb (Weeks 3-4) 

 o sign. 80% reduction in 

shoot density 

Aquatic plants were planted and 

atrazine-treated sediments were 

added to 700-L microcosms. On 

Day 1.5, 93.4% of the total 

atrazine was dissolved in water. 

In addition to photosynthesis, it 

was demonstrated that shoot 

growth was relatively unaffected 

at 130 ppb, but total biomass was 

sign. reduced after 2-4 weeks. 

Plant biomass reductions 

followed a 1 week lage after 

photosynthesis reduction. At 

1200 ppb, plant biomass had been 

virtually eliminated by the end of 

the test. Mean shoot length in the 

controls declined after week 1 

and after week 3 for 1200 ppb. 

450874-03 

Cunningham et al, 1984 

Supplemental 

Estuarine microcosm: 

22-23 days 

Single dose 

Day 0: 30000 ppb – nominal; 

measured only Day 22-23: 

16400-17000 ppb 

30,000 ppb (Day 5-22): 

 o sign. (p < 0.05) red. 

average ratio of # or ramets 

(branches): initial # or ramets 

30,000 ppb (Day 22 or 23): 

 o sign. (p < 0.05) 46-58% 

reduction in total above-ground 

biomass 

 o sign. (p < 0.05) 18% 

reduction in average dry weight 

per ramet 

Experiments were conducted with 

seagrass Halodule wrightii, 

examining the effect of atrazine 

and any interactions of salinity 

(15, 25, 35 ppt), light intensity 

(115, 140, 173 uEm-2s

-1), and 

cropping (either cut at 4-cm or 6-

cm). None of these 

environmental factors affected 

the response of the grass to 

atrazine. 

452051-01 

Mitchell, 1987 

Supplemental 

 
40

 

Table A-36. Marine/Estuarine Mesocosm Tests

Application rate (lb 

ai/A) 

Nominal/Measured 

Conc.

Concentration affecting endpoint (time to 

effect) 

o Affected Species and Life Stage

Narrative of Study Trends

MRID No. 

Author/Year

Marine Mesocosm: 

Open Ocean: 

Phytoplankton: 

(15 days; measured 

conc.) 

Measured = 

nominal at time 

zero, concentrations 

of 0.12, 0.56, and 

5.8 ppb

0.12 ppb (differences compared to controls) 

 o sign. lower pH levels (Days 5-14); 

indicative of 

 reduced photosynthesis 

 o higher dissolved organic nitrogen 

(DON) (Days 6-11) 

 o up to 50% red. primary production 

(Days 3-11) 

 o up to 60% red. particulate 

carbohydrates (Days 5-15) 

 o up to 70% red. chlorophyll (Days 4-

15) 

0.56 ppb 

 o sign. lower pH levels (Days 5-13) 

 o incr. total dis. organic phosphate 

(DOP) (Days 3-14) 

 o higher DON (Days 5-15) 

 o up to 50 % red. primary production 

(Day 3-13) 

 o up to 85% red. particulate 

carbohydrate (Days 5-15) 

 o up to 80% red. chlorophyll (Days 4-

15) 

5.8 ppb 

 o sign. lower pH levels (Days 5-11) 

 o up to 200% increase in total DOP 

(Days 3-14) 

 o up to 200 % increase in total DON 

(Days 2-15) 

 o up to 50% red. in primary 

productivity (Days 3-7) 

 o up to 60% red. in partic. 

carbohydrates (Days 5-15) 

 o up to 30% red. in chlorophyll conc. 

(Days 4-15)

Mesocosms (2 m2

) inoculated with the diatoms 

Thalassiosira punctigera, T. rotula, Nitzschia 

pungens and Skeletonema costatum and a 

prymnesiophtye, Phaeocystis globosa. 

evidenced a dose-responsive elevation in 

dissolved nitrogen and phosphorous and 

reduction in primary production at 0.12, 0.56, 

and 5.8 ppb. The NOEL was reported to be 

<0.12 ppb. Atrazine at concentrations at 0.12, 

0.56 and 5.8 ppb, adversely effects primary 

production of unicellar algal species at certain 

growth phases and causes increases in 

“excretions” of dissolved organic nitrogen and 

phosphorus. “Excretions” may be caused by 

atrazine stress on cells or lysis of cells.

450200-21 

Bester et al., 1995 

Supplemental 

Nominal 

applications of 0.4, 

4.5, or 45 lb ai/A

Salt marsh edaphic alage

Elaboration of Plumley et al., concerning the 

carbon uptake for algae in the top 0.5 cm of 

enclosure sediment. Carbon fixation was 

significantly reduced at the 0.45 and 4.5 lb ai/A 

treatment levels for 16 days and at the 45 lb ai/A 

treatment level for 42 days.

450874-06 

Plumley and Davis, 

1980 

Supplemental

A.3.7b Estuarine and Marine Field Studies (New Open Literature Data) 

As previously discussed, the 2003 IRED identified 10-20 μg/L as the range of atrazine 

concentrations in freshwater that are likely to have adverse effects on sensitive aquatic 

plants and non-target aquatic organisms including their populations and communities. As 

such, estuarine/marine field data from the open literature were considered only when the 

relevant endpoints were less than or more sensitive than the 10 μg/L aquatic-community 

effect level. In addition, data for taxa that are directly relavent to the endangered species 
41

evaluated as part of this assessment were also considered. Based on the selection criteria 

for review of new open literature, all of the available studies show effects levels to 

estuarine/marine fish, invertebrates, and plants at concentrations greater than 10 μg/L. 

One estuarine/marine field study on saltwater eelgrass (Zostera capricorni) was reviewed 

as part of the open literature because it provides data on seagrass, a potential food item 

and source of habitat for sea turtles (Macinnis-Ng, 2003; Ecotox Reference # 72996). 

The results of this study, which are summarized as part of Table A-37, show that atrazine 

is unlikely to affect the chlorophyll a concentration of estuarine/marine sea grasses at 

exposure concentrations ranging from 10 to 100 ppb. Data from this study are not used 

to quantitatively calculate RQs for estuarine/marine macrophytes because a more 

sensitive endpoint of 4 ppb was reported for wild celery (Cohn, 1985). 

 Table A-37. Estuarine/Marine Field Study from Open Literature (2007 Review)

Study type/ 

Test material

Test Organism (Common 

and Scientific Name) and 

Age and/or Size

Test 

Design

Endpoint 

Concentration 

in ppm

Citation 

(EcoRef. #) 

Rationale for Use in 

Risk Assessment(1)

Field study 

10 h exposure 

Atrazine (% ai 

NR) 

Seagrass (Zostera 

capricorni) - open-bottom cylindrical 

containers enclosed grasses 

within a seagrass meadow; 

salinity = 35 ppt; temp = 25 

+ 1 o

C 

- Atrazine doses = 0, 10, 

and 100 ppb at one 

application 

- Endpoints: total 

chlorophyll a

concentration, effective 

quantum yield via 

fluorescence measurements

NOAEC = 100 ppb 

No difference in total 

chlorophyll a 

concentration between 

treatments and control. 

Reduction in effective 

quantum yield (via 

fluorescence 

measurements) at both 

treatments relative to 

the control, but recovery 

to control values by end 

of 10 hour exposure 

period. 

Macinnis-Ng and 

Ralph, 2003 

(72996) 

QUAL: 

- no raw data provided 

- low number of 

replicates (2) 

- relevance of 

fluorescence endpoints 

is of limited use in risk 

assessment. 

(1) QUAL = The paper is not appropriate for quantitative use but is of good quality, addresses issues of concern to the 

risk assessment and is used in the risk characterization discussion. 

NR = Not reported. 
42

A.4 Toxicity to Plants 

 A.4.1 Terrestrial Plants 

Terrestrial plant testing (seedling emergence and vegetative vigor) is required for 

herbicides that have terrestrial non-residential outdoor use patterns and that may move off 

the application site through volatilization (vapor pressure >1.0 x 10-5mm Hg at 25o

C) or 

drift (aerial or irrigation) and/or that may have endangered or threatened plant species 

associated with the application site. 

For seedling emergence and vegetative vigor testing the following plant species and 

groups should be tested: (1) six species of at least four dicotyledonous families, one 

species of which is soybean (Glycine max) and the second is a root crop, and (2) four 

species of at least two monocotyledonous families, one of which is corn (Zea mays). 

Terrestrial Tier II studies are required for all herbicides and any pesticide showing a 

negative response equal to or greater than 25% in Tier I tests. Tier II tests measure the 

response of plants, relative to a control, and five or more test concentrations at a test level 

that is equal to the highest use rate (expressed as lbs ai/A). Results of Tier II seedling 

emergence and vegetative vigor toxicity testing on the technical material are summarized 

below in Tables A-38 and A-39. 

Based on the results of the tests, it appears that emerged seedlings are more sensitive to 

atrazine via soil/root uptake exposure than emerged plants via foliar routes of exposure. 

However, all tested plants, with the exception of corn in the seedling emergence and 

vegetative vigor tests and ryegrass in the vegetative vigor test, exhibited adverse effects 

following exposure to atrazine. 

Table A-38. Nontarget Terrestrial Plant Seedling Emergence Toxicity (Tier II)

Surrogate Species % ai

EC25 / NOAEC (lbs ai/A) 

Probit Slope Endpoint Affected

MRID No. 

Author/Year

Study 

Classification

Monocot - Corn 

 (Zea mays)

97.7 > 4.0 / > 4.0 No effect 420414-03 

Chetram 1989

Acceptable

Monocot - Oat 

 (Avena sativa)

97.7 0.004 / 0.0025 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Monocot - Onion 

 (Allium cepa)

97.7 0.009 / 0.005 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Monocot - Ryegrass 

 (Lolium perenne)

97.7 0.004 / 0.005 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Dicot - Root Crop - Carrot 

 (Daucus carota) 

97.7 0.003 / 0.0025 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Dicot - Soybean 

 (Glycine max) 

97.7 0.19 / 0.025 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Dicot - Lettuce 

 (Lactuca sativa) 

97.7 0.005 / 0.005 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Dicot - Cabbage 97.7 0.014 / 0.01 red. in dry weight 420414-03 Acceptable
43

 (Brassica oleracea alba) Chetram 1989

Dicot - Tomato 

 (Lycopersicon esculentum)

97.7 0.034 / 0.01 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Dicot - Cucumber 

 (Cucumis sativus) 

97.7 0.013 / 0.005 red. in dry weight 420414-03 

Chetram 1989

Acceptable

Table A-39. Nontarget Terrestrial Plant Vegetative Vigor Toxicity (Tier II)

Surrogate Species % ai

EC25 / NOAEC 

 (lbs ai/A) Endpoint Affected

MRID No. 

Author/Year Study Classification

Monocot - Corn 

 (Zea mays)

97.7 > 4.0 / > 4.0 No effect 420414-02 

Chetram 1989

Acceptable

Monocot - Oat 

 (Avena sativa)

97.7 2.4 / 2.0 red. in dry weight 420414-02 

Chetram 1989

Acceptable

Monocot - Onion 

 (Allium cepa)

97.7 0.61 / 0.5 red. in dry weight 420414-02 

Chetram 1989

Acceptable

Monocot - Ryegrass 

 (Lolium perenne)

97.7 > 4.0 / > 4.0 No effect 420414-02 

Chetram 1989

Acceptable 

Dicot - Root Crop - Carrot 

 (Daucus carota) 

97.7 1.7 / 2.0 red. in plant height 420414-02 

Chetram 1989

Acceptable

Dicot - Soybean 

 (Glycine max) 

97.7 0.026 / 0.02 red. in dry weight 420414-02 

Chetram 1989

Acceptable

Dicot - Lettuce 

 (Lactuca sativa) 

97.7 0.33 / 0.25 red. in dry weight 420414-02 

Chetram 1989

Acceptable

Dicot - Cabbage 

 (Brassica oleracea alba) 

97.7 0.014 / 0.005 red. in dry weight 420414-02 

Chetram 1989

Acceptable

Dicot - Tomato 

 (Lycopersicon esculentum)

97.7 0.72 / 0.5 red. in plant height 420414-02 

Chetram 1989

Acceptable

Dicot - Cucumber 

 (Cucumis sativus) 

97.7 0.008 / 0.005 red. in dry weight 420414-02 

Chetram 1989

Acceptable

A summary of safety studies evaluating phytoxicity of atrazine to woody plants (target 

species) was submitted to the Agency in 2006 (Wall, 2006). A total of 35 species were 

tested in 13 separate trials at application rates of 1.5 to 4.0 lbs a.i./Acre. Signs of 

phytotoxicity were summarized and reported. These data are summarized in Table A-39b 

below. 

Table A-39b. Summary of woody plant safety study (Hall, 2006). 

Species Application Rate (lbs a.i./Acre) Phytotoxicity 

(%) 

Abies balsamea 2 0 

4 3% General 

Azalea 2 5% General 

2 5% General 

Barberry 2 50% Generalb

Black pine 2 Chlorosis (IS-1)a

Boxwood 2 3.8% General 
44

Table A-39b. Summary of woody plant safety study (Hall, 2006). 

Species Application Rate (lbs a.i./Acre) Phytotoxicity 

(%) 

Chitalpa 2 0% 

Common Lilac 2 22% chlorosis 

25% necrosis 

Conifer shrubs and trees 2 0% 

Crabapples 2 0% 

Crape-Myrtle 2 Chlorosis (IS-1) a

Creeping juniper 2 7.5% General 

Cupressocyparis leylandii 2 0 – 1% General 

Cypruss leylandii 2 Chlorosis (IS-1) a

Ginko 2 0% 

Gleditsia triacanthos 2 7.5% General 

Hydrangea 2 4 – 16% General 

Juniperus 1.5 0% 

Ligustrum 2 0% 

Locust 2 0% 

Macadamia nuts 2 0% 

Maple 2 0% 

Oak 2 0% 

Pears 2 0% 

Pinus palustris 1.5 70% Generalc

Pinus strobus 2 5% General 

Pinus virginiana 1.5 90% Generalc

Pseudotsuga menziesii 4.3 0% 

Purpleleaf plum 2 Chlorosis (IS-1) a

Raywood ash 2 Chlorosis (IS-1) a

Redbud, Eastern 2 2.5% chlorosis 

0.3% necrosis 

10% general 

Rhododendron, catawba 2 5 

Shrubby althaea 2 100% chlorosis 

40% necrosis 

Spiraea 2 16b

Spruce 2 0 

Tilia 2 0 

a IS rating grades chlorosis severity (normal to excessive color) and ranges from 1 to 5 

b Phytotoxicity in controls was up to 45%; other pesticides were included in trial, and sprayer may not have been adequately cleaned. 

c Effect was noted as being atypical for conifers, and the effect may not be related to atrazine treatment 

A.4.2 Aquatic Plants 

Aquatic plant testing is required for any herbicide that has outdoor non-residential 

terrestrial uses that may move off-site by runoff (solubility >10 ppm in water), by drift 

(aerial or irrigation), or that is applied directly to aquatic use sites (except residential). 
45

Aquatic Tier II studies are required for all herbicides and any pesticide showing a 

negative response equal to or greater than 50% in Tier I tests. The following species 

should be tested at Tier II: Kirchneria subcapitata, Lemna gibba, Skeletonema costatum, 

Anabaena flos-aquae, and a freshwater diatom. Aquatic plant testing is required for 

atrazine because it is applied on crops outdoors and appears to be mobile with a water 

solubility value of 33 ppm. 

Results of Tier II toxicity testing on technical grade and typical end-use products (TEP) 

are tabulated below. The data are presented in four toxicity tables separating the 

freshwater data from the marine data and the short, 7-day or less tests from the longer 

tests. Tables A-40 and A-41 summarize freshwater plant toxicity for short-term (i.e., < 7 

days exposure) and longer-term tests. Tables A-42 and A-43 summarize short-term (< 10 

days exposure) estuarine/marine plant toxicity for technical grade and formulations of 

atrazine, respectively. Toxicity data for longer-term exposure of atrazine to 

estuarine/marine plants are provided in Table A-44. 

Field studies involving atrazine toxicity to freshwater and estuarine/marine aquatic plants 

are summarized as part of Sections A.2.8 and A.3.7, respectively. 

Table A-40. Nontarget Freshwater Plant Toxicity: short-term (< 7 days) (Tier II)

Surrogate Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit Slope % Response

MRID No. 

Author/Year Study Classification

Vascular Plants:

Duckweed 

(Lemna gibba) 

5-Day test; Static-Renewal

97 170 

(nominal) 

Slope 3.93

50% red. in growth 410652-03d 

Hughes 1986

Supplemental 

(5 days, not 14 days)

Duckweed 

(Lemna gibba) 

7-Day test; Static-Renewal

97 170 

(measured) 

Slope 2.2

50% red. in growth 420414-04 

Hoberg 1991

Supplemental 

(7 days, not 14 days)

Non-Vascular Plants:

Cyanophyceae 

Oscillatoria lutea

(1week; nominal)

76 

80 W

< 1 

1,000 

93% red. chlorophyll 

 production 

100% red. chlorophyll 

prod.

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Chlorophyceae 

Stigeoclonium tenue

(1 week; nominal)

76 

80 W

< 1 

1,000 

67% red. chlorophyll 

 production 

90% red. chlorophyll 

production

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Green Algae - Chlorophyceae 

Chlorella vulgaris

(1 week; nominal)

76 

80 W

1 

1,000 

50% red. chlorophyll 

 production 

80-87% red. chlorophyll 

production

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Xanthophyceae 

Tribonema sp. 

(1 week; nominal)

76 

80 W

1 

1,000 

42% red. chlorophyll 

 production 

75% red. chlorophyll 

production

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Xanthophyceae 

Vaucheria geminata

(1 week; nominal)

76 

80 W

1 

1,000 

41% red. chlorophyll 

 production 

100% red. chlorophyll 

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)
46

production

Ciliate 

Tetrahymena pyriformis 

(24 hrs) 

NR 5.83 50% red. In survival Toth & 

Tomasovicova 

1979 

Supplemental 

Chlorophyceae 

Chlamydomonas reinhardi

(24 hour; nominal)

Unk. 19 

44 

48

50% red. carbon uptake; 

media: Taub & Dollar (TD)

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Chlorophyceae 

Kirchneria subcapitata

=Selenastrum capricornutum

(96 hours; nominal)

Tech. 26 

26

50% red. cell growth 

50% red. floresence

Caux, Menard, 

and Kent 1996

Supplemental 

(NOAEC and raw data 

unavailable)

Chlorophyceae 

Kirchneria subcapitata

= Selenastrum capricornutum

(24 hours; nominal)

Unk. 34 

42 

53

50% red. 14-carbon uptake; 

media: Taub & Dollar 

(TD); algal assay & TD, 

respect.

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Cyanophyceae 

Anabaena cylindrica

(?? hours; nominal)

97 37 50% red. in photosynthesis Stratton & 

Corke 1981

Supplemental 

(no raw data)

Chlorophyceae 

Scenedesmus obliquus

(24 hour; nominal)

Unk. 38 

49 

57

50% red. 14-carbon uptake; 

media: Taub & Dollar (TD)

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Chlorophyceae 

Kirchneria subcapitata

=Selenastrum capricornutum

(120 hours; measured)

97.1 49 

NOAEC 16 

Slope 4.002

50% red. cell growth 430748-02 

Hoberg 1993

Acceptable

Cyanophyceae 

Anabaena inaequalis

(?? hours; nominal)

97 50 50% red. in photosynthesis Stratton & 

Corke 1981

Supplemental 

(no raw data)

Chlorophyceae 

Kirchneria subcapitata

= Selenastrum capricornutum

(120 hours; nominal)

97.4 53 

NOAEC <32 

LOAEC 32 

Slope 4.127

50% red. growth 

17% red. growth

410652-04 

Parrish 1978

Supplemental 

(NOAEC, method & 

raw data unavailable)

Bacillariophyceae 

Navicula pelliculosa 

(120 hours; nominal)

97.1 60 

NOAEC <10 

LOAEC 10 

Slope 2.31

50% red. growth 410652-03a 

Hughes 1986

 Acceptable 

(EC50 extrapolated; 

and NOAEC was not 

determined)

Chlorophyceae 

Ankistrodesmus sp. 

(24 hours; nominal)

Unk. 61 

72 

219 

50% red. 14-carbon uptake; 

media: Taub & Dollar 

(TD), TD & algal assay, 

respect.

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Ulothrix subconstricta

Tentative species identification 

(24 hours; nominal)

Unk. 88 50% red. 14-carbon uptake; 

medium: Taub & Dollar 

(TD)

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Cyanophyceae 

Anabaena variabilis

(?? hours; Nominal)

97 100 50% red. in photosnythesis Stratton & 

Corke 1981

Supplemental 

(no raw data)

Stigeoclonium tenue

Tentative species Identification 

(24 hours; nominal)

Unk. 127 

224

50% red. 14-carbon uptake; 

media: Taub & Dollar (TD)

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Chlorophyceae 

Kirchneria subcapitata

=Selenastrum capricornutum

(96 hours; measured)

97 130 

NOAEC 76 

Slope 6.628

50% red. cell growth 420607-01 

Hoberg 1991

Supplemental 

(higher light intensity 

than recommended)

Cyanophyceae 

Anabaena cylindrica

(24 hour; nominal)

Unk. 178 

182 

253

50% red. 14-carbon uptake; 

media: Taub & Dollar 

(TD), algal assay, & TD, 

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)
47

respect.

Cyanophyceae 

Anabaena flos-aquae

(120 hours; nominal)

97 230 

NOAEC <100 

LOAEC 100 

Slope 1.95

50% red. growth 

22% red. growth

410652-03a 

Hughes 1986

Acceptable 

(NOAEC was not 

determined)

Chlorophyceae 

Chlorella pyrenoidosa

(120 hours; nominal)

97.4 282 

NOAEC 130 

Slope 4.216

50% red. growth 

 7% red. growth

410652-04 

Parrish 1978

Supplemental 

(NOAEC, method & 

raw data unavailable)

Chlorophyceae 

Chlorella vulgaris

(24 hours; nominal)

Unk. 293 

305 

325

50% red. 14-carbon uptake; 

media: Algal assay, Taub 

& Dollar 

(TD), & TD, respect.

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

Euglenoid 

Euglena gracilis 

(7 days) 

NR 496 50% inhibition of 

photosynthesis 

ThuillierBruston et al. 

1996 

Supplemental 

Table A-41. Longer Term, Nontarget Freshwater Plant Toxicity

Surrogate Species/ 

Duration/ 

Measured/nominal

% ai

Conc. (ppb) 

Probit Slope % Response

MRID No. 

Author/Year Study Classification

Vascular Plants:

Broad Waterweed 

Elodea Canadensis 

(14 days; measured) 

96 0.001 50% reduction in dry 

root biomass 

McGregor et al. 

2008 

Supplemental 

Broad Waterweed 

Elodea canadensis

(20 days; measured)

Unk. NOAEC 2 

LOAEC 10

200% incr. dark 

respiration 

33% incr. net 

photosynthesis

452277-14 

Hofmann and 

Winkler 1990

Supplemental 

(raw data unavailable)

Pondweed 

Potamogeton perfoliatus

(4 weeks; initial conc. 

nominal, 

terminal conc. measured)

Unk 30 

Week 3: LOAEC 5 

 NOAEC < 5 

4 Weeks: LOAEC 50 

NOAEC 5 

50% red. O2 product. 

sign. red. O2 product. 

sign. red. O2 product. 

Kemp et al. 

1985

Supplemental 

(raw data unavailable)

Duckweed 

Lemna gibba

(14 days; measured)

97.1 37 

LOAEC 3.4 

 NOAEC < 3.4 

Slope 1.716

50% red. growth 

19% red. growth 

(frond production)

430748-04 

Hoberg 1993

Supplemental 

(NOAEC was not 

determined)

Duckweed - Lemna gibba

(14 days; measured)

97.4 43 

NOAEC 10 

Slope 1.995

50% red. growth 

(frond production)

430748-03 

Hoberg 1993

Acceptable 

Duckweed 

Lemna gibba

(14 days; measured) 

Includes recovery phase 

98.5 64 

67 

NOAEC = 18 

Slope 3.96 + 0.316 

50% red biomass 

50% red frond count 

461509-01 

Desjardins et 

al., 2003 

Acceptable 

Broad Waterweed 

Elodea canadensis

(3 weeks; nominal)

Unk. 80 50% red. shoot length 450874-10 

Forney and 

Davis 1981

Supplemental 

(raw data unavailable)

Eurasian Water-Milfoil 

Myriophyllum spicatum

(4 weeks; initial conc. 

nominal, 

terminal conc. measured)

Unk. 91 

NOAEC 5 

LOAEC 50

50% red, O2 product. 

Sign. red. O2 product. 

Kemp et al. 

1985

Supplemental 

(raw data unavailable)
48

Non-Vascular Plants:

36 freshwater algal strains 

(2 weeks; nominal)

99.0 10 

1,000 

growth <than control 

strong growth red.

Butler et al. 

1975

Supplemental 

(raw data unavailable)

Chlorophyceae 

Chlorella vulgaris

(11 days; nominal)

99.9 25 50% red. cell growth 452277-03 

Burrell et al. 

1985

Supplemental 

(raw data unavailable)

Cyanophyceae 

Anabaena inaequalis

(12-14 days1

; nominal)

>95 30 

100 

300

50% red. cell count 

50% red. growth rate 

50% red. 

photosynthesis

450874-01 

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Chlorophyceae 

Ankistrodesmus braunii

(11 days; nominal)

99.9 60 50% red. cell growth 452277-03 

Burrell et al. 

1985

Supplemental 

(raw data unavailable)

Chlorophyceae 

Scenedesmus quadricauda

(12-14 days1

; nominal)

> 95 100 

200 

300

50% red. cell count 

50% red. growth rate 

50% red. 

photosynthesis

450874-01 

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Chlorophyceae 

Chlorella pyrenoidosa

(12-14 days1

; nominal)

> 95 300 

1,000 

500

50% red. cell count 

50% red. growth rate 

50% red. 

photosynthesis

Stratton 1984 Supplemental 

(NOAEC and raw data 

unavailable)

Cyanophyceae 

Anabaena cylindrica

(12-14 days; nominal)

> 95 1,200 

3,600 

 500

50% red. cell count 

50% red. growth rate 

50% red. 

photosynthesis

Stratton 1984 Supplemental 

(NOAEC and raw data 

unavailable)

Cyanophyceae 

Anabaena variabilis

(12-14 days; nominal)

> 95 4,000 

5,000 

 100

50% red. cell count 

50% red. growth rate 

50% red. 

photosynthesis

Stratton 1984 Supplemental 

(NOAEC and raw data 

unavailable)

Table A-42. Nontarget Marine/Estuarine Plant Toxicity (Tier II)

Surrogate Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit Slope % Response

MRID No. 

Author/Year Study Classification

Vascular Plants:

Fontinalis sp. 

(24 hours; measured)

NR

NOAEC 2 

 LOAEC 10

red. net O2 production Supplemental 

(raw data unavailable)

Pondweed (Estuarine) 

Potamogeton perfoliatus

(2 hours; nominal)

NR

 77 50% red. O2 evolution 452277-18 

Jones and 

Winchell 1984

Supplemental 

(Insufficient duration; 

raw data unavailable)

Pondweed 

Potamogeton perfoliatus

(2 hours; nominal)

NR

 80 

650 

50% red. O2 product. 

87% red. O2 product..

452277-18 

Jones et al. 

1986

Supplemental 

(Insufficient duration; 

raw data unavailable)

Zannichellia palustris

(2 hours; nominal)

NR

 91 50% red. O2 evolution 452277-19 

Jones and 

Winchell 1984

Supplemental 

(Insufficient duration; 

raw data unavailable)

Pondweed (Estuarine) 

Potamogeton perfoliatus

(2 hours; nominal)

NR 100 52 to 69% red. in 

photosynthesis

450874-04 

Jones & Estes 

1984

Supplemental 

(raw data unavailable)

Widgeon-Grass (Estuarine) NR 102 50% red. O2 evolution 452277-19 Supplemental 
49

Ruppia maritima 

(2 hours; nominal

Jones and 

Winchell 1984

(Insufficient duration; 

raw data unavailable)

Non-Vascular Plants:

Prasinophyte 

Nephroselmis pyriformis 

(4 hours) 

NR 14.2 μg/L 

LOAEC = 1.1 μg/L 

50% photoinhibition Magnussun et 

al. 2010 

Supplemental 

Blue-green - Cyanophyceae 

Oscillatoria lutea

(1week; nominal)

76 

80 W

 1 

1,000 

93% red. chlorophyll 

 production 

100% red. 

 chlorophyll prod.

000235-44 

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Green Algae - Chlorophyceae 

Stigeoclonium tenue

(1 week; nominal)

76 

80 W

1 

1,000 

67% red. chlorophyll 

 production 

90% red. chlorophyll 

 production

000235-44 

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Green Algae - Chlorophyceae 

Chlorella vulgaris

(1 week; nominal)

76 

80 W

1 

1,000 

50% red. chlorophyll 

 production 

80-87% red. 

 chlorophyll prod.

000235-44 

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Xanthophyceae 

Tribonema sp. 

(1 week; nominal)

76 

80 W

1 

1,000 

42% red. chlorophyll 

 production 

75% red. chlorophyll 

 production

000235-44 

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Xanthophyceae 

Vaucheria geminata

(1 week; nominal)

76 

80 W

1 

1,000 

41% red. chlorophyll 

 production 

100% red. 

 chlorophyll prod.

000235-44 

Torres and 

O’Flaherty 

1976

Supplemental 

(raw data unavailable)

Dinoflagelate 

Amphidinium operculatum 

(96 hrs) 

NR 17.9 

NOAEC <12.5 50% red. In total 

biovolume 

DeLorenzo et 

al. 2004 Supplemental 

Marine Diatom 

Bellerochea polymorpha 

(48 hr) 

NR 19.4 50% reduction in 

population growth 

Walsh et al. 

1988 Supplemental 

Chrysophyceae 

Isochrysis galbana

(120 hours; nominal)

97.4 22 

NOAEC < 13 

LOAEC 13 

Slope 3.065

50% red. growth 

30% red. growth

410652-04 

Parrish 1978

Supplemental 

(NOAEC, method & 

raw data unavailable)

Cryptomonad 

Storeatula major

SW 96 hrs. 

NR 

22.17 

NOAEC < 12.5 

50% reduction in 

abundance 

DeLorenzo et 

al. 2004 Supplemental 

Marine Diatom 

Skeletonema costatum

(120 hours; nominal)

97.4 24 

NOAEC < 13 

LOAEC 13 

Slope 3.343

50% red. growth 

14% red. growth

410652-04 

Parrish 1978

 Supplemental 

(NOAEC, method & 

raw data unavailable)

Coccolithophorad 

Isochrysis galbana

(SW 72 hrs) 

NR 30 μg/L 50% growth inhibition Debelius et al. 

2008 Supplemental 

Marine Diatom 

Skeletonema costatum 

(120 hours; measured)

97.1 53 

NOAEC 14 

Slope 2.798

50% red. cell growth 430748-01 

Hoberg 1993

Acceptable

Marine Green - Chlorophyceae 

Chlamydomonas sp. 

(72 hours; nominal); Salinity 

30 g/L

99.7 60 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Golden Algae 

Monochrysis lutheri 

(1 hr) 

NR 77 50% red. O2 production Hollister and 

Walsh 1973 

Supplemental 

(Short duration) 

Marine Yellow - 

Chrysophyceae 99.7 77 50% red. O2 production 402284-01 Supplemental 
50

Monochrysis lutheri 

( 72 hours; nominal); Salinity 

30 g/L

Mayer 1986 (72 hrs & endpoint) 

Marine Red - Rhodophyceae 

Porphyridium cruentum

(72 hours; nominal); Salinity 

30 g/L

99.7 79 50% red. in O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Green - Chlorophyceae 

Neochloris sp. 

(72 hours; nominal); Salinity 

30 g/L

99.7 82 50% red. in O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Bacillariophyceae 

Cyclotella nana 

(72 hours; nominal); Salinity 

30 g/L

99.7 84 50% red. in O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Bacillariophyceae 

Achnanthes brevipes 

(72 hours; nominal); Salinity 

30 g/L

99.7 93 50% red. in O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Yellow - 

Chrysophyceae 

Isochrysis galbana

(240 hours; nominal); Salinity 

30 g/L

99.7 100 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Marine Green - Chlorophyceae 

Chlorococcum sp. 

(240 hours; nominal); Salinity 

30 g/L

99.7 100 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Marine Green - Chlorophyceae 

Platymonas sp. 

 (72 hours; nominal); Salinity 

30 g/L

99.7 100 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Bacillariophyceae 

Thalassiosira fluviatilis

(72 hours; nominal); Salinity 

30 g/L

99.7 110 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint) 

Marine Bacillariophyceae 

Stauroneis amphoroides

(72 hours; nominal); Salinity 

30 g/L

99.7 110 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Algae 

Microcystis aeruginosa

(120 hours - nominal)

97.4 129 

NOAEC 65 

Slope 3.162

50% red. growth 

 7% red. growth

410652-04 

Parrish 1978

Supplemental 

(NOAEC, method & 

raw data unavailable)

Marine Green - Chlorophyceae 

Chlorella sp. 

 (72 hours; nominal); Salinity 

30 g/L

99.7 140 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable

Blue-green - Cyanophyceae 

Anabaena cylindrica

(24 hour; nominal)

Unk. 178 

182 

253

50% red. 14-carbon 

uptake; media: Taub & 

Dollar (TD), algal assay, 

& TD, respect.

450200-15 

Larsen et al. 

1986

Supplemental 

(raw data unavailable)

 Marine green - Chlorophyceae 

Dunaliella tertiolecta

(120 hours; nominal)

97 180 

NOAEC < 100 

LOAEC 100 

Slope 1.95

50% red. growth 

34% red. growth

410652-03 

Hughes 1986

Supplemental 

(NOAEC unavailable)

Marine Yellow-Green NR 185 50% total fluorescence 

inhibition 

Debelius et al. 

2008 

Supplemental 
51

Nannochloropsis gaditana 

(72 hrs) 

Marine Yellow - 

Chrysophyceae 

Phaeodactylum tricornutum 

(240 hours; nominal); Salinity 

30 g/L

99.7 200 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Marine Bacillariophyceae 

Nitzschia closterium

(72 hours; nominal); Salinity 

30 g/L

99.7 290 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Bacillariophyceae 

Amphora exigua

(72 hours; nominal); Salinity 

30 g/L

99.7 300 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Green - Chlorophyceae 

Dunaliella tertiolecta

(240 hours; nominal); Salinity 

30 g/L

99.7 300 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Marine Red - Rhodophyceae 

Porphyridium cruentum

(120 hours)

97.4 308 

NOAEC <130 

LOAEC 130 

Slope 2.449

50% red. growth 

16% red. growth

410652-04 

Parrish 1978

Supplemental 

(NOAEC, method & 

raw data unavailable)

Marine Bacillariophyceae 

Nitzschia (Ind. 684) 

(72 hours; nominal); Salinity 

30 g/L

99.7 430 50% red. O2 production 402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Marine Green -Chlorophyceae 

Kirchneria subcapitata

(120 hours; nominal)

97.4 431 

NOAEC 200 

Slope 4.217

5% red. in growth 

 4% red. in growth

410652-04 

Parrish 1978

Supplemental 

(NOAEC, method & 

raw data unavailable)

Marine Bacillariophyceae 

Navicula inserta

(72 hours; nominal); Salinity 

30 g/L

99.7 460 50% red. in O2 

production

402284-01 

Mayer 1986

Supplemental 

(72 hrs & endpoint)

Table A-43. Formulation Nontarget Marine/Estuarine Algal Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Mar. Yellow - Chrysophyceae 

Isochrysis galbana

(nominal); Salinity 30 g/L

76 

80 WP

100 (240 hrs) 

200 (2 hrs) 

50% red. cell growth 

50% red. O2 production

402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Mar. Yellow Chlorophyceae 

Chlorococcum sp. 

(nominal); Salinity 30 g/L

76 

80 WP

100 (240 hrs) 

400 (2 hrs) 

50% red. cell growth 

50% red. O2 production

402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Mar. Yellow - Chrysophyceae 

Phaeodactylum tricornutum 

(nominal); Salinity 30 g/L

76 

80 WP

200 (240 hrs) 

200 (2 hrs) 

50% red. cell growth 

50% red. O2 production

402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Mar. Green - Chlorophyceae 

Dunaliella tertiolecta

(nominal); Salinity 30 g/L

76 

80 WP

400 (240 hrs) 

600 (2 hrs) 

50% red. cell growth 

50% red. O2 production

402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)
52

Table A-44. Longer-term (> 10 days exposure) Nontarget Marine/Estuarine Plant Toxicity

Surrogate Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit Slope % Response

MRID No. 

Author/Year Study Classification

Vascular Plants:

Sago Pondweed (Estuarine) 

Potamogeton pectinatus

(28 days; measured/nominal)

NR Salinity 12 ppt: 

NOAEC 7.5 

LOAEC 14.3 

Salinity 1 & 6 ppt: 

NOAEC 14.3 

LOAEC 30 

sign. red. dry weight 

sign. red. dry weight

450882--31 

Chesapeake Bay 

Program 1998

Supplemental 

(raw data unavailable)

Estuarine rush 

Juncus roemerianus

(5 weeks - 1 year; measured

97.1 LOAEC 30 

NOAEC 30 

NOAEC < 30 

250 ppb 

3, 800 ppb 

sign. red. chlorophyll a in 

5 weeks 

(1 year) 

partial recovery (1 yr) 

practically no survival

450874-05 

Lytle & Lytle 

1998

Supplemental 

(raw data unavailable)

Pondweed 

Potamogeton perfoliatus

(4 weeks; initial conc. 

nominal, 

terminal conc. measured)

NR

 30 

Week 3: LOAEC 

5 

 NOAEC < 5 

4 weeks: LOAEC 

50 

 NOAEC 5

50% red. O2 product. 

sign. red. O2 product. 

sign. red. O2 product. 

452277-20 

Kemp et al. 

1985

Supplemental 

(raw data unavailable)

Pondweed (Estuarine) 

Potamogeton perfoliatus

(3 weeks; nominal)

NR

53 50% red. ???? 450874-10 

Forney and 

Davis 1981

Supplemental 

(raw data unavailable)

Eelgrass (Estuarine) 

Zostera marina

(10 days; measured)

NR

est. 69 

50 

80

50% red. leaf growth 

25% red. leaf growth 

62% red. leaf growth

452277-29 

Schwarzschild 

et al. 1994

Supplemental 

(raw data unavailable)

Estuarine Eelgrass 

Zostera marina

(21 days; nominal)

NR

100 

 

NOAEC 10

21-day LC50 red. 

 production

452277-05 

Delistraty and 

Hershner 1984

Supplemental 

(raw data unavailable)

Wild Celery (Estuarine) 

Vallisneria americana

(6 weeks; nominal)

NR

163 50% red. shoot length 

no difference at 0, 3, or 6 

parts/thousand

450874-10 

Forney and 

Davis 1981

Supplemental 

(raw data unavailable)

 Seagrass (Estuarine) 

Halodule wrightii

(22 - 23 days; measured)

Atrazi

ne 

4L

30,000 46-58% red. total aboveground biomass452051-01 

Mitchell 1987

Supplemental 

(raw data unavailable)

Non-Vascular Plants:

Marine Brown macroalgae 

Laminaria hyperborea

(18 days; nominal)

NR NOAEC < 1 

LOAEC = 10 

sign. red. growth rate; 

delayed sporophyte 

formation

Hopkin &Kain 

1978

Supplemental 

(raw data unavailable)

Marine Yellow - 

Chrysophyceae 

Isochrysis galbana

(240 hours; nominal); Salinity 

30 g/L

99.7 100 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Marine Green - Chlorophyceae 

Chlorococcum sp. 

(240 hours; nominal); Salinity 

30 g/L

99.7 100 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Marine Yellow - 99.7 200 50% red. cell growth 402284-01 Supplemental 
53

Chrysophyceae 

Phaeodactylum tricornutum 

(240 hours; nominal); Salinity 

30 g/L

Mayer 1986 (NOAEC unavailable)

Marine Green - Chlorophyceae 

Dunaliella tertiolecta

(240 hours; nominal); Salinity 

30 g/L

99.7 300 50% red. cell growth 402284-01 

Mayer 1986

Supplemental 

(NOAEC unavailable)

Degradates: Special tests are required for algal and vascular plant species (123-2) to 

address concerns for the toxicity of atrazine degradates to aquatic plants. A summary of 

the degradate aquatic plant toxicity data for deethylatrazine, deisopropylatrazine, 

diamino-atraine, and hydroxyatrazine is provided in Tables A-45 through A-48, 

respectively. 

Table A-45. Degradate Deethylatrazine Nontarget Aquatic Plant Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Fresh. Blue-Green - Cyanophyceae 

Anabaena inaequalis

(12-14 days1

; nominal)

> 95 1,000 

4,000 

2,500

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984 Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Scenedesmus quadricauda

(12-14 days; nominal)

> 95 1,200 

2,000 

1,800

50% red. cell count 

50% red. Growth rate 

50% red. photosynthesis

Stratton 1984 Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Chlorella pyrenoidosa

(12-14 days1

; nominal)

> 95 3,200 

7,200 

1,800

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984 Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena variabilis

(12-14 days; nominal)

> 95 3,500 

7,500 

 700

50% red. cell count 

50% red. growth rate 

50 % red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena cylindrica

(12-14 days; nominal)

> 95 8,500 

5.500 

4,800

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Table A-46. Degradate Deisopropylatrazine Nontarget Aquatic Plant Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Fresh. Blue-Green - Cyanophyceae 

Anabaena inaequalis

(12-14 days1

; nominal)

> 95 2,500 

 7,000 

 9,000

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Scenedesmus quadricauda

(12-14 days; nominal)

> 95 6,900 

 6.500 

 4,000

50% red. cell count 

50% red. Growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Chlorella pyrenoidosa

(12-14 days1

; nominal)

> 95 > 10,000 

> 10,000 

 3,600

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena variabilis

(12-14 days; nominal)

> 95 5,500 

 9,200 

 4,700

50% red. cell count 

50% red. growth rate 

50 % red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)
54

Table A-46. Degradate Deisopropylatrazine Nontarget Aquatic Plant Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Fresh. Blue-Green - Cyanophyceae 

Anabaena cylindrica

(12-14 days; nominal)

> 95 > 10,000 

> 10,000 

 9,300

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green Algae 

(Scenedesmus subspicatus

(72 hours; nominal) 

NR 1,300 (slope 

= 2.18 

+0.377) 

50% red. cell density 470461-05 

Vial, 1991e 

Supplemental (study 

duration not sufficient 

to be classified as Tier 

II study) 

 230 5% red. cell density 

 370 NOAEC for red. cell 

density 

 1,500 (slope 

= 

2.36+0.382) 

50% red. biomass 

 290 5% red. biomass 

 370 NOAEC for red. biomass 

Table A-47. Degradate Diamino-Atrazine Nontarget Aquatic Plant Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Fresh. Blue-Green - Cyanophyceae 

Anabaena inaequalis

(12-14 days1

; nominal)

> 95 7,000 

 >10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Scenedesmus quadricauda

(12-14 days; nominal)

> 95 4,600 

 10,000 

>100,000 

50% red. cell count 

50% red. Growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Chlorella pyrenoidosa

(12-14 days1

; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena variabilis

(12-14 days; nominal)

> 95 >10,000 

>10,000 

 100,000 

50% red. cell count 

50% red. growth rate 

50 % red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena cylindrica

(12-14 days; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Table A-48. Degradate Hydroxyatrazine Nontarget Aquatic Plant Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Fresh. Blue-Green - Cyanophyceae 

Anabaena inaequalis

(12-14 days1

; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Freshwater Green - Chlorophyceae 

Scenedesmus quadricauda

(12-14 days; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. Growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)
55

Table A-48. Degradate Hydroxyatrazine Nontarget Aquatic Plant Toxicity (Tier II)

Species/ 

Duration/Measured/nominal % ai

Conc. (ppb) 

Probit slope % Response

MRID No. 

Author/Year Study Classification

Freshwater Green - Chlorophyceae 

Chlorella pyrenoidosa

(12-14 days1

; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena variabilis

(12-14 days; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50 % red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

Fresh. Blue-Green - Cyanophyceae 

Anabaena cylindrica

(12-14 days; nominal)

> 95 >10,000 

>10,000 

>100,000 

50% red. cell count 

50% red. growth rate 

50% red. photosynthesis

Stratton 1984

Supplemental 

(NOAEC and raw data 

unavailable)

A.5 Toxicity to Terrestrial Invertebrates 

The available open literature data for the toxicity of atrazine to terrestrial invertebrates is 

summarized in Table A-49. 

Atrazine is practically non-toxic to honey bees (LD50: 97 μg/bee). It also did not cause 

adverse effects in fruit flies exposed to 15 μg/fly. LC50 values in earthworms ranged 

from 273 to 926 ppm soil (Mosleh et al., 2003; Haque and Ebing, 1983). Atrazine did 

not produce statistically significant (p>0.05) adverse effects in studies on several beetle 

species at any level tested, which ranged from application rates of approximately 1 lb 

a.i./Acre to 8 lbs a.i./Acre (Kegel, 1989; Brust, 1990; Samsoe-Petersen, 1995). 

The most sensitive terrestrial invertebrate species tested was the springtail (Onychiurus 

apuanicus and O. armatus). Exposure to O. apuanicus at 2.5 ppm resulted in 18% 

mortality, and exposure to O. armatus at 20 ppm resulted in 51% mortality (Mola et al., 

1987); lower levels were not tested. These soil concentrations are associated with an 

application rate of approximately 1 lb a.i./Acre and 7 lbs a.i./Acre, respectively, assuming 

a soil density of 1.3 grams/cm3

 and a soil depth of 3 cm. Additional details on these 

studies may be found in Appendix A. 

Several field studies reported reduced abundance in terrestrial invertebrates (Fox, 1964; 

Fretello et al., 1985). However, in these studies, reduced abundance could have been 

caused either by direct effects or by indirect effects caused by reduced vegetation of the 

herbicide. Available studies are summarized in Table A-49. 

Table A-49. Toxixcity of Atrazine to Terrestrial Invertebrates 

Species Dose Comment Citation 

Honey bees LD50: >97 g/bee 5% mortality occurred at the highest dose tested 

(97 ug/bee) 

MRID 00036935 

Ground Beetles 

(Poecilus) 

P. versicolor 

NOAEC: 8 lbs/Acre Spiked soil study; no effects occurred at any 

level tested. 

Kegel, 1989 

Ecotox No. 64007 

P. cupreus NOAEC: 0.8 lbs/Acre Spiked soil study; no effects occurred at any 
56

level tested. 

P. lepidus NOAEC: 0.8 lbs/Acre Spiked soil study; a 25% reduction in survival 

was observed at the highest level tested that was 

not significant at the p<0.05 level. 

5 species of 

carabid beetles 

NOAEC: 2 lbs/Acre Beetles were dipped in atrazine solution then 

placed in treated soil (2.24 kg a.i./Acre); a 

transient repellency effect occurred for 6 days 

after treatment. 

Brust, 1990 

Ecotox No. 70406 

Rove beetle NOAEC: The single 

level tested was 

intended to approximate 

practical application 

rates. 

Exposure occurred via sprayed sand; “no 

measurable effect” occurred at any 

concentration tested; dose level was reported to 

approximate a practical field application rate. 

Samsoe-Petersen, 

1995 

Ecotox No. 63490 

Onychiuridae 

Onychiurus 

apuanicus 

NOAEC: <2.5 ppm soil 

(<approx. 1 lbs/Acre)a 

Exposure occurred by treated soil; 18% 

mortality occurred at 2.5 ppm compared to 0% 

in controls. 

Mola et al., 1987. 

Ecotox No. 71417 

O. armatus NOAEC: <20 ppm soil 

(<approx. 7 lbs/Acre)a 

Exposure occurred by treated soil; 51% 

mortality occurred at 20 ppm compared to 0% in 

controls. 

Micro arthropods NOAEC: 0.9 lbs/Acre Field application of 1 kg/ha; atrazine was not 

associated with adverse effects. 

Cortet et al., 2002 

Ecotox No. 75784 

Microarthopods NOAEL = 2 kg/ha 

(1.05 ppm) 

LOAEC = 6 kg/ha (3.15 

ppm) 

Field study testing several species of 

microarthopods. It could not be determined if 

reduced abundance was caused by migration 

(repellency), by toxic effects, or both. 

Fratello et. al., 1985 

Ecotox No. 

59428 

Fruit flies 

Drosphilia 

NOAEC: 15 ug/fly No increased mortality occurred in groups 

exposed to atrazine alone relative to controls. 

Lichtenstein et al., 

1973 

Ecotox No. 2939 

Earthworm 

Aporrectodea 

caliginosa 

28-day LC50: 381 ppm Spiked soil study, 

Slope: 8.37 

Mosleh et al., 2003 

Ecotox No. 77549 

Earthworm 

Eisenia fetida 

14-Day LC50: 

273 mg/kg soil (ppm) – 

926 ppm 

Spiked soil study; endpoints evaluated included 

mortality and biomass. 

Haque and Ebing, 

1983 

Ecotox No. 

40493 

Earthworm 

Eisenia fetida 

4-Day LC50: 2.9 

ug/cm2 

Filter paper study Lydy and Linck, 

2003 

Ecotox No. 71459 

Earthworm LOAEC = 8 lb/acre Field study examining the impacts of several 

herbicides on soil invertebrate populations. The 

endpoint measured was abundance of several 

species. Study authors suggested that reduced 

abundance was likely caused by repellency and 

not direct toxicity. 

Fox, 1964 

Wire worm Ecotox No. 36668 

Springtail 

An estimation of application rates was made from soil concentration by assuming a soil depth of 3 cm and a 

soil density of 1.3 g/cm3. 

 

A.6 Effects of Environmental Factors and Life-Stage on Aquatic Atrazine Toxicity 
57

 A.6.1 Interaction Effects on Atrazine Toxicity to Plants 

Some intra-laboratory studies suggest that atrazine toxicity is affected by environmental 

parameters, such as temperature, light intensity and salinity levels. Mayer et al. (1998) 

concluded that a temperature difference of 1 o

C will cause a difference in algal growth 

rate in the range of 7 to 9 percent at the typical rate increase for 10 oC temperature 

increase (Q10) of 2 to 2.3. 

In general, the toxicity of pesticides increase with increasing temperature. Mayasich, 

Karlander and Terlizzi, Jr. (1986) tested two algal species in 27 combinations of 

temperature (15, 20 and 25 o

C), light intensity (0.208, 0.780 and 1.352 mW/cm2) and 

atrazine concentrations of 0, 50 and 100 μg/L) for 7-day periods. Toxic effects of 

atrazine on Nannochloris oculata growth rates were significantly (p < 0.01) dependent on 

both temperature and light intensity as determined by the 3-way interactions. Atrazine 

toxicity increased to N. oculata with both increasing temperature and increasing light 

intensity, except at 15 oC and 1.352 mW/cm2 where growth was intermediate. Previous 

results yielded a similar anomaly and suggest that 15 oC is near the lower limit for growth 

of this algal species. With Phaeodactylum tricornutum, growth rates were significant (p 

< 0.01) for light intensity and atrazine concentrations, and also significant (p < 0.05) for 

temperature, but only light intensity was significantly (p < 0.01) related to an increase in 

atrazine toxicity. Atrazine toxicity was highest at the lowest light intensity. ”The 

response of P. tricornutum to atrazine at light intensities of 0.780 and 1.352 mW/cm2

may be a reflection of primary effects only, while at 0.208 mW/cm2

, light intensity 

includes secondary effects” (Mayasich et al., 1986). With respect to the insignificant 

effect of temperature on growth, Ukeles (1961) and Fawley (1984) found that the growth 

of P. tricornutum was unchanged by temperatures in the range of 14 to 25 oC. 

Mayasich et al. (1987) repeated the above algal study with lower atrazine concentrations 

(0, 15, 30 and 50 μg/L and fewer temperatures (15 and 25 oC) and light intensities (0.208 

and 1.352 mW/cm2

) in unialgal and bialgal assemblages. Generally Phaeodactylum 

tricornutum’s presence significantly (p < 0.01) depressed the growth of Nannochloris 

oculata, but it did not alter the magnitude of the responses to temperature, light intensity 

or atrazine concentrations. In contrast, the presence of N. oculata generally resulted in 

significant (p < 0.01) enhancement of P. tricornutum growth. The bialgal assemblage 

produced magnitudes of interactions between temperature and light intensity, and 

temperature and atrazine were both significantly (p <0.01) greater for N. oculata. P. 

tricornutum dominated the assemblage over all concentrations of atrazine under 

simultaneously low levels of temperature (15 o

C) and light intensity (0.208 mW/cm2). At 

simultaneous high levels of temperature and light intensity and the absence of atrazine, P. 

tricornutum and N. oculata tended to be co-dominant. At increased atrazine 

concentrations, P. tricornutum became the dominant of the two algal species. The 

authors concluded that the enhanced sensitivity of N. oculata to atrazine relative to that 

exhibited by P. tricornutum posed a threat to the diversity and structure of natural 

phytoplankton populations. Thus, a nutritious algal species for larval oysters (Dupry, 

1973) is replaced by what is considered to be a poor food source for larval bivalves 

(Walne, 1970). 
58

Mayer et al. (1998) tested the effect of four main environmental factors on the toxicity of 

atrazine to the green alga Selenastrum capricornutum in 3 day tests. The four factors 

tested were light intensity (44 and 198 μE/m2

), temperature (16 and 26 oC), nitrogen 

source (NH4+ and NO3-) and pH (7.6 and 8.6). Temperature influenced growth indirectly 

by interacting with light intensity. Algal growth measured as the atrazine EC50 values 

was marginally reduced under low light intensity at high and low temperatures (158 and 

159 μg/L, respectively versus the atrazine control, 164 μg/L). High light intensity at the 

low temperature reduced the toxicity of atrazine to the alga by about two fold (LC50 300 

μg/L) while high light intensity and high temperature reduced the toxicity of the atrazine 

by about 118 fold (LC50 191 μg/L). Nitrogen source and pH had no significant effect on 

atrazine toxicity affecting algal growth rates. 

The above studies indicate that the toxicity of atrazine to plants can be affected by 

environmental parameters, but differences in effects are dependant on the algal species. 

Hence, increases in temperature may increase, decrease or have no effect on atrazine 

toxicity to algal growth. Light intensity generally has a stronger effect on atrazine 

toxicity to algal growth and may, short of the point of photo-inhibition, increase the 

toxicity of atrazine. Nitrogen source and pH do not have any effect on the toxicity of 

atrazine to algae. 

 A.6.2 Interaction Effects on Atrazine Toxicity to Aquatic Animals 

A number of intra-laboratory studies suggest that atrazine toxicity to aquatic animals is 

affected by environmental parameters, such as water hardness, salinity and differences in 

the life-stages of organisms. 

High levels of water hardness usually reduce the toxicity of pesticides. Intra-laboratory 

studies on two fish species provide comparative LC50 values for two levels of water 

hardness (Birge, Black and Bruser, 1979). Embryo-larval rainbow trout were exposed to 

atrazine for 27 days at water hardness levels of 50 and 200 mg/L and produced LC50 

values of 0.66 and 0.81 mg/L, respectively. Channel catfish were tested at the same 

water hardness levels for 8 days and yielded LC50 values of 0.22 and 0.23 mg/L. With 

rainbow trout embryo-larvae, the soft water increased toxicity by about 19 percent, while 

the LC50 values for embryo-larval catfish were the same. It is uncertain if the shorter 

exposure period, yolk sac, or differences in species sensitivity, account for the difference 

in water hardness effects between embryo-larvae of channel catfish and rainbow trout. 

Salinity effects at 5, 15 and 25 g/L on the toxicity of atrazine are opposite for the 

estuarine fish larvae, sheepshead minnow and the copepod nauplii, Eurytemora affinis

(Ziegenfuss, Anderson, Spittler and Leichtweis, 1994). The 96-hour LC50 values (16.2, 

2.3 and 2.0 mg/L) for sheepshead minnow consistently increased with increasing salinity. 

In the case of the copepod nauplii, the 96-hour LC50 values (i.e., 0.5, 2.6 and 13.3 mg/L) 

consistently decreased with increasing salinity. The consistency of the two data sets 

suggest that salinity effects the toxicity of atrazine. Statistical tests for both species 
59

indicate significant differences between the LC50 valves at 5 and 25 g/L, but not at 15 

g/L. The authors concluded that the two species may be more physiologically effective 

in metabolizing and mitigating toxic effects of atrazine at various salinities. The increase 

in LC50 values for rainbow trout and sheepshead minnow are consistent for increasing 

water hardness and increasing salinity. 

For many pesticides, the earlier life-stages are normally more sensitive than later lifestages. Contrary to most pesticides, the aquatic toxicity data for toad and frog tadpoles 

suggest that the late stages are more sensitive to atrazine than early tadpole stages (Howe 

et al., 1998). The late stage of the American toad tadpole is about 2.5 times more 

sensitive to atrazine than the early stage (10.7 versus 26.5 mg/L). For the northern 

leopard frog tadpoles, the later stage is about 3.3 times more toxic than the early tadpole 

stage (14.5 versus 47.6 mg/L). 

The above studies suggest that decreases in water hardness and salinity can increase the 

toxicity of atrazine to fish, but increasing salinity may mitigate atrazine toxicity to 

copepods. Life stages show differences in sensitivity to atrazine. The later stages in frog 

and toad tadpole development show an increased sensitivity to atrazine over early tadpole 

stages. 

A.7 Pesticide Toxicity Interactions 

A number of authors have reported toxic interactions between atrazine, its dealkylated 

degradates and other pesticides. Synergism between atrazine and a number of other 

pesticides has also been reported in aquatic organisms, particularly with organophosphate 

insecticides, a carbamate insecticide and other herbicides including metolachlor. 

A.7.1 Plants 

In 1974, Putnam and Penner reported on the effects of interactions of herbicides on 

higher plants. Atrazine was cited in test combinations with 5 herbicides, 2 insecticides 

and a fungicide. Synergistic effects (i.e., increased toxicity higher than additivity) was 

identified in 6 out of the 8 test combinations. Atrazine was synergistic with 4 herbicides 

(i.e., 2, 4-D (oil), paraquat, EPTC, and alachlor) and 2 insecticides (i.e., diazinon and 

fensulfothion). Atrazine test combinations with dalapon, a herbicide, and dexon, a 

fungicide, showed antagonistic interactions. 

Torres and O’Flaherty (1976) report additive toxicity of atrazine with simazine at 

concentrations of 1.0 ug/L and 1 mg/L for Chlorella vulgaris, Stigeoclonium tenue, 

Tribonema sp., Vaucheria geminata, and Oscillatoria lutea. Additive toxicity of 

malathion with atrazine was found in Chlorella vulgaris, but could not be assessed with 

other species, because malathion produced total inhibition of chlorophyll production at 1 

ug/L or greater concentrations. At 1 and 1,000 ug/L, pesticides mixtures increased 

toxicity from 2.4 to 100 percent over the toxic levels of atrazine alone. Mixtures of these 
60

pesticides at concentrations of 0.1 and 0.5 ug/L usually enhanced the production of 

chlorophyll. 

Stratton (1984) also tested the most sensitive algal species, Anabaena inaequalis, with 

mixtures of atrazine and its two most toxic degradates, deethylatrazine and 

deisopropylatrazine. Cell count results indicate that combinations of 

atrazine/deethylatrazine (1.8) and atrazine/deisopropylatrazine (1.3) are synergistic and 

deethylatrazine/deisopropyl-atrazine mixtures are additive (1.03). For photosynthesis, 

results after 3 hour exposures indicate that all mixture combinations for these three 

chemicals are antagonistic (0.8, 0.86, and 0.89). 

Burrell et al. (1985) reported 11-day interactions between algal populations and between 

algal populations and pesticides. Population interactions showed that Chlorella vulgaris

inhibited population growth of Ankistrodesmus braunii by 32 percent. The addition of 

the bacterium, Chromobacterium violaceum, added to the algal mixture further inhibited 

population growth of A. braunii by an additional 17% and bacterial growth was 

stimulated, but the bacterium had no effect on Chlorella populations. The combined 

effect of the mixtures of atrazine (60 μg/L) and sodium pentachlorophenate (Na-PCP) (0, 

300, 800, 1,000 and 1,200 μg/L) and atrazine (40 and 100 μg/L) with Na-PCP (700 and 

1,200 μg/L) on A. braunii populations were additive over a wide range of concentrations. 

Similar results of atrazine (10 and 100 μg/L) and Na-PCP (300 and 1,200 μg/L) were 

obtained with C. vulgaris. In mixed algal cultures tested with atrazine (40 and 100 g/L), 

cell numbers of A. braunii were reduced 50 and 80 percent, respectively, which was not 

significantly different than effects when tested alone. In the same mixed culture test, 

atrazine inhibited growth of C. vulgaris by 79 and 85 percent, respectively, which 

showed a significant growth inhibition only at the lower test concentration (40 μg/L). 

The authors concluded that the high atrazine concentration (100 μg/L) did not alter the 

established population relationship between the two algal species, but at the lower 

concentration (40 μg/L), A. braunii increased the susceptibility of C. vulgaris to atrazine. 

When mixed cultures of algae were treated with both atrazine (60 μg/L) and Na-PCP 

(300, 800, 1,000 and 1,200 μg/L), chemical antagonism was observed. The addition of 

the bacterium, C. violaceum, to the microcosm, had no effect on the level of antagonism 

for A. braunii. C. violaceum modified the antagonism of atrazine toxicity to C. vulgaris

by about 40 percent, but the antagonistic effect was not eliminated. The net atrazine 

toxicity decreased as the Na-PCP concentration increased. The authors found no reason 

for the modification of atrazine effects by C. violaceum. 

Carder and Hoagland (1998) reported that pesticide interactions of atrazine (0, 12 and 

150 μg/L) and alachlor (0, 5, 90 μg/L) on benthic algal communities in artificial 

recirculating streams showed significant interaction (i.e., antagonism) only in the first 

week in the combination of high alachlor and low atrazine test concentrations. The 

authors concluded that the interaction is most likely anomalous and the lack of significant 

synergistic effects may be attributed to different modes of action. 
61

A.7.2 Animals 

A number of authors have reported synergistic effects of atrazine with terrestrial and 

aquatic animals with one or more of the following pesticides: (i.e., alachlor, chlorpyrifos, 

DDT, diazinon, malathion, methyl parathion, parathion, metolachlor, and trichlorfon). 

Liang and Lichtenstein (1975) also found atrazine synergism between soil residues of 

both DDT and parathion using fruit flies, Drosophila melanogaster and measured lethal 

effects versus the age of the pesticide residues in soil. Ten grams of Plainfield sand (1.2 

% organic matter) or Plano silt loam (4.7% organic matter) was mixed with parathion 

(2.3 μg/10 g of soil = 0.23 ppm) or DDT (30 μg/10 g of soil = 3 ppm), then was mixed 

with 10 g of the same soil type, which contained increasing atrazine levels (40 to 1000 

μg/10 g of soil = 4 to 100 ppm) or controls. Fifty fruit flies were placed in 120 ml test 

jars for 24 hours with the 10-g portions of air-dried soil untreated or treated with atrazine, 

parathion, DDT or combinations thereof. The resulting 24-hour fruit fly LD50 values for 

constant soil levels of parathion (2.3 ppm) and DDT (3.0 ppm) were as follows: parathion 

(6.2 ppm atrazine in sand and 92 ppm in loam) and DDT (8.5 ppm atrazine in sand and 

68 ppm in loam). Synergistic effects were apparent in all test combinations of soil and 

pesticides yielding a dose-response effect on fly mortality with increasing atrazine soil 

concentrations. Fruit fly mortality levels with both parathion and DDT in soils also 

clearly indicate a strong reduction in toxicity with the silt loam soil with a higher 

percentage of organic matter (4.7%) compared to sandy soil (1.2%). 

Additional loam soil toxicity tests were conducted daily for 4 days, with aged-atrazine 

soil with an initial 50 ppm aged in the dark at 22ΕC and both fresh and aging-parathion 

soil levels (0.35 ppm). In the test with fresh parathion soils and aged-atrazine soils, 

toxicity to fruit flies decreased linearly from 95% mortality on Day 0 to 43.3% over four 

days. By the fourth day, atrazine levels had declined to 19 ppm, which was barely 

enough to synergize parathion in loam soils. In another toxicity test, parathion-treated 

soils were aged under the same conditions as above and added it daily to the initial 10 g 

of atrazine-treated soil (50 ppm). In this test, the toxicity to fruit flies decreased 

logarithmically from about 68% on Day 0 to 10% mortality on Day 4. The measured 

concentrations of aging parathion in the silt loam soil decreased at a rate paralleling the 

logarithmic toxicity curve. The final parathion level on Day 4 was 0.24 ppm. 

Liang and Lichtenstein (1975) found atrazine to be synergistic with parathion in 24-hour 

aquatic tests with third-instar mosquito larvae, Aeddes aegypti and also assessed the 

effects of sand and loam soils on their individual and combined toxicity in 20 ml of 

pesticide-treated water. Atrazine at 10,000 μg/L showed no toxicity to the mosquito 

larvae; alone, parathion (15 μg/L) killed 20 + 7 percent of the larvae; and at these 

concentrations, the combination of the two pesticides produced significantly (p = 0.01) 

higher mortality (73 + 18 %). Addition of 5 g of Plainfield sand (1.2% organic matter) 

with 15 μg/L parathion reduced the toxicity of parathion from 20 + 7% to 18 +4%, but 

when sand was mixed into the water, mortality drop to 5%. Plano silt loam soil (4.7% 

organic matter) without mixing reduced parathion toxicity from 20 + 7% to 5 + 4% and 

when the loam soil was mixed into the water, no mosquito larvae died. When these two 
62

soils were added to the same combination of atrazine and parathion, sand reduced the 

mortality from 73 + 14% to 71 + 14% (unmixed) and to 18 + 4 % when mixed into the 

water; loam soil reduced the mortality from 73% to 64 + 4% (unmixed) and to no 

mortality with mixing. The combination of atrazine and parathion was significantly (p = 

0.01) more toxic than the toxicity of parathion or atrazine alone. 

The above toxicity test method was repeated using 1 and 5 grams of sand or silt loam to 

measure the effect of different amounts of soil on toxicity following 24-hour exposures. 

Atrazine (10 ppm) produced no mortality in 24 hours to mosquito larvae. Parathion 

(0.015 ppm) produced 24 + 7% mortality (no soil), 16 + 7% (1g of sand), 2 + 2% (5 g of 

sand), 7 + 0% (1 g of loam soil) and 0% (5 g of loam soil). The combination of atrazine 

(10 ppm) and parathion (0.015 ppm) showed synergistic effects on mosquito larvae 

mortality: 62 + 8% (no soil), 42 + 10% (1 g of sand), 2 + 2% (5 g of sand), 22 + 4% (1 g 

of loam soil) and 0% (5 g of loam soil). This test format was repeated using higher 

pesticide concentrations and again the mortality levels were increased with a mixture of 

atrazine (20 ppm) and parathion (0.30), but the synergistic increase was much lower than 

in the previous test. The 24-hour results indicated that atrazine alone was not toxic to 

mosquito larvae; 0.30 ppm parathion (93 + 6% mortality with on soil), 62 + 8% with 5 g 

of sand and no mortality with silt loam soil. The mixture of 20 ppm atrazine and 0.30 

ppm parathion produced 98 + 4% mortality with no soil, 76 + 4% dead when shaken with 

5 g of sand, and 38 + 10% lethality when shaken with 5 g of silt loam soil. These studies 

demonstrate that atrazine is synergistic with parathion and, like single toxicants, organic 

matter in soils and sediments will modify toxicity of pesticide mixtures, especially if the 

organic matter is suspended in the water. While this particular study has limited value for 

risk assessment, because the atrazine levels (10 and 20 ppm) exceed the normal 

environmental range of atrazine exposures, the study suggests that synergism of atrazine 

and parathion may occur at lower concentrations, possibly in the range of environment 

levels of atrazine. 

Pape-Lindstrom and Lydy (1997) tested atrazine with 6 pesticides for chemical 

interactions using 4th instar midges (Chironomus tentans). The 96-hour test results for 

the pesticide mixtures indicated that atrazine was synergistic with the phosphonate 

insecticide, trichlorfon, (0.26 toxic units) and 3 phosphorothioate insecticides (i.e., 

malathion (0.36 TU), chlorpyrifos (0.58 TU) and methyl parathion (0.59 TU). The 

atrazine-mevinophos (a phosphate) mixture was less than additive (1.34 TU), while 

methoxychlor, a organochlorine insecticide mixture was also less than additive (1.67 

TU). The results from these tests are questionable, since DMSO was used as a solvent 

with atrazine. These tests were repeated by Belden and Lydy (2000) without DMSO and 

with lower atrazine concentrations (0, 10, 40, 80, and 200 μg/L). Acute 96-hour tests 

with Chironomus tentans were conducted with each pesticide and EC1, EC5, EC15 and 

EC50 values were determined based on inability of the midge to swim when prodded with 

forceps. Chemical interactions were tested at each of these EC levels with atrazine levels 

of 0, 10, 40, 80 and 200 μg/L using 5 replicates of 10 midges each. Atrazine increased 

the toxicity of chlorpyrifos, diazinon and parathion, but not malathion. The authors 

concluded that “Interaction terms were not significant for atrazine + methyl parathion and 

atrazine + diazinon; however, a significant interaction was found for the atrazine + 
63

chlorpyrifos test (p = 0.002, df - 12, F = 2.94).” Synergistic ratios were reported as 

follows: chlorpyrifos, 1.83 at 40 μg/L and 4.00 at 200 μg/L atrazine; at 200 μg/L 

diazinon the SR was 2.71 and for methyl parathion, the SR was 1.94. The variety of 

chemical interactions produced by atrazine mixtures indicates that the effect of atrazine 

on an organism is dependent on the species, cocontaminant, and the concentration of 

atrazine. Additional tests with 200 μg/L atrazine and chlorpyrifos showed that atrazine 

increased the uptake of chlorpyrifos by 42 percent, and that the atrazine induction of 

cytochrome-P450 increased the formation of the O-analog which increased the toxicity of 

chlorpyrifos at enviromentally relevant concentrations. 

Anderson and Lydy (2002) demonstrated that atrazine concentrations as low as 80 μg/L 

significantly increased the acute toxicity of diazinon to the amphipod Hyallela azteca. 

Using larvae of the mide Chironomus tentans, Belden and Lydy (2000) demonstrated a 

significant increase in diazinon toxicity when simultaneous exposure to 40 μg/L of 

atrazine occurred. In another study by Banks et al (2005), the study authors demonstrated 

that atrazine concentrations as low as 5.0 μg/L in combination with diazinon resulted in 

significant (P < 0.05) increases in the 48-h toxicity of diazinon to Ceriodaphnia dubia. 

Atrazine induces cytochrome P450 and general esterase activities in insects (Kao et al., 

1995). It is possible that induction of the P450 system by atrazine may either increase or 

decrease the toxicity of other chemicals, depending on whether metabolites of the 

chemical in question are more or less toxic than the parent compound itself. Syngeristic 

effects of organophosphates and atrazine observed by Pape-Lindstrom and Lydy (1997) 

for the midge C. tentans suggest that processes involved with oxidation of some 

organophosphate molecules to more toxic oxon metabolites may be enhanced in the 

presence of atrazine. 

Howe et al. 1998 reported synergism between atrazine and alachlor, a herbicide, in tests 

with young rainbow trout, channel catfish and early and late tadpole stages of the 

northern frog and the American toad. The results are presented in the table below. 

(MRID # 452029-10). 

Species 

(stage)

Time 

(hour)

Atrazine LC50 

 ( 95% CI) mg/L

Alachlor LC50 

 (95% CI) mg/L

Atrazine-Alachlor LC50a

(95% CI) mg/L

Additive Indexb

(95% CI)

Rainbow trout 

(0.8-1.0-gram juveniles)

24 

96

31.6 (28.2 - 35.4) 

20.5 (18.3 - 22.9)

10.6 (9.5 - 11.7) 

 9.1 (9.0 - 9.2)

 9.5 (8.3 - 10.9) 

 6.5 (5.7 - 7.7)

-0.20 (-0.53-0.059) 

-0.03 (-0.28-0.15)

Channel catfish 

(0.9-1.1-gram juveniles)

24 

96

51.3 (44.6 - 59.0) 

23.8 (22.3 - 25.5)

23.8 (22.7 - 25.0) 

16.7 (15.1 - 18.4)

11.1 ( 9.6 - 12.4) 

 7.5 (5.3 - 8.4)

0.29 (0.067-0.55)c

0.31 (0.072-0.57)c

Northern leopard frog 

(0.7-0.9-gr early larvae)

24 

96

69.7 (63.1 - 77.2) 

47.6 (41.4 - 54.8)

14.9 (13.3 - 16.6) 

11.5 (10.1 - 13.2)

12.1 (11.0 - 12.9) 

 6.5 ( 5.7 - 7.7)

0.015 (-0.17-0.24) 

0.43 (0.054-0.87)c

Northern leopard frog 

(1.4-1.9-gr late larvae)

24 

96

45.3 (42.3 - 48.5) 

14.5 (11.9 - 17.5)

 7.3 ( 6.6 - 8.0) 

 3.5 ( 3.1 - 3.8)

 5.9 ( 5.5 - 6.4) 

 2.1 ( 2.0 - 2.3)

0.07 (-0.12-0.25) 

0.34 (0.069-0.56)c

American Toad 

(0.1-0.2-gr early larvae)

24 

96

66.4 (58.9 - 74.9) 

26.5 (23.0 - 30.5)

 5.7 ( 4.7 - 5.8) 

 3.9 ( 3.7 - 4.2)

 4.4 ( 4.2 - 4.6) 

 1.8 ( 1.7 - 1.9)

0.19 (-0.057-0.28) 

0.89 (0.68 - 1.2 )c

American Toad 

(0.4-0.5-gr late larvae)

24 

96

15.8 (13.5 - 18.4) 

10.7 ( 9.2 - 12.5)

 4.3 ( 3.8 - 4.8) 

 3.3 ( 2.8 - 3.6) 

 2.9 ( 2.6 - 3.3) 

 1.5 ( 1.4 - 1.6)

0.17 (0.11 - 0.46)c

0.68 (0.34 - 1.0 )c

a

 50:50 mixture of atrazine 4L (40.8% ai.) and alachlor EC (43.0% ai.). b

 An additive index greater than zero indicates greater than additive toxicity. 
64

c

 Significant chemical synergy interaction between atrazine and alachlor. 

Boone and Bridges-Britton (2006) examined the single and interactive effects of atrazine, 

carbaryl, and ammonium nitrate fertilizer on metamorphosis of tadpoles of the gray 

treefrog (Hyla versicolor). Tadpoles were reared in mesocosms from hatching through 

metamorphosis and were exposed to the presence or absence of the three contaminants. 

The results of the study indicated that the presence of multiple, sublethal chemical 

stressors with different modes of action may not be more determintal than that of one 

chemical factor alone. 

As previously discussed in Section A.2.4d and summarized in Table A-16, Hayes et al. 

(2006) assessed the effect of three different mixtures containing atrazine, to mortality, 

growth and development, gonadal development, thymus histology, and disease rates (i.e., 

immune function) in larval leopard frogs (R. pipiens). The three mixtures included 

atrazine and S-metalachlor at 0.1 and 10 ppb, Bicep II Magnum (reported as 33.3% 

atrazine, 0.7% atrazine-related products, 26.1% TGAI of S-metolachlor, and 40.2% inert 

ingredients), and a mixture of the 9-pesticides (atrazine, metolachlor, alchlor, 

nicosulfuron, cyfluthrin, cyhalothrin, tebupirimphos, methalaxyl, and propiconizole all at 

0.1 pbb). The specifics of the study, including uncertainties, which preclude the use of 

this data quantitatively, are discussed as part of Section A.2.4d. In summary, many of the 

confounding effects identified in previous studies by the FIFRA SAP limit the utility of 

this study. 

 Thymus histology was completed (to measure immunocompetence) after the study 

authors noted that animals exposed to the 9-compound pesticide mixture experienced 

increased incidence of bacterial infection with Chryseobacterium (Flavobacterium) 

menigosepticum. Animals exposed to the 9-compound pesticide mixture at 0.1 ppb had 

significantly longer larval periods. All mixtures resulted in reduced growth (SVL and 

BW), as compared to the solvent control, with the atrazine and S-metolachlor mixture 

having the greatest negative effect. With respect to gonadal development, the gonads and 

gametes were underdeveloped in both the control and treatment groups; therefore, it was 

not possible for the study authors to assess the affects of mixtures on sex differentiation. 

Exposure to the Bicep mixture (atrazine and S-metolachlor) and the 9-compound mixture 

resulted in damage to the thymus as measured by thymic plaques; however, the 

ecological relevance of thymic plaques is not discussed. Given the increased incidence of 

disease and evidence of histological effects on the thymus in animals exposed to the 

mixtures, the study authors suggest that exposure to pesticide mixtures renders 

amphibians more susceptible to disease as a result of immunosuppression. 

As part of the same study, Hayes et al. (2006) also examined the effects of the 9-

compound mixture on plasma corticosterone levels (stress hormone) in adult male 

African clawed frogs (X. laevis). Five males were treated with the 9-compound pesticide 

mixture (including atrazine at 0.1 ppb) and five males were exposed to ethanol only (no 

negative control was tested). Following the 27 day exposure period, blood was collected 

by cardiac puncture. The study authors report a clear effect on corticosterone levels in 

male African clawed frogs with corticosterone levels increasing 4-fold in pesticide-
65

exposed males. However, there are several flaws in the study design, which are 

discussed in Section A.2.4d, that add a high degree of uncertainty to the results. 

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