1 

Open Literature Review Summary 

Chemical Name: Atrazine 

PC Code: 080803 

ECOTOX Record Number and Citation: 

Baxter, L.R., D.L. Moor, P.K. Sibley, K.R. Solomon, M.L. Hanson. 2011. Atrazine does not 

affect algal biomass or snail populations in microcosm communities at environmentally relevant 

concentrations. Environmental toxicology and chemistry, vol. 30 (7): 1689-1696. 

Purpose of Review (DP Barcode or Litigation): 

Review for inclusion in the CELOC calculation 

Date of Review: 3/15/16 

Summary of Study and Findings: 

This study was conducted over 73 d at the University of Guelph Turfgrass Institute Microcosm 

Facility (Guelph, ON, Canada). Each 12,000-L microcosm is 1.2m deep and 3.9m in diameter, 

with an actual water depth of approximately 1m. The microcosms were lined with a black foodgrade polyvinyl chloride (PVC) pond liner, contained soil covering 44% of the bottom surface 

(14.5 % OC and 1.8% IC), and were filled with spring water from an adjacent irrigation pond. 

Water was circulated at 12,000 L/d among the microcosms for seven weeks. Circulation among 

the microcosms was stopped 3 days prior to treatment. 

 

Atrazine Treatment 

Technical grade atrazine (96% a.i.: Syngenta Crop Protection) was added in a random design 

with nominal concentrations of 0, 1, 10, 30, and 100 ug/L with 3 replicates per treatment level. 

Acetone was used as a solvent with a final concentration per microcosm at 0.001% acetone, 

controls also received solvent (no solvent free controls included). 

General chemistry included collections of total nitrogen and total phosphorous 

(d=1,7,14,28,49,70), total hardness and alkalinity (d=1,7,14,28,49,70), pH, conductivity, 

temperature and DO (Monday-Friday starting on d14). Photosynthetically active radiation (PAR) 

was measured mid-day (d=0, 8, 17, 38, 44, and 71) at a depth of 60 cm. 

Macrophytes 

Shoots (5-10 cm length) were added two weeks prior to treatment in 4 L pots. Each cosm 

received 3 pots with 6 shoots of Myriophyllum spicatum/pot and 3 pots with six shoots of Elodea 

canadensis per pot. Total biomass, wet and dry mass, for shoots (both species) and roots (M. 

spicatum only). 
2 

Phytoplankton and periphyton 

Periphyton substrates were added on the north side of each microcosm two weeks prior to 

treatment to allow colonization. A periphytometer (48 back-to-back microscope slides in a 

Plexiglas frame) was fixed at the same location in each microcosm and suspended just below the 

water surface. Additional periphyton measurements were taken using 30 x10 cm strips of PVC 

pond liner material hung from the edges of the microcosms and reaching a depth of 60 cm (or 2/3 

of the water depth). Use of periphytometers allowed quantification of periphytic growth at the 

surface and in the relative absence of snail grazing, while growth on the PVC pond liner was 

subject to conditions of increased water depth and grazing pressure. Analyses of phytoplankton 

and periphyton biomass as ash-free dry weight (AFDW) and chlorophyll a were performed on 

days 1, 4, 7, 14, 21, 28, 49, and 70. 

Phytoplankton samples were collected by filtering 1.5 L of microcosm water through Whatman 

glass fiber (GF/ C) filters (pre-combusted and pre-weighed for AFDW samples). Periphyton 

samples were collected by separately scraping each substrate and collecting the resulting slurry 

on a glass fiber filter as above. Three microscope slides were used for each of AFDW and 

chlorophyll a of periphyton at the surface (six slides total). Polyvinyl chloride liner strips were 

divided in half and each portion was scraped separately for AFDW and chlorophyll-a analysis. 

Chlorophyll-a filters were wrapped in aluminum foil and frozen until spectrophotometric 

analysis. Ash-free dry weight was analyzed immediately following filtration. 

Growth of filamentous algae masses in the microcosms was assessed weekly through a scoring 

system. Three people separately ranked the amount of filamentous algae in each microcosm on a 

scale of 1 to 3, where 1=no or low colonization, 2=some masses, 3=high colonization. 

Confidence in the assessment was given a score of 1 (low) to 10 (high). 

Snails 

Growth and fecundity of snails was tracked using four snail cages in each microcosm. The cages 

consisted of 35x25x25 cm translucent food-grade polypropylene containers, fitted with 200 

micron mesh covering four 6-cm diameter holes to allow for circulation of water through the 

containers. Lids on the containers were modified so that mesh fabric (2-mm mesh) covered 90% 

of the surface area to allow light penetration. Photosynthetically active radiation measurements 

inside and outside the cages indicated no significant shading. Floats were fixed near the top of 

each container such that the top 10 cm of each cage emerged above the water surface. One day 

before treatment, 10 adult marsh snails (Stagnicola elodes; 21.4x3.47 mm) were released in one 

cage per microcosm to track fecundity, and another 10 juveniles (6 to 9 mm) were placed in one 

cage per microcosm for quantification of growth rates. The same procedure was carried out 

concurrently in separate cages with the snail Physella spp. (adults 10.4x1.35 mm; juveniles <2 

mm). 

The shell length of caged juvenile snails was measured on days 15, 22, 38, 51, and 73 using 

calipers and the snails returned to the cages. Egg masses produced in the adult snail cages were 

removed and counted weekly, and the number of eggs per egg mass was recorded. In each 
3 

microcosm, 50 adult Physella spp. were also free-released to ensure a base population; however, 

these snails have been found to naturally inhabit the microcosms, so actual populations were 

expected to be much higher. Substrates for the enumeration of free-living snails were added two 

weeks prior to treatment. These consisted of 30x30 cm removable mats made from PVC pond 

liner, suspended at the same location in each microcosm. Average size and egg production rates 

of free-living snails were estimated from these substrates. Free-living snail size measurements 

were performed weekly starting at day 7 by removing the snail substrates and measuring shell 

sizes with calipers. The number of snail egg masses on each mat and the number of snail eggs 

per egg mass were counted and the egg masses were removed. Zooplankton traps as described in 

Boudreau et al. [see 33 in Baxter et al. 2011] were also used to quantify the free-living snail 

population on the bottom of the microcosms. These traps were deployed overnight on days 1, 4, 

7, 14, 21, 28, 36, 42, 49 and 65. Snails accumulating in the trap jar and funnel were washed into 

the sample jar, preserved in 70% ethanol, and enumerated. 

Data analysis 

Parameters were assessed individually by repeated-measures analysis of variance (ANOVA) 

(a=0.05) using the mixed procedure of SAS 9.1 for Windows with the Kenward-Rogers 

correction. Pretreatment measurements of biomass were used as baseline covariates for algal 

parameters and number of surviving snails per cage was used as a time-varying covariate for 

caged snail size. In each analysis the most appropriate heterogeneous variance structure was 

determined based on the lowest possible Akaike’s Information Criterion value. If a significant 

interaction was found, the slice command was used to identify the days exhibiting treatment 

differences and these were further assessed by one-way ANOVA. For size of caged juvenile 

snails, the treatment response prior to covariate inclusion was investigated by comparing 

regression parameters for mixed-model growth curves using one-way ANOVA. Filamentous 

algae scores were assessed by repeated-measures ANOVA on ranks using Sigmaplot 11.0 for 

Windows (Systat Software). Dunnett’s test (a=0.05) was used for all post-hoc analyses. Nominal 

concentrations of atrazine were used in all statistical analyses. 

Results 

Atrazine and general chemistry 

Concentrations of atrazine measured 1 h after treatment were within 10% of nominal values, and 

dissipation to 36% or less of initial concentrations occurred by day 70 (Table S1). 

Concentrations in control microcosms were below the limit of detection (0.05 ug/L). 
4 

Table S1. Mean actual concentration of atrazine with standard deviation (SD) for all measured 

time-points (1 h to 70 d) by nominal concentration in microcosms (n=3) after treatment at day 0, 

measured by enzyme-linked immunosorbant assay (limit of detection = 0.05 μg/L). ND = nondetect. 

Time Contro

l 

1μg/L (SD) 10μg/L (SD) 30μg/L (SD) 100μg/L (SD) 

1 h ND 1.21 (0.091) 11.30 (1.344) 28.43 (4.225) 100.57 (5.661) 

1-d ND 1.17 (0.076) 12.88 (0.980) 35.07 (6.543) 117.77 (11.580) 

4-d ND 1.03 (0.339) 9.55 (0.934) 24.93 (2.658) 75.70 (2.712) 

7-d ND 0.93 (0.130) 8.72 (1.553) 22.07 (2.159) 80.59 (4.662) 

14-d ND 0.80 (0.147) 8.40 (1.300) 25.40 (3.293) 88.20 (5.359) 

28-d ND 0.55 (0.156) 5.02 (1.028) 17.90 (2.152) 66.93 (10.826) 

49-d ND 0.40 (0.188) 5.70 (1.911) 14.80 (4.409) 64.40 (15.492) 

70-d ND 0.22 (0.083) 3.50 (1.272) 9.70 (2.458) 36.40 (8.794) 

No significant differences in water chemistry parameters including pH, dissolved oxygen, 

conductivity, temperature, hardness, alkalinity, and total nitrogen and phosphorus were found 

between treatments and controls, but all changed significantly with time. Although there were no 

differences between treatments, hypoxic conditions existed (<3 mg/L DO) on at least one day in 

13 of the 15 microcosms, and in seven microcosms this occurred on more than 20% of days posttreatment (Table 3). Because water chemistry measurements were taken between 8 and 9 AM 

after nighttime respiration, the measured values represent minimum values. Photosynthetically 

active radiation was not different between treatments, but was significantly affected by time, 

with an increase at d 38 and declining values afterward. Measurements of PAR 1m above the 

microcosms did not decline with time. 
5 

Macrophytes 

In the following summary some data that the authors indicated as not being statistically 

significant (e.g., wet weight of macrophytes and chlorophyll a for phytoplankton) are not 

discussed. The following summary is intended to identify the results that were reported as 

significant by the authors.

The authors report statistically significant declines in Myriophyllum spicatum shoot (~ 78%) and 

root (~ 77%) weights and in Elodea canadensis shoot (~81%) weights for the 100 ug/L treatment 

as compared to the controls. There were no statistically significant differences reported for the 1, 

10, or 30 ug/L treatment groups. However, the reviewer determined that biologically significant 

effects are reported for M. spicatum (Figure 2, Table 4) which shows an approximate 46% and 

19% reduction in shoot weight compared to the control for the 10 ug/L and 30 ug/L treatment 

groups, respectively. In addition, the reviewer determined that potentially biologically significant 

effects to M. spicatum root dry weight were reported at 1, 10, 30 and 100 ug/L (Figure 2, Table 

4). There is less certainty in the significance of the reductions in root dry weight as compared to 

the reductions in shoot weight. This reduced certainty stems from overlapping error bars across 

the doses (Figure 2). Lastly, effects to E. canadensis shoot weight were biologically significant 

only at 30 and 100 ug/L, with 17% and 81% reductions respectively. 
6 

 

Phytoplankton and Periphyton 

The authors report no treatment related reductions on periphyton or phytoplankton. It is difficult 

to interpret the variability for each treatment level from the presented data in Figure 3. 

Snails 

Based on the aforementioned potential effects of the high nutrient levels in the microcosms, the 

study results for snails are in question. The hypothesis that changes in the autotroph community 

from increasing atrazine levels cause increases in snail populations on a dose responsive manner 

cannot truly be tested in this study. If the uncertainty around high nutrient levels wasn’t present 

and the results do indeed reflect the pattern of the sail population effects in the presence of 

atrazine, then there would be some weight to place on this portion of the study. The authors 

report no chemical related changes in the snail populations. 

Table 4: Reviewer estimated mean dry weights and percent reduction (compared to 

controls) from Figure 2. 

Treatment (ug/L) M. spicatum shoot 

dry weight 

M. spicatum root dry 

weight 

E. canadensis shoot 

dry weight 

Control (0) 37 13 52 

1 42 (+14%) 7 (-46%) 51 (-2%)

10 20 (-46%) 6 (-54%) 60 (+15%)

30 30 (-19%) 9 (-31%) 43 (-17%)

100 8 (-78%) 3 (-77%) 10 (-81%)
7 

 
8 

Endpoints for use in the calculation of the CELOC are listed below in the summary table. 

Data Summary Table: 

Effect Magnitude 

of Effect 

relative to 

controls

Nominal 

Atrazine 

Concentr

ation 

(ug/L) 

Day of 

Study 

Effect 

Occurred 

Time Weighted 

Average 

Atrazine 

Concentration 

from Day 0 to 

when Effect 

Occurred

(ug/L) 

Did Recovery 

Occur – If so, 

when?

Comments 

Biomass, 

Macrophytes 

46% 

reduction in 

mean M. 

spicatum root 

dry weight, 

biologically 

significant 

(reviewer 

estimated 

magnitude 

and 

significance) 

1 NA 0.7 No. 

Endpoints 

measured at 

study 

termination 

Biomass, 

Macrophytes 

48% 

reduction in 

mean M. 

spicatum

shoot dry 

weight, 54% 

reduction in 

mean M. 

spicatum root 

dry weight, 

both 

biologically 

significant 

(reviewer 

estimated 

magnitude 

and 

significance) 

10 Unclear of 

initial 

event, 70-d 

used

7.4 

Biomass, 

Macrophytes 

~19 % 

reduction in 

mean M. 

spicatum

shoot dry 

weight, 31% 

reduction in 

mean M. 

spicatum root 

dry weight, 

17% 

30 Unclear of 

initial 

event, 70-d 

used

19.05 
9 

reduction in 

E. canadensis 

shoot dry 

weight, each 

biologically 

significant 

(reviewer 

estimated 

magnitude 

and 

significance) 

Biomass, 

Macrophytes 

reduction in 

mean M. 

spicatum

shoot (78%) 

root (77%) 

and in E. 

canadensis 

shoot (~81%) 

dry weights 

(reviewer 

estimated 

magnitude), 

Statistically 

and 

biologically 

significant 

(author

estimated 

significance) 

100 Unclear of 

initial 

event, 70-d 

used

68.5 

Description of Use in Document (QUAL, QUAN, INV): Qualitative 

Rationale for Use: 

This study demonstrates clear effects on macrophyte plant communities after the initiation of 

exposure to atrazine. Statistical and biologically significant effects were noted for macrophyte 

biomass at the tested concentrations of 1, 10, 30, and 100 ug/L. 

Limitations of Study: 

Summary data and statistics for many endpoints captured throughout the duration of this study 

were not presented in the report. This is critically important because the authors report 

significance information for endpoints but only averages across treatments are represented in the 

figures so within treatment trends could not be verified. 

Although there was an acclimation period, it differed for the biotic groups (macrophytes, 

phytoplankton, periphyton, and snails). 

High within-treatment variability was observed, especially but not limited to periphyton and 

phytoplankton. This was apparent even on day 0. Variability in DO measurements (Table 3) 
10 

may be reflective of the high variability in phytoplankton and periphyton response but it is hard 

to tell. The authors indicate that it wasn’t a result of block effects. In reality it is difficult to judge 

the apparent variability in DO measurements because Table 3 just shows > or < 3 mg/L instead 

of actual concentrations. 

These were outdoor microcosms but there was no discussion of weather during the experimental 

phase or if/how water levels were maintained. 

No solvent-free control treatment was included. 

Primary Reviewer: 

Frank T. Farruggia, Ph.D. Biologist ERB3 

Secondary Reviewer:

Michael Lowit, Ph.D. Ecologist ERB1 

References: 

Baxter, L.R., P.K. Sibley, K.R. Solomon, M.L. Hanson. 2013. Interactions between atrazine and 

phosphorous in aquatic systems: Effects on phytoplankton and periphyton. Chemosphere 90: 

1069-1076. 

Digitally signed by FRANK FARRUGGIA 

DN: c=US, o=U.S. Government, 

ou=USEPA, ou=Staff, cn=FRANK 

FARRUGGIA, dnQualifier=0000048865 

Date: 2016.03.24 11:29:43 -04'00'

2016.03.24 13:45:02 

-04'00'
1

Open Literature Review Summary 

Chemical Name: Atrazine 

PC Code: 080803 

ECOTOX Record Number and Citation: 

King, R.S. 2014. Effects of pulsed atrazine exposures on autotrophic biomass, community 

structure and production in field-based stream mesocosms. Baylor University, Center for 

Reservior and Aquatic Systems Research. Waco, TX. 

MRID 49535501 

Purpose of Review (DP Barcode or Litigation): 

Review for inclusion in the CELOC calculation 

Date of Review: 3/15/2016 

Summary of Study and Findings: 

Method: 

This study examined responses of community structure and production for a photoautotrophic 

community established from local native communities of plankton and periphyton, and 

Ceratophyllum demersum. 

The study used flow through mesocosms (60 cm wide, ~20 m long) consisting of riffle (8m long, 

3% slope and ~10 cm depth, turbulent flow velocity 0.5 m/s, ceramic tile substrate), glide (9 m 

long, ~25 cm depth, flow velocity 0.05 m/s, ceramic tile substrate) and pool (1.75 m diameter, 

50 cm depth, “flow negligible except at outflow”, unlined HDPE tanks without sediment) 

sections, and included a grazing enclosure to the glide by adding minnows (Campostoma 

anomalum) to evaluate atrazine effects under both ungrazed and grazing pressures. Water was 

sourced directly from the North Bosque River, through a wetland (2-3 days) before reaching the 

intake for the research facility. Flow to the mesocosms was controlled by a constant head 

regulated tank with 12 regulatory valves at 200 L/min with recirculation. 99% of water was 

recirculated and ~1% of the “polished wetland water” was metered into the headbox mixing 

zones to ensure continuous replacement of associated natural balance of dissolved solids, 

nutrients and other ions. Resulted in a 1.5x replacement of recirculating water every 24 hrs. 

Riffle Design 

Tile sheets cut into strips of ten 25cm2 unglazed ceramic tiles, beginning 10 cm from the mixing 

box to 10 cm above the transition to the glide. Every 12 tiles a double stack of tiles was used to 

create the riffle. 

Glide Design 

Strips of 9 tiles were used. Enclosures for ungrazed portions were upstream of the grazed 

portion, with an additional ungrazed at the downstream section of the glide. Wild caught 
2

minnows were added (10 per stream) to the grazing portion of the glide, based on sex and 

biomass to even out the distribution across treatments and replicates. 

Pond Design:Five tip-cuttings of Ceratophyllum demersum were secured to the bottom of a 

shallow pot with cable ties, the lower 20 mm of stems were buried under coarse sand. 12 pots 

were added to each pond. For each sampling event one pot was removed and not replaced. 

Target atrazine concentrations were 60-day averages of 10, 20, and 30 ug/L. Methanol used as 

a solvent (ultimately 0.15 ppb). All treatments and the solvent control were replicated in 

triplicate. Exposures occurred after a 30-day colonization period (February 12 – March 13 

2014). Colonization was aided by placing rocks from the wetland into the headboxes, as well as 

through “standardized collections of benthos from the riffle, glide and pool habitats of the 

North Bosque River (near Valley Mills). Each exposure was a 4-day pulse (~50, 100, and 150 

ug/L respectively) followed by a 7-day period without dosing. Each mesocosm was dosed 3 

times, then were monitored for an additional 26 days. Dosing began March 13 2014. 

Additionally, bromide was used as a tracer (0.05 mg/L), and nutrients, NO3-N (1 mg/L) and PO4-

P (0.15 mg/L), were added and kept at stable concentrations throughout the study to 

“stimulate autotrophic production and estimate daily nutrient uptake”. Analytical 

measurements of atrazine, bromide, nitrogen and phosphorous were provided on a daily basis, 

and continuous reporting for dissolved O2, pH, and conductance. 

Periphyton was monitored in the riffle and glide (grazed and ungrazed) sections of the 

mesocosms. Phytoplankton and Ceratophyllum were monitored in the pool section. All 

biological measures occurred before and after each pulse of atrazine and at intervals 

throughout the “recovery period”, totaling 10 sampling events. 

The study authors stated that “the [source] water coming out of the Lake Waco Wetlands is 

considered typical of relatively pristine streams in the Great Plains region of the USA”, however 

low levels of atrazine were reported in some samples. Water temperature ranges from 5 – 30 

degrees C, conductivity 200-500 uS/cm @ 25deg C. Nutrients are filtered through the wetland, 

Nitrate-N and NH4-N are often near or below detection limits (5-50 ug/L) and Phosphate-P is 

also very low and rarely exceeds 10 ug/L. 

Results: 

Atrazine chemographs were fairly consistent across treatments of the same concentration, and 

across the 3-pulses. In all treatments, atrazine remained present above detection limits (0.05 

ug/L) after the final pulse and through day-60. Measured 60-day average concentrations were 

10.7, 20.9, and 31.0 ug/L. The authors describe that controls contained atrazine at levels above 

the limits of detection but were generally below 0.1 ug/L throughout the study. One exception 

to this was the detection of levels up to 4.2 ug/L during the second pulse phase of the study in 

control stream #3. This occurred between March 28th and April 3rd, showing a clear decline 

curve over a week (4.2, 3.7, 1.0, 0.3, 0.1, 0.08 and 0.06 ug/L) until reaching the detection limit. 

Throughout the study the controls continued to show detections but remained below 0.1 ug/L. 
3

The study reported on several different endpoints reflecting community changes and/or 

responses over time (e.g., DO, AFDM, CHLA, and Community Composition). All of these 

endpoints are discussed for the various portions of the stream mesocosms, with the exception 

of community composition (see Study Limitations below). 

Periphyton (Riffle Portions) 

The riffle periphyton endpoints were reported to be the most sensitive endpoints in the study. 

The authors report that AFDM in the treatment groups was significantly reduced compared to 

the control cosms on day 5. The controls remained significantly higher in AFDM through day 27. 

A decline in control group AFDM was reported between the day 27 and day 34 sampling 

periods, which was attributed to a sloughing event of filamentous algae. This same event 

occurred later in the treatment groups (days 34-48), which the authors report as “due to 

dampened production during the pulse events”. 

The provided photographs of the riffle portions on day 27 of the study (the final day of the 

exposure phase) show clear differences in the coverage of tiles between controls and treatment 

cosms an in a dose response manner. Two and three weeks later (days 41 and 53) it is evident 

in the photographs that sloughing events have occurred in the controls, but differences 

between treatments are less evident. At three weeks (day 48) there are more signs of sloughing 

in treatments and there remains a visible difference between the 30 ppb exposure cosms and 

the remainder of the treatments and controls. By the end of the study, the filamentous algal 

growth on the controls and treatment cosms are rampant and seem to have sloughed off more 

frequently than discussed in the report. There is a slight difference between the 30 ppb cosms 

and the remaining cosms. 

Control AFDM was higher than all treatments from days 5 through 60; during this period the 

difference between the treatment groups and controls is considered biologically significant by 

the reviewer. Statistical significance between the treatment groups and controls was reported 

for the 10 ug/L group on days 5, 11, 16, 22, 27, and 48, the 20 ug/L group on days 5, 22, 27, and 

48, and the 30 ug/L group on days 5, 11, 16, 22, 27, and 48. 

Control CHLA was higher than all treatments. Statistically and biologically significant 

differences were reported for 10 ug/L on days 11, 22, 27, and 48, for 20 ug/L on days 22, 27, 

and 48, and for 30 ug/L on days 5, 11, 22, 27, and 48. Between days 22 and 60, the reported 

reduction in CHLA was biologically significant across all test concentrations as compared to 

controls (Table 2). 
4

Table 2. Riffle section Periphyton percent reduction of mean CHLA as compared to controls. 

(bolded statistically significant at p=0.05 based on Generalized Least Squares analysis reported 

authors) 

SAMPLE 

DAY 

10 PPB 20 PPB 30 PPB 

-7 -39 -49 12 

0 -26 -15 8 

5 27 17 43 

11 35 2 59 

16 29 -13 22 

22 42 27 48 

27 42 46 45 

34 16 -44 10 

48 42 30 47 

60 31 41 60 

Periphyton (Glide Portion -Grazed Section) 

The results are similar to those for periphyton in the riffle portion of the study, except that the 

magnitude of effects was lower. The grazing fish suppressed accumulation of algal biomass 

from days 0-27. Despite this, AFDM was higher in the controls than in the treatments during 

the pulses, these were biologically significant for all pulses, with statistical significance for all 

treatments on days 5, and 16. After the pulsed exposures, there was recovery to control levels 

for both AFDM and CHLA in the grazed section of the glide. The rapid recovery was attributed 

to the filamentous algae Cladophora and Hydrodictyon growth. 

Several fish died during the study, however there was no relationship to atrazine dose. 

Periphyton (Glide Portion –Ungrazed Section) 

AFDM and CHLA accumulated rapidly from days 0-16, and was only suppressed during the 

exposure pulses. Significant declines across all treatments and controls occurred from day 48-

60 due in part to shading, senescing and significant accumulation of metaphyton from the 

upstream sloughing events. 

Metaphyton 

Floating algal mats were reported as prevalent in the pools and the ungrazed glide portions of 

the mesocosm. They began removing the metaphyton from pools on day 22, and continued to 

remove them throughout the remainder of the study. By day 27, the mats covered large areas 

of the pools, and the authors report that they were in decreasing density in a dose response 

manner, and that the shading in the controls may have negatively influenced growth and 

productivity of the macrophytes and likely the phytoplankton community. The controls had 

significantly more metaphyton biomass removed than the treatment pools throughout the 

study. 
5

The heavy production of the metaphyton would have produced differential light conditions for 

the controls versus the treatments ponds. It is likely that the stable and high nutrient levels 

used in the study design caused these mats to grow rapidly and that the atrazine reduced the 

growth of the metaphyton mats. The end result is a dose response effect on metaphyton with 

significant effects at all concentrations (NOAEC <10.5 ug/L). 

Phytoplankton 

The author’s analysis of community structure indicates that there is little to no difference 

between the controls and treatment pool phytoplankton communities throughout the study. 

Their analysis does indicate that these communities changed throughout the study but it was 

directionally related to the day of sampling rather than atrazine concentration. 

The metaphyton community likely had a confounding effect on algal communities in the 

sections downstream of the riffle section. This is a clear limitation of the study and may have 

obscured treatment related effects. 

The phytoplankton results for CHLA and AFDM were not significantly different from the control. 

These endpoints showed considerable variability across the study. 

Macrophytes 

Reduced biomass and stem length were reported for treatments versus the controls from Day 

16 thorough day 34 however, these were only statistically significant for biomass on day 22 at 

the 20 and 30 ppb levels. 

Dissolved Oxygen 

There are clear and significant differences between control and treatments with regard to 

maximum dissolved oxygen throughout the study. During the pulsed atrazine exposure phases 

this separation was greater than between pulses however, controls remained higher between 

pulses as well. It is unclear as to the cause of the drop in % saturation in the controls during the 

pulses, however the authors attribute it to a decline in Photosynthetically Active Radiation 

(PAR) during rain events. 

Nutrient Removal 

Significant declines in nitrate removal were evident and in a dose response manner during the 

exposure phase, the amplitude of the differences between controls and test concentrations 

declined by the final pulse. This may indicate a shift in the response of the community to the 

atrazine exposures, possibly indicating a more tolerant community to these exposure levels. By 

the end of the study there were no differences between controls or treatment groups with 

nitrate removal, but they were extremely high. The authors were unable to discern if there 

were effects on denitrification or suppression of nitrate uptake during the exposure pulses. 

Also, the recovery cannot be entirely attributed to algal response post exposure, because they 

didn’t account for the denitrification by bacterial communities in the study. 
6

Phosphate removal was highly variable and didn’t show clear differences between the controls 

and treatment levels for most of the study. The authors reported significant declines on a few 

days, noting the significant difference between 30 ppb and controls during the third pulse 

exposure period. The author makes an argument that because the phosphate sequestration is 

relatively low as compared to the nitrate sequestration, denitrification by bacteria was a major 

role in removing nitrate from the cosms. 

Authors Conclusions: 

- They believe that these results demonstrate that atrazine had no effect on the community 

structure. 

- There were significant effects on most other endpoints measured. 

- Recovery from the effects occurred for all but metaphyton biomass and DO by the end of 

the study. 

- In streams that already have high nutrient and sediment loads, atrazine effects are 

transient and may not be ecologically significant to stream periphyton, phytoplankton, and 

aquatic macrophytes. 

Reviewers Conclusions: 

- The statistical approaches used to evaluate community structure were not appropriate for 

comparison between treatment levels and controls, see Limitations section below. 

- There were statistically and/or biologically significant effects on some of the measured 

endpoints. 

- The effects on riffle section periphyton biomass, pool section metaphyton biomass, and DO 

did not recover by the end of the study. 

Endpoints for use in the calculation of the CELOC are listed below in the summary table. 
7

Data Summary Table: 

Effect Magnitude of Effect 

relative to controls 

Nominal Atrazine Concentration (ug/L) 

Day of Study Effect Occurred

Estimated Maximum 60-day 

average atrazine concentration (ug/L) 

Did Recovery Occur – If so, when? 

Comments 

Metaphyton Biomass

D-27 ~ 80%↓ dry wt;D-60 ~50%↓ dry wt 

10 27-60 10.7 (60-day 

estimated average) 

No Recovery

Statistically significant decrease in metaphyton production starting on day 34 and continued throughout the study. Biologically significant effects started on day 27. 

Metaphyton Biomass

D-27 ~ 80%↓ dry wt;D-60 ~50%↓ dry wt 

20 27-60 20.9 

Metaphyton Biomass

D-27 ~ 80%↓ dry wt;D-60 ~50%↓ dry wt 

30 27-60 31.0 

Riffle Section Periphyton Biomass (AFDM) 

D-05 ~ 30% ↓D-16 ~ 28%↓D-27 ~ 24%↓D-60 ~ 35%↓

10 5, 16, 27 10.7 Recovery 

occurred between and after the pulsed exposure.

Statistically and biologically significant declines in biomassstarted ~day 5 and were associated with the end of each pulsed addition of atrazine.

Riffle Section Periphyton Biomass (AFDM) 

D-05 ~ 29% ↓D-16 ~ 23%↓D-27 ~ 21%↓D-60 ~ 1%↑

20 5, 16, 27 20.9 

Riffle Section Periphyton Biomass (AFDM ) 

D-05 ~ 35% ↓D-16 ~ 31%↓D-27 ~ 22%↓D-60 ~ 8%↑

30 5, 16, 27 31.0 

Riffle Section Periphyton Biomass (CHLA) 

D-05 ~ 27% ↓D-11 ~ 35% ↓D-16 ~ 29%↓D-22 ~ 42%↓

10 5-60 10.7 No 

Recovery

Statistically significant declines in biomass: 10 ppb: days 11, 22,27,48 
8

D-27 ~ 42%

↓

D-34 ~ 16%

↓

D-48 ~ 42%

↓

D-60 ~ 31%

↓

20 ppb: days 22, 27, 48 30 ppb: days 5, 11, 22, 27, 48, 60.Although reductionswere not always statistically significant the observed reductions 

were considered biologically significant. 

Riffle Section Periphyton Biomass (CHLA) 

D-05 ~ 17% 

↓

D-11 ~ 2% 

↓

D-16 ~ 13%

↑

D-22 ~ 27%

↓

D-27 ~ 46%

↓

D-34 ~ 44%

↑

D-48 ~ 30%

↓

D-60 ~ 41%

↓

20 5-60 20.9 

Riffle Section Periphyton Biomass (CHLA) 

D-05 ~ 43% 

↓

D-11 ~ 59% 

↓

D-16 ~ 22%

↓

D-22 ~ 48%

↓

D-27 ~ 45%

↓

D-34 ~ 10%

↓

D-48 ~ 47%

↓

D-60 ~ 60%

↓

30 5-60 31.0 

Maximum Daily Dissolved Oxygen 

D-27 ~ 19%

↓

D-60 ~ 14%

↓

10 1-60 10.7 No 

Recovery

All 3 pulses of atrazine resulted in statistically significant but temporary (mainly during pulses) reduction of DO in all treatments relative to the control. After the 3 pulsed exposures statistically and biologically 

Maximum Daily Dissolved Oxygen 

D-27 ~ 26%

↓

D-60 ~ 16%

↓

20 1-60 20.9 

Maximum Daily Dissolved Oxygen

D-27 ~ 29%

↓

D-60 ~ 17%

↓

30 1-60 31.0 
9

significant reductions in DO were reported from day 27 through day 60. 
10

Description of Use in Document (QUAL, QUAN, INV): Qualitative 

Rationale for Use: 

This study demonstrates clear effects on periphyton and metaphyton communities after the 

initiation of exposure to atrazine at the tested concentrations of 10, 30, and 100 ug/L. 

Limitations of Study: 

The utility of this study is limited for use in the calculation of the CELOC due to the potential 

mitigating effects of high nitrogen and phosphorous levels used in the study design. High 

nutrient levels would likely be present in most aquatic ecosystems adjacent to and receiving 

runoff from agriculture areas, however phosphorous is typically a limiting factor for algal and 

macrophytes over the long term exposures to atrazine. Additionally, the concentrations tested 

in this study are at the extreme upper end of the measured total nitrogen and total 

phosphorous in the NAQWA water monitoring database. Furthermore, recent research (e.g., 

Baxter et al. 2013) indicates that there are clear interactions with atrazine and phosphorous 

regarding exposure and observed effect, and that concentrations as high as those tested here 

are enough to mask effects of atrazine in some taxa. 

These nutrients are expected to runoff with atrazine however their concentrations would be 

expected to decline rapidly due to biological uptake and movement downstream, not unlike 

atrazine. Therefore the constant nutrient addition in this study does not represent the 

expected natural conditions of streams in the Great Plains. It is unfortunate that the source 

water, as described by the study author as representing “pristine water” was not the control 

baseline for between pulses. Nutrients should have been added as pulses with the atrazine to 

better reflect the conditions of a runoff event such as those that they simulated with the 

atrazine exposures. 

The results for the downstream sections of the cosms (glide and pool) were confounded and 

the ability to detect any treatment related effects may have been reduced. The constant 

addition of high levels of nutrients in this study compromised the utility of many endpoints due 

to the rampant growth of filamentous algae (metaphyton), which sloughed off of the riffle 

portion of the study, often resulting in a scrubbing of the tiles as it went past, then accumulated 

in the ungrazed glide and pool portions of the study causing a difference in light dynamics of 

the pool. The metaphyton likely severely impacted many of the macrophyte and phytoplankton 

endpoints in the pool section that would have been collected later in the study because of the 

decreased light conditions. The metaphyton impacts began around day 22 of the study in the 

controls, which is 5 days short of the last day of exposure, and were more likely to be of greater 

influence in the controls throughout the study. 

Another limitation is that the “pristine” source water clearly had a background level of atrazine. 

It was not reported if other herbicidal chemicals were also present within the water. The 

resident algal community (used to colonize the cosms) may have already been selected for 

more atrazine resistant algae. 
11

While there were solvent controls (methanol added) negative controls were not used in this 

study. It is unknown if this would have impacted the results of the study. 

Lastly, the authors did not find a difference in community structure; however, that finding may 

simply be due to the method used to analyze the raw data. 

First, the NMDS ordination was conducted separately for each test group (only 

comparing the similarity among communities within a test group over time). The 

ordination containing all the treatment groups appears to simply be an overlay of the 

separate ordinations (the study authors state that this is this case on pg 30). The 

ordinations show a strong temporal shift over time but do not have meaning in terms of 

the (dis)similarity among all the treatment group communities. A single NMDS 

ordination based on a dissimilarity matrix of all treatment groups is needed to answer 

the question “are there differences among the treatment groups compared to the 

control?” This could be done with all the time points or separately for each time point. 

The ordination would provide a visual way to assess how different the communities 

were. 

Second, the study authors used PERMANOVA to test for statistically significant 

differences among the communities. However, the analysis only asked the question “is 

there a treatment related effect?” (see appendix 17). It does not assess whether or not 

there were treatment related effects at each individual test concentration. 

Primary Reviewer: 

Frank T. Farruggia, Ph.D. Biologist ERB3 

Secondary Reviewer: 

Michael Lowit, Ph.D. Ecologist ERB1 

References: 

Baxter, L.R., P.K. Sibley, K.R. Solomon, M.L. Hanson. 2013. Interactions between atrazine and 

phosphorous in aquatic systems: Effects on phytoplankton and periphyton. Chemosphere 90: 

1069-1076. 

Digitally signed by FRANK FARRUGGIA 

DN: c=US, o=U.S. Government, 

ou=USEPA, ou=Staff, cn=FRANK 

FARRUGGIA, dnQualifier=0000048865 

Date: 2016.03.24 13:16:15 -04'00'

2016.03.24 13:43:13 

-04'00'
1 

Open Literature Review Summary 

Chemical Name: Atrazine 

PC Code: 080803 

ECOTOX Record Number and Citation: 

Pannard, A., B. Le Rouzic, F. Binet. 2009. Response of phytoplankton community to 

low-dose atrazine exposure combined with phosphorous fluctuations. Arch. Environ. 

Contam. Toxicol 57: 50-59. 

Purpose of Review (DP Barcode or Litigation): 

Review for inclusion in the CELOC calculation 

Date of Review: 3/16/16 

Summary of Study Findings: 

This study investigated the response of microalgal dynamics to long-term exposure (7-

weeks) to increasing atrazine doses, which were non-inhibiting during short-term 

exposure (a two days). The experiment was performed on a controlled phytoplankton 

community, sampled from the natural environment and maintained in semi-continuous 

culture. The dynamics of the phytoplankton community, exposed to a gradient of atrazine 

doses in the short or long term, were examined from photosynthetic activity (short-term 

exposure) or from photosynthetic activity, biomass, and community structure (long-term 

exposure).

Atrazine (TGAI) was used for short- and long-term exposure experiments. An aqueous 

atrazine solution consisting of 1.2 ug mL-1 was prepared by dissolving atrazine in 

distilled water using sonication without any organic solvent. 

The natural plankton community was collected by sampling 40 liters of water from a 

freshwater wetland in Brittany (Pleine-Fougeres, France) in autumn 2001. 

Macrozooplankton community was removed by filtration. 

Short-Term Sensitivity of the Phytoplankton Community to Atrazine

Short-term experiments (48 h of atrazine exposure) were first performed to determine the 

non-inhibiting doses to test in the long-term atrazine exposure experiment. Five nominal 

atrazine doses (controls and 0.05, 0.5, 5.0, and 50 ug/L) were tested on the community. 

Phytoplankton photosynthetic activity was monitored (five replicates per atrazine dose) 

from the rate of 14C incorporation after 1, 16, 22, 40, and 46 h of atrazine exposure in 

borosilicate glass vessels. These were incubated with 14C bicarbonates for 1 h in a 

temperature-controlled incubator, under light and temperature conditions similar to those 

for the initial phytoplankton community. The EC50 and EC10, which correspond to the 
2 

inhibitory doses reducing 50% or 10% of the biological activity, respectively, were 

calculated by adjusting the model of Bailer and Oris (1993; 1997) to the incorporation 

rates according to atrazine dose. 

Design of the Long-Term Atrazine Exposure Experiments

The initial community was first starved by reducing nutrient inputs and making it 

phosphorus deficient a few weeks before starting the long-term experiment. Phosphorus 

was then resupplied to obtain medium input (52.6 ug P-PO4 3- L-1) from the day of 

atrazine input (day 0) onward. 

The community was exposed to atrazine for 7 weeks in 500-mL borosilicate Erlenmeyer 

bottles. Two hundred forty milliliters of the phytoplankton community was placed in 

each of the 16 bottles, with four replicates per dose tested (controls and nominal doses: 

0.1, 1.0, and 10 ug atrazine/L). Semi-continuous culture conditions were maintained 

(discontinuous fresh input once a week), and similar atrazine doses were added weekly to 

each medium input to prevent dilution. Given that the atrazine half-life in a water column 

is between 80 and 150 days (Klassen and Kadoum 1979), the atrazine dose was assumed 

to remain almost constant throughout the 7 weeks of the experiment, i.e., more than 80% 

of the initial dose at the lowest half-life calculation (day 48). The phytoplankton biomass 

was measured by chlorophyll a concentration (Lorenzen 1967) and the biological activity 

was measured by carbon dioxide incorporation weekly. Taxonomic composition was 

determined at the beginning of the experiment, then after 1, 4, and 7 weeks of exposure. 

Fluctuations in the biomass of the coexisting species were evaluated by counting cells 

and colonies under a microscope using a Nageotte chamber and expressing the 

concentrations as cell units per milliliter for single-cell species and colony cell units per 

milliliter for colonial species (Aphanocapsa sp., Oscillatoria sp.). 

Dominance within the community was characterized by calculating Simpson’s index D of 

diversity 

Statistical Analysis 

The nonparametric two-factor statistical analysis of Friedman was used to test the effects 

of atrazine doses and time exposures on the rate of carbon dioxide incorporation (for 

short- and long-term experiments) and the evolution of biomass. A chi-square analysis 

was applied to test the homogeneity of community structures at different times and doses. 

The hypothesis that atrazine has no effect on the evolution of species densities was tested 

in a single-factor (dose) or two-factor (time and dose) analysis of variance. 

Lastly, a Kruskall-Wallis analysis was applied to test the effects of atrazine on Simpson’s 

index of diversity. In all statistical tests used, the probability level up to which the effect 

is significant was p<0.05. A factorial correspondence analysis, using software R was 

performed to see whether atrazine exposure was a predominant factor responsible for the 

final composition and structure of the phytoplankton assemblage. 
3 

Results Summary: 

Short-Term Sensitivity of the Community to Atrazine Exposure 

Atrazine-treated samples showed significantly lower biological activity than controls (S = 

42.58, 4 df, p<0.001). Communities exposed to 50 ug/L atrazine were inhibited after as 

little as 1 h with a 30% to 50% decrease in carbon incorporation (Fig. 1a). Results with 

longer exposure times, 16, 22, 40, and 46 h, confirmed this atrazine toxicity level (Fig. 

1a). The calculated EC50 was 60.7 ± 4.0 ug/L. 

 
4 

Long-Term Atrazine Exposure 

Biological Activity and Biomass 

The changes in primary production over time, based on the amounts of incorporated 

carbon dioxide, followed the same pattern regardless of atrazine treatment (Fig. 2). 

According to the author, carbon incorporation after 3 weeks decreased significantly 

compared to the control followed by potential recovery at six weeks (judged by 
5 

reviewer). For measured chlorophyll a, there were no significant differences observed 

between controls and treated communities (Fig. 2c). In the first period, increasing growth 

rates (C absorption rates) were significant following nutrient resupply (still available 

even 1 week after P-enriched medium input), which induced progressive biomass 

accumulation (chlorophyll-a abundance). In the second period, i.e., after 4 weeks, the 

growth rate decreased with accelerated nutrient impoverishment due to the higher 

phytoplankton biomass. Whereas biomass production exceeded loss due to weekly 

culture removal in the first period, it simply compensated this loss during the second 

period, as the phytoplankton biomass remained almost stable. 

Community Structure and Dominance 

The major impact on community structure, evaluated as a comparison of the initial and 

final densities of enumerated cells or colonies, was attributed to the biomass response 
6 

following P resupply (Table 1). Modification of the community structure due to low-dose 

atrazine exposure was also shown after 7 weeks of exposure, with a clear atrazine dose 

effect (Fig. 3). The first axis explained more than 61% of the variance of the data set. 

Going from left to right, the ordination on axis F1 differentiated the control communities 

from the atrazine exposed communities, at doses of 10, 1, and 0.1 ug/L, although the 

effect of the 0.1 ug/L dose showed high variability. 

It was concluded that community structure was significantly affected by 7 weeks of 

exposure to a dose of atrazine as low as 10 ug/L or less. In accordance with the 

correspondence analysis, significant changes in algal density occurred depending on the 

atrazine dose and taxonomic group (Table 1). 
7 

Further evaluation by the reviewers illustrate the percent reduction in cell densities 

(species, genus, and community-level) between the controls and treatment groups. 

Table 2. Percent Reduction of Treatment Final Cell Densities Compared to Controls

Treatment 

Skeletonema 

bibraianum 

Chlorolobion 

sp. 

Ankistrodesmus 

falcatus 

Chlorella 

sp. 

Oocystis 

sp. 

Unidentified 

chlorophyte 

Aphanocapsa 

sp. 

Oscillatoria 

limetica 

Total 

(Community) 

Density 

0.1 28 73 71 18 69 43 40 79 62 

1 -10 39 37 69 60 43 27 40 50 

10 22 54 66 73 78 56 33 49 67 

Bold values indicate significant difference versus the control. Biological significance without statistical 

significance described by the authors are italicized. 

A shift in community structure was also reflected in changes to dominance and diversity, 

as demonstrated by changes in Simpson’s index of diversity (1 – D) (Fig. 5). After 7 

weeks of exposure, (1 – D) was significantly higher in the community exposed to atrazine 

than in the controls (H = 9.2, 3 df, p = 0.027). This higher diversity accounted for a lower 

dominance in the atrazine treatments. The (1 – D) value was proportional to the atrazine 

dose, demonstrating a consistent dose-response effect. 
8 

Reviewer Conclusions: 

The authors present effects of atrazine on the phytoplankton assemblage, in terms of 

primary production and community structure for all tested concentrations (NOAEC <0.1 

ug/L). Their inclusion of phosphorous limitation as a variable in the study adds 

complexity to interpreting the results, as the nutrient limitation followed by the addition 

of phosphorous resulted in dramatic changes in abundance for all tested species 

independent of atrazine addition. Nonetheless, the data provided in Tables 1 and 2, and 

Figures 3 and 5, suggest that even low doses of atrazine were impacting the abundance 

of several tested species compared to those in the control community. 

The summary table below includes only those endpoints for use in the calculation of the 

CELOC, thus excludes the results from the short term experiment (Fig 1 and Fig 2). 

Data Summary Table for the Long Term Exposure Experiment 

Effect Magnitude of Effect 

relative to controls 

Nominal 

Atrazine 

Concentration 

(ug/L)

Day of 

Study 

Effect 

Occurred 

Time 

Weighted 

Average 

Atrazine 

Concentration 

from Day 0 to 

when Effect 

Occurred 

(ug/L) 

Did 

Recovery 

Occur –

If so, 

when? 

Comments 

Chlorophyll a No Effect 0.1 NA Not calculable NA 

Chlorophyll a No Effect 1.0 NA Not calculable NA 

Chlorophyll a No Effect 10 NA Not calculable NA 

Carbon 

incorporation 

~47% ↓ week 2, 

~18% ↓ week 3 

~25% ↓ week 4 

~62% ↓ week 5 

0.1 7-14 Not calculable Recovery 

week 6 

Difficult to 

interpret 

significance with 

available 

information. 
9 

Carbon 

incorporation 

~47% ↓ week 2, 

~12% ↓ week 3 

~33% ↓ week 4 

~23% ↓ week 5 

1.0 7-14 Not calculable Recovery 

week 6 

Difficult to 

interpret 

significance with 

available 

information. 

Carbon 

incorporation 

~47% ↓ week 2, 

~12% ↓ week 3 

~17% ↓ week 4 

~38% ↓ week 5 

10 7-14 Not calculable Recovery 

week 6 

Difficult to 

interpret 

significance with 

available 

information. 

Cell Density, 

Individual 

Phytoplankton 

Species and 

Communitylevel

Chlorolobion sp. (73% ↓) Ankistrodesmus 

falcatus (71 %

↓)

Oocystis sp. (69 %↓)

Unidentified 

chlorophyta (43%↓)

Aphanocapsa sp. (40 %↓)

Oscillatoria limnetica 

(79%↓)

Community (62%↓)

0.1 49 Not calculable No 

Recovery 

Effects only 

reported in terms 

of final 

measurement. 

Concentrations 

held constant by 

weekly additions 

of compound. 

Cell Density, 

Individual 

Phytoplankton 

Species and 

Communitylevel

Chlorolobion sp. (39% ↓) Ankistrodesmus 

falcatus (37 %

↓)

Oocystis sp. (69 %↓)

Chlorella sp. (60%↓)

Unidentified 

chlorophyta (43%↓)

Aphanocapsa sp. (27 %↓)

Oscillatoria limnetica 

(40%↓)

Community (50%↓)

1.0 49 Not calculable No 

Recovery 

Effects only 

reported in terms 

of final 

measurement

Cell Density, 

Individual 

Phytoplankton 

Species and 

Communitylevel 

Chlorolobion sp. (54% ↓) Ankistrodesmus 

falcatus (66 %

↓)

Oocystis sp. (78 %↓)

Chlorella sp. (73%↓)

Unidentified 

chlorophyta (56%↓)

Aphanocapsa sp. (33 %↓)

Oscillatoria limnetica 

(49%↓)

Community (67%↓)

10 49 Not calculable No 

Recovery 

Effects only 

reported in terms 

of final 

measurement

Community 

Structure

Changes in Simpson’s 

index of diversity and 

CCA results (shift in 

composition) 

0.1 49 Not calculable No 

Recovery 

An increase in the 

Simpsons index 

as well as a shift 

in the 

composition 

(changes in the 

relative 

abundance of the 

same species) in a 

dose response 

manner indicates 

Community 

Structure

Changes in Simpson’s 

index of diversity and 

CCA results (shift in 

composition) 

1.0 49 Not calculable No 

Recovery 

Community 

Structure

Changes in Simpson’s 

index of diversity and 

10 49 Not calculable No 

Recovery 
10 

CCA results (shift in 

composition)

that the 

concentrations 

tested affected the 

community 

structure leading 

to more variable 

communities than 

the controls and 

that the 

dominance in the 

community had 

shifted. 

Description of Use in Document (QUAL, QUAN, INV): Qualitative 

Rationale for Use: 

This study demonstrates clear effects on multiple aspects of plant communities after the 

initiation of exposure to atrazine. While both the short and long-term experiments 

demonstrated effects, only the long-term experiments is applicable for use in the CELOC 

estimation. Effects reported for carbon incorporation suggest biologically significant 

reductions in primary productivity across all concentrations with recovery by week 6, 

however chlorophyll a did not reflect the same reductions across treatments. Statistical 

and biologically significant effects were noted for biomass (cell density) and different 

measures of community structure at the tested concentrations of 0.1, 1.0, and 10 ug/L. 

Limitations of Study: 

The method used in this study refreshed (weekly) each test solution and control with an 

aliquot of medium plus test material or medium only, respectively. The authors assumed 

that this maintained a relatively constant concentration at the intended nominal dose 

concentration based on the study duration and published half-lives of atrazine. They 

report greater than 80% recovery at the end of the study. Therefore, the reviewer 

assumed constant exposures at nominal concentrations. 

Primary Reviewer: 

Frank T. Farruggia, Ph.D. Biologist ERB3 

Secondary Reviewer:

Michael Lowit, Ph.D., Ecologist ERB1 

Digitally signed by FRANK FARRUGGIA 

DN: c=US, o=U.S. Government, 

ou=USEPA, ou=Staff, cn=FRANK 

FARRUGGIA, dnQualifier=0000048865 

Date: 2016.03.24 11:31:35 -04'00'

2016.03.24 13:44:12 -04'00'