Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

ECOTOX Record Number and Citation:

Seguin, F., F. Le Bihan, C. Leboulanger, and A. Berard. 2002. A risk assessment of pollution:

induction of atrazine tolerance in phytoplankton communities in freshwater outdoor mesocosms,

using chlorophyll fluorescence as an endpoint. Water Research. 36(13): 3227-3236. (MRID

48261133)

Purpose of Review:

Determine potential effects of atrazine on an aquatic community. Endpoints from this study

contribute to the weight-of-evidence regarding effects of atrazine on aquatic plant communities

and associated determination of a Level of Concern (LaC).

Date of Review:

October 8, 2009

Purpose of Study:

This study examines the potential effects of atrazine on phytoplankton in experimental ponds

(mesocosms) over 25 days, including short-term toxicity tests on the mesocosm communities to

assess induction of atrazine tolerance over the course ofthe mesocosm experiment.

Summary of Study Findings

Methods:

The experiment took place during spring 2000. Mesocosms consisted of 4 outdoor circular tanks

at the INRA (Institut National de la Recherche Agronomique, Rennes, France) experimental

platform. The tanks were 3.2 m in diameter, 1.2 m high, held approximately 5000 L, and were

sunk about 0.4 m into the ground to keep temperatures more stable. The mesocosms were

created by first filling the tanks to 7 cm with natural sediment from a local uncontaminated pond,

then filling them to a depth of 0.7 m with natural pond water from a nearby site (not stated

whether the site is the same as the sediment collection pond, or whether sediment and/or pond

water were sampled for atrazine contamination). The natural pond water was used as the source

for phytoplankton. Zooplankton added to the mesocosms were sampled from "several local

ponds" (not described further) using a net with a mesh size of 63 Jlrn. Aquatic macrophytes

- 1 -

1111.1.111

2087862
(Glyceria maxima) were also added. Seguin et al (2001 b, also reviewed) is cited for more details

about the mesocosm setup. Mesocosms had 3 weeks to develop before treatment. Two

mesocosms were treated with 30 ~g/L atrazine and two were left as controls. Brand, grade, and

application method of atrazine were not described, and it is not stated whether a solvent was

used.

Dissolved oxygen and pH were monitored in the rnesocosms daily (early morning). Water

temperature was measured continuously in situ, and surface irradiation measurements were taken

from a nearby meteorological station (exact location/distance from mesocosms not stated).

Phytoplankton was sampled using a homemade sampler consisting of a ?O-cm long Plexiglass

tube with a total volume of 2.5 L. Samples were pooled from four different points in each

experimental unit (mesocosm). Chlorophyll a was determined once a week in each mesocosm.

One liter water samples from each mesocosm were filtered through a Whatman GFIC filter, then

chlorophyll a was extracted using 90% acetone for 24h at 4°C and measured according to

SCOR-UNESCO (1966). Phytoplankton dry weight was measured after filtering samples

(unknown volume) through 1 ~m Nucleopore filters and drying at 105°C to a constant weight.

Cells and filaments were counted in preserved samples at 400x using the Utermohl method.

Phytoplankton analysis was done on days -1 (the day before atrazine treatment), 2, 4,9, 11, 16,

22, and 25 after treatment.

Short-term phytoplankton community tolerance tests (effects of atrazine on fluorescence) were

conducted three times a week on water samples from each mesocosm. Samples (volume not

reported) were placed in 20 mL Corning glass tubes and 10 ~L of atrazine-acetone stock solution

was added to each tube. Concentrations ranged from 1 to 10,000 nM atrazine (0.22 - 2160

~g/L). Only some ofthe intermediate concentrations were provided (Figure 7). Based on the

log scale in Figure 7, it appears that a dilution series of 101\0.5 may have been used, without a

treatment level at 0.68 ~g/L. The final acetone concentration was 0.05% in treatments and

controls. Six replicates were used as solvent controls, and three replicates were used at each

atrazine concentration. After incubating tubes under 115 ~E/m2 Is of continuous light at 10±2°C

for 1 hour, followed by a 30 min dark period, the in vivo fluorescence was measured using a

Turner fluorometer (model 111).

Shannon-Weaver diversity (H') was calculated for the mean species densities ofthe two

replicates for the treatment and control communities. Bray-Curtis dissimilarity indices (BCl) for

differences between treatment and control communities were calculated for each sampling day.

BCl was calculated from phytoplankton cell densities. The Mann-Whitney test was used to

detect significant differences between C-C (within-control) BCls and A-C (control vs. treatment)

BCls. A principal component analysis was conducted on the total densities of dominant species

in the treatment and control communities using the ADE software package.

For the short-term tolerance tests, EC125 values were calculated. EC125 was defined as the

atrazine concentration that increased fluorescence by 25% over controls. It was not possible to

- 2 -
accurately determine the more common EC50 measure because the maximal range of

fluorescence increase could not be predicted. Dose-response curves were compared between the

mesocosm treatment levels using the Wilcoxon signed rank test after log-transforming the values

to fulfill normality assumptions. Correlation analysis was used to compare short-term

sensitivities to experimental factors (water quality and biological characteristics ofthe

mesocosms). The correlations were determined by calculating a Pearson correlation matrix

using ADE software.

Results:

Initial pH and DO were the same in all four mesocosms, but starting about 3 days after atrazine

treatment, the two treatment mesocosms had lower pH and DO than controls (Figure 1).

Atrazine treatments and controls showed less difference in DO about 12 days after treatment, but

the difference increased again toward the end ofthe experiment The exact dates in Figure 1 are

unclear because the x-axis labels do not match the scale. In general, nutrient levels were similar

between treatments and controls (Table 1).

Chlorophyll a and dry weight of phytoplankton samples in the treatment mesocosms were lower

than in controls nine days after contamination (4/11), and the difference became more

pronounced with time (Table 1 and Figure 2). Additionally, changes in phytoplankton

community structure with atrazine treatment were visible starting 11 days after contamination;

Cyanobacteria were more abundant in the controls relative to the treatments through the end of

the experiment and Chlorophyceae were more abundant in treatments relative to controls through

day 22 (there was a small difference on day 25) (Figure 3). This change in community structure

was also reflected in the principle component analysis (Figure 4) that showed an increasing

separation oftreatments and controls about 12 days after treatment (4/14) on factor two (i.e., axis

2, which explained 16% ofthe total variance). Bray-Curtis indices (BCIs) between controls and

treatments showed a decreasing trend starting nine days after treatment, and were significantly

different from within-control BCIs from day 9 on as well (Figure 5, Mann-Whitney test, "90%",

the reviewer assumes that "90%" represents 1 - p-value, with the resultant p-value = 0.1). The

study authors state that the results, taken together, indicate a simplification ofthe communities in

both the control and treated mesocosms which they attributed to the phenomenon of

confinement. This is perhaps most apparent from the lower species diversity by the end ofthe

experiment (Table 1).

Short-term community tolerance tests showed similar dose response curves for all mesocosms

prior to atrazine treatment ofthe mesocosms. The dose response curves oftreated and control

mesocosms began to diverge one day after treatment ofthe mesocosm. According to the study

authors, the dose-response curves ofthe treated mesocosms were significantly lower (Wilcoxon

signed-rank test, p-value not stated) than those ofthe controls starting on April 5 through the end

ofthe experiment (Figure 7: dose-response curves only shown for d-l, d+1, and d+24).

Additionally, the treatment mesocosm EC125 values were significantly higher than those of

controls (Wilcoxon signed-rank test, no p-value provided) and varied with time (Figure 6). It is

not clear ifthe significant differences reported by the study authors were for each date or for the

- 3 -
entire study period. The tolerance ofthe atrazine-treated communities peaked (highest ECl25)

on day 3 after treatment and there was a sharp decline in tolerance of both treatment and control

communities on day 15 after treatment (Figure 6).

Short-term atrazine sensitivity (i.e. EC125) ofthe control mesocosm communities was

significantly correlated with dry weight biomass, Shannon diversity index, 02 concentration,

nutrient concentration (orthophosphates, ammonium), and temperature (Table 2). For atrazine

treated mesocosm communities, EC125 was significantly correlated with temperature and

orthophosphate. Over all ofthe tolerance tests, the ratio between control and treatment

sensitivity (EC125) was shifted from the 1: 1 line (shifted to a higher tolerance in the atrazinetreated mesocosm communities) (Figure 8). The study authors interpret these results as showing

that environmental conditions during the experiment had a strong influence on community

tolerance, but that there was a stronger effect from prior atrazine exposure at 30 ~g/L; they point

to the decreased correlations oftolerance with other factors in the atrazine-treated mesocosm

communities as opposed to control communities (Table 2).

- 4 -
c

,. 100

90

fJl A

:.; 80 ....,~ ,......

9

8.5

8

d-l

B

d+2 d+7 d+lO d+15

days to contamination

d+21

[]

7.5 +- -..--.I'-""I'"'"""'l~ ......

d-l d+2 d+7 d+lO d+15

days to contamination

d+21

Figure 1. Water quality changes over time in the four mesocosms. "Days to contamination" means days

since treatment (d-l = day before treatment). Squares = control mesocosms, circles = atrazine treatment

mesocosms (30 J.1g/L). Labels on x-axis do not seem to correspond to the scale, making it difficult to determine

exact dates of data plotted on x-axis (study figure 1)

- 5 -
Table 1. Water quality and phytoplankton community characteristics of the mesocosms during the experiment. Values are averages over 2 replicates

(control or 30 !!g/L atrazine). H' = Shannon-Weaver diversity index. (study table 1)

Date Temp. (0C) NH4

+ N02

- N03- PO/ Chi a Dry weight H'

(mg NIL) (mg NIL) (mg NIL) (mg P/L) (!!g/L) (mg/L) (bits/individual)

Controls

4/2 9.30 2.14 0.00 7.20 0.02 13.66 4.93 0.93

4/4 8.26 1.30 0.06 4.20 0.01 25.42 5.90 0.89

4/6 7.30 8.60 0.00 0.93

4/9 10.08 7.60 0.03 0.91

4/11 7.20 0.78 0.15 5.60 0.02 24.42 6.32 0.91

4/13 8.84 7.40 0.02

4/16 7.62 7.66 0.88

4/18 9.50 8.76

4/20 10.38 0.09 0.17 9.60 0.00 30.11 8.80

4/25 12.26 9.40 0.81

4/27 12.40 0.02 0.15 7.00 0.00 28.63 9.04 0.67

Atrazine Treatment

4/2 9.30 2.18 0.00 7.00 0.01 13.93 4.89 0.91

4/4 8.26 1.35 0.06 4.25 0.01 23.09 5.35 0.91

4/6 7.30 10.75 0.01 0.93

4/9 10.08 6.25 0.03 0.86

4/11 7.20 1.20 0.12 5.50 0.02 19.07 4.40 0.92

4/13 8.84 7.50 0.01

4/16 7.62 5.70 0.9

4/18 9.50 5.70

4/20 10.38 0.18 0.14 7.75 0.00 20.86 5.93

4/25 12.26 4.05 0.87

4/27 12.40 0.49 0.16 6.75 0.00 12.23 2.93 0.76

- 6 -
CJ 0

...-......-.

0+----......---.....---.....---.....---...

d-l d+2 d+9 d+16

days to contamination

d+23

Figure 2. Growth of phytoplankton in the four mesocosms expressed as chlorophyll a. "Days to

contamination" means days since treatment (d-l = day before treatment). Squares =control mesocosms,

circles = atrazine treatment mesocosms (30 J.1g/L). (study figure 2)

80000

-.

60000

c: .-........

.~ 40000 rJ:

20000

IiCyanobacteIia

• Cryptophyceae

:J Bacillariophyccac

o Xanthophyceae

Chlorophyceae

CA CA CAe A CA CA CA

d-l d+2 d+4 d+9 d+ll d+16 d+22

days to contamination

CA

0+25

Figure 3. Class-level taxonomic composition (as population density) of algal communities in mesocosms (C =

control, A = atrazine treatment) over time. "Days to contamination" means days since treatment (d-l = day

before treatment). (study figure 3)

- 7 -
A62

A7~' ~1

Axis 1

(26~~ of variance)

A

Axt~l

(16 °'0 ofYanance-)

\

B

I

--_._---_.....

Figure 4. Principal component analysis of phytoplankton communities at various sampling times during the

experiment. Figure A: Label XIJ defined as: X (A for atrazine treatment, C for control); I (sample number, 1

for 4/3, 2 for 4/5, 3 for 417, 4 for 4/12, 5 for 4/14, 6 for 4/19, 7 for 4/25, 8 for 4/28); J (replicate, 1 or 2). Figure

B: Correlation circle of explanatory variables (corresponding to the PCA ordination shown in Figure A). 1:

Chlamydomonas sp.; 2: Chlorella vulgaris; 3: Scenedesmus quadricuada; 4: Dictyosphaerium pulchellum; 5:

Crucigenia apiculata; 6: Crucigenia quadrata; 7: Synedra acus; 8: Nitzschia acicularis; 9: Pediastrum duplex;

10: Oocystis naeglii; 11: Scenedesmus sp.; 12: Tetraedron minimum; 13: Chodatella quadriseta; 14:

Scenedesmus acuminatus; 15: Monoraphidium minitum; 16: Hyaloraphidium contortum; 17: Scenedesmus sp.;

18:Xanthopyceae; 19: Scenedesmus spinosus; 20: Cryptomonas ovata; 21: Closterium acutum; 22: Nitzschia sp.;

23:Scenedesmus sp.; 24: Rhodomonas minuta; 25: Actinastrum hantschii; 26: Navicula sp.; 27:

Pseudoanabaena sp.; 28: Crucigeniafenestrata; 29: Oscillatoria limnetica; 30: Pseudoanabaena sp. (study

figure 4)

- 8 -
1

0.9

0.8

0.7

0.6

<] 05 CO .

0.4

0.3

0.2

0.1

o

d-l d+2 d+4 d+9 d+l1 d+16 d+22 d+25

days to contamination

Figure 5. Bray-Curtis indices of the phytoplankton communities over time, as calculated for the density of

replicate communities between treatment and controls. Difference between treatment vs. control BCI (A-C)

and within-control BCI (C-C) was tested for statistical significance using the Mann-Whitney test ("90%"

assumed to mean p-value = 0.10) and days with significant differences are marked with an asterisk (*).

"Days to contamination" means days since treatment (d-l = day before treatment). (study figure 5)

10000

- 1000 "i

100 '-"

l.('";

N

U 10

1

d-l d+3 d+8 d+13 d+17

days to contamination

d+24

Figure 6. Calculated (from fluorescence measurements) EC125 values for the four mesocosms over time.

"Days to contamination" means days since treatment (d-l = day before treatment). Squares = control

mesocosms, circles = atrazine treatment mesocosms (30 ,.g/L). (study figure 7)

- 9 -
200

] 180

§

u 160 ,j,~,~ ,p .i ·:.:. e:

...

u 140 .. c ,

120 j. '"

c i-'. . .I· .i:: : ', £ 100

80 d-l

0 10 100 1000 10000

A [atrazine] 11M

200 J;J

e 180 JJ' . c

c .0' 160

,,e" u

0,- IIJ 140 . , u

II,l

c -0'" _.-e u 120

I:'" -' e"··

§ 100 ••• I ~~: i- " !;::

80 d+l

a 10 100 1000 10000

B [atrazine] 11M

200

C 180 .,.•' 0••

c

'-' -.. o 0

t, 160 ..- 0

." 0 i .i·· IIJ 140 '-' . '0 6

.,8' ~. ' j. . . '-' '" 120 ....

g 100 =: j:' e·' c;:

d-r24

80

0 10 100 1000 10000

C [atrazine] 11M

Figure 7. Short-term effects of atrazine on phytoplankton community fluorescence, using phytoplankton

community samples from the 4 mesocosms. Tests were conducted the day before mesocosm atrazine

treatment (4/3), the day after treatment (4/5), and at the end of the experiment (4/28). Fluorescence is

expressed as percentage of control fluorescence. Squares = control mesocosms, circles = atrazine treatment

mesocosms (30 Jlg/L). (study figure 6)

- 10 -
Table 2. Correlation analysis results between short-term atrazine sensitivity (log ECI2S) and different

environmental parameters and biological characteristics of the mesocosms. NS = Not Significant. (study

table 2)

Tee) NH/ po/- O2 Chi a Dry Weight H'

Mean (controls)

r -0.7021 0.8713 0.6830 0.6814 -0.7243 -0.9334 0.9123

n 11 5 8 11 5 8 8

P 0.01 0.05 0.05 0.05 NS 0.001 0.001

Mean (atrazine-treated)

r -0.6006 0.5011 0.6518 0.2532 0.0411 -0.1628 0.4530

n II 8 8 II 5 8 8

p 0.05 NS 0.05 NS NS NS NS

1

1

y = 0.8692x + 0.8165

R2 =0.7298 •

•

2

log [Ee125 (nM)] - controls

3

Figure 8. Correlations between atrazine sensitivities (log ECI2S) in control vs. treatment mesocosm

communities. Means are plotted. (study figure 8)

- 11 -
Data Summary Table

Time

Weighted Did

Magnitude of Nominal Day ofStudy Average Recovery

Effect Effect relative Atrazine Effect Atrazine Occur- if

Concentration Concentration so, when Comments

to controls Occurred (f.lg/L) from Day Oto (see

When Effect comment)?

Occurred

Effect magnitude

Decrease in

calculated from

review Table 1

chlorophyll a 22% 30/lg/L Day 9 Unknown (no No mean values (also

concentration measurements) see Figure 2).

No significance

tests provided.

Effect magnitude

Decrease in dry

calculated from

weight of 30% 30/lg/L Day 9 Unknown (no No

review Table 1

phytoplankton measurements) mean values.

No significance

tests provided.

Change in

phytoplankton

community No change 30/lg!L Not

diversity Not applicable Not applicable See review Table

(Shannon

applicable 1.

diversity index)

- 12 -
Time

Weighted Did

Magnitude of Nominal Day ofStudy Average Recovery

Atrazine Atrazine Occur-if Effect Effect relative Concentration Effect Concentration so, when Comments

to controls (pg/L) Occurred from Day Oto (see

When Effect comment)?

Occurred

Effect magnitude

estimated from

review Figure 3.

No significance

tests provided.

Abundance in

Lower abundance ~50% 30 J.lglL Day 11 Unknown (no No control increased

of cyanobacteria measurements) relative to the

treatment group to

day 16 then on,

day 22 the

treatment group

abundance started

to decrease relative

to the control.

Change in

abundance of Not See review Figure Cryptophyceae, No effect 30 J.lg/L Not applicable Not applicable

Bacillariophyceae, applicable 3.

Xanthophyceae

Effect magnitude

Increase in estimated from

abundance of ~100% 30 J.lg/L Day 11 Unknown (no Yes -Day review Figure 3.

measurements) 25 Chlorophyceae No significance

test provided.

See review figure

Change in 5.

phytoplankton Effects were

community Unknown (no statistically composition (BCI within-contro1 30 J.lglL Day 9 Unknown (no No significant ("90%" between control & BCls provided) measurements) according to the

treatment, vs. BCI study authors). of within- The reviewer

controls) assumed the pvalue = 0.10.

Change in Unknown Unknown (no See review Figure

phytoplankton (cannot 30 J.lglL Day 12 measurements) No 4A. Axis 2

community quantify) accounts for 16%

- 13 -
Time

Weighted Did

Magnitude of Nominal Day ofStudy Average Recovery

Atrazine Atrazine Occur-if Effect Effect relative Concentration Effect Concentration so, when Comments

to controls (pg/L) Occurred from Day Oto (see

When Effect comment)?

Occurred

composition ofthe total

(divergence of variance.

treatments and

controls on axis 2

of principal No significance

component test provided.

analysis based on

species densities)

See review figure

1.

No significance

test provided.

Decreased Unknown (no dissolved oxygen -20% 30llgIL ~Day3 measurements) Day 12 Days of effects and

(% saturation) recovery are

approximate

because scale on

Figure 1 is difficult

to interpret as

presented.

Not Effects estimated

~5% 0.221lg/L 1.5 hours Not applicable applicable from Figure 7A

(short-term effects

Decreased of atrazine on

efficiency of mesocosm

photosynthesis communities prior

(increased to long-term

fluorescence exposure to

yield) atrazine).

2.15 Ilg/L 1.5 hours Not applicable Not ~5% applicable

No significance

test provided

- 14 -
Time

Weighted Did

Nominal Average Recovery Magnitude of Atrazine Day ofStudy Atrazine Occur-if Effect Effect relative Comments Concentration Effect Concentration so, when

to controls Occurred (pglL) from Day Oto (see

When Effect comment)?

Occurred

Dose for three

other atrazine

treatments was not

defmed.

Unknown (no Not ~20% 21.5/lg/L 1.5 hours measurements) applicable Effects at 0.22 and

2.15 /lg/L are not

considered

different from the

control.

Although in some

cases the

magnitude of

effects are greater

for communities

sampled later

Unknown (no Not ~50% during the 215/lg!L 1.5 hours measurements) applicable mesocosm

experiments

(Figure 7B and

7C), those results

may have been

affected by

changing

conditions

(community and

water quality) over

the experiment.

In addition, shortUnknown (no Not term exposure for ~70% 2156/lg/L 1.5 hours measurements) applicable atrazine-treated

mesocosm

communities is

uncertain (see

reviewer

comments)

- 15 -
Reviewer Comments:

The study was presented relatively clearly with several limitations similar to those ofrelated

studies by this lead author (also reviewed). The descriptions ofthe sources and sampling

methods for sediment, water, and plankton are sparse, and it is unclear whether all came from

uncontaminated natural water bodies. Control mesocosms were not measured for atrazine

contamination. Therefore, background exposure to atrazine in the mesocosms cannot be ruled

out. No information is provided on what type or brand of atrazine was used or how it was

applied. The study authors do not report using a solvent for the mesocosm experiments.

According to the primary reviewer, if a solvent was not used, then the atrazine may not have

dissolved enough for the actual initial concentrations in the mesocosms to approximate the

nominal concentrations. Since actual atrazine concentrations in the mesocosms were never

measured, and the application method is not described, it is unclear if nominal concentrations

adequately estimate the actual atrazine concentration at the beginning ofthe experiment.

Only 2 replicates were used and only 1 treatment level was employed (30 Ilg/L). For the shortterm tests, 8 concentrations were tested, three of which the authors did not provide the exact

concentration.

No information was provided on how nutrients were measured in the mesocosms.

Some endpoints are difficult to interpret due to the data analysis. The Bray-Curtis index was

used, but its implementation was not well-described, which may lead to some misinterpretation.

Since BCl is never defined with an equation, it is unknown exactly which version ofit is being

used, over what set ofspecies or taxonomic groups it is being defined, and so on. The Principal

Component Analysis, while qualitatively interesting, is limited in usefulness. The only

component (Axis 2) showing visible changes with treatment explains only 16% ofthe variance,

and the first two components together account for less than halfthe variance. Finally, as with

other studies by these authors which have been reviewed, p-values are generally not provided

when statistical tests are applied, and many endpoints have no statistical analyses performed at

all. The reviewer assumed a p-value = 0.1 for the Mann-Whitney test (regarding this test, the

study authors state "90%" with no context ofwhat this means).

Exposure concentrations are uncertain for the short-term toxicity testing on communities from

mesocosms that were pre-exposed to atrazine (nominal = 30 Ilg/L). For these tests, water

samples were used from the atrazine treated mesocosms which contained not only the

phytoplankton but also the nominal amount of atrazine added to the mesocosms at the beginning

ofthe experiment (30 Ilg/L). Therefore, the actual concentrations would have been higher than

the nominal values reported for the short-term experiments. Moreover, the nominal

concentration of atrazine in the atrazine-treated mesocosms was greater than three ofthe nominal

concentrations added to the samples for the short-term tests. Finally, this is also an indication

that the actual exposure for the short term experiments would not have been the same for

communities from atrazine-treated mesocosms and those from control mesocosms. Short-term

- 16 -
toxicity data from the atrazine-treated mesocosm communities was not considered for the data

summary table due to the uncertainty surrounding exposure concentrations.

Some ofthe dates provided in the tables and figures do not match statements made by the study

authors in the text. For example, the chlorophyll analysis seems to suggest that 4/3 was the date

of atrazine application in the mesocosms, whereas the caption offigure 7 implies the date was

4/4.

Over time, there was increasing short-term sensitivity (i.e. EC125) ofthe control mesocosm

communities to atrazine. Results from correlation analysis suggest that mesocosm characteristics

which changed over time (i.e. community composition and environmental conditions) likely

accounted for the increased sensitivity in the control mesocosm communities over time.

Although fewer mesocosm characteristics were significantly correlated with EC125 in the

atrazine-treated mesocosms, the temporal change in atrazine sensitivity oftreated mesocosms

communities may have been a product of atrazine exposure in combination with environmental

and biological factors as well. It is uncertain to what degree factors other than atrazine affected

fluorescence.

Description of Use in Document: Qualitative

Rationale for Use: The study contributes to the weight of evidence regarding effects of atrazine

on aquatic plant communities.

Limitations of Study: The study is limited by a single atrazine test concentration (mesocosms),

low replication (mesocosms), lack ofinformation about atrazine treatment methods and actual

concentrations of atrazine over time, lack of clear statistical results (i.e. no p-values) for most

endpoints, and the potential for background atrazine exposure. Fluorescence tests were shortterm (l.5 hours of exposure) and performed on communities either pre-exposed or not preexposed to atrazine. Actual exposure in the short-term tests is uncertain; confounded by the

addition of atrazine from water used in the treated mesocosms.

Primary Reviewer: Sara H. Hendrix, M.S., Subcontracting Scientist, Cambridge

Environmental Inc.

/'A/J ' J.

Secondary Reviewer: Michael Lowit, Ph.D., Ecologist, EPA f/1tW c7tJ

Tertiary Reviewer: Anita Pease, M.S., Senior Biologist, EPA 't~ fa (l3/1 \

- 17 -