Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

ECOTOX Record Number and Citation:

Van den Brink, PJ., E. van Donk, R Gylstra, SJ.H. Crum, and T.C.M. Brock. 1995.

Effects of chronic low concentrations ofthe pesticides chlorpyrifos and atrazine in indoor

freshwater microcosms. Chemosphere. 31 :3181-3200. (MRID 47543516)

Purpose of Review:

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

study were also used to parameterize the Comprehensive Aquatic System Model (CASM)

and establish the model-associated LOC for atrazine.

Date of Review:

January 15,2009

Purpose of Study:

This study examines the potential effects of atrazine to aquatic plants and animals in

laboratory aquaria (microcosms).

Summary of Study Findings:

Methods: This study examined potential effects of exposure to low concentrations of an

insecticide, chlorpyrifos, as well as to atrazine. Only methods pertaining to atrazine will

be described here.

Two groups of four microcosms each were designed to receive 0 (controls) or 5 jlg/L

atrazine, and then dynamics in water quality, zooplankton, phytoplankton, and

macroinvertebrates were studied over an 8-week period (treatment occurring after the

first week), from May 3, 1993 to June 28, 1993. Each microcosm consisted of a glass

aquarium (1.1 m x 1.1 m x 0.7 m high, water volume 600 L) filled with 2 cm oflake

sediment and a 50 cm water column. (Source oflake sediment and water not described.)

The microcosms were placed in a room at constant temperature, 19 ± 2°C, with high

pressure metal halide lamps (Philips HPL-T, 400W) lighting them with an intensity of

120 jlE/m2/s at the water surface and a daily photoperiod of 14 hours light, 10 hours dark.

(Another paper is cited for more details.) Plankton and macroinvertebrates were

\111111111

2087834
introduced to the microcosms (sources of organisms not described) together with the

natural sediment and a nutrient addition of phosphorus and nitrogen at initial

concentrations of 0.05 mg/L and 0.30 mg/L, respectively. The microcosms were then

allowed 3 months to stabilize their biotic communities, during which time they were all

connected by tubes (2.6 cm internal diameter) with a circulation flow rate of3.5 Llmin to

achieve uniformity.

The initial dose of atrazine was distributed evenly over the water surface of each

microcosm and mixed as rapidly as possible. Aeration stones maintained water

movement. Atrazine was added twice a week to compensate for losses, which were

calculated from concentration measurements. Atrazine concentrations were measured by

combining duplicate 100 mL water samples (taken at mid-depth with a glass pipette),

shaking the water samples for two hours with 30 mL dichloromethane in 250 mL bottles

to extract the atrazine, and analyzing the atrazine concentration in the dichloromethane

by splitless injection of 3 !J.L on an HP 5890 gas chromatograph. A wide-bore WCOT

fused silica capillary column (25 m long) coated with CP Sil 5 CB stationary phase (film

thickness was 4.75 !J.m) was used. Operating parameters were: 205°C oven temperature,

10 mLimin helium carrier flow, 240°C injection block temperature, NDP detector, 280°C

temperature, 3.5 mLimin hydrogen flow, 90 mLimin air flow and 20 mLimin auxiliary

nitrogen gas flow, with a retention time of 3.5 min. The detection limit was 6 pg, and

recovery from water was 99.9 ± 2.8% (mean ± standard error, n=4).

Zooplankton were sampled weekly (week -1 to 7) by taking a depth-integrated water

sample with a 40 cm long, 1 L volume Perspex tube, with at least 5 samples per

microcosm. The samples were then concentrated on a nylon zooplankton net (55 !J.m),

preserved in 4% formalin, stained with Lugol, and then a subsample was counted at 25x

using a counting chamber.

Phytoplankton were analyzed from week -1 to week 4. Of a 2.1 L sample as taken above,

1 L was used to study species composition, and 1.1 L was used for analysis of

chlorophyll a and nutrients. Phytoplankton samples were stained with 3.5% Lugol and

stored in bottles for sedimentation. After 6 days, 90% ofthe water of each sample was

extracted and the remaining sample preserved with 4% formalin. Cell counts were made

with Burker Turk counting chambers (0.04 mm

2

x 0.10 mm).

Macroinvertebrates were sampled every two weeks (weeks -1, 2, 4, and 6) in two litter

bags per microcosm. (A paper headed by a coauthor is cited for details.) The litter bags

consisted of a glass Petri dish (diameter 11.6 em), closed with a cover ofstainless steel

wire (0.7 mm mesh), in which two 0.5 em diameter holes allowed passage of

macroinvertebrates. Each litter bag was filled with 2 g dried Populus leaves as

substratum. After two weeks of colonization, the contents ofthe litter bags were

transferred to a tray to separate macroinvertebrates from leafmaterial. The

2
macroinvertebrates were identified and counted alive, then released back to their home

microcosm.

Water quality measurements (dissolved oxygen [DO], pH, conductivity, and alkalinity)

were taken once a week in the afternoon throughout the experimental period.

Measurements were performed at 10 cm depth using a WTW oxygen meter (Oxi 196)

and oxygen probe (EO 196), a Metrohm Herisan pH meter (E-488), and a WTW

conductivity meter (LF 191). Alkalinity estimation was done by titration of 100 mL of

water sample with 0.05 M HCl down to pH 4.2. From week -1 through week 6, plankton

chlorophyll a and soluble inorganic nitrogen and soluble reactive phosphorus (SRP) were

determined, the lattertwo quantities with a Skalar 5100 Autoanalyser. Chlorophyll a was

estimated by concentrating alL water sample over a Whatman GF/C glass fiber filter

(1.2 11m) and analyzing with spectrophotometry (as described in a cited 1978 paper). The

remaining 100 mL ofthe subsample was filtered and stored at -20°C.

Bioassays were performed with crustaceans (Gammarus pulex and Asellus aquaticus)

inside each microcosm in cages, 10 individuals per species in a 10 cm x lO cm x 50 cm

cage with separate cages for each species, with the cage bottom 45 cm below water level

and one side ofthe cage consisting of 55 11m gauze mesh to allow water exchange. The

cages were stocked with Populus leaves, providing the organisms with their own separate

food supply. Bioassays lasted 24 days, from week 3 to week 7, with surviving

individuals counted regularly and dead removed. Neonates were counted at the end of

the experiment.

Data analysis was carried out with both univariate methods (for effects oftreatment on

individual taxa or physicochemical parameters) and multivariate methods (for

community-level or multi-component water quality effects). Univariate analyses used

analysis of variance (ANOVA) with the Dunnett test to detect significant differences

between treatment and control, as implemented by the computer program TOXSTAT

Release 3.2. Where necessary to meet assumptions of homogeneous variance and normal

distribution, the data were natural-log (In) transformed, and ifthat failed, the nonparametric Steel's rank sum test was used. Statistical significance was judged at a pvalue::; 0.05.

Multivariate analyses used the Redundancy Analysis (RDA) ordination technique, and

significance tested by Monte Carlo permutation testing. (Sources are cited for details on

the theory and application ofthese methods.) RDA produces a diagram where samples

with similar species combinations lie close together, and those with dissimilar species

combinations lie far apart. Points are shown for each species, and samples where that

species was abundant will lie close to that species' point.

3
RDA and the Monte Carlo pennutation tests were performed with the CANOCO version

3.14 computer program, for the zooplankton, phytoplankton, macroinvertebrate, and

physicochemical data. Water quality was expressed as the "community" ofthe

physicochemical parameters (DO, pH, alkalinity, conductivity). For plankton and

macroinvertebrates, default RDA options were chosen, but with the physicochemical

data, parameters were standardized to make them commensurate. Before analysis,

however, the plankton and macroinvertebrate communities' species abundance values

were In( IOx+ I) and In(2x+I) transformed, respectively, to better analyze low abundance

values. Sample points were defined by all data on a specific community, from a specific

pesticide (treatment), and on a specific sampling day. For each ofthese sample point

datasets, the total variance in the variables is only partly expressed by the two axes ofthe

RDA diagram, and this "percentage of variance explained" is commonly 30-40% in

ecological applications. For Monte Carlo tests (performed under the RDA option), each

sampling time and pesticide treatment was permuted against the control microcosms. Pvalues < 0.05 were considered "significant" and p-value between 0.05 and 0.10 were

considered "a trend ofsignificance".

Results: This study examined potential effects of low concentrations of an insecticide,

chlorpyrifos, as well as atrazine. Only results pertaining to atrazine will be described in

this review.

Atrazine concentrations in the microcosms varied between 4.2 and 6.0 Ilg/L (see Figure

1). Mean concentration (determined from the area under the curve) was 5.08 Ilg/L, with

a standard error of 0.03 Ilg/L.

The most abundant zooplankton taxa in the microcosms were Copepoda and the rotifer

Keratella quadrata (Table 1). The only zooplankton showing a significant (but brief)

response to atrazine was Cyclopoida, which increased in week 3 relative to controls (see

also Figure 2). The most abundant phytoplankton taxa in the microcosms were:

Botryococcus spp., Chlamydomonas spp., Choomonas spp. (Chlorophyceae)

Navicula spp., Cocconeis spp., Achnanthes minutissima (Bacillariophyceae)

Cryptomonas spp. (Cryptophyceae)

Gymnodinium spp. (Dinophyceae)

Ofthese, only one showed significant differences from controls in the atrazine

microcosms: Botryococcus spp. was significantly less abundant in treatment microcosms

in week -1 (which was prior to treatment). See Table 2. Macroinvertebrate communities

were dominated by Gastropoda and Crustacea, the former increasing in abundance with

time and the latter decreasing. See Table 3. No significant effects of atrazine treatment

on macroinvertebrates were found.

4
In the water quality parameters, there were no significant differences in any parameter

due to atrazine treatment. DO and pH in the atrazine treated microcosms were somewhat

lower, and conductivity and alkalinity somewhat higher, compared to controls, but not

significantly so (p>0.05). See Table 4. In all microcosms, nutrient and chlorophyll a

concentrations were very low, and there were no significant (p<0.05) differences between

treatments and controls. Ranges were:

SRP: 0.000 0.009 mg/L

Inorganic N: 0.000 0.093 mg/L

chlorophyll a: 0.00 6.22 Jlg/L

In multivariate analyses, no significant differences due to atrazine treatment were found

in zooplankton, phytoplankton, or macroinvertebrate communities. In the zooplankton

community RDA diagram, 75% ofthe total variance was explained (see Figure 3), and in

the macroinvertebrate community RDA diagram, 77% of the total variance was explained

(see Figure 4). (The phytoplankton community RDA diagram is not provided in the

article because no significant differences were found.) There was a "trend of difference"

(p-value < 0.10) in the physicochemical parameters in week 5 (see Figure 5; 90% of the

total variance is explained in this RDA diagram).

No significant effects of atrazine were found in the crustacean bioassays. See Table 5.

!J'JIO~I_~,a!~.!_~OI1 _"

1 ? J

••A.IR 1 , AlR;?,

-- ATR 4

n~e after start of exposure (wlJBks)

Figure 1. Mean atrazine concentrations (J.lg/L) over time at mid-depth in the four treatment

microcosms. (from study figure])

5
.., 5 II

HI'r

,~~-~--'--~------~--~-~-

-I 0 7

A

3 4 5

10

'tt

; I O.1L-~

.j 0

...I

-

..Q

E

:::'l

:z

Time aUer at~ut expolure (we.ka) Time after 8tart exposure (weeki)

....... Con .-- Cpf -- Atr -- Con -<0- Cct

Figure 2. Dynamics in numbers (mean ± standard error, n=4) of cyclopoida (A) and Keratella

quadrata (B) in the control (Con, small solid diamonds), chlorpyrifos (Cpf, closed squares), and

atrazine (Atr, open squares) treated microcosms. (study figure 2)

6
cpfS" / +(p16

cpf7 tL

•

Cali.U"lIt>t:.;. ~;

(on3,

Figure 3. Ordination diagram (RDA) showing effects of chlorphyrifos (cpf, dotted line), atrazine

(atr, dashed line), and control (con, solid line) treatments on the zooplankton community. Lines

represent changes over time. *indicates significant differences from controls at p::;O.05. (study

figure 3)

7
cpfGU

+

;'cpf2

, , jl ~-I-;rt ... .. 4 ...

, ... ..-" ....

'.-'.

.. "' ....

Figure 4. Ordination diagram (RDA) showing effects of chlorphyrifos (cpf, dotted line), atrazine

(atr, dashed line), and control (con, solid line) treatments on the macroinvertebrate community.

Lines represent changes over time. * indicates significant differences from controls at p~O.05 (no

such differences were found); ** indicates "trends of difference" (O.05<p~O.10). (study figure 4)

8
AIk:~iflltY •

atr4*

I

tonSI 1

I \

;(.. \

atrS U \

\

1

at.r3 . :

[

' (on1 ••••..f- " •••-.. cpf1

c~1--' .-'..-",

I

i

I

cpf"

t;.c.on.4

I'"

.' cpf:5; :

,

.+

..

cen3 (on2

C>O.

Figure 5. Ordination diagram (RDA) showing effects of chlorphyrifos (cpf, dotted line), atrazine

(atr, dashed line), and control (con, solid line) treatments on the water quality parameters. Lines

represent changes over time. * indicates significant differences from controls at p~O.05 (no such

differences were found); ** indicates "trends of difference" (O.05<p~O.lO). (study figure 5)

9
Table 1. Abundance (individuals/L, mean and standard error [Slq with n=4) ofthe zooplankton taxa and the macroinvertebrate Bothromesostoma

essenii summarized over 3 periods: week -1 (pretreatment), week 0-3, and weeks 4-7. Only the taxa present in more than 10% ofsamples are shown.

No significant differences between atrazine treatment and control microcosms were found, except for an increase in Cyclopoida spp. abundance in

treatment microcosms in week 3 (significant at p<0.05). (from study table lA)

Taxon ! Control I

Mean SE ~--- --- --~---

Daphnia galeata Sars 1.5 1.1 1.4 0.7 I 1.5 1.0 2.9 0.9 0.6 0.3 2.0 0.6

Simocephalus vetulus (Muller) 0.0 0.0 0.1 0.1 0.4 0.3 1.5 0.8 0.2 0.\ 0.8 0.6

Acroperus harpae (Baird) 0.1 0.1 0.0 0.0 I 0.0 0.0 0.1 0.0 0.\ D.\ 0.0 0.0

Ceriodaphnia sp. 0.0 0.0 0.0 0.0 0.3 0.3 0.9 0.9 D.l D.\ 0.1 0.\

~QlLeIJoda

Cyclopoida spp. 46.5 \4.5 24.7 6.1 1 22.7 4.5 27.7 3.8 3.0 0.5 2.8 0.7

Calanoida spp. 1.8 0.\ D.7 0.3 \O.D 3.5 \2.4 0.7 17.5 7.5 16.4 2.7

52.6 9.3 53.\ 16.71 35.2 12.5 31.8 4.4 28.2 4.4 30.7 4.7

Ostracoda spp. 0.\ 0.\ 0.0 0.0 0.4 0.2 0.3 0.\ 0.3 0.2 0.\ 0.1

Rotifera

Keratel/a quadrata (Muller) I J35.D 32.8

TurbeIlaria I

Bothromesostoma essenii Braum ! 4.0 1.2

10
Table 2. Abundance (individuals/L except Volvox spp. in 1,000 indiv.lL, mean and standard error (SE) with n=4) of the phytoplankton taxa

summarized over 3 periods: week -1 (pretreatment), weeks 0-3, and week 4. Only the taxa present in more than 10% ofsamples are shown. No

significant differences between atrazine treatment and control microcosms were found, except for a decrease in Botryococcus spp. abundance in

treatment microcosms in week -1 (significant at p<0.05). (from study table lB)

Taxon

1.1

0.0

0.6

0.2

0.0

0.3

0.0

0.0

0.2

0.0

0.17

0.7

0.6

1.0

0.0

0.0

0.0

1.7

3.9

0.0

0.7

0.0

0.0

0.3

0.3

0.0

2.2

0.0

0.2

0.5

0.2

0.0

0.0

0.2

0.0

5.4

0.0

0.3

0.0

0.9

1.0

0.0

0.0

0.3

3.1 0.9 I 3.8 1.0

0.1 0.1 I 0.3 0.2

0.2 0.2 0.1 0.1

3.4 0.6 4.3 1.2

1.5 0.2 1.8 0.7

0.9 0.2 1.1 0.5

1.0 0.4 1.4 0.5

0.4 0.2 0.5 0.2

0.3 0.2 0.3 0.3

0.13 0.10 0.01 0.00

3.2 0.7 2.2 0.5

3.3 0.3 2.7 0.3

1.6 0.4 4.1 l.l

0.7 0.3 0.0 0.0

0.3 0.1 0.0 0.0

0.1 0.1 0.0 0.0

0.5

0.2

0.6

0.7

1 1

0.9

0.8

0.3

0.3

0.00

27.4

1.1

0.8

0.0

0.0

0.0

2.3

2.3

2.8

1.7

1.4

0.5

0.3

0.7

0.2

0.00

60.2

3.9

2.2

0.0

0.0

0.0

SE SE ~-----+

0.07 0.05 0.28

2.0 1.3 1.5

1.9 7.0 0.9

0.3 0.2 1.6

0.0 0.0 0.0

0.0 0.0 I~ 0.0

0.0 0.0 0.0

3.4 1.0

2.1 0.5

2.0 0.6

0.9 0.3

0.8 0.6

0.4 0.2

0.3 0.2

1.0 0.7

0.2 0.2

0.01 0.00

177.8 44.5

5.4 1.1

1.6 0.5

0.7 0.3

0.4 0.4

0.1 O.

Chlorophyceae

Volvox spp.

Botryococcus spp.

Chlamydomonas spp.

Chroomonas spp.

Kirchneriella spp.

Monoraphidium spp.

Oocystis spp.

Bacillariophyceae

Navicula spp.

Cocconeis spp.

Gomphonema spp.

Achnanthes minutissima

Synedra spp.

Epithemia zebra

Cyanophyceae

Phormidium spp.

Anabaena spp.

Cryptophyceae

Cryptomonas spp.

Dinophyceae

11
Table 3. Abundance (individuals/L, mean and standard error [SE] with n=4) of the macroinvertebrate taxa summarized over 3 periods:

week -1 (pretreatment), week 2, and weeks 4 and 6. Only the taxa present in more than 10% of samples are shown. No significant (p<O.05) differences

between atrazine treatment and control microcosms were found. (from study table Ie)

Weeks 4 & 6

Taxon I Control Control AtrazilJe

Mean SE lv/ean SE j\1ean SE Mean SE Mean SE ~~~--

Dugesia lugubris (Schmidt) 0.0 0.0 0.0 0.0 1.3 0.5 0.3 0.3 1.5 1.2 0.0 0.0

Polycelis tenuis Ijima 1.5 0.3 1.5 0.5 5.5 1.2 3.5 0.7 11.1 2.9 I 7.9 1.9

Bothromesostoma essenii Braum 1.3 0.8 0.8 0.5 6.0 0.7 7.0 2.2 3.1 0.6 3.9 0.4

Nemertea 2.0 0.7 1.5 0.3 0.0 0.0 0.0 0.0 1.5 0.6 I 0.3 0.1

Lumbriculus variegatus (MUller) 0.0 0.0 0.0 0.0 0.3 0.3 0.5 0.5 0.0 0.0 0.6 0.6

Turbificidae 5.0 1.8 ,., ,., .:l •.:l 1.0 0.3 0.3 0.0 0.0 0.4 0.4 1.0 1.0

Dero digitata (MUlier) 0.8 0.5 1.5 1.5 0.0 0.0 2.0 1.7 0.0 0.0 8.6 8.1

Hirudinae I

0.0 I I Glossiphonia heteroclita (Linnaeus) i 0.0 0.0 0.0 I 2.3 1.9 I 0.0 0.0 I 0.8 0.8 I 0.0 0.0

GastroIJoda

Physa acuta (Draparnaud) 6.3 3.8 14.5 13.5 37.5 18.2 23.5 10.0 50.9 28.9 55.6 4.2

Potamopyrgus antipodarum (Gray) 5.3 2.7 3.0 1.2 38.8 30.9 14.3 10.0 21.8 10.3 8.5 2.9

Bithynia tentaculata (Linnaeus) 22.8 6.6 16.0 2.5 11.0 2.8 4.3 1.8 6.8 1.0 6.0 1.5

Lymnaea stagnalis (Linnaeus) 0.0 0.0 0.0 0.0 0.0 0.0 2.8 2.8 0.3 0.1 I 7.8 5.5

Valvata piscinalis (MUlier) 8.5 3.4 3.3 1.7 4.8 3.8 I 1.3 1.0 3.5 1.3 1.5 0.9

Gammarus pulex (Linnaeus) 12.8 1.9 11.0 3.1 6.3 2.5 5.3 2.9

Asellus aquaticus Linnaeus 6.0 0.6 7.0 2.0 3.5 1.3 7.5 4.9

Proasellus meridianus (Raeovitza) 1.5 0.9 1.5 1.0 2.0 I.l 2.0 1.7

2.3 0.9

12
Table 4. Measurement results on the physicochemical parameters (mean and standard error [SE) with n=4) summarized over 3 periods: week -1, weeks

0-3, and weeks 4-7. All parameters were not measured in week 6, and pH was not measured in week 7. No significant (p<O.05) differences between

atrazine treatment and control microcosms were found. (from study table 1D)

I Week-l ~~WeeksO=3~~--1·· Weeks 4-7 I

Parameter Control [Atrazine Control Atrazine Control Atrazine I

Mean SE Mean SE Mean SE Mean SE Mean SE I Mean SE I

Dissolved oxygen (mg/L) I 9.4 0.2 9.2 0.1 9.9 j 9.3 0.2 9.9 OJ! 9.7 0.1 1

pH 8.4 0.2 8.4 0.1 9 0.2 8.6 0.2 8.8 0.2 I 8.4 0 I

Conductivity (JlS/cm) 1189.3 2.8 189.5 1.2 175.1 6.5 18~ 159.3 4.21169.3 2.3.

Alkalinity (mL) 2.2 0 2.2 0 1.9 0.1 2.1 0.1 1.4 ~~~ - ._~ ..~-_...._. ..•..-

0.1 1.7 0.1 I

13
Table 5. Results of bioassays (in numbers, mean and standard error ISED with Gammarus pulex and

Asellus aquaticus. No significant (p<O.05) differences between atrazine treatments and controls were

found. (from study table 2)

Gammaru:>Jl!!1<:~ Asellus aquaticus

I t1tDl~ne Con!!:Ql I Afrazine

Alean SE i Alean SE Afean SE i Alean SE

I 10.0 0.0 10.0 0.0 10.0 0.0 10.0 0.0

2 10.0 0.0 10.0 0.0 9.3 0.4 9.5 0.3

3 10.0 0.0 10.0 0.0 9.0 0.4 9.5 0.3

4 10.0 0.0 10.0 0.0 8.8 0.2 9.5 0.3

5 10.0 0.0 10.0 0.0 8.5 0.4 9.5 0.3

6 9.8 0.2 9.8 0.2 8.3 0.4 9.5 OJ

7 9.5 OJ 9.8 0.2 8.3 0.4 8.8 0.5

10 9.5 0.3 9.3 0.2 8.0 0.4 8.0 0.4

13 9.5 0.3 9.0 0.4 6.5 0.8 7.0 0.4

17 9.5 0.3 8.5 0.6 5.0 1.2 6.0 0.6

20 0.4 8.8 0.4 4.0 1.3 4.8 0.4

24 0.4 3.8 1.1 0.4

24 10.6 29J 12.8 5.8

14
Data Summary Table:

Comments

[

Effect Magnitude of Nominal Day of Time Did

Effect Atrazine Study Effect Weighted Recovery

relative to Concentration Occurred Average Occur - if

controls (flg/L) Atrazine so, when

Concentration (see

from Day 0 to comment)? I

I!

-C-h-a-ng-e~in---I---------i-~"---~'---I--~--~"-----II--=-'::"'::"'::::":":-=----l- Occurred

When Effect

----

1~:~; t~u~~d

, phytoplankton No effect 5 Ilg/L NA NA NA , study text p.

community! i 3193.

Change in

zooplankton

community

(increase in

Cyclopoida spp.)

No adverse

effect (22%

increase

observed)

, 5 Ilg/L

I

21 NA NA

From study

table lAo

Effect

magnitude is

based on

Week 0-3

averages.

Change in

macroinvertebrate

community

No effect NA

From study

table IC and

Fig. 4.

I

From study

table 2.

From

Figure

3

Effect only

reported for

Week 5

NA

NA

5 ug/L

Week 5 (no

subsequent

evaluations)

I

Slight 5 ug/L

No effect

Change in

chlorophyll a

concentration

Change in I

crustacean IN f"' t . I ( I ' 1 0 e lee survlva extema I

food provided)----.J --l-. t- +- -t.__. + --i

"Trend of

difference" for

water chemistry

(DO, pH,

alkalinity,

conductivity)

Note: NA=Not ApplIcable

Atrazine concentrations were maintained very close to nominal during the experiment by

multiple analyses and corrective additions. By visual inspection of Figure 1, it was

determined that the above-nominal fluctuations were roughly balanced out by the belownominal fluctuation from Day 0 to Day 21 (week 3). The figure is somewhat illegible

due to the separate lines for each microcosm. Therefore, it was assumed that Day 21 time

weighted average atrazine concentrations were equal to nominal, 5 Jlg/L. It is expected

that this is accurate to ±O.5 Jlg/L.

Reviewer Comments:

Four replicates were used for treatments and controls; the study had a reasonably long

time for microcosms to stabilize (3 months, during which time they were hydraulically

15
connected); and the data analysis techniques used are appropriate, sophisticated and welldescribed. The results are presented clearly and completely, with many tables.

Several study limitations were noted. The sources ofsediment, water, and organisms

used to create the microcosms are not described, so results may be confounded by prior

atrazine exposure in the biotic community. The use ofPopulus leaves in both the

macroinvertebrate litter bags and in the bioassay cages distorts the ability ofthe

experiment to capture indirect effects of atrazine on non-producer elements ofthe aquatic

food chain. Finally, as a microcosm experiment with a limited artificial ecosystem (no

macrophytes, fish, seasonality, etc.), the results may not scale up directly to a larger and

more complex natural environment

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

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

for atrazine to affect aquatic communities. However, some limitations were noted, and

the study did not provide a sensitive endpoint (no effects were observed in this study).

Limitations of Study: The macroinvertebrate and crustacean bioassay results are limited

because they provided Populus leaves as substrate/food source, thus preventing potential

indirect effects of atrazine on food or detritus availability. As a whole, the microcosms

were oversimplified in comparison to natural aquatic ecosystems: they contained no

macrophytes or fish, the climate was artificially stable, and the sources ofthe organisms

used to populate them were not provided and may have given the biota previous exposure

to atrazine.

Primary Reviewer: Sara Hendrix, M.S., Staff Scientist, Cambridge Environmental Inc

Secondary Reviewer: Brian Anderson /

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