Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

ECOTOX Record Number and Citation:

Stay, F.S., Larsen, D.P., Katko, A., and Rohm, C.M., "Effects of Atrazine on Community

Level Responses in Taub Microcosms," Validation and Predictability 0/Laboratory

Methods/or Assessing the Fate and Effects o/Contaminants in Aquatic Ecosystems,

ATSMSTP 865, T.P. Boyle, Ed., American Society for Testing and Materials,

Philadelphia, 1985, pp. 75-90 (MRID 45087419).

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 (LOC).

Date of Review:

November 24, 2009

Purpose of Study:

This study examines the effects of atrazine on aquatic plants and animals in Taub

mIcrocosms.

Summary of Study Findings:

Methods: An aquatic microcosm bioassay was developed according the protocol of Taub

(as described in Taub, F.B. and Crow, M.E. in Microcosms in Ecological Research, J.P.

Giesy, Jr., Ed., Technical Information Center, U.S. Department of Energy, 1978, pp. 69-

104). Initially 30 microcosms were constructed. Each microcosm was constructed in a

3.7-L wide-mouth pickle jar, with 3 L of nutrient-rich Taub and Dollar media (see

Limnology and Oceanography, Vol. 9, 1964, pp. 61-74), 200g white silica sand, 0.5-g

ground chitin, and 0.5-g ground cellulose. Microcosms were autoclaved, cooled to

incubation temperature, and then populated with ten species of algae (see below) on Day

0. 1 Each algal species was added to achieve an initial microcosm concentration of 10

1 N.B.: Throughout the review text, Day X refers to the day numbers as defined in the study, with atrazine

application occurring on Day 7. In the Data Summary Table and related tables and spreadsheets, however,

day numbers are listed with Day 0 as the day of atrazine application (study day number minus 7).

IIIIIIIIII

2087836
cells/mL per species. On Day 4, Daphnia magna and other animals were added (Table

1).

Algae species added on Day 0: Anabaena cylindrica, Chlamydomonas reinhardi,

Chlorella vulgaris, Nitzschia kutzigiana, Scenedesmus obliquus. Selenastrum

capricornutum, Ankistrodesmus sp., Lyngbya sp., Stigeoclonium tenue (tentative species

identification), Ulothrix subconstricta (tentative species identification)

Table 1 Animals added to microcosms on Day 4

Organism Initial Number per Microcosm

Daphnia magna (Cladoceran) 6 large (3 gravid), 10 small

Hyalella azteca (Amphipod) 3 mating pairs, 6 small

Cypridopsis sp. (Ostracod) 6

Philodina sp. (Rotifer) 90

Hypotricha (Protozoan) 330

Atrazine stock solution at a concentration of 23 mg/L was prepared from reagent grade

atrazine and Taub and Dollar media. On Day 7, the 27 of30 microcosms with the most

similar dissolved oxygen (DO), algal counts, D. magna counts, and primary productivity

were chosen for the experiment. Appropriate amounts of atrazine solution were added to

achieve given nominal concentrations. Ofthe 27 microcosms used for the experiment,

five were used as controls, five for treatment at an atrazine concentration of 60 Ilg/L,

three at 100 Ilg/L, five at 200 Ilg/L, five at 500 Ilg/L, three at 1000 Ilg/L, and one at 5000

Ilg/L. No additional atrazine was applied to the microcosms after the initial application

on Day 7.

The microcosms were incubated at 20 ± I°C under 900± I00 foot-candle cool-white

fluorescent bulbs (GE F96PG17.CW) with a light cycle of 12 hours on and 12 hours off.

Twice a week from Day 7 to Day 60, measurements of DO, 14C-uptake, chlorophyll a,

and D. magna were made, after scraping periphyton from the walls and mixing the

microcosm. All measurements were made from 5 cm below the surface, following

scraping of periphyton from the container walls and mixing ofthe microcosm contents.

No additional solute was added to make up for losses from evaporation and sample

collection. Atrazine concentrations in the microcosms were measured on Days 7, 28, 53,

and 60.

Analysis methods followed U.S. EPA's "Methods for Chemical Analyses of Water and

Wastes" (1979, EPA-600/4-79-020) or the 1980 American Public Health Association's

"Standard Methods for the Examination of Water and Wastewater" whenever possible.

Atrazine was extracted from a 100-mL water sample with 20 mL of pesticide-grade ethyl

acetate followed by concentration of extract and analysis by gas chromatography with a

nitrogen-phosphorus flame ionization detector. Algae were filtered from 20-mL samples

of microcosm media with glass fiber filters (Millipore AP 40 024 05) and analyzed for

2
chlorophyll a according to Lorenzen, Limnology and Oceanography, Vol. 12, 1967, pp.

343-346. (Acid concentration used for phaeophytin correction was reduced to 8E-03 M

HCl to avoid absorption spectra interferences.) 14C-uptake (primary productivity) was

measured by the 14C-HC0 3 method using 15-mL samples incubated for 1 hour at

microcosm light intensities. A YSI Model 54 dissolved oxygen meter was used to

measure DO. Daphnia magna counts were made on 100 mL of water collected from

each microcosm after gentle mixing with a glass rod to evenly distribute the organisms

without injuring them (contents settled again in 2-4 hours). Animals were counted

immediately and returned to the microcosm.

Net primary productivity and respiration were calculated by estimating the amount of DO

change over a 24-hr light/dark cycle and correcting for oxygen exchange with the

atmosphere. Oxygen exchange with the atmosphere was modeled as a first-order

process: dCldt = K*(Cs-C), where C is DO concentration, Cs is DO concentration at

saturation, with a mass transfer coefficient K that was experimentally determined to be

0.026 1/hr for a 2 L microcosm and proportionally scaled to the actual microcosm

volume. During the dark cycle, the oxygen exchange rate was reduced by respiration,

which was assumed to occur at a constant rate for 12 hours. During the light cycle, the

oxygen exchange rate was increased by net primary productivity. The solution ofthe

resulting set of equations based on known or measured information allowed respiration,

and therefore net primary productivity, to be calculated.

Statistical analyses ofthe data used the folded F and Cochran C tests to determine

homogeneity ofreplicate variances among treatment groups. If, for a particular variable,

replicate variances were not significantly different (p-value < 0.05), a t-test with pooled

variance was used to find the probability of difference between control and treatment

groups; otherwise, non-pooled variance was used with degrees of freedom calculated.

Results:

14C-Uptake

At atrazine treatments of 500, 1000, and 5000 Ilg/L, primary productivity (14C-uptake)

was almost completely inhibited (no p-value cited). At treatments of 60, 100, and 200

Ilg/L, primary productivity was significantly (p-value < 0.05) different from controls

through Day 20. However, the controls' primary productivity decreased sharply after

Day 14 during a D. magna bloom between Days 18 and 35 when nutrients (nitrogen and

phosphorus) generally reached minimal concentrations. After the D. magna bloom

ended, primary productivities were similar between the controls and the 60, 100, and 200

Ilg/L treatments (no p-value cited). See Figure 1. Note that ofthe three highest treatment

groups, only 500 Ilg/L is shown; the 1000 and 5000 Ilg/L treatment results were similar

to the 500 Ilg/L treatment results. (Magnitudes are not described explicitly in the study

text but are shown in the figure.)

3
Dissolved Oxygen

Dissolved oxygen was measured at the end ofthe dark and light periods on measurement

days. DO concentrations in the 500, 1000, and 5000 ~g/L treatment microcosms

decreased sharply until after D. magna bloom after both light and dark periods (no pvalues cited); after the bloom ended, the DO after dark periods approached control levels,

but the DO after light periods gradually approached DO saturation (9.07 mg/L) while

remaining significantly (p-value < 0.01) less than the controls for the rest ofthe

experiment. The microcosms treated with 60, 100, and 200 ~g/L atrazine had DO

concentrations between the higher treatment levels and the controls (on Day 11, DO

concentrations were lower than controls withp-value < 0.01 after both light and dark

periods), and had recovery of DO after both photoperiods to control levels (no significant

difference at p-value < 0.05). On the maximum primary productivity day, Day 14, DO

after the light period was similar to the controls for treatments of 60 and 100 ~g/L, but

200 ~g/L treatments had lower DO after the light period than the controls (p-value <

0.01). During the D. magna bloom, DO in the 100 and 200 ~g/L treatments were

generally significantly less than controls (p-value < 0.05), whereas DO in the 60 ~g/L

treatments was significantly (p-value < 0.01) less than controls only on Day 21. See

Figure 2 for DO after light periods and Figure 3 for DO after dark periods. Note that of

the three highest treatment groups, only 500 ~g/L is shown; the 1000 and 5000 ~g/L

treatment results were similar to the 500 ~g/L treatment results. (Magnitudes are not

described explicitly in the study text but are shown in the figures.)

Net Productivity and Respiration

Net productivity and respiration were estimated from DO changes over the light/dark

cycle and corrected based on the deviations of measured DO from saturation. The

correction resulted in maximum changes of 1.8 and 1.5 mg 02/L/12 h for net productivity

and respiration, respectively. Net productivity for the higher treatment groups (500,

1000, and 5000 ~g/L) was significantly (p-value < 0.01) less than controls and did not

recover during the experiment, often falling below zero (respiration greater than

production). For the 200 ~g/L treatments, net productivity remained significantly (pvalue < 0.01) less than controls until after the D. magna bloom had passed, then

recovered to near control levels (no p-value cited). For the 60 and 100 ~g/L treatments,

net productivity was similar to controls both before and after the D. magna bloom (no pvalue cited), but during the bloom were lower than controls, particularly during the

growth phase ofthe bloom when differences were significant at p-value < 0.01. See

Figure 4. Note that ofthe three highest treatment groups, only 500 ~g/L is shown; the

1000 and 5000 ~g/L treatment results were similar to the 500 ~g/L treatment results.

(Magnitudes are not described explicitly in the study text but are shown in the figure.)

Respiration for the higher treatment groups remained at pretreatment levels immediately

following atrazine treatment and then gradually increased for the rest ofthe experiment.

Respiration for the 200 ~g/L treatment group remained lower than controls until the end

ofthe D. magna bloom, then recovered to near control levels (no p-values cited). For the

4
60 and 100 /lg/L treatments, respiration was similar to controls both before and after the

D. magna bloom (no p-values cited), but during the bloom were generally lower than

controls (although these differences were not statistically significant at p-value < 0.05

due to high variation among the replicate microcosms). See Figure 5. Note that ofthe

three highest treatment groups, only 500 /lg/L is shown; the 1000 and 5000 /lg/L

treatment results were similar to the 500 /lg/L treatment results. (Magnitudes are not

described explicitly in the study text but are shown in the figure.)

P,/Rni Ratio

The ratio between primary productivity and respiration was also examined. This measure

remained above 1 in the control for the first 20 days ofthe experiment, and remained near

1 for the rest ofthe experiment. In the higher treatment groups (500, 1000, and 5000

/lg/L), the Pn/Rni ratio decreased sharply to under 0.4 and remained significantly (p-value

< 0.01) less than controls for much ofthe remainder ofthe experiment. The Pn/Rni ratio

for the 200 /lg/L treatment group also remained significantly (p-value < 0.01) less than

the controls until after the D. magna bloom, when it recovered to near 1. For the 60 and

100 /lg/L treatments, the Pn/Rni ratio did not differ significantly from control levels at pvalue < 0.05 throughout the experiment. See Figure 6. Note that ofthe three highest

treatment groups, only 500 /lg/L is shown; the 1000 and 5000 /lg/L treatment results

were similar to the 500 /lg/L treatment results. (Magnitudes are not described explicitly

in the study text but are shown in the figure.)

14C-Uptake/Chlorophyll a Ratio

The 14C-uptake/chl a ratio, an index ofthe effectiveness ofthe algal photosynthetic

systems, was the most sensitive measure ofthe effects of atrazine. Throughout the

experiment, the 14C-uptake/chl a ratio was significantly (p-value < 0.01) lower in all

treatment groups than in the controls, with somewhat stronger effects noted for the higher

treatment groups (500, 1000, and 5000 /lg/L) compared to the lower treatment groups.

The ratio did not seem to be significantly affected by the D. magna bloom. Low numbers

for the ratio resulted from a combination ofreduced 14C-uptake as well as increased

chlorophyll a per unit biomass. See Figure 7. Note that ofthe three highest treatment

groups, only 500 /lg/L is shown; the 1000 and 5000 /lg/L treatment results were similar

to the 500 /lg/L treatment results. (Magnitudes are not described explicitly in the study

text but are shown in the figure.)

5
'2.00

.c -0 ug/r

L 60 ug/l

1.76 0-'" 100 vg/I

U 6--6200 UA/I

01 01:l 500 ug/l

E 1.60

~.

1.25 ;:;

f=

u 1.00

;:j

Cl

0 0.76 a:

Q.

>- 0.60 a:

<t

:e 0.25

a:

l1.

20 25' 30 35 40 45 50 55 60 65

DAY NUMBER

Figure 1. Mean primary productivity e4C-uptake) of microcosms exposed to atrazine. Points of

significant (p-value < 0.05) linear contrast from control are presented with darkened symbols. The

shaded region represents the D. magna bloom.

12.0 _0 ug /l

0-<> 60 VV/I

, 1.0 0--0 100 \.I~/~

"""0 200 ugrJ

- o--<J 500 uo"\ 10.0 01

E 9.0

Z

w 8.0

C)

)0- 7.0

X

0 6.0

Cl

W 6.0

>.... 4.0 0

<I)

<Il 3.0

0 2.0

1.0

0.00 6 10 16 ~o 25 30 35 40 46 60 Sf> 60 66

DAY NUMBER

Figure 2. Mean DO concentration at the end of the 12-hour dark cycle in microcosms exposed to

atrazine. Symbols as in Figure I.

6
18.0

17.0

16.0

:r:. 15.0

Ql 14.0

E·13.0

i 12.0

11.0

>- 10.0

9.0

o 8.0

w 7.0

6.0

o 5.0

4.0

o 3.0

2..0

1.0

0.0 0

Figure 3.

atrazine.

9.5

86

.r:. 7.5 N

... 6.5

-

<5 5.5

1;71 4.5

E 3.5

)0'

I- 2.5

:; 1.5 i=

U 0.5

;:)

0 ·0.5

0

IX: ·1.5

D-

·2.5

.3.6

0

Figure 4.

Figure 1.

- 0 vg/l

0-0 &0 vQII

0--0 100 ug/l

6--0 200 u011

500 Ugll

5 10 15 20 2.6 30 35 40 45 50 65 60 65

DAY NUMBER

Mean DO concentration at the end of the 12-hour light cycle in microcosms exposed to

Symbols as in Figure 1.

- 0 vgll

0-<> 60 vgll

0--<> 100 vgll

6-- -0 200 ug/l

0-0 500 vgll

5 10 15 20 25 30 36 40 45 60 65 60 6,6

DAY NUMBER

Mean net primary productivity (Pn) in microcosms exposed to atrazine. Symbols as in

7
9,0

8,0

.c

N 7,0

L

0 6.0

Ol

e 6,0

Z

0 4.0

et 3.0 IX:

0:

(I) 2.0 w

IX:

1.0

0.0

0

Figure 5.

Figure 1.

- 0 ug/l

0-<> 60 ug/l 0-.., 100 "Il/l

ll--l> 200 Ug/l

o-<J 500 ug/l

5 to 15 20 26 30 36 40 46 60 56 60 66

DAY NUMBER

Mean 12-hour dark respiration (Rni) in microcosms exposed to atrazine. Symbols as in

o 4.0

j:

c:t: a: 3.0

Z

o 2.0 j:

<

1,0

(I)

0.0

"-

-1.0

>

j:

U -2.0

:I.

o

·3,0

0..

-4 ,0 .........LU~UJ.J'-"

o

- 0 ug/l

C>-O 60 ug/l

0--0 100 ug/l

b--€> 200 uglJ

0--0 500 ug/l

50 55 60 65

Figure 6. Mean net primary productivity/respiration (Pn/Rni) ratios in microcosms exposed to

atrazine. Symbols as in Figure 1.

8
o.ou.........u.~~

o 5 10 1& 20 25 30 35 40 45 60 155 60 66

DAY NUMBER

Figure 7. Mean primary productivity/chlorophyll a e 4C-uptake/chlr a) ratios in microcosms exposed

to atrazine. Symbols as in Figure 1.

Data Summary Table:

Nominal Time.

Atrazine Weighted

Magnitude of Concen- Day ofStudy Average Did

Effect Effect relative tration Effect Atrazine Recovery Comments

to controls (initial Occurred) Concentration Occur- if

test cone) fromDayOto so, when?

(pg/L) When Effect

Occurred

4 Recovery after

(less than D. magna

bloom.

~40% 60 (53) controls at 52 Ilg/L Yes - Day Magnitude of p<0.05 28 effects through Day estimated from 20) Figure 1.

4 Recovery after

Primary (less than D. magna

bloom. productivit ~55% 100 (84) controls at 82.1 Ilg/L Yes - Day Magnitude of

ye 4C p<0.05 28 effects uptake) through Day estimated from 20) Figure I.

4 Recovery after

(less than D. magna

bloom.

~70% 200 (170) controls at 164.1 Ilg/L Yes - Day Magnitude of p<0.05 28 effects through Day estimated from 20) Figure I.

9
Time Nominal Weighted Atrazine Average Did

Magnitude of Concen- Day ofStudy Atrazine Recovery Effect Effect relative tration Effect Comments Concentration Occur- if to controls (initial Occurredl

fromDayOto so, when?

test cone) When Effect (pg/L) Occurred

Magnitude of

effects 500 (430) 4 414.3Ilg/L No estimated from ~90%

Figure 1.

Magnitude of

1000 effects 4 790.2Ilg/L No estimated from ~90% (820)

Figure 1.

Magnitude of

5000 effects 4 3781 Ilg/L No estimated from ~90% (3980)

Figure 1.

Recovery after

D. magna

~15-20% 4 (lower than bloom.

52 Ilg/L Yes - Day after both 60 (53) controls at Magnitude of 28 photoperiods p<O.OI) effects

estimated from

Figures 2-3.

Recovery after

D. magna ~20% after 4 (lower than bloom. Yes - Day Magnitude of dark period, 100 (84) controls at 82.1 Ilg/L 28 effects ~30% after p<O.OI)

estimated from light period

Figures 2-3.

Recovery after

D. magna ~45% after 4 (lower than bloom. Dissolved

Yes - Day Magnitude of oxygen dark period, 200 (170) controls at 164.1 Ilg/L 28 effects ~55% after p<O.OI)

estimated from light period

Figures 2-3.

~60% after Magnitude of

dark period, effects 500 (430) 4 414.3Ilg/L No ~70% after estimated from

light period Figures 2-3.

~60% after Magnitude of

dark period, 1000 effects 4 790.2Ilg/L No ~70% after (820) estimated from

light period Figures 2-3.

~60% after Magnitude of

dark period, 5000 effects 4 37811lg/L No ~70% after (3980) estimated from

light period Figures 2-3.

10
Nominal Time

Atrazine Weighted

Magnitude of Concen- Day ofStudy Average Did

Effect Effect relative tration Effect Atrazine Recovery Comments

to controls (initial Occurred] Concentration Occur- if

test cone) from Day Oto so, when?

(pg/L) When Effect

Occurred

Yes-Day Recovery after

21 (less than D. magna

controls at bloom peaked.

~60% 60 (53) 14 51.1 flg/L p<O.OI Magnitude of

during effects

growth estimated from

period) Figure 4.

Yes - Day Recovery after

28 (less than D. magna

controls at bloom.

~55% 100 (84) 4 82.1 flg/L p<O.OI Magnitude of

during effects

growth estimated from

period) Figure 4.

Net Recovery after

primary Yes - Day D. magna

28 (less than bloom. productivit ~100% 200 (170) 4 164.1 flg/L controls at Magnitude of

y p<O.O 1 until effects

after bloom) estimated from

Figure 4.

No (less Magnitude of

<100% (went 500 (430) 4 414.3 flg/L than controls effects

negative) at p<O.OI for estimated from

duration) Figure 4.

No (less Magnitude of

<100% (went 1000 4 790.2 flg/L than controls effects

negative) (820) at p<O.OI for estimated from

duration) Figure 4.

No (less Magnitude of

<100% (went 5000 4 3781 flg/L than controls effects

negative) (3980) at p<O.OI for estimated from

duration) Figure 4.

Recovery after

D. magna

Yes - Day bloom.

<10% 60 28 49.3 flg/L Magnitude of 32 effects

estimated from

Respiration Figure 5.

Recovery after

D. magna

Yes - Day bloom.

<20% 100 28 73 flg/L Magnitude of 32 effects

estimated from

Figure 5.

11
Nominal Time

Atrazine Weighted

Magnitude of Concen- Day ofStudy Average Did

Atrazine Recovery Effect Effect relative tration Effect Concentration Occur- if Comments

to controls (initial Occurred! from Day 0 to so, when?

test cone) When Effect (J-lg/L) Occurred

Partial

recovery after

D. magna

200 4 164.1 Ilg/L Somewhat - bloom. ~55% Day 35 Magnitude of

effects

estimated from

Figure 5.

Magnitude of

500 4 414.3Ilg/L No effects ~65% estimated from

Figure 5.

Magnitude of

1000 4 790.2Ilg/L No effects ~65% estimated from

Figure 5.

Magnitude of

5000 4 3781 Ilg/L No effects ~65% estimated from

Figure 5.

Recovery after

D. magna

Yes - Day bloom peaked.

~25% 60 14 51.1 Ilg/L 21 Magnitude of

effects

estimated from

Figure 6.

Recovery after

D. magna

Yes - Day bloom peaked.

Ratio of net ~35% 100 14 77 Ilg/L 21 Magnitude of

effects

primary estimated from

productivity Figure 6.

to Recovery after

respiration Yes - Day D. magna (Pn/Rni) 28 (less than bloom.

~100% 200 4 164.1 Ilg/L controls at Magnitude of

p<O.OI until effects

after bloom) estimated from

Figure 6.

No (less Magnitude of

>100% (went 500 4 414.3Ilg/L than controls effects

negative) at p<O.Ol for estimated from

most days) Figure 6.

>100% (went 1000 4 790.2Ilg/L No (less Magnitude of

negative) than controls effects

12
Nominal Time

Atrazine Weighted

Magnitude of Concen- Day ofStudy Average Did

Effect Effect relative tration Effect Atrazine Recovery Comments

to controls (initial OccurredJ Concentration Occur- if

from Day Oto so, when? test conc) When Effect (pg/L) Occurred

at p<O.OI for estimated from

most days) Figure 6.

No (less Magnitude of

>100% (went 5000 4 3781 flg/L than controls effects

negative) at p<O.OI for estimated from

most days) Figure 6.

No (less Magnitude of

~50% 60 (53) 4 52 flg/L than controls effects

atp<O.OI for estimated from

most days) Figure 7.

No (less Magnitude of

~55% 100 (84) 4 82.1 flg/L than controls effects

at p<O.OI for estimated from

most days) Figure 7.

Ratio of No (less Magnitude of

primary ~65% 200 (170) 4 164.1 flg/L than controls effects

productivit at p<O.OI for estimated from

y to most days) Figure 7.

chlorophyll No (less Magnitude of

a e4C- ~80% 500 (430) 4 414.3 flg/L than controls effects

uptake / at p<O.OI for estimated from

chlr a) most days) Figure 7.

No (less Magnitude of

~80% 1000 4 790.2 flg/L than controls effects

(820) at p<O.OI for estimated from

most days) Figure 7.

No (less Magnitude of

-80% 5000 4 3781 flg/L than controls effects

(3980) at p<O.OI for estimated from

most days) Figure 7.

I Only atrazIlle effects that occurred pnor to the daphmd bloom (pnor to Day 18) are consIdered III the

"Cosm Data Points and Exposure Profiles" spreadsheet.

Bolded values are those data points specified in the "Cosm Data Points and Exposure Profiles" spreadsheet.

The table below is a linked object showing the calculations for the time weighted

averages used in the Data Summary Table. Effect day concentrations did not occur on

days when atrazine concentrations were measured, and were interpolated in a piecewise

linear fashion (see "Stay 1985 TWA.xls", sheet "Stay1985_Attach5" for calculations and

a graph showing the results for the nominal 60 /lg/L case).

13
Nominal Day 0 Effect TWA

Cone. Day of Cone. Day Cone. **

Endpoint (ug/L) Effect (ug/L) Conc.* (ug/L)

primary prod. 60 4 52.4 51.6 52.0

primary prod. 100 4 84.1 80.0 82.1

primary prod. 200 4 169.3 158.8 164.1

primary prod. 500 4 430.2 398.5 414.3

primary prod. 1000 4 820.3 760.2 790.2

primary prod. 5000 4 3980 3581.9 3781.0

DO 60 4 52.4 51.6 52.0

DO 100 4 84.1 80.0 82.1

DO 200 4 169.3 158.8 164.1

DO 500 4 430.2 398.5 414.3

DO 1000 4 820.3 760.2 790.2

DO 5000 4 3980 3581.9 3781.0

NPP (Pn) 60 14 52.4 49.7 51.1

NPP (Pn) 100 4 84.1 80.0 82.1

NPP (Pn) 200 4 169.3 158.8 164.1

NPP (Pn) 500 4 430.2 398.5 414.3

NPP (Pn) 1000 4 820.3 760.2 790.2

NPP (Pn) 5000 4 3980 3581.9 3781.0

Respiration 60 28 52.4 46.3 49.3

Respiration 100 28 84.1 62.0 73.0

Respiration 200 4 169.3 158.8 164.1

Respiration 500 4 430.2 398.5 414.3

Respiration 1000 4 820.3 760.2 790.2

Respiration 5000 4 3980 3581.9 3781.0

Pn/Rni 60 14 52.4 49.7 51.1

Pn/Rni 100 14 84.1 69.9 77.0

Pn/Rni 200 4 169.3 158.8 164.1

Pn/Rni 500 4 430.2 398.5 414.3

Pn/Rni 1000 4 820.3 760.2 790.2

Pn/Rni 5000 4 3980 3581.9 3781.0

14C/ch1r a 60 4 52.4 51.6 52.0

14C/ch1r a 100 4 84.1 80.0 82.1

14C/chlr a 200 4 169.3 158.8 164.1

14C/chlr a 500 4 430.2 398.5 414.3

14C/ch1r a 1000 4 820.3 760.2 790.2

14C/ch1r a 5000 4 3980 3581.9 3781.0

* interpolated from chemograph in Stay85_Attach5 (piece-wise linear

** average of Day 0 and Effect Day concentrations

14
Reviewer Comments:

The methodology is well documented. All analytical methods as well as statistical

procedures are fully described. The few instances where the authors deviate from

published standard practice are supported with clear explanations.

The study uses highly controlled microcosms as opposed to the mesocosms of primary

interest for the literature review. Because ofthe more controlled conditions, there is little

chance of confounding from environmental factors; however, it is likely that communitylevel responses are unrealistic in such a controlled setting. In particular, the Daphnia

bloom, which occurred between Day 18 and 35, interacted significantly with the effects

ofthe atrazine to create the effects observed in the aquatic communities. Therefore, only

atrazine-related effects that occurred before the daphnid bloom on Day 18 ofthe study

were considered. Given the highly controlled nature ofthe experiment, the relevance of

the study results to mesocosms or natural field systems is uncertain.

The authors note two factors making the Taub microcosms different from the seminatural pond communities ofdeNoyelles et al. (Ecology 63:5, pp. 1285-1293, 1982 as

well as the 1985 study in the same volume as this study). First, the microcosms are very

nutrient-rich and could be considered hypereutrophic, whereas the ponds are roughly

mesotrophic and have much lower oxygen demand. Second, reaeration is different

between the two systems. They also note that the 14C-uptake/chl a ratio, the most

sensitive measure to atrazine they found, is the measure that is least similar between their

results and deNoyelles et al (1982).

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

Rationale for Use: Although the study has limited utility, given the Daphnia magna

bloom occurring between Days 18 and 25 (in all controls and treatment groups), the

results document decrease in community-level endpoints for phytoplankton at all atrazine

treatment levels (:::: 60 ug/L) with no recovery at atrazine concentrations of 500, 1000, and

5000 ug/L and recovery within 32 days at treatment levels of 60, 100, and 200 ug/L.

Limitations of Study: The use of microcosms allowed a highly controlled setting;

however, the Daphnia magna bloom occurring between Days 18 and 35 strongly

interacted with the effects of atrazine treatments and is not to be commonly expected in

the real world. According to the study authors; the nutrient status ofthe control and

treated microcosms could not be assessed because samples collected prior to day 30 of

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the study were contaminated. Further details on the "contamination" issue were not

provided. Given the uncertainties associated with the daphnid bloom on Days 18-35,

only those atrazine-related effects that occurred prior to Day 18 ofthe study were

considered. Additionally, the reaeration regime of a pickle jar is much different than that

of a pond. Results, therefore, have limited applicability to mesocosms or natural aquatic

systems.

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

Secondary Reviewer: Anita Pease, M.S., Senior Biologist, Environmental Fate and

Effects Division, U.S. Environmental Protection Agency. {}X(t~ 0/t3/1 \

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