Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

ECOTOX Record Number and Citation:

Dewey, S.L. 1986. Effects ofthe herbicide atrazine on aquatic insect community

structure and emergence. Ecology. 67:148-162 (MRID 47543611).

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 potential effects of atrazine to aquatic plants and animals

(particularly benthic insects) in experimental ponds (mesocosms).

Summary of Study Findings:

Methods: The study was part ofthe 80S-day experimental pond study described in

deNoyelles et ai., 1989, and also described in Carney, 1983 and deNoyelles et ai., 1994.

Eight experimental ponds ofsurface areas 0.045 ha each at the University of Kansas

Nelson Environmental Study Area were used. See Figure 1 for a diagram ofthe

experimental pond system. The ponds were left full, uncontaminated, and undisturbed

for 17 months before being drained on May 20, 1981 and refilled from the storage

reservoir on May 30, 1981 to a depth of 2.1 meters. At that time ponds were stocked

with bluegill sunfish (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), and

channel catfish (lctalurus punctatus). In May 1982, four adult grass carp

(Ctenopharyngodon idella) were added to each pond, and in June 1982, 10% of each

pond's surface area was fenced off to exclude the grass carp. Since the exclusion areas

were established after this study started, they are not part ofthis study's experimental

design.

11111••111

2087825
In 1981, two replicate ponds at 3 atrazine treatment levels (0, 20, and 100 Ilg/L) were

prepared using reagent grade 97% atrazine, and two additional ponds were prepared at 20

Ilg/L using commercial atrazine (CO-OP liquid atrazine, EPA registration number 1990-

318,41 % active ingredient). The ponds with commercial atrazine were converted to 500

Ilg/L treatment using reagent grade atrazine on May 30, 1982. At this time all other

ponds received a second annual atrazine application, and additionally the ponds were all

brought back to 2.1 m depth by adding well water. 1 Periodic atrazine concentration

measurements were made. Insect emergence samples were taken from the 0 (control),

20, 100, and 500 Ilg/L treatment ponds over 16 weeks beginning on June 8, 1982. Two

additional samples were taken in May before the 20 Ilg/L commercial treatment ponds

were converted to 500 Ilg/L, and one preliminary control pond sample was taken on April

24. Water temperature was measured between 1600 and 1800,30 cm above the pond

bottom in the center of each pond, on the first day of each sampling period. Additionally

water quality measurements, taken "periodically" (no further details provided) as part of

the larger mesocosm study, included water depth, morning oxygen concentration at 0.5 m

below the water surface, and turbidity.

Adult insect emergence was sampled using partially submerged funnel emergence traps.

The traps (modifications of earlier designs - 6 papers from 1954-1980 are cited)

consisted oftransparent rigid vinyl funnels attached to 3.76-L semitransparent

polyethylene jars, each jar with two ventilation windows covered with 175-11 nylon mesh.

In each pond, four emergence traps were suspended from the access pier, and were set for

48 hours (except for one 24 hour sample period that occurred on June 12-13) before

collection. Following collection, jar contents were preserved in 80% ethanol, then later

sorted and identified to lowest possible taxon (usually species) using keys and

descriptions from several sources.

2 Several chironomid species required slide mounting

in Euparal for identification to species. Females of Orthocladiinae, Chironomini, and

Tanytarsini (Chironomidae) groups could not be identified to species due to the lack of

comprehensive keys available. Females and severely damaged males of most families

could not be identified further than tribe or genus.

Several measures were used to describe the insect communities: percentage similarity

(PS), abundance (the number ofindividuals in a community or sample), species diversity

(H'), species richness (S, the total number ofspecies in a sampled community), and the

species evenness or equitability index, J'. Definitions ofPS, H', and J' are:

1 Reviewer note: the 200 IlgiL treatment ponds were also created at this time, according to Carney 1983,

but Dewey does not mention them, presumably because they were not sampled in the insect emergence

study.

2 Ross, 1944 ("The caddis flies, or Trichoptera, ofIllinois" from the Illinois Natural History Survey

Bulletin); Townes, 1945 ("The nearctic species ofTendipedini [Diptera, Tendipedidae (=Chironomidae)]"

from American Midland Naturalist); Burks, 1953 ("The mayflies, or Ephemeroptera, ofIllinois" from the

Illinois Natural History Survey); Roback, 1971 ("The adults of the subfamily Tanypodinae in North

America (Diptera: Chironomidae)" from Monographs ofthe Academy of Natural Sciences of

Philadelphia); and Oliver, 1981 ("Chironomidae" in pages 423-458 ofthe Manual ofnearctic Diptera, vol.

I, Canada Department of Agriculture Research Branch Monograph 27).

2
s'

PS =1- 0.5· L!Pai - Phil i~1

s

H'= - LPi logpi i~1

J' = H' / H' = H' /log(S) max

where Pi is the pro~ortion of individuals comprised by the i

th species (Pai and phi, the

proportion ofthe l species in community a or b, respectively), and s' in the PS equation

is the total number ofspecies in both communities being compared.

Statistical tests were conducted for significance and trends. One-way analysis of

variance (ANOVA) was used with critical levels at a = 0.10 for the F tests to test for

significant differences, and linear regression of mean values with logarithm atrazine

concentration used to evaluate trends. If a variable had a significant ANOVA result, the

Student-Newman-Keuls (SNK) a posteriori test was used to determine significant

differences among all treatments. Other methods were dendrogram cluster analysis of

ponds based on percentage similarities, and the Smimov two-sample test (on temporal

emergence-frequency curves, to test for significant distributional similarity). Sample

totals from both replicate ponds were used for between-treatment comparisons testing for

significant differences.

3
o 500 o 20 T 20 500

<

N

20 n

Figure 1. Experimental pond system layout. Numbers below ponds refer to nominal atrazine

treatment level (p.1g/L); ponds with 5 and 200 p.1g/L were not used in this study. T = varied treatment;

D = pond was drained for much ofthe study period. Numbers inside ponds are the unique pond

labels, 1-8, used in some data tables.

Results: Atrazine concentrations decreased in all ponds over the study period by an

average of 0.2 flg/L/day after addition on May 30, 1982. Pond water depths decreased

due to evaporative loss at an average rate of 5 cm/wk; however, water depths did not

differ significantly between replicates (ANOYA). Mean pond temperatures changed

seasonally (low of l7.5°C on May 8, high of30.4°C on August 1) and again did not

differ significantly between replicate pairs (ANOYA) (a graph oftemperature over time

is presented in the paper as Figure 2, but not reproduced here). Oxygen concentrations

did not significantly vary among treatment levels (ANOYA) or change with time (linear

regression) and ranged from 5.1 to 11.0 mg/L (mean = 7.46 mg/L). Mean turbidity

varied significantly with treatment level (ANOYA, p-value < 0.10), and increased with

increasing atrazine concentration up to 100 flg/L (see Table 2) (regression results: r

2 =

0.85, p-value < 0.10 according to the table, but the text states r = 0.82, which is

inconsistent). Species richness and total abundance of emerging benthic insects were

regressed to turbidity to see ifturbidity was a significant predictor ofthese variables, but

results were not significant. The study author attributes changes in turbidity with

atrazine-related elimination of emergent and submergent vegetation resulting in windinduced mixing of benthic and limnetic zones.

4
Phytoplankton and macrophyte community responses are discussed briefly and

qualitatively, with references to deNoyelles et al., 1982, deNoyelles and Kettle, 1983, and

Carney 1983. Qualitative personal observations ofperiphyton are noted: on the

permanent walkway supports, periphyton in control ponds was dense and green with

thicknesses of a few mm up to 4-5 cm, but was absent on structures in 100 Ilg/L and 500

Ilg/L ponds.

Forty-seven (47) insect species were collected from emergence traps in all ponds between

May 8 and September 26, 1982. All ofthese species except for Chaoborus punctipennis

have benthic or epiphytic habitat as larvae, and for this reason C. punctipennis was

considered separately from the benthic insect community (not included in the benthic

community measures). For all species collected, the trophic habitat, microhabitat, and

lifestyle are listed with references in the study's Table 1 (not reproduced here). The traps

used in the study did not sample the Odonata anddytiscid beetles, which crawl out ofthe

water to emerge, or the baetid mayflies and ceratopogonid flies, although both groups are

known to be present in the pond benthos and to emerge in the pelagic zone.

The abundances (total numbers) ofthe chironomid Labrundinia pilosella varied

significantly among treatments (ANOYA, p-value < 0.005), declining drastically even at

atrazine concentrations of20 Ilg/L (SNK, no p-value provided, see Table 2). Emergence

rates of Cricotopus cf. trifasciatus, Parakieferiella cf. coronata, Parachironomus

chaetoalus, P. tenuicaudatus, and the remainder ofthe Chironomini (unidentified)

showed similar responses at this low treatment level (raw data provided in the appendix;

see Table 3), but significant heterogeneity among treatments was not detected, probably

because ofthe small numbers involved. Species equitability, J', and total abundance of

emerging benthic insects both varied significantly among treatment levels (ANOYA, pvalue = 0.05). J' increased between controls and 20 Ilg/L, but declined on the higher

treatment levels (statistical significance results were mixed; see Table 2). Mean values of

total abundance and species richness S declined significantly with atrazine addition

(linear regression, r

2 = 0.90 and 0.93, p-value < 0.10 and < 0.15, respectively; see Figure

2 and Table 2) and were significantly reduced at the 20 Ilg/L level (SNK, no p-value

provided, Table 2). H', the diversity index, declined somewhat with treatment, but

results were not significant (see Table 1).

Cluster analysis was performed on all eight ponds based on taxonomical percentage

similarity (Figure 3). Differences between controls and treatments were clear, but the

treatment levels did not show a clear identification ofreplicate pairs. In particular, pond

8 (the 500 Ilg/L treatment pond, physically located between the two controls) was shown

to be most similar to a 20 Ilg/L pond, which may indicate confounding effects such as

immigration and egg deposition occurring from proximity to controls. The tendency for

pond 8 to provide samples similar to a lower-concentration pond is further demonstrated

by examination ofthe raw data in Table 3.

5
To further investigate the trends, insects were grouped into two feeding guilds: predatory

and nonpredatory. The former group includes omnivores and is expected to have the

least dependence on periphyton for food supply. The latter group consists of herbivores,

including collector-gatherers, scrapers, selective grazers, macrophyte leaf-miners, and

filterers of benthic particles, and is expected to depend on periphyton for food supply. As

can be seen in Table 2, the nonpredatory insect community declined significantly in

abundance and richness significantly with any atrazine treatment level (ANOVA with pvalue < 0.1 0 [abundance] and < 0.1 0 [richness], SNK, and linear regression with r

2 =

0.94 [abundance] and = 0.90 [richness] and p-value < 0.10 [abundance] and < 0.05

[richness]) (see also Figure 4). The nonpredator abundance and richness appeared more

sensitive to atrazine treatment than the predatory insect community (see Table 1, no

statistics provided). The author also describes the raw data (see Table 3; predators

include Ablabesmyia, Procladius, and the pelagic predator Chaoborus punctipennis, and

nonpredators include Labrundinia pilosella, species of Cricotopus, most Chironomini,

Caenidae, Hexagena limbata, and Oxythira pallida) as supporting this differential

atrazine sensitivity by feeding guild, although no statistics are provided. Various

mechanisms for the differential sensitivity are proposed.

Temporal emergence trends were investigated for the 11 species collected that emerged

from all treatments in sufficient numbers to allow statistical (Smirnov two-sided, twosample test) and/or visual comparison oftemporal emergence distribution curves. Three

ofthe 11 species are predatory and eight are nonpredatory (herbivorous). Ofthe

predatory species, two (Procladius bellus and Chaoborus punctipennis) were very

abundant, and showed no statistically significant difference between control and any

atrazine treatment level, while Ablabesmyia annulata was not abundant enough for

statistical comparison and did not visually appear different (see Figure 5). Ofthe

herbivorous species, Cladotanytarsus viridiventris showed no statistically significant

difference between control and any treatment level. Labrundinia pilosella and Oxyethira

pallida were analyzed by comparing the controls with all atrazine treatments combined,

finding statistical significance in the latter but not in the former species (see Figure 6; no

p-value provided). Visual inspections only were possible on Dicrotendipes modestus,

Parachironomus chaetoalus, and Cricotopus cf. sylvestris temporal emergence

distributions, but these species all clearly showed earlier emergence in the atrazine

treated ponds (see Figure 7). The single Parachironomous tenuicaudatus from a

treatment pond emerged towards the early side ofthe distribution for controls, and Caenis

simulans showed no clear change in emergence pattern under atrazine treatment (Figure

7). The author speculates that early emergence may occur as a stress response to atrazine

treatment (perhaps indirectly as a result of decreased food supply for the herbivores),

although some herbivorous species showed no change in emergence time due to

treatment.

6
40

......

V) 35

(/)

(/)

w 30 S = 18.40 - 2.85 log C

Z

I 25

\

()

a::

rJ) 20

W

() 15 +,,--- j W

ll.

(/)

10 f

5

400

« 300

W A 127.0 - 32.7 log C ()

z

<:

a 200

z

:::l

co

<:

100

t + +

0

0 100 200 300 400 SOD

ATRAZINE CONCENTRATION ()jg/L)

Figure 2. Benthic insect community response to atrazine concentration in eight experimental ponds

over the total sampling period. Vertical bars represent range ot'two replicate samples. Lines fitted

by the linear regression equation shown.

7
ATRAZINE

POND NO. CONC.(ug/U

7

5

6

3

8

4

2

500

100

100

20

500

20

a

a

30 40 50 60 70 80 90 100

PERCENT FAUNAL SIMILARITY

Figure 3. Dendrogram cluster analysis of eight experimental ponds based on percentage similarity

(PS) of the benthic insect community.

=1

250

200

UJ

U

Z

« 150

0

z

::l

ltl

« 100

50

0

NONPREDATORS

NP = 84. 1 - 3 O. 1 log C

o 100 200 300 400 500

ATAAZINE CONCENTRATION ()Jgl L)

Figure 4. Nonpredatory benthic insect community response to atrazine concentration in eight

experimental ponds over the total sampling period. Vertical bars represent range of two replicate

samples. Line fitted by the linear regression equation shown.

8
A. Prock/diUI> bellvs

5~

45

u.J

0

Z 35 q

a

z

:) ~~

m

«

1 5

B. CtI'JoborU$ PiA'lCflpor/nt$

c. Ablac/!!imp'o

oflfll.Jla!c

MAY JUNE JULY

DATE

AUGUST SEPTEMBER

Figure 5. Emergence frequency distributions of three abundant predatory insect species. Solid: the

combined numbers of individuals emerging from the six atrazine-treated ponds. Hollow: the

combined numbers of individuals emerging from the two control ponds.

9
25

1<r ,,, Cl

Z

c, ~_••L- ""'.""'.L...1JLi,

.t. C'I'JdManylan'l5

vir"'d/~J6\.,tl'is

o

l.!AY .JUNE .JULY

DATE

AUGUST ~; [P 1L f,' BEll

Figure 6. Emergence frequency distributions of three abundant herbivorous insect species. Solid:

the combined numbers of individuals emerging from the six atrazine-treated ponds. Hollow: the

combined numbers of individuals emerging from the two control ponds.

10
A Dicro/en dipt'5

modest"s

EI Por{}~h..,on()m()s

ch'Jelooliis 10

w

U

7:

«

C'l

2:

:;

ro

<l'.

n C G,icotop"s ct, Sy,Wislr.• ,

~~u.-..L..\.--U--l.J,l.,I....,ll-iJ,----__

o 1''a1(J{:nirONJf!)I.,'S

'f!''''ili:~iJ(Joh./$

{; COf.'tlis !i!mvlonS

ij 14

MAY

B '~7 10 ir,t 2GZS

JU~Y

DATE

AUGUST

11 i i

19 :?e

~;EPl EMBER

Figure 7. Emergence frequency distributions of five moderately abundant herbivorous insect

species. Solid: the combined numbers of individuals emerging from the six atrazine-treated ponds.

Hollow: the combined numbers ofindividuals emerging from the two control ponds.

11
Table 1. Benthic insect predators (excluding Chaoborus punctipennis) vs. nonpredators emerging

from experimental ponds (from Table 2 ofstudy). Diversity indices also provided (taken from study

text).

Nominal atrazine concentration

oflg/L 20 flg/L 100 flg/L 500 flg/L

Pond number

I 2 3 4 5 6 7 8

Predators

Abundance 62 51 32 17 28 46 40 58

% ofindividuals 17 29 57 41 90 74 87 50

No. taxa 7 4 5 4 5 5 3 5

% oftotal taxa 19 19 31 31 71 50 43 29

Nonpredators

Abundance 294 127 24 24 3 16 6 58

% of individuals 83 71 43 58 10 26 13 50

No. taxa 30 17 II 9 2 5 4 12

% of total taxa 81 81 69 69 29 50 57 71

Diversity Index (H') 1.02 0.9 0.86 0.84 0.52 0.7 0.48 0.71

Table 2. Statistical results for variables for which one-way ANDVA showed significant differences

among treatments at p<O.10 or for which there was a significant regression (p<O.10). SNK results

are shown via underbars: means spanned by the range bar were found to not differ significantly (no

p-values provided for significant differences found). Chaoborus punctipennis is excluded from the

community measures. From study table 3.

Treatment Means

Nominal atrazine concentration ANOVA R . I egreSS1?n

Variable oflg/L 20 flg/L 100 Ilg/L 500 flg/L p-value 0

r- p-value

Turbiditl 30.36 39.02 49.06 50.05 <0.10 0.85 <0.10

Abundance

Total 267 48.5 46.5 81 <0.10 0.90 <0.10

Nonpredators 210.5 24 9.5 32 <0.10 0.94 <0.05

Labrundia pilosella 35 3.5 1.5 3.5 <0.005 0.96 <0.25

Species richness (S)

Total 29 14.5 8.5 12 <0.15 0.93 <0.05

Nonpredators 23.5 10 3.5 8 <0.10 0.90 0.05

Species evenness (J')3 0.65 0.72 0.62 0.55 0.05 0.79 >0.10

I Linear regression oftreatment means on the logarithm of atrazine concentration (equations appear in the

study table but are not reproduced here)

2 Turbidity in Nelson Turbidity Units

3 The mean J' value for the control treatment is not significantly different from the 100 or 500 flg/L

treatments

12
Table 3. Cumulative total number of insects caught in emergence traps in experimental ponds, May

8 - September 26, 1982. Study Appendix table At.

Nominal atrazine concentration

oJ.!g/L 20 J.!g/L 100 J.!g/L 500 J.!g/L

Pond number

Taxon 2 3 4 5 6 7 8

Diptera

Chironomidae

Tanypodinae

Tanypodini

Tanypus concavus 1 0 0 0 0 0 0 0

T. stellatus 3 1 0 1 0 0 0 2

Macropelopiini

Procladius bellus 35 46 25 13 24 35 38 50

P. subletti 1 0 1 1 1 1 I 0

Pentaneurini

Ablabesmyia annulata 4 0 2 2 0 4 0 I

A. mallochi 0 0 0 0 1 1 0 0

A. peleensis 3 0 1 0 1 0 0 0

A.!>pp. 6 2 2 0 0 2 0 0

Labrundinia pilosella 31 39 5 2 0 3 0 7

Larsia cf. decolorata 0 1 0 0 0 0 0 0

Paramerina smithae 13 0 0 0 0 5 0 1

Orthocladiinae

Corynoneura celeripes 1 0 0 0 0 0 0 0

Cricotopus cf. sylvestris 0 15 I 0 0 0 0 0

C. cf. trifasciatus 9 4 0 0 0 0 0 0

c. sp. 7 0 2 0 0 0 0 0

Nanocladius cf. mallochi 2 1 0 0 0 0 0 0

Parakieferiella cf. coronata 3 2 0 0 0 0 0 0

Orthocladiinae unidentified 0 5 0 0 0 0 1 2

Chironominae

Chironomini

Chironomus decorus 1 0 0 0 0 0 0 0

C. staegeri 0 0 0 0 0 0 0 1

Cladopelma collator 1 4 0 0 0 0 0 4

C. edwardsi 6 0 0 0 0 0 0 0

C. viradula 0 0 0 0 0 0 0 2

Cryptochironomusfulvus 0 0 0 1 0 0 0 3

Cryptotendipes emorsus 1 0 0 0 0 0 1 3

Dicrotendipes modestus 11 2 1 0 1 0 0 I

D. nervosus 1 0 0 0 0 3 0 0

Endochironomus nigricans 3 0 0 0 0 0 0 0

Harnischia incidata 0 0 0 0 0 0 1 0

Parachironomus sp. B 3 0 0 0 0 0 0 0

P. carinatus 1 0 0 0 0 0 0 0

P. chaetoalus 38 7 4 0 I 0 0 0

P. directus 1 0 0 0 0 0 0 0

P monochromis 0 1 0 1 0 0 0 0

13
Nominal atrazine concentration

oflg/L 20 flg/L 100 flg/L 500 flg/L

Pond number

Taxon I 2 3 4 5 6 7 8

P. potamogeti 1 0 0 0 0 0 0 0

P. tenuicaudatus 14 3 0 0 0 0 I 0

Polypedilum simulans 0 1 0 0 0 0 0 0

P. sp. 0 0 0 a a a 1 a

Pseudochironomous pseudoviridus a a 2 1 a a 0 a

P. richardsoni 1 a a 0 a a 0 0

Chironomini unidentified 92 23 0 2 1 2 a 5

Tanytarsini

Cladotanytarsus viridiventris 2a 3 3 4 a 1 0 26

Paratanytarsus sp. 2 a 0 a 0 a 0 0

Stempellina sp. a 1 2 0 0 0 0 1

Tanytarsus sp. 5 a 0 a 0 0 0 0

Tanytarsini unidentified 7 2 2 1 0 3 0 1

Chaoboridae

Chaoborus punctipennis 24 22 20 19 15 19 17 86

Ephemeroptera

Caenidae

Caenis delicata 2 2 I 2 0 0 0 1

C. simulans 4 7 a 0 0 2 2 0

C. spp. 8 0 1 1 0 0 0 1

Ephemeridae

Hexagenia limbata 0 3 0 0 0

Trichoptera

Hydroptilidae

Oxyethira pallida 13 5 6 0 0 2

TOTAL 380 200 76 60 46 81 63 202

14
Data Summary Table:

Effect Magnitude Nominal Day of Time Weighted Did Comments

ofEffect Atrazine Study Effect Average Recovery

relative to Concentration Occurred Atrazine Occur - if

controls (fJg/L) Concentration so, when

from Day 0 to (see

When Effect comment)?

Occurred

Total emerging

insects3

Nonpredatory

benthic insect

abundance4

Labrundinia 90% 20 ).tg/L integrated 8.1 ).tg/L no Calculated

pilosella 96% 100 flg/L over 16 88.1 flg/L no from study

abundances 90% 500 ).tg/L weeks 488.1 ).tg/L no Table 3.

Periphyton on NR 20 flg/L NR not calculable not Dewey

artificial applicable personal

surfaces 100% 100 flg/L NR not calculable no observation

(walkway described in

supportS)6 100% 500 flg/L NR not calculable no study text.

Increase in +30% 20 ).tg/L integrated 8.1 ).tg/L no Calculated

turbidity +60% 100 flg/L over 16 88.1 flg/L no from study

(NTU)7 +65% 500 ).tg/L weeks 488.1 ).tg/L no Table 3.

Benthic insect 50% 20 flg/L integrated 8.1 flg/L no Calculated

community 70% 100 flg/L over 16 88.1 flg/L no from study

species richness weeks Table 3.

(S)8 60% 500 flg/L 488.1 flg/L no

Benthic insect +10% 20 flg/L 8.1 flg/L Calculated

(increase) integrated no community from study

species 5% 100 flg/L over 16 88.1 flg/L Table 3.

weeks no

evenness (],)9 15% 500 ).tg/L 488.1 ).tg/L no

Benthic insect 10% 20 flg/L integrated 8.1 ).tg/L no Calculated

community 15% 100 flg/L over 16 88.1 flg/L no from review

diversity index weeks Table 1.

(H,)IO 17% 500 flg/L 488.1 flg/L no

Note: NR=Not Reported

Time weighted average atrazine concentrations were estimated from the limited

information available in the study: the date of annual atrazine addition in 1982, and the

3 See deNoyelles et al., 1994 data summary table. Effect magnitudes could be more precisely determined

using the information in this study.

4 See deNoyelles et aI., 1994 data summary table, entries for Parachironomus, Endochironomus, and

Ablabesmyia (all nonpredatory). This study has precise measured totals for the nonpredatory guild, but

there is significant overlap with the 1994 study endpoints.

S ANOVA significant at p<0.005, regression significant at p<0.025

6 A similar endpoint appears in Attachment 2 (Endpoint No. 44), but does not list this study.

7ANOVA and regression significant at p<O.1 0

8 ANOVA significant at p<0.15, regression significant at p<0.05. Statistically comparable results found for

nonpredatory community, which is not shown due to overlapping data sets.

9 ANOVA significant at p=0.05, regression not significant with p>O.1 O.

10 Results were not statistically significant (ANOVA).

15
observation that atrazine concentration decreased "in all ponds over this study period by

an average of 0.2 Ilg/L per day after it was added on 30 May 1982." Although at the time

ofthe annual addition, one ofthe 500 Ilg/L treatment ponds was created from a 20 Ilg/L

commercial treatment pond, and all ponds would have had quite low atrazine

concentrations relative to nominal before the addition, time weighted averages were

calculated ignoring the fact that a few samples were taken prior to May 30. The reason

was a lack of information and need for transparency and computational simplicity.

Assuming that concentrations on May 30 were nominal and extrapolating September 26

concentrations from the stated average 0.2 Ilg/L per day reduction rate, time weighted

averages were calculated as shown below. (Note that concentrations ofthe 20 Ilg/L

ponds went negative by September 26; clearly the average reduction rate is a poor

predictor of low-treatment pond concentrations.)

Atrazine, Ilg/L

Date Day Conc_20 Conc_100 Conc_500

30-May-82 0 20 100 500

26-Sep-82 119 -3.8 76.2 476.2

Time weighted average: 8.1 88.1 488.1

Reviewer Comments:

This study was part ofthe larger 1981-1983 mesocosm study by deNoyelles and

colleagues. As such, many fundamental problems exist with the basic experimental

design, and the experiment cannot be considered well-controlled. See reviews of

deNoyelles et al., 1989 and Carney, 1983 for details.

The study's sampling period overlapped with the timing of annual atrazine addition to the

ponds (sampling began May 8, while atrazine was added on May 30). The time weighted

average concentrations do not account for concentrations prior the addition, since the

study provided no information on these concentrations. Also, a 500 Ilg/L pond was

created out ofthe 20 Ilg/L commercial treatment pond at the time ofthe addition, so

results from this pond (the study did not identify which pond it was) are confounded by

the change in treatment level. It would have aided interpretation ofthe results ifsamples

prior to May 30, 1982 had been left out ofthe total abundances and other community

measures.

In terms ofthe adult emerging insect sampling method, it appears that some insects are

better at evading or escaping from the traps. The author mentions that baetid mayflies

and ceratopogonid flies were not caught by the method, despite knowledge that these

insects were present in the pond benthos and emerged in the pelagic zone. Some ofthe

differences in abundances could be explained by limitations ofthe trapping method.

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The author notes that Pond 8 was an outlier in terms of displaying unexpectedly high

levels of insects, and that this may have been due to its physical location in between the

two control ponds. It is also possible that if Pond 8 was the pond converted from 20 Ilg/L

treatment, that would be another explanation for the unexpected behavior. The problems

with Pond 8 highlight the uncontrolled nature ofthe experiment design.

The author used a wide range ofstatistical methods and data visualizations to analyze the

results, which are well described, appropriate, and correctly implemented. However, it

would have been informative to include p-values for the SNK multiple comparison

analyses and for the Smirnov tests for differences in emergence-frequency curves. The

author's conclusion about the different effects on predatory and nonpredatory feeding

guilds in the benthic insect community is not well supported by the statistical results.

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

Rationale for Use: The macrophyte and phytoplankton data reported in this study were

part ofthe 80S-day experimental pond study described in deNoyelles et af., 1989 and

Carney, 1983. In addition to the reported aquatic plant data, the study has some utility in

that it provides evidence of potential indirect effects to nonpredatory insects at atrazine

concentrations as low as 20 ug/L, presumably through reduction in food (periphyton and

macrophytes), and habitat (macrophytes).

Limitations of Study: Despite the well-done quantitative analyses ofthe dataset,

problems with the experimental design (see Reviewer's comments) limit the usability of

the results. Similar to the deNoyelles et al. (1989) an Carney (1983) reports, other

limitations ofthe study are small sample size (two replicates at each oftwo treatment

levels plus two controls) and lack of measured atrazine exposure concentrations over the

duration ofthe study. No effort was made to document whether other chemicals

(including atrazine) were present in the treatment and/or control ponds prior to study

initiation. Pre-sampling was not conducted to determine whether aquatic communities

were similar to one another prior to study initiation. Controls exhibited wide variability

and given that there were only two controls and two replicates for each treatment level,

the ability ofthe study to detect treatment-related effects is limited. Given these

limitations, results should be taken as suggestive indications of possible effects, not as

well-controlled evidence.

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

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

Effeels Division, U.S. Environmental Protection Agency. fr-., b(I'!>/ II

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