Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

PC Code: 080803

ECOTOX Record Number and Citation: Baxter, L.R., P.K. Sibley, K.R. Solomon, and M .L. Hanson. 2013. Interactions between atrazine and phosphorus in aquatic systems: Effects on phytoplankton and periphyton. Chemosphere

90: 1069-1076.

Date of Review: February 23, 2016

Abstract “It has been proposed that the herbicide atrazi ne may increase rates of parasitic trematode infection in amphibians. This effect may occur indirectly as a result of increased biomass of periphyton and augmented populat ions of aquatic snails, which are the trematode’s primary larval host. Evidence has also shown that nutrients alone may induce the same indirect responses. Since both atrazine and nutrients co mmonly enter surface waters from agricultural run-off, their spatial and temporal co-occurrence are highly probable. In light of recent widespread declines in amphibian populations, a better understanding of the role of atrazine in the proposed ecological mechanism is necessary. A microcosm study was conducted to quantify biomass of phytoplankton and periphyton ov er a range of atrazine and phosphorus concentrations (from 0 to 200 lg L_1 each) usin g a central composite rotatable design. Over 10 weeks, biomass and water chemistry were monito red using standard methods. Regression and canonical analyses of the response surfaces for each parameter were conducted. We found significant effects of atrazine and phosphoru s on dissolved oxygen, pH, and conductivity throughout the study. Additions of phosphorus mitigated the apparent inhibition of these photosynthetic indicators caused by atrazine. De spite these changes, no consistent treatmentrelated differences in algal biomass were observed. These results indicate that the indirect impacts of atrazine on total growth of periphy ton and likely, subsequent effects on aquatic snails, are not expected to be ecologically signif icant at the concentrations of atrazine tested (up to 200 lg L_1) and over a range of nutrient conditions commonly occurring in agroecosystems.”

Study Description:

This study conducted a 10 week microcosm study with different combinations of atrazine and phosphorus. Microcosms were colonized naturally by taxa occurring in an adjacent irrigation pond by circulating water for three weeks (circula tion ceased 2 days prior to study initiation). The study was designed around a central composite rotatable design with a core of 4 cosmswith similar atrazine and phosphorous concentr ations (14.1 and 100 ug/L respectively) then
two or less cosms with different combinations of atrazine and phosphorus (Table 1).

Table 1: Nominal and Measured Concentrations of Atrazine and Phosphorus in each microcosm. Shaded cells indicate central cosms for comparat ive basis, changes in atrazine and phosphorus concentrations were made to the other cosms with maximum replication of 2 cosms.

Microcosm Nominal atrazine concentration (measured day-1, d-63) ug/L Nominal phosphorus concentration (ug/L)

1 0 (0,1) 100

2 0 (0, 0.25) 100

3 2.2 (2.2, 2.0) 30

4 2.2 (2.2, 1.9) 170

5 14.1 (14.9, 11.4) 0

6 14.1 (16.1, 12.9) 0

7 14.1 (13.35, 13.4) 100

8 14.1 (13.6, 13.6) 100

9 14.1 (13.4, 11.5) 100

10 14.1 (12.9, 13.7) 100

11 14.1 (13.8, 13.4) 200

12 14.1 (14.4, 14.3) 200

13 92 (91, 68) 30

14 92 (91, 80) 170

15 200 (221, 154) 100

16 200 (196, 166) 100

Reviewer description of results.

Water Chemistry: Dissolved Oxygen

Clear differences between the tested -0, 14 ug and 200 ug/L exposures when phosphorous concentrations were 100 ug/L or less. There ap pears to be a mitigation of the atrazine effects on dissolved oxygen when phosphorus concentrat ions are 200 ug/L. Figure 1 below illustrates this however only presents a subs et of the test cosms, and fails to show the results for the core cosms which had 14 ug/LFigure 1. mean concentrations of dissolved oxygen in microcosms over the 63-d exposures to atrazine and phosphorus for the start point treatment concentrations in a CCRD (n=2 microcosms/treatment)

Figure 2 provides more complete comparison of the DO concentrations at day 7 and day 21. The day 7 effects of atrazine are apparent at 2.1, 14.2, 92, and 200 ug/L, however by day 21
most of these effects have been reduced. Ther e are several complications that arise from the comparisons. First, in the absence of added phosphorus, the effects of atrazine appear to remain at day 21, due to the cosm maintaining a reduced DO compared to the cosms with no added atrazine. The comparison is complicated because the cosms with no atrazine added had 100 ug/L of phosphorus added. The impact of phosphorus on the cosms without atrazine added isn’t explored well with this study de sign, however looking across cosms that had 2.1 ug/L atrazine or less there are negligible reductio ns in DO at day 7 however by day 21 there is a clear difference in DO that is responding in a dose response manner. Similar patterns of
reduced DO in the cosms without atrazine could be expected if there was rampant consumption of the available phosphorus resultin g in an algal or bacterial decay bloom that caused the reduction, similar to results seen in eutrophic conditions. Another comparison that can be made is across the cosms with 100 ug/L of phosphorus. These include 0, 14.2, and 200 ug/L atrazine. The DO levels across the cosms we re significantly different at day 7 however had recovered to similar levels by day 21. This can be interpreted as the phosphorus mitigation of atrazine effects, or a balancing of effects of atrazine and effects of phosphorus across these cosms (with low atrazine cosms being more influe nced by phosphorus than in high atrazine concentrations). In low concentrations phosph orus effects are expected to be less on the cosms without atrazine, so comparison of those cosms with the lowest phosphorus concentrations results in 21-day reduction of DO in an atrazine dose response manner.- Figure 2. Observed values (black circles) and predicted response surfaces for dissolved oxygen on d 7 (left; R2 = 0.94) and 21 (right; R2 = 0.73 ) in microcosms after treatment with atrazine and phosphorus on d 0.

Water Chemistry: pH

The pH in all ponds increased with time with the exception of an initial decrease in the 200 ug/L atrazine cosms. Trends in the shape of respon se surfaces for pH were similar to those of dissolved oxygen (figure 2) and the description provided above. However, the surface of the response at day 21 is steeper than that predicted in day 21 of figure 2. There appears to be a poor fit of the surface with regard to the cosm s with low atrazine and high phosphorus at day 21 in figure 4, suggesting an increasing trend, however the data shows a reduction in pH as compared to adjacent cosms in the CCRD (Fig ure 3 does not illustrate test cosm #4).

Fig. 3. Mean pH in microcosms over 63-d exposures to atrazine (ATZ) and phosphorus (P) for the star-point treatment combinations in a CCRD ( n = 2 microcosms per treatment).Figure 4. Observed values (black circles) and pred icted response surfaces for pH on d 7 (left; R2 = 0.97) and d 21 (right; R2 = 0.86) in microcos ms after treatment with atrazine and phosphorus
on d 0.

Algal Response: Chlorophyll-a

Influence of phosphorus is consistent with resu lts of DO, cosms without added atrazine and 100 ug/L of phosphorus show significant increases in chlorophyll a in both phytoplankton and periphyton between days 0 and 7 as compared to all other cosms displayed in figure 5 (note the central cosms are not included in the figure). Between day 7 and day 21 significant decreases in chlorophyll for both periphyton and phytoplankton are observed. The influence of atrazine is evident by the significant difference between the cosms with 100 ug/L phosphorus. Cosms with 200 ug/L atrazine had phytoplankton communities with significantly less chlorophyll than those without atrazine exposure. Comparative redu ction of chlorophyll a in the phytoplankton community are also seen with the two displayed test groups with 14 ug/L atrazine added. Convergence in the cosm phytoplankton chlorophyll a was seen by day 21 of the study. The periphyton response to atrazine exposure is al so clear at day 7, with cosms exposed only to atrazine having the highest reduction compared to the cosms without atrazine. The potential mitigation of atrazine effects by increased phosphorus at day 7 may explain the higher chlorophyll a concentration s in the other two reported atrazine exposure concentrations having higher concentrations of phosphorus and less atrazine leading to higher chlorophyll a measurements. Convergence of the cosm periphyton in terms of chlorophyll a concentration occurred by day 28.Figure 5. Mean chlorophyll -a of phytoplankton (top) and periphyton fr om tiles at the microcosm base (bottom) over the 63-d exposures to atrazine (ATZ) and phosphorus (P) for the star-point treatment combinations in a CCRD. Symbols are the mean of n = 2 microcosms per treatment ± SD.

Algal Response: Ash Free Dry Mass (AFDM)

AFDM results are less clear than the other meas ured effects (Figure 6). Phytoplankton AFDM shows some separation of the 14.1/0 exposure cosms at day 7 of the exposure, however these do not appear to be significant compared to their relative change between days 0 and 7, nor the day 7 direct measured AFDW. Periphyt on results show the same rampant growth suspected by DO, and chlorophyll a.Figure 6. Mean ash-free dry weight (AFDW) of phytopla nkton (top) and periphyton from tiles at the microcosm base (bottom) over 63-d exposures to atrazine (ATZ) an d phosphorus (P) for the star-p oint treatment combinations in a CCRD. Symbols are the mean of n = 2 microcosms per treatment ± SD.

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

Rationale for Use: The study contributes to the unders tanding of aquatic plant community responses to atrazine and phosphorus under a la boratory testing setting. Because of the listed study limitations this study will not be included in the methodology for developing the CELOC.

Limitations: The primary limitation in this study is the lack of a set of comparable negative controls, and the poor reporting of the central cosms tested in the study. Therefore, it is difficult to isolate either ATZ or phosphorous independent effects because the study design and provided analyses. In addition, the study doesn’ t include saturated soil substrate as this would
influence the amount of free phosphorous in the system.

Primary Reviewer: Frank T. Farruggia Ph.D., EPA/OCSPP/OPP/EFED/ERB3

Digitally signed by FRANK
FARRUGGIA DN: c=US, o=U.S. Government, ou=USEPA, ou=Staff, cn=FRANK FARRUGGIA, dnQualifier=0000048865
Date: 2016.03.24 09:54:47 -04'00'