APPENDIX H.

This appendix provides more detail on several studies submitted by Syngenta after EPA’s submission 

cutoff date of November 2014. While the vast majority of registrant-submitted studies are discussed or 

considered in the body of the risk assessment, for clarity and transparency, a few studies were selected 

for inclusion in this appendix, as they were not specifically incorporated into the risk assessment. None 

of the information provided below in this appendix changes the risk conclusions presented in the 

assessment.

Terrestrial Plants

In late 2015 Syngenta submitted two new terrestrial plant toxicity studies. These studies followed the 

seedling emergence (850.4100) and vegetative vigor (850.4150) guidelines, however, also included

concurrent continuation studies for both studies to explore the potential recovery from atrazine caused 

inhibition of biomass and height endpoints across the tested species. A comparison to the endpoints 

used in the risk assessment and a brief discussion of the continuation studies are discussed below.

Seedling Emergence

The Martin 2015 seedling emergence study resulted in less sensitive endpoints than those for the same 

taxa tested in Chetram 1980. Several of the species indicated that little to no effect had been observed 

based on the 14-day results. When the study was continued out to 28-days, significant effects on dryweight were observed for several species. For cabbage and onion the results were similar (within an 

order of magnitude) to the endpoints reported in the Chetram (1980) study, while other taxa were less 

sensitive by approximately 10-20x. The results of this study indicate that atrazine effects on terrestrial 

plant growth and biomass may continue and have long term impacts after an exposure at or near seed 

germination.

Table 1. Comparison of the toxicity of atrazine when exposed to terrestrial plants at the seedling 

emergence phase of plant development. (Bolded IC25 values indicate the most sensitive endpoint for 

each taxon).

Study Chetram 1980 Martin 2015

Final 14-day Study

Martin 2015

Final 28-day Study

Species Endpoi

nt

NOEC EC25/IC

25

Endpoi

nt

NOE

C

EC05/IC

05

EC25/IC

25

Endpoi

nt

NOEC EC05/IC

05

EC25/IC

25

Cabbage Dry 

weight 0.01 0.014 Dry weight

0.09

7

0.0035

1

0.0299 Dry 

weight

0.009

9

0.0014

3

0.0177

Carrot Dry 

weight

0.002

5

0.003 None 0.04

9

>0.049 >0.049 None 0.049 >0.049 >0.049

Cucumb

er

Dry 

weight 0.005 0.013 None 0.1 >0.10 >0.10 Height 0.0047

0.0037

6

>0.10

Lettuce Dry 

weight

0.002

5

0.0025 None 0.04

9

>0.049 >0.049 Dry 

weight 0.049 0.0222 0.0475

Oat Dry 

weight

0.002

5

0.004 Dry 

weight

0.02

1

0.0403 0.0456 None 0.047 >0.047 >0.047
Study Chetram 1980 Martin 2015

Final 14-day Study

Martin 2015

Final 28-day Study

Onion Dry 

weight 0.005 0.009 None 0.1 >0.10 >0.10 Dry weight 0.025 0.00432

0.0341

Ryegrass Dry 

weight 0.005 0.007 None 0.1 >0.10 >0.10 Dry weight 0.1 0.0285 >0.10

Soybean Dry 

weight 0.025 0.19 Dry weight 0.44 0.316 >0.44 Dry weight 0.44 0.0493 >0.44

Tomato Dry 

weight 0.01 0.034 Dry weight

0.04

7

0.0168 0.0527 Dry 

weight 0.095 0.0776 0.146

Vegetative vigor

The Martin 2015 study provides several lower IC25 endpoints for the 21-day study as compared to the 

Chetram 1980 study (Table 2). The continuation study showed that after 42-days some species may 

have recovered to control biomass and growth levels. However, several species had continued impact 

on dry-weight and height endpoints, and several showed plant survival as the most sensitive endpoint. 

In the case of oat and soybean, endpoints after 42-days of post treatment recovery were more sensitive 

than those at 21-days.

The addition of these new data into the species sensitivity distribution (SSD) for vegetative vigor 

endpoints only slightly affected the resulting distribution. As Figure 1 illustrates, the SSDs with and 

without the additional 21-day data are nearly the same. There were relatively minor changes in the 

concentrations at the low end of the distribution, and slightly greater changes for higher HCp 

estimations (Table 3). While these are more sensitive endpoints, the conclusions presented in the risk 

assessment would not change with their addition given that risk to terrestrial plants and communities 

was identified off the field for large proportions of the 2015 SSD.

Table 2. Comparison of the toxicity of atrazine when exposed to terrestrial plants at the seedling 

emergence phase of plant development. (Bolded IC25 values indicate the most sensitive endpoint for 

each taxon).

Study Chetram 1980 Martin 2015

Final 21-day Study

Martin 2015

Final 42-day Study

Species Endpoi

nt

NOE

C

EC25/IC

25

Endpoi

nt

NOEC EC05/IC

05

EC25/IC

25

Endpoi

nt

NOEC EC05/IC0

5

EC25/IC

25

Cabbage Dry 

weight

0.00

5

0.014 Dry 

weight 0.044 0.0148 0.059 None 0.22 >0.22 >0.22

Carrot Dry 

weight 2 1.7 Dry weight

<0.009

5

0.0123 0.0544 Survival 0.22 0.22 0.31

Cucumb

er

Dry 

weight

0.00

5

0.008 Dry 

weight

<0.009

9

0.0013

2

0.0145 Survival 0.047 0.0828 0.134

Lettuce Dry 

weight 0.25 0.33 Dry weight 0.0044 0.00653

0.0215 Dry 

weight 0.0095 0.00844 0.061

Oat Dry 

weight 2 2.4 Dry weight 0.45 0.211 0.354 Survival 0.047 0.0919 0.204
Study Chetram 1980 Martin 2015

Final 21-day Study

Martin 2015

Final 42-day Study

Onion Dry 

weight 0.5 0.61 Dry weight <0.044 0.00673

0.0379 Dry 

weight 0.092 0.0145 0.0996

Ryegrass Dry 

weight 4 >4 Dry weight 0.22 0.0292 0.243 Survival 0.97 0.983 2.08

Soybean Dry 

weight 0.02 0.026 Dry weight 0.0074 0.00422

0.018 Dry 

weight

<0.004

4

0.00041

9

0.0039

7

Tomato Dry 

weight 0.5 0.72 Dry weight 0.0074 0.00572

0.0286 Dry 

weight 0.094 0.0411 0.119

Figure 1. Species Sensitivity Distributions calculated with (2016 VV SSD) and without (2015 VV SSD) 

the addition of the Martin (2015) 21-day toxicity data reported in Table 2. 
Table 3. Specific HCp values estimated with the vegetative vigor SSDs presented in Figure 1.

HCp

2015 VV SSD 

(lbs a.i./A)

2016 VV SSD 

(lbs a.i./A)

5 0.016 0.019

25 0.057 0.063

50 0.149 0.126

75 0.383 0.253

95 1.361 0.819

Algal Symbionts of Salamanders

Syngenta submitted a few new studies describing the isolation, culturing and testing for atrazine toxicity 

on the algae Oophila sp., an algae that forms a symbiotic relationship with some salamander species

(MRIDs 49639109, 49639110, 49535803, 49535801). These studies, while relevant to the potential 

effects due to atrazine environmental exposures, and prior study identification as a potential risk 

concern (Oliver et al. 2010), do not test the effect of atrazine on the salamander eggs or algal symbiont 

while in the symbiotic relationship. The direct effects on the algae do not differ greatly from those seen 

with other free living algal species and thus do not contribute new data for refinement of the current 

risk assessment. 

Water Monitoring Data Analysis and Accounting for Uncertainty

Two studies were submitted by Syngenta in late 2015 that evaluated bias factors (Chen and Mosquin 

2015) and different kriging methods for predicting concentrations of atrazine in surface water (Chen et 

al. 2015). These two studies are summarized here and are in general agreement with the atrazine risk 

assessment.

Chen and Mosquin (2015) derived additional bias factors estimates from the Atrazine Monitoring 

Program (AMP) and the Atrazine Ecological Effects Monitoring Program (AEEMP) from 2011, 2012, and 

2013. Bias factors were estimated using systematic sampling intervals of 4, 7, 14, and 28 days for 

estimation of annual maximum, 4 day average, 7 day average, 14 day average, 30 day average, and 60 

day rolling average atrazine concentrations. The monitoring data, expressed on a site-year basis, were 

aggregated according to hydrology (static vs. flowing), watershed size, and sampling time for estimation 

group means and 95th centile multiplicative factors. The bias factor is equal to the 95th centile 

multiplicative factors. It is calculated by the true value divided by the 5th percentile subsample value. 

The estimated BF factors for yearly maximum daily atrazine concentration range from 1.14 to 2.75 for a 

4 day sampling interval, 1.40 to 6.62 for 7 day sampling interval, 1.70 to 15.57 for 14 day sampling 

interval, and 2.36 to 38.28 for the 28 day sampling interval. The estimated BF factors for 60 day average 

atrazine concentration range from 1.05 to 1.44 for a 4 day sampling interval, 1.06 to 1.84 for 7 day 

sampling interval, 1.13 to 3.13 for 14 day sampling interval, and 1.51 to 5.54 for the 28 day sampling 

interval. From this analysis, the data illustrate that atrazine BFs are higher for flowing water bodies 
compared to static water bodies. Also, the highest BF are associated with small Midwestern streams 

with highly variable flow conditions (i.e., AMP). 

Chen et al. 2015 explored various data interpolation methods including ordinary kriging, universal 

kriging with use of PRZM time series predictions as a covariate, and linear interpolation using log-scale 

data were evaluated for 42 site-years of atrazine monitoring data from the Atrazine Ecological Effects 

Monitoring Program (AEEMP). These data have daily monitoring during the atrazine runoff period. The 

interpolation methods were evaluated on the monitoring data using a 7 and 14 day systematic sampling 

interval for estimation of 1day (maximum yearly), 7 day,14 day, and 30 day rolling average of atrazine 

concentrations. Root mean square errors were calculated by comparing interpolated estimated atrazine 

concentrations to actual atrazine concentrations. Estimation of the 1 day (maximum yearly) was no 

different among the various interpolation methods. Longer duration exposure concentrations (ie, 7, 14, 

and 30 day rolling average concentrations) were better estimated using ordinary kriging. Linear 

prediction of log transformed data can provide a reliable interpolation method for right skewed data. 

Kriging predictions intervals was comparable atrazine concentrations for non-sampled days. 

Surface Water Monitoring Data

Syngenta submitted 2015 AEEMP and AMP monitoring program data results in early 2016. The results 

indicate exceedances of ecological thresholds. Table 4 below includes the 2015 peak and 60-day 

average concentrations for the sites that were monitored in 2015, and also includes the historical data 

for these sites, which were included in the risk assessment. These data illustrate that concentrations will 

vary year to year within a site, however they also indicate that exceedances of the aquatic plant 

community CELOC are common within and across these sites, and that peak concentrations continue to 

exceed many of the aquatic animal endpoints. Table 5 provides the summary statistics for the 2015 

AMP monitoring program results, which also showed multiple exceedances of the ecological thresholds.
Table 4. AEEMP monitoring program data for sites submitted for the 2015 growing season. Peak and 

60-day maximum average concentrations are provided for each year the site was monitored. Bold 

values indicate exceedance of the CELOC (3.4 ug/L).

State Site Year Peak (ug/L)

Maximum 60-day 

average (ug/L)

IA IA-04 2010 73.4 10.4

IA IA-04 2011 36.0 4.3

IA IA-04 2012 78.4 10.9

IA IA-04 2013 46.1 8.9

IA IA-04 2014 142.4 26.1

IA IA-04 2015 31.5 5.2

IA IA-05 2010 74.2 11.9

IA IA-05 2011 169.0 12.8

IA IA-05 2012 33.5 7.0

IA IA-05 2013 56.5 6.9

IA IA-05 2014 344.3 96.6

IA IA-05 2015 34.7 6.3

LA LA-04 2010 32.9 6.3

LA LA-04 2011 167.4 27.4

LA LA-04 2012 59.0 11.5

LA LA-04 2013 193.7 24.2

LA LA-04 2014 76.8 9.7

LA LA-04 2015 140.8 26.5

MO MO-01 2004 65.9 19.4

MO MO-01 2005 182.8 26.1

MO MO-01 2006 82.8 17.8

MO MO-01 2007 91.6 10.7

MO MO-01 2008 78.2 7.3

MO MO-01 2009 73.0 11.5

MO MO-01 2010 25.2 5.1

MO MO-01 2011 18.8 4.5

MO MO-01 2012 13.6 1.4

MO MO-01 2013 19.2 2.4

MO MO-01 2014 16.9 3.0

MO MO-01 2015 90.6 14.4

MO MO-02 2004 53.8 16.8

MO MO-02 2005 28.1 11.5

MO MO-02 2006 43.2 15.4

MO MO-02 2007 16.2 3.5

MO MO-02 2008 56.6 12.6

MO MO-02 2009 155.2 14.6

MO MO-02 2010 31.0 8.4

MO MO-02 2011 40.7 6.6
State Site Year Peak (ug/L)

Maximum 60-day 

average (ug/L)

MO MO-02 2012 8.7 1.9

MO MO-02 2013 64.1 3.0

MO MO-02 2014 39.6 6.9

MO MO-02 2015 19.1 6.1

MO MO-07N 2010 92.5 19.8

MO MO-07N 2011 90.9 14.6

MO MO-07N 2012 41.1 12.4

MO MO-07N 2013 42.4 10.1

MO MO-07N 2014 285.9 69.0

MO MO-07N 2015 43.4 9.0

MO MO-08 2010 69.7 14.5

MO MO-08 2011 68.2 14.1

MO MO-08 2012 66.3 13.2

MO MO-08 2013 41.2 6.0

MO MO-08 2014 64.8 17.4

MO MO-08 2015 34.7 9.9

NE NE-04 2005 49.9 49.4

NE NE-04 2006 125.0 102.3

NE NE-04 2007 - -

NE NE-04 2008 147.7 21.2

NE NE-04 2009 38.2 38.2

NE NE-04 2010 189.3 49.6

NE NE-04 2011 13.0 3.9

NE NE-04 2012 8.4 2.4

NE NE-04 2013 6.9 2.9

NE NE-04 2014 4.2 0.9

NE NE-04 2015 6.3 1.5

TX TX-01 2010 105.2 19.5

TX TX-01 2011 6.4 3.0

TX TX-01 2012 133.9 15.6

TX TX-01 2013 56.0 20.7

TX TX-01 2014 39.3 8.0

TX TX-01 2015 98.4 33.1
Table 5. AMP surface water monitoring program data for sites submitted for the 2015 growing season. Bold values indicate exceedance of 

the CELOC (3.4 ug/L).

State Site ID Site Code

Number 

of 

Detections

Number 

of NonDetections

Peak 

concentration 

(ug/L)

Maximum 21-

day average 

concentration 

(ug/L)

Maximum 60-

day average 

concentration 

(ug/L)

Illinois IL1570250 Evansville 35 0 12.8 6.7 6.1

Illinois IL1910100 Fairfield 26 0 22.0 16.6 9.9

Illinois IL0290250 Mattoon 36 7 1.6 1.5 1.1

Illinois IL1170700 Mt. Olive Water 

Works (Old Lake and 

Finished)

35 0 2.2 2.2 2.1

Kansas KS2012301 Beloit Water 

Department 35 0 20.8 14.4 7.3

Kansas KS2012513 Coffeyville 35 6 7.0 5.3 3.0

Kansas KS2012520 Elk City 35 20 7.5 4.0 2.5

Kansas KS2009911 Great Plains

Development 

Authority

35 1 9.4 7.6 5.4

Kansas KS2004102 Herington 35 0 0.8 0.7 0.7

Kansas KS2004901 Howard, City of 24 0 0.2 0.2 0.2

Kansas KS2000111 Humboldt 35 0 26.7 10.8 6.3

Kansas KS2012508 Independence, City of 35 6 8.0 4.4 2.4

Kansas KS2000103 Iola 35 1 30.0 17.7 9.1

Kansas KS070000002 Kickapoo Tribal 

Waterworks 28 0 12.8 9.7 5.9

Kansas KS2010703 La Cygne (Marais des 

Cygnes River and 

Finished)

34 0 2.6 2.5 2.0

Kansas KS2012109 Marais Des Cygnes 

Public Utility Authority 35 0 3.8 3.0 2.3

Kansas KS2020502 Neodesha 30 15 17.8 8.0 3.4

Kansas KS2009908 Oswego 35 0 5.5 5.1 4.2

Kansas KS2005906 Ottawa, City of 34 0 1.0 0.8 0.8
State Site ID Site Code

Number 

of 

Detections

Number 

of NonDetections

Peak 

concentration 

(ug/L)

Maximum 21-

day average 

concentration 

(ug/L)

Maximum 60-

day average 

concentration 

(ug/L)

Kansas KS2009914 Parsons, City of 35 3 0.8 0.5 0.3

Kansas KS2000119 Public Wholesale WSD 

#5 31 0 10.2 8.9 5.1

Kansas KS2016703 Russell Water 

Department 35 7 10.0 7.3 3.7

Kentucky KY0890071 Central City Water & 

Sewer 34 10 1.8 1.3 0.9

Kentucky KY0920181 Hartford Municipal 

Water Works 36 7 3.8 2.9 2.3

Kentucky KY0160294 Morgantown Water 

System 34 7 5.3 2.5 1.3

Missouri MO1010425 King City 36 0 0.8 0.7 0.7

Ohio OH1400111 Blanchester 35 10 60.1 41.3 24.5

Ohio OH7200311 Fremont City PWS 35 1 1.2 1.2 1.1

Ohio OH3500711 McClure Water 

Treatment Plant 35 5 15.2 12.5 7.3

Ohio OH7400614 Ohio American Water 

CO-Tiffin District 34 4 27.0 18.6 9.5

Ohio OH5501211 Piqua (Gravel Pit) 35 8 17.1 12.4 6.8

Tennessee TN0000001 Adams-Cedar Hill 

Water System 34 14 6.1 2.7 1.7

Texas TX0290005 GBRA-Port Lavaca 35 23 0.8 0.4 0.2

Texas TX2040032 Waterwood MUD #1 34 2 0.4 0.3 0.3
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