1 

EFED response to public comments from Syngenta

3.0 ECOLOGICAL RISK 

Comment 1: 3.1 Ecological Risk Assessment Endpoints: As the Agency intends to utilize 

endpoints from surrogate test species to estimate treatment-related effects on acute 

mortality and chronic reproductive, growth and survival assessment endpoints, it is 

important to ensure the most appropriate values for a particular taxon are used. 

EFED Response: For baseline ecological risk assessments, EFED uses the most 

sensitive data available (e.g., lowest LC50) that comply with Harmonized Test Guidelines

and Good Laboratory Practices Standards. Other toxicity endpoints may be used if 

professional judgment and lines of evidence determine that they can be linked to 

assessment endpoints in a reasonable manner.1

 Fish are used as surrogates for aquaticphase amphibians, for which toxicity data are not typically available for pesticides. In 

addition, birds are used as surrogates for terrestrial-phase amphibians and reptiles. 

Comment 2: 3.1.1 Avian Reproduction NOAEC with TGAI: On page 8, Table 2, the 

NOAEC of 350 mg prodiamine/kg diet (ppm) listed for the bobwhite quail reproduction 

study endpoint does not correspond to the value of 1000 mg/kg diet (ppm) prodiamine 

generated in the cited study (Beavers et al., 1992, MRID 43181803). Syngenta requests 

that this endpoint be updated to 1000 mg/kg in future reviews. 

EFED Response: MRID 43181803 was originally classified as invalid because 

performance of control birds was poor compared to historical control data for the 

bobwhite quail indicating that potential reproductive effects may have been masked. 

Equipment malfunction was cited as the cause for loss of eggs and hatchlings which 

increased test variability.2

 Later, the study was reclassified as acceptable3 only by 

adjusting the NOAEC to 350 ppm, the second highest test concentration, rather than 

1000. After examining the data, which showed probable effects at 1000 ppm, a 

determination was made that any statistically significant difference from controls was 

masked by the high variability of the data. Therefore, the registrant was given the option 

of repeating the study if they believed this value to be inappropriate. Since the study was 

not repeated, the NOAEC remains at 350 ppm and the LOAEC at 1000 ppm. 

 

1 http://www.epa.gov/oppefed1/ecorisk_ders/toera_analysis_eco.htm 2 Data Evaluation Record, May 24, 1994, for “Beavers, J.B., K. Chafey, L. Mitchell and M. Jaber. 1992. Prodiamine 

Technical: A Reproduction Study with the Northern Bobwhite. Prepared by Wildlife International Ltd., Easton, 

Maryland. Laboratory Project No. 131-170. Submitted by Sandoz Agro, Inc., Des Plaines, IL. EPA MRID No. 

431818-03. 

3

 Doug Urban for Anthony Macriowski, EFED to RD, November 15, 1994. EPA Internal Memo. Prodiamine: 

reclassification of avian reproduction study with bobwhite quail.
2 

Comment 3: 3.1.2 Freshwater Fish Early Life Stage Study with TGAI: On page 9, 

Table 3a, Freshwater fish ELS is identified as a data gap. A study report has been 

submitted previously (Graves and Swigert, 1993; MRID 42807103) and rated as CORE. 

Syngenta requests that this study be considered in future reviews. 

EFED Response: EFED has re-reviewed this study and reclassified it as supplemental 

due to uncertainty associated with the test concentrations. Prodiamine concentrations in 

the test were at or near solubility, and water samples were not centrifuged or alternatively 

filtered prior to processing and analysis. Centrifugation or filtration is important for 

prodiamine because the high Log Kow suggests that it may bind to organic carbon in the 

test system, which may limit its bioavailability and affect its toxicity. 

Comment 4: 3.1.3 Freshwater Invertebrate (Daphnia magna) Life Cycle Study with 

TGAI: On page 9, Table 3a, the cited chronic daphnia study (MRID 41787302) was 

considered supplemental and a daphnid reproduction study was identified as a possible 

data gap. However, a more recent study by Zelinka et al., (1993, MRID 42807102) was 

submitted previously and rated as CORE. The NOEC for this CORE study was 23 ppb, 

while that for the cited unacceptable study resulting in the data gap statement (MRID 

41787302) was reported as 1.5 ppb. Syngenta requests that this Zelinka study (MRID 

42807102) be used for the chronic freshwater invertebrate endpoint. 

EFED Response: The previously submitted daphnid life cycle study (MRID 42807102) 

was downgraded to Invalid due to a re-analysis of the data that showed unacceptable 

differences between the negative and solvent controls and uncertainty associated with the 

actual test concentrations, which were at or near the solubility limit but not centrifuged or 

alternatively filtered prior to processing and analysis.

Comment 5: 3.1.4 Freshwater and Saltwater Fish Full Life Cycle (FFLC) Studies with 

TGAI: On page 9, Table 3a, EPA identifies FFLC studies with freshwater and 

estuarine/marine species and TGAI as possible data gaps (850.1500). FFLC data can be 

required if the product is intended for direct application to water, or if the product is 

expected to enter water in significant concentrations. There is a use of prodiamine for 

irrigation ditch banks; however Syngenta products are not labeled for this type of 

application, and Syngenta does not support the use. The environmental fate profile of 

prodiamine indicates that this AI is unlikely to enter water via run-off in significant 

concentrations, thus aquatic exposure is expected to be low. 

Further, based on the very short aquatic half-life of prodiamine and the availability of 

chronic data on fathead minnows; Syngenta suggests that the conduct of freshwater or 

saltwater FFLC studies does not provide additional useful input for risk assessment. 

EFED Response: EFED’s request for the freshwater and saltwater fish full life cycle 

data was based on more than the irrigation ditch use. All outdoor uses have the potential 
3 

to enter freshwater, and several of the uses (e.g., turf) would also be expected to be used 

in areas with access to saltwater environments. 

Per footnote 18 to Guideline 850.1500 (40 CFR Part 158.630, Subpart G), a freshwater 

fish full life-cycle test is required when a product is “expected to be transported to water 

from the intended use site, and when any of the following conditions apply: 

i. If the ...(EEC) is ≥ 0.1 of the no-observed-effect level in the fish early-life stage or 

invertebrate life cycle test; 

ii. If studies of other organisms indicate that the reproductive physiology of fish may be 

affected.” 

EFED believes that the conditions for requiring a freshwater fish full life cycle test (as 

defined in footnote 18) are met for prodiamine. As indicated on pp. 39-40 of the problem 

formulation, available data for prodiamine indicate that “potential reproductive effects on 

fish (egg production and hatchability) and endpoints in birds were reduced (MRID 

43181803) and reduced offspring weights in rats (MRID 40593421) and the EEC 

according to the GENEEC screen is > 0.1 of the NOAEC value (using the NOAEC value 

from a supplemental freshwater invertebrate study, (MRID 41787302)). Additionally, 

prodiamine has potential to bioaccumulate which may result in reproductive effects that 

an Early Life Stage test would not capture.” 

Similarly, footnote 17 to the guideline indicates that an estuarine/marine fish life cycle 

study is required if “the product is expected to enter this environment in significant 

concentrations because of its expected use or mobility patterns.” Some registered uses 

for prodiamine are geographically widespread and certainly allow exposure to the 

saltwater environment (e.g., turf). 

3.2 Projection of Prodiamine and Prodiamine Benzimidazole Toxicities to 

Aquatic Organisms using Quantitative Structure-Activity Relationships: 

Comment 6: 3.2.1 Estimation of Toxicity Endpoints for Prodiamine Parent TGAI: On 

page 10, Table 3b, QSAR modeling is used to estimate toxicity endpoints for TGAI. 

However, study-derived endpoints are available for many of these toxicity values. It is 

notable that the values estimated by QSAR in Table 3b overestimate the available 

measured toxicity values. Most of the QSAR values are well above the water solubility of 

prodiamine. Syngenta requests that measured values be used when available, and that 

estimations of toxicity be made using conventional methods that involve measured 

toxicity inputs for the AI in question, e.g. for the calculation of acute-to-chronic ratios. 

EFED Response: QSAR estimates for pesticides and degradates are used in conjunction 

with empirical toxicity data on a case-by-case basis for estimates, such as comparisons 
4 

between parent and degradate when data are not available. The purpose of Table 3b on 

p. 10 was to illustrate how toxicity of prodiamine parent would be expected to compare 

with that of degradate, prodiamine benzimidazole. EFED included the QSAR estimates 

in order to predict whether prodiamine would be expected to be more or less toxic than 

prodiamine benzimidazole. 

Comment 7: 3.2.2 Estimation of Toxicity Endpoints for Prodiamine Benzimidazole 

Degradate: On page 10, Table 3b, acute and chronic aquatic toxicity values derived 

using QSARs are presented for the degradate, prodiamine benzimidazole. EPA states that 

model estimates indicate the degradate may have similar acute toxicity to the parent, and 

greater chronic toxicity compared to parent prodiamine. Based on these modeled 

estimates, numerous acute and chronic aquatic toxicity studies have been identified as 

potential data gaps. Results from laboratory studies demonstrate that the environmental 

fate profile of prodiamine benzimidazole does not present a risk for chronic exposure due 

to its short aquatic half-life, as described below. 

Syngenta suggests that the conduct of extensive aquatic studies on prodiamine 

benzimidazole would not be useful due to the brief and very limited potential exposure of 

aquatic organisms to this degradate. 

EFED Response: This degradate is a major degradate with a structure similar to the 

parent and appears to be stable under some conditions. EFED considers this degradate to 

be of concern for chronic exposure. The problem formulation states on p. 13, “The only 

major metabolite was 6-amino-2-ethyl-7-nitro-1-propyl-5-trifluoromethyl-benzimidazole 

(prodiamine benzimidazole). The benzamidazole concentration peaked at 0.82 μg/g (33% 

of applied) at 270 days, and had declined to 0.74 μg/g (29.60% of applied) at 365 days” 

(MRID 4059342). While photolysis (as mentioned below) may degrade the 

benzimidazole degradate, photolysis would be unlikely to be fast enough to eliminate 

acute risk or be thorough enough to eliminate chronic risk. 

3.3 Environmental Exposure 

Comment 8: 3.3.1 Henry’s Law Constant: On page 12, Table 5, the value given for the 

Henry’s Law Constant is 8.89x10-2 atm-m3/mol. The correct value is 8.89 x 10-7 atmm3/mol (Erstfeld, 1987). 

EFED Response: The Henry’s Law Constant value in Table 5 (i.e., 8.89 x 10-2

atm·m3

·mol-1) appears to be typographical error. EFED agrees that the Henry’s Law 

Constant for prodiamine should be 8.89 x 10-7 atm·m3

·mol-1. This value is calculated 

from the vapor pressure and solubility values listed in the Registration Review Problem 

Formulation.
5 

This value may also in fact not be correct as the cited vapor pressure value cannot be 

tracked to a measurement. The citation provided (Erstfeld, 1987) is not complete. A 

search of the public literature and through documents submitted to the Agency to support 

prodiamine registration for those Erstfeld from 1987, both regarding prodiamine Henry’s 

Law Constant specifically or chemical physical properties in general, did not find this 

citation. Other available citations for the Henry’s Law Constant and vapor pressure all 

further cite the British Crop Protection Manual. This is not a primary source based on 

measurements and cannot be used to support pesticide risk assessments for FIFRA. In the 

absence of citable measured for values for vapor pressure and/or the Henry’s Law 

Constant, the Agency will assess the risks of prodiamine using QSAR estimates from tool 

such as EPISuite. The current best estimate of vapor pressure for prodiamine from 

EPISuite is 2 x 10-7 torr and for the Henry’s Law Constant is 5 x 10-8 atm·m3

·mol-1. 

Comment 9: 3.3.2 Fate and Transport Properties: On page 13, Table 6, the cited 

mobility parameters for prodiamine reflect Kd values calculated using a linear isotherm 

model. However, based on the current test guidelines (OECD 106 and OPPTS 835. 1230) 

the Freundlich isotherm model is preferred. The Freundlich isotherm results were given 

in the cited report (MRID # 40593525) within Appendix 1 (pp. 317-336). The Koc values 

calculated using the Freundlich adsorption isotherm ranged from 8035 to 16283 mL/g 

with a mean Koc of 11,195 mL/g. Syngenta requests that the Freundlich isotherm-derived 

values be used, as per OECD and EPA guidance. 

EFED Response: The study cited in the Registration Review Problem Formulation for 

prodiamine is a column leaching study. The cited MRID of 40593525 is not correct. The 

correct MRID is 40593425. Estimates of partition coefficients from column leaching 

studies are much less accurate than those for batch equilibrium studies. An acceptable 

batch equilibrium study is available for prodiamine (MRID 41727202). While visual 

inspection of the data indicates the the isotherms are curvilinear, the study authors only 

estimate Kd for adsorption and desorption for the soils in the study. The measured Kd for 

adsorptions were 119.7 and 303.9 L·kg for a’#58’ clay and a Kenyon silt loam 

respectively. Given that these data are likely to be much more accurate, these values will 

be used in the risk assessment rather than those from the column leaching study. 

Fruendlich coefficients will be calculated from the original data for use in the risk 

assessment. 

Comment 10: On page 13, Table 6, the prodiamine aerobic soil half-life is given as 57 days. 

Using the data points in the cited report (MRID # 4059342), half-lives were re-calculated 

by two different non-linear kinetic methods to determine the best fit: single first order 

(SFO) and double first order in parallel (DFOP). Based on the linear regression 

coefficients (R2), the DFOP gave an excellent fit (R2 of 0.9996) with a calculated aerobic 

soil half-life of 42.1 days. The SFO approach provided a half-life of 56.6 days (R2 of 

0.9734). Syngenta suggests that the appropriate aerobic soil half-life value is 42.1 days. 
6 

EFED Response: The value reported in the Table 6 is a correctly estimated first-order 

half-life estimated using non-linear regression on untransformed concentration data. Note 

that because all EFED environmental fate models use first-order kinetics, estimates of 

first-order rate constants must be estimate for use in simulation modeling. Alternative 

kinetics models such as DFOP is not first order and the kinetics parameters from DFOP 

cannot be used in the models. 

Comment 11: On page 13 and in Appendix I – The physical-chemical properties as well as 

the environmental fate and ecological effects of prodiamine are well characterized in 

accepted EPA guideline studies. (See endpoints presented in Tables 2, 3 and 5). 

Estimation of prodiamine’s persistence using the Level III fugacity model in EPI-SUITE 

v4.0 is not appropriate for chemicals with well characterized fate and effects data. The 

use of the screening level model, PBT Profiler, to assess the persistence, 

bioaccumulation, and toxicity of prodiamine and its degradate (prodiamine 

benzimidazole) is not appropriate since the model is clearly not intended to be used for 

chemicals with experimental data. 

EPA Response: The Agency agrees that measured environmental fate data should be 

used preferentially to estimates based on the structure-activity relationships in pesticide 

risk assessments. However, the estimates made using the EPI-SUITE’s Level III fugacity 

provide useful ancillary information for characterizing the behavior of prodiamine in the 

environment. 

3.4 Risk Hypothesis 

Comment 12: 3.4.1 Analysis Plan: In Section13.A.2, on page 20 of the EFED problem 

formulation document the maximum use rate of 2.64 lbs ai/A cannot be confirmed. Based 

on Appendix V of the same document, “Uses and Application Rates of Prodiamine”, the 

maximum annual rate is 1.5 lb ai/A/yr. Based on this rate, Syngenta calculates a 90th 

percentile EPA-defined pond drift EEC as 5.18 ppb using AgDrift 2.01. 

EFED Response: For the Registration Review ecological risk assessment, EFED will 

base maximum use rates on all current label information. EFED will reconsider the 

maximum annual use rate at that time. 

3.5.1 Environmental Fate (pg 28-29) 

Comment 13: 3.5.1.1 Proposed data gap: 835-2240, Photodegradation in Water 

(Parent Prodiamine): Syngenta has recently submitted a study entitled Photolysis of 

14C-Labelled Prodiamine in Sterile Natural Water and Sterile pH 7 Buffer under 

Laboratory Conditions, by A. D. Hurt, G. Mason and K. Anderson, 15 September 2005 
7 

(MRID 48308301). This study was conducted to comply with Japanese and OECD 

guidelines and should also address EPA questions regarding the photodegradation of 

parent and prodiamine benzimidazole (SYN-530120). The study demonstrated that 

prodiamine rapidly degrades photolytically with half-lives of less than 8 hours in both 

sterile natural water and pH 7 buffer.

EFED Response: The cited study is currently being reviewed by EFED. If the study is 

scientifically valid, the data will be considered in the registration review risk assessment. 

Comment 14: 3.5.1.2 Proposed data gap: 835-2410, Photodegradation in Soil (Parent 

Prodiamine): Syngenta has recently submitted a study entitled Artificial Sunlight 

Photodegradation of 14C-Prodiamine on a Representative Agricultural Soil by R. N. 

Fathulla, 17 January 1996 (MRID 48308302). Prodiamine photodegraded rapidly in 

treated soil (half-life of ~5 days). Prodiamine benzimidazole was only a minor 

photodegradate (peak at 1.9% applied radioactivity) and underwent further 

photodegradation.

EFED Response: The cited study is currently being reviewed by EFED. If the study is 

scientifically valid, the data will be considered in the registration review risk assessment. 

Comment 15: 3.5.1.3 Proposed data gaps: 835-4300, aerobic aquatic metabolism 

(Parent Prodiamine) and 835-4400, anaerobic aquatic metabolism (Parent 

Prodiamine): Syngenta is submitting a study entitled Prodiamine – Degradation of 

[14C]-Prodiamine in Two Aquatic Sediment Systems, under Aerobic and Anaerobic 

Conditions, by M. Simmonds and E. Mackenzie, 3 September 2009 (Syngenta 

Report/Study Number NC/08/043). Aerobic and anaerobic aquatic sediment studies were 

conducted separately to satisfy OECD guidelines (308), but reported in a single final 

report. Key findings demonstrated: 

• Aerobic Aquatic Sediment: 

• Prodiamine dissipation half-lives in both system water phases were very rapid 

(1-5 days). 

• Parent total system half-lives in both test systems ranged from 14.4-17.5 days. 

• Only trace amounts of prodiamine benzimidazole were found in the water and 

sediment phases of both test systems. 

• Anaerobic Aquatic Sediment: 

• Prodiamine dissipation half-lives in both system water phases were rapid (2-5 

days). 

• Parent total system half-lives in both test systems were even more rapid (3-7 

days) than under aerobic conditions. 

• Prodiamine benzimidazole was only found in trace levels in the sediment 

phase of both test systems. 
8 

An anaerobic soil metabolism study entitled Anaerobic Soil Metabolism of Prodiamine 

by J. Krueger and R. Butz, January 21, 1988 (Sandoz Crop Protection Project # 480425, 

report # 4) is being submitted. This study substantiates the findings in the anaerobic 

aquatic metabolism study (see above) and also provides insight into the environmental 

fate of prodiamine benzimidazole. In the report an aerobic-anaerobic half-life (0-93 day 

after treatment, DAT) of 30 days was calculated. However, under induced anaerobic 

conditions (30-93 DAT), the anaerobic soil half-life of prodiamine was considerably 

shorter, only 11.7 days. Prodiamine benzimidazole (SYN530120) reached a peak level of 

8% applied radioactivity (AR) at 30 DAT. Thereafter, under induced anaerobicity (30-93 

DAT), SYN530120 readily declined with an estimated half-life of 25.6 days (SFO). 

EFED Response: EFED will review these studies when they are submitted. If the 

studies are scientifically valid, the data will be considered in the registration review risk 

assessment. 

Comment 16: 3.5.1.4 Proposed data gap: 835-6200 Aquatic Field Dissipation (Parent 

Prodiamine): None of Syngenta’s product labels allow for direct aquatic application 

nor does Syngenta support aquatic uses. In the event prodiamine should move off-target 

due to turf runoff or spray drift it would dissipate quickly due to degradation by sunlight 

and aerobic metabolism processes. 

EFED Response: The aquatic field dissipation study is ony required to support aquatic 

uses. Application to irrigation ditches is considered an aquatic use. Therefore, in order to 

fulfill this data gap, registrants who support this use should provide the data. 

Comment 17: 3.5.1.5 Proposed data gap: 835-2240, Photodegradation in Water 

(prodiamine benzimidazole, SYN530120): As indicated above, Syngenta has recently 

submitted photolysis studies which should address questions regarding the behavior of 

prodiamine benzimidazole under photolytic conditions: 

From these two photolysis studies, prodiamine benzimidazole was found as only a minor 

or transitory photodegradate which rapidly underwent further degradation to one or more 

photodegradates. 

Syngenta contends that the e-fate of both prodiamine and prodiamine benzimidazole 

(SYN530120) are well understood and supported by existing studies. Available e-fate 

data clearly indicate SYN530120 is not of concern environmentally since it is degraded 

rapidly under photolytic, aquatic/sediment (aerobic and anaerobic) and anaerobic soil 

conditions. The photolysis and mobility studies clearly indicate that under field 

conditions SYN530120 photodegrades rapidly and is likely only a minor metabolite with 

low leaching potential. 
9 

EFED Response: As noted in the response to Comment 12, the two photolysis studies 

are currently being reviewed by EFED. Also, as noted in Comment 16, the 

aquatic/sediment studies are forthcoming, and have not yet been submitted or reviewed. 

Together, these data may be used to evaluate the potential exposure potential of the 

degradate. If the studies are scientifically valid, the data will be considered in the 

registration review risk assessment. 

Comment 18: 3.5.1.6 Proposed data gap: 835-1230, Adsorption/desorption (batch 

equilibrium) (using SYN530120 aka 6-amino-benzimidazole): A legacy company of 

Syngenta, Sandoz Crop Protection, conducted an aged soil column leaching study per 

specific EPA guidance in addressing the mobility of SYN530120. The study was entitled 

Soil Column Leaching of 14C-Prodiamine and Its Soil Degradates, by Tsun-Min Rosa 

Tong, Rakesh Jain, Paul Moore, and Yousef Atallah, September 1992 (MRID # 

42483201). On 10-23-91, Brinson Perks (an EPA reviewer) recommended Sandoz use 

the soil column leaching method instead of the earlier proposed batch equilibrium method 

in order to address EPA’s concerns on the mobility of SYN530120 (see Appendix 1 in 

cited report, in particular, the original protocol objectives and subsequent protocol 

amendment 1 following EPA guidance). Kd and Koc values are provided in Appendix V 

of the report (pages 104-107) which clearly demonstrate both parent and SYN530120 are 

not likely to leach.

EFED Response: While leaching studies are adequate for showing a pesticide does not 

leach, current risk assessment methods require a quantitative estimate of mobility (i.e.

Kd) in order accurately account for mobility. Aged column leaching studies do not 

provide accurate estimates of Kd for compounds of moderate and lower mobility and are 

no longer solely acceptable for meeting pesticide mobility data requirement. An 

acceptable batch equilibrium study, MRID 41727202, discussed in Comment 10 above 

was submitted to the Agency and will be used to quantify mobility rather than the column 

leaching study. 

3.5.3 Studies on Degradates 

Comment 19: 3.5.3.1 Proposed data gap: Guideline Number 850.1400, Freshwater 

and Saltwater Fish Early Life Stage Study with benzimidazole degradate: The 

chronic exposure to the degradate, prodiamine benzimidazole, for aquatic organisms is 

expected to be very low. This degradate is a short-lived intermediate in the aqueous 

photolysis of prodiamine (see comment addressed in 3.5.1.5), and therefore will not 

represent an environmentally-relevant metabolite in the field, particularly for chronic 

exposure. 

EFED Response: Please see EFED Response 16. 
10 

Comment 20: 3.5.3.2 Proposed data gap: Guideline Numbers 850.1300 and 850.1350, 

Freshwater and Saltwater Invertebrate Life Cycle Toxicity Study with 

benzimidazole degradate: The chronic exposure to the degradate, prodiamine 

benzimidazole, for aquatic organisms is expected to be very low. This degradate is a 

short-lived intermediate in the aqueous photolysis of prodiamine (see comment addressed 

in 3.5.1.5), and therefore will not represent an environmentally-relevant metabolite in the 

field, particularly for chronic exposure. 

EFED Response: Please see EFED Response to Comment 16. 

Comment 21: 3.6 Testing of Prodiamine TEP (Formulation): Results of ecotoxicity 

testing of prodiamine TEP have been identified as potential data gaps, including daphnid 

acute, oyster embryo larvae or shell deposition, and mysid acute studies. 40 CFR 158 

requires data for TEP for products applied to water, OR when the maximum EEC ≥ 0.5 

LC50, OR when the end product produces increased toxicity: 

• There is a use of prodiamine for irrigation ditch banks. However, Syngenta 

products are not labeled for this type of application and Syngenta does not 

support the use. There is thus no application to water. 

• Preliminary modeling by Syngenta indicates that the maximum EEC is not ≥

0.5 LC50. Syngenta requests that EPA confirm the EEC/LC50 ratio for 

Syngenta-labeled uses in order to verify whether this trigger for TEP testing is 

met. 

• Finally, there is no indication that the end product produces increased toxicity; 

formulations are typically less toxic on an a.i. basis than technical ingredient 

(e.g. Mayer and Ellersieck, 1986; Schmuck et al. 1994). 

In addition, with an EC50 value of 0.37 mg/L, mollusks are one of the least sensitive taxa 

to prodiamine. Syngenta suggests that studies on the TEP should not be triggered for 

Syngenta-supported uses. 

EFED Response: In answer to the first bullet (Syngenta products are not labeled for 

ditch bank uses), the data requirement is triggered for the ditch bank use regardless of the 

identity of the registrant that supports this use. If no registrant supports the ditch bank 

use, then the data would not be required. 

For the second bullet, concerning max EEC and TEP testing, the second condition 

mentioned above (from 40 CFR Part 158) is met. Applications of approximately 1 lb 

a.i./acre by aerial spray result in drift only EECs that are approximately 1⁄2 the solubility 

limit of prodiamine in the standard pond. The maximum application rate of prodiamine 

is 2.64 lbs a.i./A. Therefore, determining whether or not ingredients found within 
11 

formulated products of prodiamine may enhance its toxicity or solubility is useful to the 

risk assessment. 

For the third bullet, if the registrant believes that the formulated products used in cited 

sources are representative of TEPs, then they can submit those data and the justification 

of the test formulations as TEPs to fulfill this data gap. 

The registrant may submit for consideration a waiver request for the mollusk data further 

outlining their justification.