UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: October 31, 2013 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: Tefluthrin: Revised Response to Comments by the Syngenta Crop Protection, 

LLC on the Registration Review for Tefluthrin 

PC Code: 128912 

Decision No.:Lt17??R 

Petition No.: N/A 

Risk Assessment Type: N/A 

TXRNo.: N/A 

MRID No.: N/ A 

FROM: Chris Schlosser, Toxicologist 

Risk Assessment Branch VI 

DP Barcode: D41 1269 

Registration No.: NIA 

Regulatory Action: N/A 

Case No.: N/A 

CAS No.: 79538-32-2 

40CFR: N/A 

and _,..-.........._~ Charles Smith, Branch Chief c_ ~ · 

Risk Assessment Branch I 

Health Effects Division (7509P) 

Office of Pesticide Programs 

THROUGH: Jeffery Dawson, Acting Branch Chief 

Risk Assessment Branch VI 

Health Effects Division (7509P) 

Office of Pesticide Programs 

TO: Molly Clayton, Chemical Review Manager 

Risk Management and Implementation Branch 3 

Pesticide Re-Evaluation Division (7508P) 

Office of Pesticide Programs 

This memo responds to the TFL Dermal Toxicity Assessment submitted by Syngenta Crop 

Protection, LLC to support the Registration Review ofTefluthrin. 

In the recent Health Effects Division (HED) 2012 Human Health Risk Assessment for Proposed 

Section 3 Registration on Sugar Beat Seed (Non-Food Use), the Agency used a NOAEL ofO.l 

mglkg based on evidence of "splayed gait" as the point of departure for short-term dermal 

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exposure of the granular formulation. In the current submission Syngenta has proposed the 

following: "We believe the evidence from these studies and the additional information provided 

demonstrates that the fmding of "splayed gait" in the dermal study was not reflective of a 

systemic effect and therefore, not appropriate for risk assessment purposes". Additionally, 

Syngenta has identified that: "These daily observations were performed as part of a general 

assessment of toxicity; they were not conducted by technical staff trained to perform specific 

neurologic observations such as the functional observational battery (FOB)". 

HED response: Upon re-evaluation ofthe two 21-day dermal toxicity studies (1985 and 1989)1

, 

HED concurs with Syngenta that daily observations of clinical toxicity were conducted by staff 

that was not specifically trained to identify neurologic observations, such as those in the 

Functional Observational Battery (FOB). Upon consultation with EPA's Office of Research and 

Development (ORD), several inconsistencies have been identified with the results reported in the 

clinical observations. Anatomically, it is unclear how downward curvature of the spine and tiptoe gait could occur simultaneously as reported. In addition, without further clarification on the 

timing of the observed effects, it is difficult to interpret how both upward and downward 

curvature of the spine could occur in the same animals (i.e., 10/10 animals at the higher two dose 

levels). As effects related to the FOB are critical to assess the neurotoxic potential of 

pyrethroids, HED has determined that the dermal toxicity studies are inappropriate to assess the 

neurotoxic potential of tefluthrin via dermal application. 

HED acknowledges that the margins_of exposure (MOE) for the granular formulation as reported 

in the 2012 human health risk assessment are below the level of concern for dermal exposure. As 

an alternative approach, HED will use the NOAEL of 0.5 mg/kg/day from chronic dietary study 

in Beagle dogs, used to assess the dermal exposure of the microencapsulated formulation, with a 

default pyrethroid dermal apsorption value of 5%. Use of 5% is consistent with the default 

pyrethroid dermal absorption factor utilized in the pyrethroid cumulative risk assessment 

(USEPA; 10/4111 ). In general, pyrethroid dermal absorption estimates based on potency 

comparisons between oral and dermal studies within the same rat strain, direct measures of in 

vitro skin penetration (Hughes and Edwards 2010), or penetration rates based on lower dermis 

levels of skin that are more likely to be absorbed by the body are <5%. HED is confident that 

use of a 5.0% dermal absorption factor for granular tefluthrin formulations is health protective. 

1 EPA MRID 40141306: Southwood, J. (1985): Subacute Dennal Toxicity to Rats: Laboratory Project ID: CTUP/1147. Prepared by ICI Central 

Toxicology Laboratory 314 p. Unpublished 

EPA MRID 41080002: Leah, A. (1989) Teluthrin: 21-Day Dennal Toxicity to the Rat: Pro-ject ID: Report No. CTUP/2488; Study No. LR0524. 

Prepared by ICI Central Toxicology Laboratory. 589 p. Unpublished 

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