Attachment 1.pdf

Potential study design to address food use residue data requirements for the use of sodium nitrite to control feral swine: OPPTS 860.1480 Meat/Milk/Poultry/Eggs

Prepared by: USDA APHIS WS National Wildlife Research Center June 20, 2018

Problem Statement

A sodium nitrite (NaNO2) based toxicant for the control of feral swine is designated a food use product by EPA.

However, the OPPTS 860.1480 Meat/Milk/Poultry/Eggs study guidelines are not completely compatible with this type of pest and application. In this case, the pest species (feral swine) is also the potential food source, and thus the intended dose of toxicant is lethal to pigs. A modified study design is necessary to address food residues in the meat (muscle, fat and liver) of feral swine that consume the sodium nitrite bait, and may then be harvested by hunters or captured for processing. APHIS is seeking EPA input on the 7 assumptions and the study design outline below.

Assumptions Pertinent to Study Design

1) The concern for nitrite residues in meat is based on the possibility that sub-lethal or lethally dosed pigs may be harvested for consumption by hunting or trapping.

2) The study design measures tissue residues during the period(s) of time that pigs may be harvested for processing.

3) A reasonable person would not harvest for food a pig that appeared visibly distressed or collect a pig found dead. Pigs typically die within 2-3 hours after feeding on toxic bait.

4) The likely scenario for harvesting a pig is after it has ingested a sub-lethal or lethal dose of the toxic bait and before onset of obvious symptoms, or after pigs are nearly recovered from receiving a sub-lethal dose.

5) The study design outline specifies dosing domestic pigs with the active ingredient, sodium nitrite, via oral gavage. Oral gavage may speed onset of symptoms and death. An alternative is to allow fasted pigs to feed on encapsulated sodium nitrite mixed into bait.

6) The tissues for collection and analysis include muscle, fat, and liver pending consultation with EPA.

7) Nitrite is the analyte of concern in tissues. The target LOQ will be decided pending consultation with

EPA.

Proposed Study Design Outline

In-life phase: The proposed treatment groups and sampling times are shown below. APHIS proposes to conduct a dosing study administering a single dose of NaNO2 via oral gavage to each domestic pig (~20 kg).. Tissue sampling time periods will conform to the guidelines with samples collected within 24 hours of dosing. The rationale for the tissue sampling time points and doses is provided on page 2.

Treatment Groups Dose Administered to Pigs by Gavage

(mg/kg)

Number of Pigs per Treatment

Group

Tissue Sampling Time Points

(hours post-gavage) Control 0 4 1.5

Sub-lethal - NaNO2 80 4 1.5 Sub-lethal - NaNO2 80 4 10

Lethal - NaNO2 400 4 1.5

Attachment 1, 12639521Q0024

Analytical Phase: Muscle, fat, and liver tissue samples will be analyzed for the presence of nitrite. The target nitrite LOQ is to be determined.

Study Design Rationale

1) The low sodium nitrite dose level was selected to reflect a sublethal dose (80 mg/kg) most likely to ensure survival. Cowled et al. (2008) reported the minimum lethal dose (MLD) of sodium nitrite delivered to pigs by gavage was 90 mg/kg. Texas Parks and Wildlife (TPW) (TPW, 2011) reported an MLD for sodium nitrite of 113 mg/kg when delivered by oral gavage, and an LD50 of 133 mg/kg. Both Cowled et al. and TPW reported an LD99 of ~ 400 mg/kg for pigs. The dose levels for this study were selected to cover sub-lethal bait consumption and consumption of multiple doses. Some feral swine may consume more than two lethal doses. However these animals may die more quickly, thus impacting the proposed sampling time. The average time to death for a pig receiving 400 mg/kg sodium nitrite is 2 - 3 hours.

2) The most relevant sampling periods represent times when pigs would be likely to be harvested, before onset of symptoms at 1.5 hours, and cessation of symptoms for sub-lethally dosed pigs at 10 hours.

Snow (unpublished data) reported onset of incoordination at ~ 1.6 hours in pigs receiving sodium nitrite at 400 mg/kg. The time to death is typically 2 -3 hours after feeding on toxic bait. See graph below.

Cowled et al. (2008) showed that pigs receiving sub-lethal doses of 90 mg/kg sodium nitrite recovered at approximately 600 ± 187 minutes (~10 hours) post-dose. Time to onset of symptoms and death are accelerated with increasing dose. Cowled et al. (2008) reported onset of symptoms within 0.9 hours with death at ~2.15 hours, and Snow (unpublished data) reported onset of symptoms at < 0.5 hours and death at < 0.66 hours. Thus, pigs consuming multiple lethal doses of sodium nitrite mixed in bait die quickly and closer to bait stations, and therefore are less likely to be harvested than pigs consuming ≤ 400 mg/kg.

3) The analytical phase of the study will measure one analyte, nitrite. Dietary nitrite is metabolized to nitric oxide which is unstable (ATSDR 2017). The bioavailability of nitric oxide is 2-6 seconds. Nitric oxide may be converted to nitrate, which in turn may be converted to nitrite. Given the difficulty in distinguishing endogenous from exogenous sources of nitrite, the control animal tissues will serve as a baseline of endogenous nitrite and possible dietary exogenous sources unrelated to treatment.

Study Design Deviation

1) Deviation from the guideline requirement of 28 days is requested based on the intended use pattern of the toxicant in field applications and its effect to feral swine. Currently, baiting with the toxicant would not extend beyond 2 days. In addition sodium nitrite is being proposed as a toxicant for use against feral swine, therefore animals would succumb to the effects of sodium nitrite much sooner than 28 days if applied at expected doses that would occur during field application. The current guideline requirement is designed to measure pesticide residues in food items that have been treated with a pesticide and then are used as a source of food for domestic animals that may be harvested for human consumption which is not the intended use of sodium nitrite for feral swine. For these reasons APHIS is proposing one dose of sodium nitrite administered to each pig and then tissue would be collected for residue analysis at 1.5 or 10 hours depending on the treatment group.

References

1. ATSDR. 2017. Toxicological profile for nitrate and nitrite. 278 pages.

https://www.atsdr.cdc.gov/toxprofiles/tp204.pdf

2. Cowled, B.D., P. Elsworth, and S.J. Lapidge. 2008. Additional toxins for feral pig (Sus scrofa) control:

identifying and testing Achilles’ heels. Wildlife Research 35, 651-662.

https://www.publish.csiro.au/wr/wr07072.

3. Snow, N.P., J.A. Foster, E.H. VanNatta, K.E. Horak, S.T. Humphrys, L.D. Staples, D.G. Hewitt, and K.C.

VerCauteren. 2017. Potential secondary poisoning risks to non-targets from a sodium nitrite toxic bait for invasive wild pigs. Pest. Manag. Sci, 74: 181-188.

https://onlinelibrary.wiley.com/doi/abs/10.1002/ps.4692.

4. TPW. 2011. Effects of Sodium Nitrite on Feral Swine and Non-Targets, TX Dept. of Ag. Project Number FH-1-05. 8 pages.

https://www.atsdr.cdc.gov/toxprofiles/tp204.pdf https://www.publish.csiro.au/wr/wr07072 https://onlinelibrary.wiley.com/doi/abs/10.1002/ps.4692