APPENDIX C-4

Summary of Toxicological Information on Commonly Used Adulticides

Introduction

A number of different pesticide products containing numerous different active ingredients are registered in New York State for mosquito control. Broadly, these products can be broken down into either larvicides (those pesticides that control immature forms of mosquitoes) or adulticides (those pesticides that control adult forms of mosquitoes). Many larvicides and adulticides have uses other than vector control for public health protection on their label directions and may have residential mosquito control only as an incidental use to more general residential treatments (e.g., cockroach or carpenter ant control in and around the house). These types of pesticides were not included in the following analysis. The pesticide products and their active ingredients that are included are those that are adulticides and are either labeled strictly for public health vector control and are likely to be considered for this use or contain these label directions and have been used in this manner. The selected products have both aerial and ground application directions on their labels. The products that are considered in this comparison are: Fyfanon ULV, Dibrom Concentrate, several permethrin products (e.g., Aqua-Reslin, Biomist 1.5 + 7.5 ULV), Scourge and Anvil 10 + 10 ULV. Collectively, these products contain malathion, naled, permethrin, resmethrin, sumithrin and piperonyl butoxide as active ingredients. Piperonyl butoxide is a synergist that is present as a co-active ingredient in the permethrin, Scourge and Anvil products. Piperonyl butoxide is in these formulations to enhance the insecticidal activity of the pyrethroid active ingredients.

The risk associated with the use of a chemical depends on the toxicity of the substance and the extent of exposure an individual or population has to that substance. Toxicity is a term that describes the types of effects produced by a substance as well as the potency with which it produces the effects. The following tables compare different types of toxicity for several different mosquito adulticide active ingredients. The types of toxicity are broken down into acute toxicity, chronic toxicity, reproductive toxicity and developmental toxicity (these terms will be defined later in the document). Before a pesticide active ingredient is registered by the U.S. Environmental Protection Agency, studies that determine these types of toxicity must be conducted, and the tables summarize the results of these studies. Also included is a table on the reference dose and its basis for each of the selected active ingredients. The reference dose (defined more fully later in the document) is a value based on the toxicity of a chemical that can be used to characterize risk.

The tables allow a comparison of the relative toxicity of the selected active ingredients. However, it is important to recognize that the different studies used different dose levels and may have differences in the study design and conduct. In addition, the results may present toxicity endpoints which differ in their severity, tissue site, reversibility and biological significance. As a result, comparing effect levels from the studies on different active ingredients must be done with these considerations in mind. The same also holds true when comparing reference dose values for the different active ingredients as the basis and quality of the study used for the reference dose derivation can greatly affect its numerical value.

Aside from toxicity, exposure potential is integral to determining risk posed by use of a given mosquitocide. The application rate is one of the most important factors in determining exposure, and although the application rate for each of the selected active ingredients is relatively low, they differ by as much as 65-fold. The method of application (e.g., aerial vs. ground spray) as well as the frequency of application are also influential in determining exposure. Exposure can occur during or shortly after an application from inhalation of the spray, as well as from direct contact with skin, eyes or mucous membranes. Exposure to the active ingredients or their degradates can also occur after an application through contact with surface residues (e.g., from patio furniture or swingsets), from food (e.g., homegrown vegetables or fruit) and possibly from drinking water and contact with or ingestion of soil. The extent to which exposure to an active ingredient will occur subsequent to an application depends on its chemical/physical properties and the rate at which it dissipates in the environment.

Mosquito adulticides are applied either singly or periodically for a relatively short period of time (i.e., weeks or months) rather than continually for long periods (i.e., years). Consequently, for the evaluation of potential health effects from mosquitocide applications, it is important to compare application rates or estimated exposures to toxicity endpoints evaluated in either single exposure studies (e.g., LD₅₀ studies, discussed later) or in limited repeat exposure studies (e.g., developmental toxicity studies). Developmental toxicity studies involve the exposure of pregnant animals to a chemical repeatedly for a short period of time during gestation for the purpose of measuring birth defects and other endpoints that may indicate impacts to developing offspring and are appropriate for this comparison. Chronic exposures are not likely to result from mosquitocide applications given the limited number of applications made per year, the limited portion of the year when applications are made and the dissipation of a pesticide once it is applied. Chronic toxicity effects, both cancer and non-cancer, generally result from continual, frequent exposures over a prolonged period of time, sometimes many years. However, people may also be exposed to these same chemicals, possibly on a long-term basis, because of their use for purposes other than mosquito control. Therefore, the chronic toxicity endpoints should also be considered. The relative importance given by risk managers to the different toxicity endpoints may vary, depending on such factors as anticipated mosquito adulticide use.

Revised: August 2000