Human Health and Environmental Relative Risks of WNV Mosquito Control Products

RESULTS: ENVIRONMENTAL RISKS; ADULTICIDES

Absolute Risks, Adulticides; Aquatic Species

EPA evaluates the environmental toxicity database with respect to non-target species, models the exposure potential and evaluates associated risks to non-target organisms. Following this assessment, EPA requires certain label language to protect non-target species (Appendix III; section 1). The label information for the adulticides is found in Appendix III; Tables 1 to 5, Environmental Hazards section.

EPA risk assessment methods for determining the absolute risks for nontarget species involve the calculation of risk quotients and comparing these values with levels of concern (LOC). The exposure assumptions for adulticides include an estimated environmental concentration (EEC) based on a direct application into a standardized pond (1 acre pond 6 inches or 6 ft deep). EPA's LOCs are: acute risk 0.5, restricted use applications 0.2, and endangered species 0.1. EPA incorporates multiple treatments and environmental fate parameters in their modelling. Similar to the mammalian situation, EPA has recently released Environmental Fate and Effects Division chapters for malathion (19) and naled (18). EPA has not released EFED chapters with current evaluations of absolute risks for the synthetic pyrethroids.

For malathion, EPA's risk evaluation is presented in Table 4. The bluegill was evaluated not as the most sensitive species, but rather the most representative species for warm water fish. EPA's calculations for mosquito control did not account for multiple sprays. They also assumed that aquatic exposure for ground applications was a maximum of 20% due to continuous drift from micro droplets on air currents (23).

EPA's assessment of the aquatic risks for naled were abstracted from the 1997 EFED Reregistration Chapter C for Naled (18). The assumptions made by EPA for mosquito control with naled include 0.4 lbs per acre and five applications. EPA generated estimates of the EEC using a model and the risk estimates are presented in Table 5.

(a.) Assumes 20% hit to water for ground application

Relative Risks, Adulticides; Aquatic Species

A modified RQ (modRQ) was used to evaluate relative risks for the adulticides . Multiple treatments and environmental half lives were not included in this analysis. Similar to the method used for relative risk comparison in humans, modification of the exposure factor was used. Unlike the method used for human risk assessment, the lower the risk quotient the lower the risks. This process does not include multiple applications or environmental fate of the insecticides. Environmental fate information is found in Appendix V. Tables 1 and 2 and is being used qualitatively in the decision making process.

Maine's relative risk assessment used a worse case exposure scenario by taking the highest application rate (for mosquitoes) found on a product and using this as a surrogate for exposure (modExp). The toxicity endpoint selected was the most sensitive species for warm water fish (WW), cold water fish (CW), estuarine and marine species (EM) and freshwater invertebrates (INV). The estimated risk to aquatic species for mosquito adulticides is summarized in Table 6.

Absolute Risks, Adulticides; Avian Species

In EPA's evaluation of the absolute risk for malathion, the acute avian risks for malathion exceeded the level of concern for multiple agricultural applications at rates equal to or greater than 3.75 lb ai/A. The level of concern (LOC) for birds is 0.5. Mosquito ULV use rates are lower than this rate; 0.054 lb ai/A to 0.6 lb ai/A (23). Avian chronic risk quotients exceed EPA's level of concern for malathion broadcast applications at application rates above 0.5 lbs ai/A (23). The purpose of the analysis performed by EPA was to set tolerances for malathion residues on crops. As such, public health mosquito control uses of malathion were not addressed in this analysis (23).

Similar to malathion, EPA's evaluation of avian risks was calculated for naled use on agricultural crops, short grass, long grass and leafy crops. The use rates were 0.65, 0.9, 1.35, 1.8 and 7.2 lbs/acre. The acute avian risks identified for naled exceeded the LOCs for applications at rates greater than 1.9 lbs ai/A. Here again, the LOCs are 0.5 for general applications, 0.2 for restricted use applications and 0.1 for endangered species (18). The mosquito use rates are 0.1 to 0.2 pounds per acre (Appendix IV, Table 1), an order of magnitude lower than the 1.9 lbs per acre which exceeded the LOCs.

Relative Risks, Adulticides; Avian Species

Estimation of relative risk for birds was done using the modRQ method. This method does not estimate an actual environmental exposure dose and there is no information on deposition for ground, environmental half life of the compound, multiple applications, number of animals per acre and other parameters are included in this process. Mathematically, the modRQ is the inverse of the modMOE. The results are found in Table 7.

Adulticides, Bee risks

From the label information in Appendix III Tables 1 to 5 and the toxicity summary in Appendix IV Table 6., it is apparent that bee toxicity is a major issue with use of the adulticides. The WNV steering committee should work with the State Apiarist, Department of Agriculture Food and Rural Resources regarding the location of hives and strategies to reduce bee mortality in the event of an adulticide treatment.

Adulticides, Threatened and Endangered Species

Similar to the bee issue above, the steering committee should make every effort to work with Inland Fisheries and Wildlife regarding known habitats for threatened and endangered species, and the Department of Marine Resources in the event of a coastal zone concern.

Note: The lower the RQ or modRQ the lower the risks.

NEXT: Results: Environmental Risks; Larvicides