Human Health and Environmental Relative Risks of WNV Mosquito Control Products

HUMAN HEALTH RISKS; LARVICIDES

Absolute Risks

Information from the labels found in the label review (Appendix III; Tables 6 to 10, Human Health Precautions) addresses precautions that the applicators, mixers and loaders need to take when using specific concentrated larvicide products. As with the adulticides, the EPA required label language is found in Appendix III; section 1. All of the larvicide product labels reviewed here, with the exception of the 5% temephos product also have "CAUTION" labels. The "WARNING" label on the temephos product reflects the higher concentration and greater potential for exposure. Fewer precautions for applicators are required on the labels of the larvicides due to their lower mammalian toxicity.

In their 1998 RED for Bt containing products (1) EPA summarized the acute toxicity of Bacillus thuringiensis (Bt) to humans and other mammals in the following manner:

"The Agency has an historical toxicology data base for Bacillus thuringiensis (See 4/23/86 Memorandum from William Woodrow to Arturo Castillo). In addition, a summary review of mammalian toxicity studies was published by Agency reviewers (McClintock, J.T., C.R. Schaffer, & R.D. Sjoblad (1995) A Comparative Review of the Mammalian Toxicity of Bacillus thuringiensis - Based Pesticides. Pestic. Sci. 45, 95-105). To date, no known mammalian health effects have been demonstrated in any infectivity/pathogenicity study (Table 1, Acute Mammalian Toxicity for Bacillus thuringiensis ). The sum total of all toxicology data submitted to the Agency complete with the lack of any reports of significant human health hazards of the various Bacillus thuringiensis strains allow the conclusion that all infectivity/pathogenicity studies normally required under 40 Code of Federal Regulations, Part 158, for the use patterns of

the registered products be waived in the future as long as product identity and manufacturing process testing data indicated there is no mammalian toxicity associated with the strain (1)."

Bacillus sphaericus has a mechanism similar to Bt and has a low level of mammalian toxicity profile. Methoprene is an insect growth regulator which mimics juvenile hormone, here again with low mammalian toxicity (3). The POE MMF acts by suffocating the larvae and has low toxicity for mammals (34). Temephos is characterized as a low to moderate toxicity compound relative to the other organophosphates. It has an incomplete database for reproductive, developmental, chronic toxicity including carcinogenicity (39, 40). If temephos were to be considered, a detailed review of the toxicity and exposure database would have to be undertaken.

Relative Risks

Due to the low level of mammalian toxicity of the biological and oil larvicides and the low potential for bystander exposure, the Medical Advisory Committee concluded that a bystander human health risk assessment was not warranted for the larvicides.

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