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Rotenone
Beyond Pesticides Rating: Toxic

The widely used botanical insecticide rotenone (Derris™, Prentox™, Chem Fish™) is often used by home and commercial "organic" gardeners as an alternative to commercial "chemical" insecticides. Yet, farmers and gardeners should be aware of rotenone's potential hazards and toxicity.  

Despite widespread use and findings that residues are persistent, all agricultural uses of rotenone were exempted from tolerances (the establishment of maximum legal residue levels) in 1955 by the Food and Drug Administration (FDA), and, therefore, most data requirements were waived. EPA, now responsible for the establishment of tolerances, is reevaluating the 1955 exemption and has issued a special Data Call-in notice for residue data. 

Rotenone and rotenone resins are found in the roots of 68 species of legume plants, but most commercial supplies come from the South American cubé, the Malaysian derris, and Brazilian tembo plants. The resins are not very soluble in water, and are usually used either as a dust or in an oil or kerosene solution, sometimes mixed with the quicker-acting pyrethrins and the synergist piperonyl butoxide. Dust formulations have also long been used on animals to control lice and ticks, and on humans for treatment of chiggers and scabies. Noxfire™ has been used as a drench to control fire ants on lawns, and one formulation is registered as a mosquito larvicide.           

Rotenone is non-phytotoxic and unstable to sunlight, air and water, so applications lose their efficacy within a week. 

Toxicologically, rotenone is a slow-acting nerve poison which acts by inhibiting respiratory metabolism in cells, essentially paralyzing affected insects. Specifically, rotenone interferes with the mitochondrial electron-transport system. In animals, it is very poorly absorbed by the gastro-intestinal tract, and is so irritating that it promptly induces vomiting. However, in prolonged feeding tests in rodents, rotenone caused growth depression. Test animals fed dust formulations of rotenone developed muscle tremors, severe pulmonary and skin irritation from exposure to dust, severe hypoglycemia (low blood sugar), clonic convulsions, and respiratory depression resulting in death. EPA has no record of human fatalities or clinical poisoning reports. 

EPA conducted a Pre-Special Review investigation of rotenone in 1975. This was triggered by data indicating that rotenone could arrest cell multiplication and cause developmental abnormalities in frog eggs and chick embryos. Also, a controversial Spanish carcinogenicity study purported to find high incidences of mammary tumors in rats. In 1981, the Agency concluded that the Spanish study had major deficiencies, and that attempts by an EPA contractor and the National Toxicology program to duplicate it in two species of rats and one mouse species had filed to detect any increase in tumors over the control animals. 

In 1980, the U.S. Fish and Wildlife Service took on the burden of paying for further toxicological studies (chemistry, environmental fate, teratology, mutagenicity, metabolism, and residue studies in water and fish) in order to maintain rotenone's registration when it became clear, according to EPA, that 'no industrial sponsors (were) willing to conduct or fund the research studies needed to obtain registrations by fishery managers and fish culturists. At best, the gross sales of one of the major fishery chemicals is less than $500,000 per year." 

Researchers have found that rotenone dust residues persist on lettuce and tomatoes nearly twice as long as do wettable powders, with half-lives between 3 and 5 days, and that both the parent and major metabolite are stable to boiling in tomato homogenate. Still, despite outstanding questions of ecological and health effects, the use of rotenone is widely accepted under organic certification programs. 

References:

DeWilde, A.R., et al. 1986. "A case of fatal rotenone poisoning in a child." J. Forensic Sci. 31:1492-98. 

Gosselin, R.E. 1984. Clinical Toxicology of Commercial Products. Williams & Wilkins, Baltimore, MD. 

Hayes, W.H. 1982. Pesticide Studies in Man. Williams & Wilkins, Baltimore, MD. 

Newsome, W.H. & J.B. Sheilds. 1980. "Residues of rotenone and rotenolone on lettuce and tomato fruit after treatment in the field with rotenone formulations." J. Agric. Food Chem. Jul/Aug. p. 772. 

Thomson, W.T. 1984. Agricultural Chemicals: Insecticides. Thomson Publications, Fresno, CA. 

U.S. Department of Health & Social Services. 1988. "Toxicology and carcinogenesis studies of rotenone in F344/N rats and B6C3F1 mice." National Toxicology Technical Report Series No. 320. National Institutes of Health. Bethesda, MD. 

U.S. EPA. 1988. Guidance for the reregistration of pesticide products containing rotenone as the active ingredient. Office of Pesticide Programs. Washington, DC. 

U.S. EPA. 1983. Data call-in notification: Rotenone. Office of Pesticides and Toxic Substances. Washington, DC. 

U.S. EPA. 1981. Rotenone; Completion of Pre-RPAR Review. [46 FR 36745]. 

U.S. EPA. 1980. Minutes of meeting between EPA & FWS regarding rotenone: November 3, 1980. Office of Pesticide Programs. Washington, DC. 

U.S. EPA. 1980. Rotenone: Pre-RPAR Review. Office of Pesticides & Toxic Substances. Washington, DC. 

Reprinted from Pesticides and You, Volume 7, No. 3, August, 19807.