Isobenzan / published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organisation, and the World Health Organization

ABSTRACT

Evaluates the risks to human health and the environment posed by exposure to isobenzan. This cyclodiene insecticide was manufactured in the Netherlands from 1958 to 1965 and used from existing stocks for several years thereafter. Present sources of human and environmental exposure are restricted to the original waste-disposal sites and to polders which were built up using mud dredged from contaminated harbour areas. Although recent research on this insecticide has been limited, the report draws heavily on a number of proprietary toxicological studies made available by the manufacturer. The opening sections summarize the physical and chemical properties of isobenzan and review data on mechanisms of biodegradation in soil and water. A section devoted to environmental levels and human exposure assesses findings from the monitoring of water and soil samples, food crops, dairy products, and terrestrial and aquatic organisms. Other studies reviewed show that isobenzan is readily absorbed through the gastrointestinal wall, accumulates in the tissues and organs of laboratory animals, is very persistent in the environment, and is highly toxic to fish, shrimp, and birds. Concerning the results of toxicological studies in laboratory animals, the report cites over-stimulation of the central nervous system, resulting in convulsions, as the predominant effect of exposure. This observation is supported by 15 cases of clinical intoxication in exposed workers, including eight cases with convulsions. No studies of teratogenicity or mutagenicity were available for evaluation. Despite the limited number of studies, the report concludes that isobenzan poses a significant hazard to the environment and to exposed workers, and that no human or environmental exposure to this substance, whether used as an insecticide or for any other purpose, should be allowed