Trends in birth defects for a Hawaiian population exposed to heptachlor and for the United States.

The 1980-1982 milk supply contamination on the island of Oahu, Hawaii, by the insecticide heptachlor offered an opportunity to investigate the possible human teratogenicity of this organochlorine. An analysis of incidence rates for 23 major congenital malformations, derived from hospital-generated data collected by the Birth Defects Monitoring Program of the Centers for Disease Control, failed to show any remarkable rate increase on Oahu in 1981-1983, based on comparisons with the rates for previous time periods on this island and with the rates for two unexposed populations (the other Hawaiian islands and the total U.S.). A rise in the rates of cardiovascular malformations and hip dislocation was apparent but antedated the exposure. These results suggest that no major rate increase for malformations recognized at birth resulted from the heptachlor contamination on Oahu. However, misclassification of exposure status in this study may have obscured a more moderate effect.