Fluorosis risks to resident hispid cotton rats on land-treatment facilities for petrochemical wastes

Land-treatment of petroleum wastes is a widely used industrial practice, ye t there has been no comprehensive evaluation of the long-term risks to huma n or terrestrial ecosystems from such practices. We evaluated cotton rat (S igmodon hispidus) populations on three sites in Oklahoma (USA) that histori cally used land-treatment for disposal of various petroleum wastes (July 19 95-March 1997). Average concentrations of fluoride in soil from these sites ranged from 878 to 4317 mg/kg. A census of resident cotton rats on land-tr eatment sites revealed a high incidence (40% overall) of dental lesions com pared to reference populations (<1% dental lesions). During winter there wa s a 34% to 65% increase compared to summer in frequency of dental lesions i n cotton rats on two of the three land-treatment sites. Incidence of dental lesions on two land-treatment sites was greater (9-16%) in female cotton r ats compared to males. Cotton rats from land-treatment sites had higher con centrations of fluoride in bone and greater severity of dental lesions comp ared to reference animals. Dental lesions were considered to be most consis tent with dental fluorosis because of elevated fluoride in bone. Neither co ncentration of fluoride in soil nor level of fluoride in bone was a good pr edictor of severity of dental lesions in cotton rats on land-treatment site s.