Efficacy of histopathology in detecting petrochemical-induced toxicity in wild cotton rats (Sigmodon hispidus)

A variety of chemical mixtures exist in the soil of petrochemical waste sit es, and many of these compounds are known immunotoxicants that have been ob served to induce immune alterations in wild rodents inhabiting many of thes e petrochemical waste sites. Conventional histopathological assessments hav e been widely used with considerable success to investigate immunotoxicity of various agents under laboratory conditions. We hypothesized that histopa thologic assessments would be equally sensitive for detecting exposure to c omplex mixtures of toxicants in cotton rats (Sigmodon hispidus) residing in contaminated habitats. Histopathological parameters were examined from a t otal of 624 cotton rats that were seasonally collected from 13 petrochemica l-contaminated waste sites and 13 ecologically matched reference sites in O klahoma over a 3-year period. Histopathological examination did not reveal any lesion associated with exposure to petrochemical wastes except renal in clusion bodies. Prevalence and severity of histologic lesions in liver and kidneys of cotton rats were significantly influenced by season, where preva lence and severity were lower in winter than summer on all study sites. The se results suggest that the evaluation of toxicity from exposure to contami nants in the soil of industrial waste sites using histopathological assessm ents is not sensitive enough to detect exposure to the low levels of enviro nmental contaminants present on most waste sites. (C) 2001 Elsevier Science Ltd. All rights reserved.