Chronic toxicity of methylmercury chloride in rats: clinical study and chemical analysis.

Abstract

Four groups of 56 Sprague-Dawley SPF rats of both sexes were maintained on diets containing 0, 0.4, 2 or 10 ppm methylmercury chloride (MMC) for 130 weeks to evaluate the chronic toxicity and to quantify the accumulation of the compound in various organs and tissues. Ten animals of each group at 13 and 26 weeks, 6 animals at 52 and 78 weeks, and all suvivors at 130 weeks were killed for clinical examinations and mercury analysis. In the 10 ppm group, reduced body weight gain was noted in both sexes, and all the males died within 119 weeks. Neurological signs due to MMC intoxication such as ataxic gait and/or crossing reflex of hindlimbs occurred in 10 males and 7 females after 22 weeks and 46 weeks, respectively. Anemia was seen in males at each designated period. Significant increases in plasma total cholesterol and urea nitrogen indicated impairment of renal function in this group. Tissue mercury level was remarkably high in the hair and lowered in the kidney, blood, liver, and nerve tissues in that order in the 10 ppm group. Accumulation of mercury in the hair and blood increased constantly until reaching plateau at 78 weeks. The mercury levels in the cerebrum, cerebellum, spinal cord and sciatic nerve were relatively constant at lower levels after 26 weeks. The average mercury level in the cerebrum from 26 to 78 weeks was 5.3 and 6.7 ppm in males and females, respectively.