Early developmental effects of separate or combined perinatal exposure to methylmercury (MeHg) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) in the rat

Abstract

Objectives: Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are ubiquitous and persistent environmental pollutants and food contaminants. Both are neurotoxic, especially for the developing nervous system.

Material and methods: Female rats were exposed from day 7 of pregnancy up to day 21 after the delivery to MeHg in drinking water, PCB 153 per os or MeHg+PCB 153. Assessment of the exposure effects in mothers included food and water intake, body weight and reproduction success. Assessment of the progeny comprised determination of body weight, time of pinna detachment, eye opening, incisor eruption, and the negative geotaxis, grip strength and righting reflex.

Results: The following effects of the exposures were observed: A) MeHg: 0.5 mg/kg/day - no effect on maternal health status and reproduction. In the progeny: faster incisor eruption and hastened negative geotaxis development. MeHg 2.0 mg/kg/day: In mothers: signs of MeHg toxicity (reduced food intake and body weight, ataxia) during lactation. In the progeny: reduced rate of body weight increase, accelerated incisor eruption but delayed development of the righting reflex. B) PCB 153 exposure: 1.0 mg/kg/day: no effect on maternal health status, reproduction success or morphological and physical development of the progeny; 5.0 mg/kg/day: no effect on maternal health status and reproduction. In the progeny: accelerated growth in females, faster pinna detachment and incisor eruption but delayed development of the grip strength. C) MeHg+PCB153 exposure: none overt effect was noted in mothers or in their progeny.

Conclusion: The results confirm the ability of a low level perinatal exposure to MeHg or PCB 153 to affect the early development in the rat. They have not provided, however, an evidence of a synergistic interaction of these contaminants. To the contrary, the results suggest that, at least under the conditions prevailing in the present study, MeHg and PCB 153 interact antagonistically.