Methyl Mercury and PCB Combination Impairs Motor Skills in Young Rats

Susan Schantz, Ph.D. and Victor C. Wang
University of Illinois at Urbana-Champaign
P01ES11263 and T32ES07326

Background: Methyl mercury and polychlorinated biphenyls (PCBs) are both contaminants that accumulate in the environment and in the tissues of fish. Both compounds have also been linked to neurological and motor deficits in humans in a number of epidemiologic studies. A recent paper from NIEHS-supported researchers at the FRIENDS Children's Environmental Health Center, a five-institution research consortium based at the College of Veterinary Medicine at Illinois, provides additional evidence that the two compounds act together to cause nervous system impairment.

Advance: The researchers exposed female rats to low doses of methyl mercury, PCBs, a combination of the two compounds, or control conditions starting four weeks prior to breeding and continuing through 16 days after birth. Offspring were run through a battery of motor skills tests. Rat pups from the combined exposure group showed significant motor skill impairment in a test of traversing a rotating rod. Rats exposed to PCBs alone were somewhat impaired and rats exposed to methyl mercury alone were unimpaired as compared to the control animals.

Implication: This study demonstrated that combined treatment with methyl mercury and PCBs produced neurological impairments in the pups of exposed female rats. The researchers point out that PCB exposure contributed more to the motor impairment than did methyl mercury possibly due to the low dosage used. Rats exposed to methyl mercury alone demonstrated no significant impairments. The current study could offer an explanation as to why previous epidemiologic studies of humans exposed to methyl mercury by eating contaminated fish have produced conflicting results. The scientists will continue their studies to determine if the two compounds have the same or independent mechanisms of action.

Citation: Roegge CS, Wang VC, Powers BE, Klintsova AY, Villareal S, Greenough WT, Schantz SL. Motor impairment in rats exposed to PCBs and methyl mercury during early development. Toxicol Sci. 2004 Feb;77(2):315-24.