Investigations on methyl mercury contamination of fishes in the Second Songhua River.

Fishes in the middle reaches of the Second Songhua River in Jilin Province were heavily contaminated by methyl mercury, the average content of 61 fish samples being 0.42 mg/kg. The upper and lower reaches were less contaminated and the averages were 0.12 mg/kg (53 samples) and 0.08 mg/kg (20 samples), respectively. The average methyl mercury content of fishes (20 samples) collected from a nearby "nonpolluted" water reservoir was 0.03 mg/kg. In a total of 134 fish samples collected from the Second Songhua River, 41% of the samples had a methyl mercury content exceeding the National Tolerance Limit of 0.2 mg/kg.