Mercury toxicity in the aquatic oligochaete Sparganophilus pearsei: I. Variation in resistance among populations.

Mercury contamination has become a problem in many San Francisco Bay Area watersheds due to its elevated presence in sediments and aquatic organisms. The present study used laboratory lethal toxicity (LC50) tests to examine the mercury tolerance of aquatic oligochaete worms, Sparganophilus pearsei, from contaminated and uncontaminated areas. The oligochaetes were collected in the following fresh water reservoirs: Sandy Wool (reference area), San Pablo, Lake Anza, Lake Herman, and Guadalupe. These last four reservoirs were contaminated with levels of mercury that ranged from 1.5 to 2 mg/kg (wet weight). Mercury concentrations in sediment and tissue from Sandy Wool were below detection limits and worms from this site were the least tolerant of mercury in laboratory exposures (LC50 = 0.22 mg/L). Worms from the other, more contaminated, reservoirs contained elevated tissue mercury concentrations and were more tolerant in laboratory tests (LC50 = 1.48-2.19 mg/L). The present study demonstrates that different populations of the aquatic oligochaete S. pearsei have developed different tolerances to mercury depending on their previous history of exposure to mercury contamination.