Inheritance of mercury tolerance in the aquatic oligochaete Tubifex tubifex.

Resistance to contaminants is an important yet unmeasured factor in sediment toxicity tests. The rate at which mercury resistance develops and its genetic persistence in the oligochaete worm Tubifex tubifex were studied under laboratory conditions. Worms were raised for four generations under two different sediment treatments, one reference clean sediment, the other contaminated with mercury. Worms raised in mercury-contaminated sediment developed mercury tolerance that persisted even when the worms were raised for three subsequent generations in clean sediment. Mercury tolerance was determined by comparative water-only toxicity tests with mercury as the only stressor. Control worms had a mean lethal concentration (LC50) of 0.18 mg/L(-1). Worms exposed to high levels of mercury in sediment had high mercury tolerance with a mean LC50 of 1.40 mg/L(-1). When mercury-tolerant and control mercury-intolerant worms were crossed, their descendants also demonstrated mercury tolerance during lethal toxicity tests. The LC50 for worm descendants resulting from this cross was 1.39 mg/L(-1). Adaptation to mercury exposures occurred rapidly in this group of worms and appears to be due to both phenotypic and genotypic mechanisms. Development of contaminant resistance and adaptation may be common phenomena in aquatic benthic invertebrates, which should be considered during the design and interpretation of toxicity tests.