Purpose

This study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.

Materials and methods

Water-only (96 h) and sediment (14 days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC₁₀ and LC₅₀) and effect (EC₁₀ and EC₅₀) concentrations were also determined to assess metal sensitivity for both species.

Results and discussion

Both test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.

Conclusions

Study findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.