Australian freashwater mussel Velesunio ambiguus (Philippi) as a biological monitor for zinc, iron and manganese

Abstract

The hyriid mussel V. ambiguus has been proposed as a biological monitor of zinc where there are wide environmental fluctuations. However, in the River Murray there is high variation in zinc content among individuals and between populations; part is systematic, associated with body weight and age, but a larger part remains statistically unexplained. Further, although V. ambiguus readily accumulates zinc, depuration is slow. At zinc concentrations of 20 mg I^-1 and above, mussels avoid taking up zinc by significantly curtailing siphoning, movement and valve opening. Zinc levels above 20 mg l^-1 are lethal, with most deaths occurring in the post-exposure periods immediately after 96-, 176- and 336-h toxicity tests. The estimated 336-h LC₅₀ is 66 mg I^-1, with 95% confidence limits 55 and 77 mg I^-1. Exposure of caged mussels in the zinc-contaminated Molonglo River, N.S.W., suggests that V. ambiguus is not a suitable species to monitor variations in zinc loads between sites, and does not accurately reflect environmental fluctuations of zinc, iron or manganese, although it may have potential for materials other than heavy metals.