Avoidance responses to aluminium in the freshwater bivalve Anodonta cygnea

This study examined the effect of aluminium (Al) on the filtering behaviour (shell opening or gape) of the freshwater bivalve Anodonta cygnea L in neu tral fresh water. Parallel measurements of Al concentration in the soft tis sues were made to examine the relationship between changes in behaviour and accumulation of Al. The number of lysosomal granules in the gill, kidney a nd digestive gland were counted, as lysosomes are known to be involved in t he excretion and detoxification of trace metals. The bivalves were exposed to two environmentally relevant concentrations of added Al i.e. 250 and 500 mug l(-1) (9.25 and 18.5 muM l(-1)) at neutral pH for 15 days and shell mo vement monitored continuously. Aluminium affected the mussels' filtering ac tivity, producing an avoidance reaction whose magnitude was concentration-d ependent; 250 mug l(-1) added Al produced no detectable change, while 500 m ug l(-1) Al reduced mean duration of shell opening by 50%. This effect was irreversible over a 15 day recovery period. Tissue levels of Al after 15 da ys exposure were an order of magnitude higher in animals exposed to 250 mug l(-1) added Al than in those exposed to 500 mug l(-1). This was consistent with the inhibition of filtering activity due to valve closure at the high er concentration, which may have prevented uptake of Al. In addition, proba ble different chemical speciation of Al in the water column (soluble for 25 0 and colloidal for 500 mug l(-1) may lead to marked differences in tissue uptake. The kidney and digestive gland were the main sites of accumulation of Al and concentrations remained significantly elevated 15 days after tran sfer of animals to clean water. It is suggested that mucus plays a role in the exclusion of Al as elevated concentrations were measured in the pseudof aeces of animals during and after exposure. Lysosomal granules may be invol ved in the intracellular handling and detoxification of Al as numbers incre ased significantly in all organs during exposure and continued to increase after the animals were transferred to clean water. The present study provid es evidence for the bioavailability and toxicity of Al to mussels at neutra l pH and at concentrations which are known to enter neutral freshwaters whe n mobilised by natural or anthropogenic acidity. The changes in behaviour a nd uptake of Al in the mussel observed in this investigation are, therefore , likely to be reflected in the natural environment and the degree to which Al affects the 'fitness' of the mussel populations and the transfer of Al through the food chain merit investigation. (C) 2001 Elsevier Science B.V. All rights reserved.