Assessing the toxicity of lead in sediments to Hyalella azteca: the significance of bioaccumulation and dissolved metal

The relationship between bioaccumulation and toxicity of Pb to Hyalella was the same for animals exposed: to Pb in water alone and for those exposed t o ph-spiked sediments, provided that the animals were gut cleared before Pb analysis. The same critical body concentration (about 126 nmol.g dry mass( -1)) can be used to predict Pb toxicity in both water-only and sediment exp osures. Furthermore, Pb bioavailability in Pb-spiked sediments was due prim arily to dissolved metal: animals caged above the sediments accumulated the same amount of ph and had the same mortality as animals exposed directly t o sediment. Increasing the water to sediment ratio from 4:1 to 67:1 resulte d in a lower dissolved organic C and lower total dissolved Pb concentration in the water but no change in bioavailable Pb (i.e., bioavailable Pb was n ot proportional to total dissolved Pb). The overlying water concentration m ay be a useful indicator of bioavailable Pb in sediment tests, provided a l arge water to sediment ratio is used to reduce the effect of sediment on ov erlying water quality (i.e., Pb-complexing capacity). Although less reliabl e than body concentration measurements, this could provide a useful screeni ng tool for possible Pb-induced toxicity because it can be measured without test animals present.