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 to 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 exposures. Furthermore, Pb bioavailability in Pb-spiked sediments was due primarily to dissolved metal: animals caged above the sediments accumulated the same amount of ph and had the same mortality as animals exposed directly to sediment. Increasing the water to sediment ratio from 4:1 to 67:1 resulted 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 not proportional to total dissolved Pb). The overlying water concentration may be a useful indicator of bioavailable Pb in sediment tests, provided a large water to sediment ratio is used to reduce the effect of sediment on overlying water quality (i.e., Pb-complexing capacity). Although less reliable than body concentration measurements, this could provide a useful screening tool for possible Pb-induced toxicity because it can be measured without test animals present.