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Appraisal taken from International Programme on Chemical Safety, Environment Health Criteria 85, Lead - Environmental aspects (see attachment to summary in section 6.1).
The toxicity of lead-contaminated water to fish varies considerably, depending on the availability and uptake of the lead ion.
Factors affecting this availability are water hardness (presence of divalent anions), pH, salinity, and organic matter. Uptake is affected by the presence of other cations and the oxygen content of the water.
Organic lead is taken up more readily than inorganic lead. The 96-h LC50 for inorganic lead in sensitive species can be as low as 1 mg dissolved lead/litre; nominal concentrations being up to 100 times higher in hard water. The few data available suggest that the toxicity of organic lead may be 10 to 100 times higher than that of inorganic lead. Long-term exposure of adult fish to inorganic lead induces sublethal effects on morphology, amino levulinic acid dehydratase (delta-ALAD) and other enzyme activities, and avoidance behaviour at available lead concentrations of 10-100 mg/litre. Juvenile stages are generally more sensitive than adults, but eggs are often less sensitive because lead is adsorbed onto the egg surface and excluded from the embryo.

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