Evaluation of chronic toxicity of water lead for carp Cyprinus carpio using its blood 5-aminolevulinic acid dehydratase

Carp Cyprinus carpio were exposed for 20 days to test waters consisting of combinations of four lead concentrations (0, 10, 100, and 1,000 ppb) and four levels of water hardness (50, 150, 500, and 1000 ppm as CaCO3), and 5-aminolevulinic acid dehydratase (ALA-D) activities and lead concentrations in the fish blood were measured. ALA-D activities decreased with increasing blood lead concentrations, and the activities were negatively correlated to the log of the blood lead concentrations (r = -0.93). Blood lead concentrations increased with increasing water lead concentrations. However, lead accumulation in the blood lowered with increasing water hardness. ALA-D activities in the lead-contaminated fish blood decreased to about 40% of that of the control fish when carp were exposed for 20 days to test water with a water hardness of 50 ppm CaCO3 and a water lead concentration of 10 ppb (Environmental Water Quality Standards relating to Human Health in Japan). Judging from the inhibitory degree of carp blood ALA-D, the standard value is the concentration that may cause chronic toxicity to carp.