Concentration thresholds in accumulation of heavy metals by Haliotis discus and Batillus cornutus.

Abstract

The black abalones and the top shells were exposed to concentration gradients of heavy metals for 120 and 80 days, respectively. The regression formulae, log Y=log A+B log X…(I), were calculated from the relations between metal concentrations in soft bodies (Y) exposed to respective concentration gradients and exposure days (X). Furthermore, the equations, log y=a+bx…(II), were obtained from the correlations between regression coefficients (x) represented as “B” in the formulae (I) and the respective values in concentration gradients (y). The concentration thresholds were estimated as the values of y intercept in the equation(II). In the black abalone, the concentration thresholds for cadmium, chromium, copper and lead were 0.96, 1.61, 3.94 and 2.17μg/l, respectively, and in the top shell, the threshold for cadmium was 0.87μg/l. These values were clearly higher than those of the ordinary concentrations in natural seawaters. On the contrary, the thresholds were extremely lower than the metal concentrations regulated in Environmental Criteria for Human Health (10 for cadmium, 50 for chromium and 100μg/l for lead), Discharge Criteria for Industrial Waste Water (100 for cadmium, 500 for chromium, 1000 for lead and 3000μg/l for copper) and Drinking Water Criteria (10 for cadmium, 50 for chromium, 1000 for copper and 100μg/l for lead). Under these concentrations of metals adopted in the Criteria, the metal contents should be tremendously raised in the soft bodies of the black abalones and the top shells when the life spans and the durations attaining to commercial sizes are taken into consideration.