Effects of chronic dietary hexavalent chromium on bioaccumulation and immune responses in the sea cucumber Apostichopus japonicus

Sea cucumbers Apostichopus japonicus (3.54 {+/-} 0.01 g of wet weight) were exposed to five concentrations of dietary hexavalent chromium [0 (control), 100, 200, 400, and 800 mg Cr6+/kg dry weight] amended with K2Cr2O7 for 30 days. The bioaccumulation and immune responses [antioxidant enzymes: superoxide dismutase (SOD) and catalase (CAT); hydrolytic enzymes: acid phosphatase (ACP) and alkaline phosphatase (AKP)] of sea cucumbers were subsequently evaluated. This study found that the order of Cr accumulation in the experimental tissues was respiratory tree > intestine > body wall. Significantly lower SOD activities occurred in the 400 mg/kg group compared to that in the control group. Higher dietary Cr6+ exposure (400 and 800 mg Cr6+ /kg dry weight) did not negatively alter the CAT activities, but significantly inhibited CAT activities in 100 mg/kg group, compared to control group. ACP activities in groups 200, 400 and 800 mg/kg were significantly lower than those in control group, while no significant differences occurred in AKP activities among groups. The present study provides important information into the bioaccumulation and immune responses of the sea cucumber A. japonicus in response to chronic dietary Cr6+ exposure.