Distribution Of Heavy Metals In The Sea Cucumber Aquaculture Ponds And Its Potential Ecological Risk Analysis

With the development of social economy and modern industry, the influence of land-based pollution on nearshore environment is more and more significant. As special physicochemical property and toxic effect, heavy metals exert its high hazard and hensce difficult to be repaired. The sea cucumber Apostichopus japonicus is a deposit-feeding benthic animal. During the growth and development, the animal can be affected by heavy metals pollutants, resulting in its unsafety as food.In the present study, three types of samples, sea cucumbers, particulate matters and surificial sediments, were collected from sea cucumber aquaculture ponds in Zhuanghe, Liaoning province. The sampling time is May, July, September and November in one year. Samples are cheated for the detection of Pb, Cd, Hg, As, Cr, Cu, Ni. Based on the data obtained, the distribution pattern of heavy metals in sea cucumbers and water body was analized. Furthermore, the data of sediments would be used to assess the potential ecological risk of heavy metals.The results show that:a) The heavy metals level in intestinal contents is significantly higher than that in all tissues or organs. An obvious relevance of heavy metals content can be observed between body wall and intestinal content, but negative between body wall and suspended particulate matter/surficial sediment. This indicats that the heavy metals in body wall are obtained mainly from the indirect bioavailability of food in the digestive tract, not absorbed from the ambient water by body surface.b) The distribution of heavy metals in biotic facies and abiotic facies follows some regularity. Broadly speaking, suspended particulate matter mainly contributes to the heavy metals exposure of sea cucumbers’ intestinal content, while relatively few by sediment, implying the difference between closed pond water body and open marine environment. The heavy metals in suspended particulate matter could deposit on the sediment, and then enter the intestinal tract through the feeding activity of sea cucumbers. Subsequently, these heavy metals are released and transported to the body wall.c) To compare with the limited standard in China, we analized the heavy metals content in the edible parts(body wall and longiditunal muscle) of sea cucumbers. The content of Cu, Cd, Hg in all samples does not exceed the limited values. However, the content of Pb, Cr, Ni, As in some samples significantly exceed the permitted values. Among them, exceeding content and exceeding standard rate of Pb, Cr are particularly high, indicating an existing risk of food safety.d) According to the hazard coefficient, the potential hazard of seven heavy metals follows the order: Ni<Cr<As<Cd<Cu<Pb<Hg. From the hazard index of multiple metals, the pollution level of heavy metals in sea cumcumber aquaculture ponds is considered as medium. In the low temperature months May and November, the potential hazard of heavy metals is relatively higher. In May, it shows a high risk of lead pollution. In November, the risk mainly comes from mercury.