Effect Of Geochemical Characteristics To Metals Bioavailability In Marine Sediment

In the process of evaluation of metals toxicity, metal bioavailability is an essential consideration because different sediments can exhibit differing degrees of toxicity for the same concentration of metal contaminant. Various sediment phases are responsible for binding trace metals and rendering them non-bioavailable. In 1990, it was shown that acid volatile sulfide (AVS) is responsible for binding certain divalent metals on a molar basis. By measuring AVS and the simultaneously extracted metals (SEM), potential metal bioavailability may be determined. In this research, sediments from Longwangtang and animals from Xiaoping Island beach areas were analyzed by a variety of methods to determine the extent and distribution of metal contamination and further the prediction of metal biotoxicity. For more accurately describe metal bioavailability in marine sediment, the other two factors, clay minerals and organic matter of sediment were also considered to make pilot study in metal bioavailability.The field sites selected for validating laboratory results, Jinzhou Bay is the region with significant metal contamination which has natural gradient of metals concentration. In Jinzhou Bay, analysis of sediment and pore-water samples showed that AVS took effect on binding metal and decreased their bioavailability. In general, bioavailability predictions based on SEM-AVS analyses compared favorably with sediment toxicity testing results. The investigation results showed that when the molar difference between SEM and AVS (i.e., SEM-AVS) was less than 0 umol/g, the concentration of metals in the sediment interstitial water was low and few toxic effects were observed. Conversely, when difference of SEM-AVS exceeded 0 umol/g, a dose-dependent increase in the relative concentration of metals in the pore water was detected and apparent organisms toxic effects were observed.In this study, clay minerals in sediment take effect on metals bioavailability mainly through powerful adsorption to metals. In the metals spiked experiment of sediment with different clay minerals content, it was found, when AVS in the sediment was exhausted, sediment samples of higher clay minerals content still makes metals concentrations in pore water maintain lower level than that of relavant low clay minerals content. At the same time, different adsoption extent of clay minerals to metals was presented in different metals spiked sediment samples.Organic matter in sediment also takes effect on metals bioavailability, in this study, organic matter in sediment present significantly influence in Cu spiked sediment sample, while few impact on Cd spiked sediment. Organic matter insediment can increase Cu concentration in pore water, mainly because of humus high solubility in water which occupied the major part of organic matter. The effect of organic matter takes contrary influence in metals partitioning between solid and liquid phase in sediment comparing with AVS and clay minerals.The laboratory plus field experiments performed to find, in addition to AVS, the grain size and organic matter (mainly of humic substances) are important for binding particular metals. Taking into account metal partitioning affected by organic material and grain size factor allow the prediction of metal bioavailability work well in low AVS environments.