Subcellular cadmium distribution, accumulation, and toxicity in a predatory gastropod, thais Clavigera, fed different prey.

Bioaccumulation and toxicity of Cd were investigated in a marine predatory whelk, Thais clavigera, after being fed with the rock oyster, Saccostrea cucullata, or the herbivorous snail, Monodonta labio, for up to four weeks. The oysters and snails had different subcellular Cd distributions and concentrations in their bodies given their different metal-handling strategies and were exposed to dissolved Cd for two weeks before being fed to the whelks. After four weeks of dietary exposure, the Cd body concentrations in T. clavigera increased from 3.1 microg/g to between 22.9 and 41.8 microg/g and to between 22.7 and 24.1 microg/g when they were fed with oyster and snail prey, respectively. An increasing proportion of Cd was found to be distributed in the metallothionein (MT)-like proteins and organelle fractions, whereas the relative distribution in the metal-rich granules fraction decreased when the whelks were fed Cd-exposed prey. At the highest Cd dosage, more Cd was distributed in the pool of metal-rich granules when the whelks were fed the oysters than when they were fed the snails. Among all the biomarkers measured (MT induction, condition index, lipid peroxidation, and total energy reserve including carbohydrate, lipid, and protein), only MT showed a significant difference from the control treatments, and MT was the most sensitive biomarker for dietary Cd exposure. No toxicity was found in the whelks fed different Cd-exposed prey as revealed by various biomarkers at the different biological levels. Our results imply that metal fractionation in prey can alter the subsequent subcellular metal distribution in predators and that dietary Cd toxicity to the whelks was low, even when the accumulated Cd body concentrations were high.

Microporous chiral metal coordination polymers: hydrothermal synthesis, channel engineering and stability of lanthanide tartrates.

L-Tartrate ions can endure hydrothermal conditions up to 160 degrees C to form the robust, enantiopure open-framework coordination polymers [Ln2(L-TAR)3(H2O)2]3H2O, 1; the addition of succinate results in formation of the related [Ln2(L-TAR)2(SUC)(H2O)2]5.5H2O, with larger channels than , whereas racemic D/L-tartrate gives the more condensed [Ln2(D/L-TAR)3(H2O)2], . TAR = [C4H4O6]2-.

Influences of different selenium species on the uptake and assimilation of Hg(II) and methylmercury by diatoms and green mussels.

We examined the influences of different concentrations and species of Se (selenite, selenate, and seleno-l-methionine) in the ambient environment on the accumulation of inorganic Hg(II) and methylmercury (MeHg) by the diatom Thalassiosira pseudonana and the green mussel Perna viridis. At the experimental concentrations tested (< 500 microgl(-1)), selenite and selenate did not significantly affect the uptake of either mercury species by the diatoms and the green mussels. The assimilation efficiency of Hg(II) and MeHg by the mussels from ingested diatoms was also independent of the inorganic Se loadings in the food particles. In contrast, selenomethionine significantly inhibited the uptake of MeHg and enhanced the uptake of Hg(II) by the diatoms and the mussels, but it did not affect the assimilation from the ingested diatoms. The influence of tissue body burden of Se in the green mussels following pre-exposure to selenite and selenomethionine for different periods (1-5 weeks) on the accumulation of Hg(II) and MeHg was further investigated. Our results showed that tissue Se concentrations did not significantly affect the dietary assimilation of mercury, but the influences on the aqueous uptake were variable. Our study thus, strongly highlights the specificity of the Se-Hg interaction in marine mussels for different Se and Hg species. Both dissolved and dietary uptake appeared to be equally important in the accumulation of Hg(II) and MeHg in the green mussels.

Distribution and behavior of trace metals in the sediment and porewater of a tropical coastal wetland.

Vertical profiles (0-30 cm below surface) of four trace metals-Cadmium (Cd), Chromium (Cr), Lead (Pb) and Zinc (Zn)-in the sediment and sediment porewater of an ecologically important intertidal mudflat in the Mai Po and Inner Deep Bay Ramsar Site were thoroughly studied over a period of 10 months (from March 1999 to January 2000). Two surveys, one in summer and another in winter, involving a total of eight sampling stations were conducted to study the seasonal variation of the remobilization characteristics of these trace metals in the mudflat sediment. The range of depth averaged concentration of these trace metals in the mudflat sediment was: 0.3-0.8 microg/g (Cd); 9.8-91.0 microg/g (Cr); 7.3-69.1 microg/g (Pb); and 39.5-192.0 microg/g (Zn), while that in the sediment porewater was: 0.3-121.1 microg/l (Cd); 3.0-2704.1 microg/l (Cr); 2.6-105.6 microg/l (Pb); and 32.6-4238.3 microg/l (Zn). In general, levels of dissolved trace metals in the sediment porewater were much higher in the summer than in the winter while their concentrations in the sediment were more or less the same throughout the year. Enrichment of Cd, Pb and Zn in the sediment porewater of the upper oxic layer and that of Cr in the oxic-sub-oxic boundary was generally observed. Regions in the vicinity of the Mai Po mangroves and the river mouths of Shenzhen River and Shan Pui River were found to be hotspots of trace metal pollution. Benthic diffusive fluxes of trace metals from the mudflat sediment were also estimated. Of the four trace metals, cadmium showed the greatest tendency toward remobilization from the sediment phase to the more bio-available porewater phase.

Metal partitioning in river sediments measured by sequential extraction and biomimetic approaches.

We quantified the concentrations and distributions of metals (Cd, Cr, Cu, Ni, Pb, and Zn) in the sediments of Tuen Mun River, Hong Kong. The potential bioavailability of metals was assessed with a biomimetic extraction method using the sipunculan gut juices. The sediments were characterized by relatively high concentrations of trace metals. Field collected sediments were highly anoxic and the ratio of simultaneously extractable metal (sigmaSEM) to acid volatile sulfide (AVS) was much less than one in these sediments. The majority (>67%) of Cd, Pb, and Zn were bound to AVS, thus their concentrations in the sediment porewater were low. In contrast, Ni was little bound to AVS due to its lower ratios of SEM-Ni to total Ni concentrations. For Cu, relatively high concentrations in the sediment porewater was found, and total organic carbon, AVS and other resistant sulfide phase were the controlling factors for sedimentary Cu partitioning. Net metal adsorption from gut juices to anoxic sediments was observed in metal extraction experiments, suggesting that AVS determined the bioaccumulation and potential bioavailability of most metals in these sediments. Extraction of metals from the oxidized sediments by the gut juices was mainly attributed to metal redistribution from AVS to other geochemical phases. The gut juices were the most effective solvent or extractant than the simple electrolyte solution [I (NaNO(3)) = 0.01 M] and the natural overlying water. Cd was more easily extracted from the oxidized sediments than Zn that tended to have a stronger binding affinity with Fe-Mn oxide, clay and organic matter. The application of partial removal techniques in metal extraction experiments further demonstrated the differential controls of various sediment geochemical phases in affecting metal bioavailability, with the order of TOC > Fe-Mn oxides > carbonate.