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Shellfishes can easily accumulate metals via water and sediment and which may pose a human health risk by consumption. This study assessed the distribution of metals, including Cd, Cr, Cu, Pb, Ni, Zn, and Hg, in soft tissues of hard clam (Meretrix lusoria), surrounding water body, and sediment in the southwest coast of Taiwan. Hard clams contained the relatively higher concentration of the essential element, such as Zn, Cu, and Ni, and the metal concentration from high to low was Zn > Cu > Ni > Cd > Cr > Pb > Hg. However, the metal concentrations found in hard clam all were lower than the Sanitation Standard for Aquatic Animal of Taiwan. Results of bioaccumulation factors indicated that hard clam shows the ability of metal accumulation from water was higher than that from sediment. Moreover, the metal concentrations in hard clam were negatively correlated with body size except for Hg, which could be presented by the significant power function. Generally, hard clams from the aquaculture pond located on the southwest coast of Taiwan would not be harmful to adult consumers, except for people that consume shellfish more than 100 g. Besides strengthening the management of seafood safety and aquaculture, adjusting the eating and purchasing habits of the consumer could be a practical and feasible way for decreasing health risks. These results can assist the government in determining seafood safety and its implementation in Taiwan.

The tetramethylarsonium ion has been found in the gill of the clam Meretrix lusoria. We attempted to confirm the conversion of arsenobetaine to the tetramethylarsonium ion in a culture with marine microorganisms occurring in the gill of the clam Meretrix lusoria. Arsenobetaine was aerobically incubated with microorganisms. A garlic-like odor was faintly detected after 5 to 8 days incubation. The mass spectrum of the odorous substance was essentially identical with that of synthetic trimethylarsine. Trimethylarsine oxide (TMAO) was also detected in the culture medium after 3 weeks incubation. Arsenobetaine was biotransformed to TMAO during the incubation in the culture growth by the marine microorganisms. Tetramethylarsonium ion was not detected in the culture medium even after 72 days incubation.

The uptake and transfer of 2,2′,4,4′-tetrachlorobiphenyl (an isomer of polychlorinated biphenyls, PCBs) in the culture of two species of phytoplankton, Nannochloropsis oculata and Isochrysis galbana, to brine shrimp (Artemia sp.) nauplii and hard shell clam (Meretrix lusoria) were investigated in a short-term laboratory ecosystem. Three PCB concentrations, 0 ppb, 50 ppb and 500 ppb, were prepared in the algal culture for examing the levels of PCB bioaccumulation and growth effects on these biota. Artemia and hard shell clam each when exposed to 500 ppb contaminated Nannochloropsis and Isochrysis for 4 d could significantly bioaccumulate PCB concentrations up to 318.81 ppm and 22.55 ppm (dry basis), respectively. This may account for the high PCB residues that bioaccumulated in contaminated Nannochloropsis (257.52 ppm) and Isochrysis (64.22 ppm) through the aquatic food chain. Biomass of PCB treated algae were apparently depressed (p < 0.05) relative to that of the control group (0 ppb). Growth conditions (length and larva/mL) of Artemia when fed with Nannochloropsis under PCB environments also showed stronger inhibition effects compared to that of the control group (p < 0.05).

This study surveyed the total arsenic (As) and As species contents in clams (Meretrix lusoria) farmed in areas of hyperendemic blackfoot disease (BFD) in southwestern Taiwan. Total As and As species in sediment and pond water were also analyzed to examine the bioaccumulation of As in clams in their exposure environment. Moreover, potential carcinogenic risks associated with the ingestion of As in aquacultural clams were evaluated probabilistically. The average total As contents in medium-sized and small clams were 7.62 and 10.71 microg/g (dry wt), respectively. The content of the As species in this study was approximately 61% of the total As content. The other unquantified As species are possibly arsenocholine, arsenosugar and arsenolipid. The average ratios of inorganic As contents to total As contents in clams ranged from 12.3% to 14.0% which are much higher than that found in the farmed oyster (Crassostrea gigas), indicating that humans may expose to larger quantities of inorganic As by ingesting the same amount of clam as oyster. Using different ingestion rates derived by the average consumption method and the questionnaire method, the estimated risks to human health associated with consuming clams from the BFD area ranging from slightly to largely exceed the standard target risk. Based on the estimation of the TR model, a 0.18g/day-person of the safe ingestion rate of clams in the BFD region is recommended.

Since October 1994, a long-term program of Asia/Pacific Mussel Watch: Taiwan Regional Studies has been carried out. The results indicate that trace metal contents in mollusca varied among 30 different species and the environments (water and sediments) along the Taiwan coast. The orders of bioaccumulation of trace metals in mollusca were: Cu (over 200 μg/g), Thais clavigera > Isognomon legumen > Clibanarius rivescens > Crassostrea gigas ; Zn (over 700 μg/g), Moruta granulata > C. gigas > Asiatica cypraea arabica > T. clavigera ; Cd (over 5 μg/g), Trochus hanleyanus > Acanthopleura japonica > Nerita albicilla > Patella flexuosa ; Pb (over 2 μg/g), P. flexuosa > C. gigas > T. hanleyanus > T. clavigera > C. gigas > Capiyulum mitella ; Ni (over 10 μg/g), Meretrix lusoria > Philine sp. > Littoraria scabra > Tridacna squamosa > T. hanleyanus ; Cr (over 30 μg/g), Littoraria undulata > T. hanleyanus > N. albicilla > Nerita chamaelor > M. granulata ; As (over 20 μg/g), Perna viridis > L. scabra ; and Sn (over 5 μg/g), P. viridis > L. undulata > C. mitella > C. gigas . Their seasonal and regional variations as well as their correlation are evaluated and discussed.