Studies on the accumulation and elimination of mercury in the oyster Crassostrea gigas

Abstract

The accumulation and elimination of mercury in the oyster Crassostrea gigas were examined. Two groups of oysters were exposed to sea water containing 20μg/l and 200μg/l of mercury for 44 days respectively, then removed to mercury free sea water for another 12 days for self-depuration of accumulated mercury. The mercury contents of the edible portion of the oyster were monitored by flameless atomic absorption spectrophotometry throughout the experiment. Those oysters exosed to high concentration uptook more mercury than did those exposed to low concentration but the rate of subsequent elimination was found to be on the contrast. The lower mercury concentration was in the ambient water, the higher concentration factor was found in the oyster in the first 24 days. Both groups were found to have the highest concentration factor on the 44th day. The mercury accumulation behavior of the oyster was proved to be very strong and the fact may raise to several hundred if the waters are seriously polluted. The FDA of U. S. A. suggested that fish meat containing more than 0.5μg/g are not to be consumed. However, if the oysters are exposed in clean sea water for a period, the mercury content may be decreased to an acceptable level.本實驗探討水中溶解汞在牡蠣(Crassostrea gigas)體內之蓄積與排出的情形。將牡蠣分別飼育於含汞20μg/ℓ及200μg/ℓ之海水中，結果顯示，牡蠣可食部份之汞蓄積量隨著蓄積天數的增加而增高，200μg/ℓ組之汞蓄積量均高於20μg/ℓ組。經過44天後，20μg/ℓ組及200μg/ℓ組其可食部份的平均含汞量分別可達9.9μg/ℓ及91.3μg/ℓ。濃縮因素(Concentration factor)在前24天時，20μg/ℓ組大於200μg/ℓ組，到了第32天後20μg/ℓ組則小於200μg/ℓ組。牡蠣對汞的蓄積能力很強，其濃縮因素可達數百倍之高，因此生長在汞污染水域之牡蠣，其可食部份之汞含量可能會超過美國FDA（美國食品藥物管理局）0.5μg/ℓ之限制標準而不宜食用。將牡蠣置於不添加汞之海水中，經過12天後，其含汞量20μg/ℓ組及200μg/ℓ組分別降為3.97μg/ℓ及53.9μg/ℓ，顯示牡蠣體內的汞在清潔海水中有顯著減少的情形，因此牡蠣採收後，宜放置於清水中一段時問後上市較妥。