Clams and oysters in the shell should be alive and the shells should be closed tightly or should close when the mollusks are tapped. The U.S. Public Health Service, in cooperation with the States, has a sanitation control program that covers the labeling and shipment of clams, mussels, and oysters. These shellfish may be harvested only from non-polluted waters and processed for shipment in sanitary plants inspected by State shellfish inspectors. Authorities periodically test water for sewage pollution and ban catches from polluted areas.
Shellfish from polluted waters are dangerous to man, causing mild to severe illness, sometimes death. Both sewage and industrial wastes can affect shellfish.
Cooking does not entirely make sewage-polluted shellfish safe to eat. Cooking will kill bacteria that cause some diseases, but it is not known whether certain virus diseases, such as infectious hepatitis, can be prevented by cooking.
It is possible to purify shellfish from sewage polluted water for safe eating. Sewage polluted shellfish transplanted to clean water purify themselves rapidly and become safe to eat.
Shellfish do not contain mercury levels dangerous to man's health. Tests of shellfish to date have shown mercury levels to be below those considered dangerous to humans.
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