There are three main risks of oysters: microbial pathogen pollution, heavy metal pollution and shellfish toxin pollution.

Oysters that can be eaten raw are generally required to grow in first-class waters; Aquatic products in the secondary sea area are only suitable for cooked food; The three types of sea areas are generally only suitable for swimming, and aquaculture and fishing of aquatic products are not allowed in countries with standardized food management; It is not suitable for swimming in Grade IV waters. Generally, such sea areas are only suitable for docks.

Due to the weak management of China's sea areas, offshore pollution is very serious. From June 65438 to July 0997, the United States banned the import of China oysters on the grounds of unequal management of sea areas; At the same time, the EU has also issued 386 regulations prohibiting the import of China oysters.

Microbial pathogen pollution can be avoided by cooking, and heavy metal pollution is easily ignored. Oyster is a filter-feeding organism, which has a strong ability to enrich heavy metals, but conventional cooking methods can not eliminate the harm of heavy metals. Shellfish toxins, like microorganisms and heavy metals, are not produced by oysters, but by environmental impact. Shellfish poisoning is mainly caused by oysters eating some algae in polluted and eutrophic seawater, which leads to the accumulation of shellfish poisoning. Shellfish toxins mainly include paralytic shellfish toxins and diarrheal shellfish toxins. These toxins can not only be used for raw food, but also for cooked food, because high temperature can not destroy shellfish toxins.

Some oysters in China claim to be eaten raw, but they are actually purified oysters. It is to send unqualified oysters contaminated by microbial pathogens, heavy metals and shellfish toxins to a clean and closed pool for culture until they reach the specified indicators before entering the market. Even after purification, there are still great risks.