Depuration and relaying

Bivalve molluscan shellfish feed by filtering large volumes of seawater and accumulating food particles from their surrounding environment. When that environment is contaminated by sewage, shellfish will also accumulate human pathogenic bacteria and viruses during filter-feeding and present a health risk when consumed raw or only lightly cooked. In order to render such shellfish fit for consumption three principal commercial treatment processes have been traditionally used. Firstly, heat treatment (cooking) can be used to destroy pathogens before consumption. Secondly, shellfish harvested from polluted areas can be replaced in clean areas (areas free of microbiological contamination) to allow shellfish to cleanse or purge themselves by continuation of their normal filter-feeding and digestive processes. This process is called ‘relaying’ or ‘container relaying’. Thirdly, the ‘natural cleansing’ process can be performed in a controlled environment by immersion in tanks of clean seawater to allow sewage contaminants to be purged. This process is called ‘depuration’ or ‘controlled purification’. The relaying and depuration processes, unlike cooking,