What type of contamination risks do oysters pose after exposure in seawater?

Oysters are filter feeders that can accumulate microorganisms from the seawater in which they live. After exposure to seawater, oysters can harbor viruses and bacteria, such as norovirus, Vibrio species, and other pathogens found in contaminated water. The risk arises because these pathogens can be concentrated in the oyster's tissues and can survive even after the oysters are harvested. When consumed raw or undercooked, these contaminated oysters pose a significant health risk to humans, leading to foodborne illnesses.

While oysters can also be affected by chemical additives, toxins, or heavy metals, the primary concern related to food safety and contamination after exposure to seawater is the presence of viruses and bacteria, making this the correct answer. Understanding this contamination risk is crucial for food safety practices, particularly in preventing foodborne illness associated with shellfish consumption.