Impacts on human health

One of the clearest direct impacts on human health comes from the ingestion of pathogenic micro-organisms. One study estimated that there are some 250 million cases of gastroenteritis and upper respiratory disease every year arising simply from people bathing in polluted seas. Some of these can lead to long-lived incapacity and it has been estimated that the global burden of disease adds up to some 400,000 disability adjusted life years, comparable to the impacts of other diseases such as diptheria or dengue fever. The estimated cost to society is some US$1.6 billion.

Shellfish are highly efficient at concentrating pathogens and the consumption of contaminated shellfish is an even greater cause of illness and disease than bathing waters. Even when cultivated in clean waters, shellfish can harbour bacteria and viruses. They are often eaten raw, or are only lightly steamed, which is not enough to kill most of these pathogens. It has been estimated that some 8 billion shellfish meals are consumed annually world-wide and that, among other problems, these are responsible for about 2.5 million clinical cases of infectious hepatitis, many causing deaths or long-term disabilities. The overall impact from this illness alone accounts for some 1.8 million disability adjusted life years and an economic impact of US$7.2 billion per year.

In addition to pathogens, marine biotoxins present a considerable health hazard. Generally speaking ingestion from bathing is not a problem, however bioaccumulation of toxins in higher predators, long-lived species, or filter feeders such as shellfish means that they can present a considerable problem from ingestion. Among the best known are paralytic, neurotoxic or diarrhoeic shellfish poisoning, but also ciguatera which is a poison that becomes concentrated through the food-chain and reaches dangerous levels in higher predators. These have all been linked to the consumption of toxic algae, particularly during toxic algal blooms. As such there may well be a natural background level of such problems, however in many cases such blooms have been linked to increased nutrient levels and even to climate change.