Ocean Health / Human Health

Poisoning Through Bioaccumulation of Heavy Metals, Organochlorides, and Other Toxins

Effluents that find their way into the sea have significant impacts on human health, thanks to our tendency to eat high on the marine food chain. Whereas our diet from land sources is dominated by plants and by animals that eat plants, much of our diet originating from the sea centers on animals that eat animals, which causes toxic compounds to be concentrated in their flesh (a process known as bioaccumulation)¹⁵. Farmed fish products may be even more dangerous than wild caught, especially preferred species like salmon that as predators bioaccumulate toxins themselves¹⁶.

Contaminants in the aquatic food chain are threatening all fishing communities that rely on seafood for their subsistence¹⁷. The highest body burden of methyl mercury or organochlorines (OCs) such as DDT and PCBs, have been found in remote maritime populations in the Northern and Southern hemispheres. Recent reports show that highest human concentrations and related health effects were found in children living in the Canadian Arctic and remote Canadian fishing populations. Various biological effects as well as clinical effects have been seen on the immune system and the brain development of exposed children. More recently, these compounds have been found to possess endocrine properties and have been associated in animals and humans with male fertility problems, however we do not have exposure data for most parts of the world.

Heavy metal contamination is a growing problem as well. Mercury levels in certain seafood species, especially in large specimens of top predators like swordfish and tunas, are often so high that countries release advisories limiting consumption. There is currently much controversy about whether the health benefits of eating such fish products, loaded in omega-3 fatty acids and protein, are outweighed by the risks of ingesting high levels of heavy metals and other toxins. One difficulty in understanding the public health impacts of such toxins is that the effects can be sub-lethal, and may manifest as neurological problems that are slow to surface, or mutagenic effects that are not seen until the next generation.

Freshwater Contamination

The link between healthy oceans and availability of potable water is not obvious, but the link does indeed exist. In experimental settings, polluted seawater was shown to affect water quality in freshwater aquifers; this is thought to have particular implications for arid coastal regions, where potable water is already a scarcity¹⁸. At the same time, hydrological balances are regulated by functioning coastal ecosystems. The destruction of such ecosystems can and does wreak havoc with such balances, affecting freshwater recharge and freshwater quality.

Reduced Protein Intake and Paucity of Healthful Food

For approximately 2 billion people around the world, marine fisheries provide the sole or primary source of dietary protein. Billions more eat fish from the sea for its nutritional benefits, since marine fish are not only rich in protein but provide the best source of healthful omega-3 fatty acids. Marine fisheries provide products that are also culturally important, with seafood playing a key role in celebrations and special events in coastal and even inland communities all across the globe. Fisheries landings from coastal seas have averaged around 82 million tons annually from 1991-2000, but have been declining since, largely due to overfishing¹⁹.

As oceans become degraded, these important sources of protein and essential nutrients which support human societies around the world are fast disappearing. Overfishing has both reduced stocks of healthful fisheries species, and caused imbalances in marine food webs that affect overall ocean productivity. Indiscriminate and destructive fishing practices further undermine marine ecosystems. At the same time, loss of coastal nursery habitats, provided by estuaries, saltmarshes, mangrove forests, and other coastal ecosystems, has made fisheries increasingly unable to regenerate themselves.

Paradoxically, the very same forces of globalization that have made marine products more widely available for sale and consumption have added to the stresses on marine ecosystems which impede continued productivity. Marine transportation (of goods including seafood) has impacted marine ecosystems by conventional pollution and by introducing alien species through the release of ballast water (see Exporting Pollution, World Ocean Observer archives). Fish processing for export has harmed many coastal ecosystems and atolls, adding to the ocean pollution burden.

Declining Availability of Marine Pharmaceuticals

Pollution and the wearing down of ocean health is causing public health and human well-being to deteriorate in many parts of the world, and these trends are expected to accelerate²⁰. At the same time we are sliding down this slippery slope, the ability of the oceans to come to our rescue with marine pharmaceuticals is being compromised, as marine biodiversity is impacted by the very same things that threaten ocean health more generally.

Compounds derived form marine organisms have much potential in fighting human disease, including cancers and viral diseases. Over 20,000 biochemical compounds have been isolated from marine organisms, and many are used as anti-cancer, anti-viral, anti-inflammatory, and anti-neurodegenerative agents today. Approximately 70% of recently patented anti-cancer compounds that are derived from marine sources come from sponges²¹. Novel pain therapies are also being developed from marine organisms, including, strangely enough, the toxins that some naturally produce and emit. Alarmingly, we are losing many marine species even before they are documented and tested for their pharmaceutical properties.