Environmental pollution has long been a serious problem both on land and at sea. While solid waste entering the oceans can cause serious injuries, persistent organic pollutants (POPs), dioxins, industrial fallouts, oil and heavy metals can lead to severe health problems for species at the top of the food chain.
Once in the marine environment, chemical substances can accumulate over time (known as bioaccumulation), and/or with each step up in the food chain their concentration can increase in the tissue and body fat of large bodied animals (known as biomagnification).
Most of the hazardous waste is from the terrestrial environment. Pesticides and insecticides can enter the waterways through agricultural run-offs. PCBs (polychlorinated biphenyls) originate i.e. from old electrical equipment and PAHs (poly-aromatic hydrocarbons) come mainly from oil spills and burning of wood and coal. Heavy metals, for example cadmium, chromium, lead and mercury could come from i.e. factories and power plants, while plastic based materials act as a perfect sponge soaking up toxins. But even the cigarette butts discarded on beaches are considered to be small poisonous chemical time bombs.
Almost all marine species are afflicted but cetaceans, sentinels of ocean health, especially those that live close to the coast, are even more exposed to anthropogenic toxins. They have long life spans, they feed on the top of the food chain, and during periods of physiological demands, such as starvation or lactation, the chemicals accumulated in their fat stores can be remobilised affecting the health of both adult and calves.
Due to the prevailing wind and ocean currents, the Arctic and sub-Arctic environment is a hotspot for toxins (i. e. “Arctic haze”). Here, POPs (persistent organic pollutants) can become trapped and readily available in the biological system. Inhabitants such as narwhals, pinnipeds, bowhead whales and belugas are just a few of the species affected by POPs. The blubber and internal organs of beluga whales living in the sub-Arctic waters of St. Lawrence River contain DDT and heavy metals in such large quantities that their population is considered as toxic waste. But at lower latitudinal areas species such as sharks, seals and sea lions also amass anthropogenic pollutants in their tissues.
The health effects of bioaccumulation of contaminants can be severe for marine mammals, as it can cause nervous system damage, chromosomal problems, cancer and birth defects. But it’s not only the Artic that is considered to be dangerous when it comes to pollution. At other areas, for example in the Pacific Northwest the level of toxins became so high that the average life expectancy of male killer whales dropped by half, while first born calves die soon after birth as they receive the accumulated toxins through their mother’s breast milk. Following the Deepwater Horizon oil spill in the Gulf of Mexico bottlenose dolphin populations are still suffering from health problems like lung disease and sperm whale skin samples show high level of toxic metals.
As humans are also on the top of the food chain, we are just as much exposed through our diet. The presence of mercury, arsenic and various fat-soluble pollutants in the seafood has long been a problem. Both mercury and arsenic are insoluble, cannot be excreted and can enter the food web at the base where with each successive trophic level they will magnify and accumulate in larger and larger amounts. Hence the limited intake of seafood, especially of those species that are known to contain toxins in their tissue, is highly recommended.
Although, our understanding of current and future effects of anthropogenic pollutants is limited, with the implementation precautionary principle to manage marine ecosystems and with further scientific research, the health and population of these beautiful animals could be preserved.
By Wanda Bodnar
Image Source: Scripts Julie van der Hoop