Two recent studies show that organochlorine chemicals are found in measurable concentrations worldwide, even in regions far removed from sources of pollution. Organochlorines, such as DDT, PCBs and dioxins, have been linked to a range of negative health and environmental impacts, including cancer, birth defects, endocrine disruption and neurological damage, as well as harm to wildlife.
In a study of the global distribution of 22 potentially harmful organochlorine compounds, Indiana University researchers found high concentrations of organochlorines not only in some developing countries, but also in industrialised countries where use of many of these compounds is now restricted.
Scientists have long speculated that some organic pollutants move through the atmosphere from relatively warm regions and condense at colder, higher latitudes onto vegetation, soil and bodies of water. This process, known as the global distillation effect, could be the reason that high concentrations of some pollutants are found in the Earth's Arctic regions.
The Indiana University study found that distribution of relatively volatile organochlorine compounds demonstrate the global distillation effect, whereas less volatile organochlorine compounds such as endosulfan tend to remain in the region of use. However, as a result of its widespread use, endosulfan was found in high concentrations in many areas throughout the world.
Low but measurable organochlorine concentrations were found in tree bark samples from remote regions, including the Orinoco rainforest in Venezuela and the rainforests of Ecuador and Belize. Tree bark samples from remote islands such as the Marshall Islands, Guam, Bermuda and Tasmania also had low but measurable concentrations of organochlorine compounds. High concentrations of organochlorine compounds were measured in tree bark from mainland Australia, Europe, India, Japan, the Middle East, Russia and the US.
According to the New York Times, a second study has found high levels of organochlorine compounds in black-footed albatrosses on the Midway islands, a relatively remote atoll in the North Pacific. Researchers, sponsored by World Wildlife Fund and the US Environmental Protection Agency, chose to study Midway because it is considered a pristine environment. Midway is 5000 kilometres from Los Angeles, 3800 kilometres from Tokyo and 1850 kilometres from Honolulu.
Despite their remote location, albatrosses in the Midway islands were found to exhibit classic signs of exposure to organochlorine chemicals, including deformed embryos, eggshell thinning and a 3% reduction in nest productivity. Nest productivity measures the rate at which eggs hatch.
Researchers found levels of DDT, PCBs and dioxin-like compounds in albatross adults, chicks and eggs nearly as great as levels found in bald eagles from the North American Great Lakes, according to Dr James Ludwig, an ecologist on the research team. Fish-eating birds that nest in the Great Lakes have suffered embryo deaths and chick deformations such as crossed bills and club feet due to DDT, PCBs and dioxin-like compounds in their diet.
The New York Times reports that contaminants in the birds' diet probably originate in India, south-east Asia and Japan. Ludwig states that a large DDT plume is being carried by ocean currents from the coast of south-east Asia to the north-central Pacific. He emphasised that this is fresh DDT, possibly from DDT currently used in mosquito and crop pest control.
[From Pesticide Action Network North America Updates Service.]