Best available scientific information on the effects of deposition of heavy metals from long-range atmospheric transport

Canadian guidelines among women of childbearing age in Arctic populations that consume marine mammals.Cadmium.Cadmium is emitted to the atmosphere primarily in the particulate phase.While the majority of larger diameter particles are deposited relatively close to the source, the finer particles have the potential for long-range transport.Deposition of cadmium resulting from long-range atmospheric transport has been reported in remote areas.Evidence suggests that deposition rates in remote areas peaked at several times pre-industrial rates during the 1960s and 1970s and has since decreased to levels only slightly higher than pre-industrial.These results are consistent with results of EMEP modelling and monitoring in Europe, which suggest, in general, a two-fold decrease in atmospheric concentrations and deposition between 1990 and 2003.EMEP modelling suggests that 10-80% of deposition in European countries is derived from emissions in other European countries.Recent results from the International Cooperative Programme on Integrated Monitoring (ICP-IM) suggest that remote forest catchments of northern and central Europe continue to accumulate deposited cadmium.In general, soil cadmium concentrations in remote regions do not exceed thresholds for adverse effects on microbiota or vegetation.Vegetation, which accumulates cadmium from a number of sources, including atmospheric deposition, is the primary source of cadmium exposure for terrestrial herbivores that tend to accumulate cadmium in their liver and kidneys.Available information indicates that levels of cadmium in terrestrial wildlife are generally low and do not exceed thresholds of effects.Cadmium is relatively mobile in freshwater ecosystems and can be accumulated by freshwater biota.However, unlike mercury, cadmium does not biomagnify in freshwater ecosystems.While lakes in northern Europe were found to contain elevated concentrations of cadmium as a result of long-range atmospheric transport, the levels that were reported do not exceed the estimated thresholds for toxic effects.Overall there appears to be generally a low risk of adverse effects due to environmental exposure to cadmium through freshwater ecosystems.However, under conditions of very soft water there is concern that there may be some risk because the "estimated thresholds" may not be sufficiently protective for these water conditions.In marine ecosystems cadmium can achieve relatively high levels in some marine mammals.The contribution of anthropogenic cadmium to marine ecosystems, however, is thought to be relatively small.The vast majority of cadmium circulating in the world's oceans arises from natural sources and processes.v Food is the greatest source of human cadmium exposure, accounting for about 99% of cadmium intake in non-smokers, on average.Cereals, potatoes and leafy vegetables, represent the greatest source of dietary cadmium; however, consumption of organ meats and shellfish can also represent a significant dietary source.Cadmium-containing fertilizers, natural soil content, and atmospheric deposition all contribute to levels in food crops.In general, levels of dietary intake of cadmium are below applicable consumption guidelines for the prevention of kidney damage and there does not appear to be any risk of adverse effects to the general population as a result of long-range atmospheric transport.However, the safety margin for human health effects due to current exposures is considered to be small.Thus, further accumulation of cadmium in agricultural lands could result in exposures of concern.Lead.Lead is emitted to the atmosphere primarily in the particulate phase.While the majority of larger diameter particles are deposited relatively close to the source, the finer particles have the potential for long-range transport.Organic forms of lead, such as tetraethyl and tetramethyl lead, are significantly more volatile than inorganic forms of lead and are more amenable to atmospheric transport.Evidence suggests that atmospheric deposition rates of lead in remote regions peaked during the 1970s and early 1980s at levels up to 200 times higher than historic background.Deposition rates appear to have decreased rapidly since the early 1980s.This is consistent with results of EMEP monitoring and modelling in Europe, which suggest a general two to three-fold decrease in atmospheric concentrations and deposition between 1990 and 2003.EMEP modelling suggests transboundary transport within Europe can account for 10-90% of deposition in European countries.In North America, lead air concentrations decreased greatly in the 1980s and early 1990s, and continued to decline through the mid-to late-1990s, although at a slower rate.Results from Arctic monitoring indicate that lead concentrations in air generally decreased since the 1980s, though recent average levels are relatively stable.Recent results from ICP-IM indicate that atmospherically deposited lead is accumulated in forested catchments of Northern and Central Europe.Concentrations of lead measured in some forest humus layers and reported by the International Cooperative Programme on Forests (ICP-Forests) may exceed thresholds for effects in soil organisms.However, these ICP-Forests sites are not necessarily in remote locations.Lead does not appear to reach concentrations of toxicological significance in terrestrial wildlife as a result of deposition from long-range atmospheric transport.Concentrations of lead in freshwater ecosystems influenced by long-range atmospheric transport are relatively low and are not considered a toxicological threat to aquatic

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