Contemporary Patterns And Historical Rates Of Increase Of Mercury Contamination In Different Marine Food Chains

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We present measured trends in mercury contamination over the past 100 years in epipelagic, mesopelagic and deep sea marine food webs, showing 3-10 fold increases in mercury concentrations. The most rapid increases, and highest contemporary levels, occur in mesopelagic food chains in southern ICES areas. Congruent patterns are evident in fish and in seabirds, but the latter permit ready analysis of long term trends because of the availability of museum study-skin collections. Laboratory and field studies fully validate the use of seabird feathers as a reliable monitor of mercury contamination in their food. Although local mercury contamination 'hot-spots' can be identified within the North Sea, most of the North Sea food chains can be considered 'mercury-depleted' relative to those in North Atlantic environments. This pattern supports the view that point source and riverborne mercury is of minor importance relative to inputs from atmospheric deposition. The latter suggests that jet stream transport of mercury pollution from North America is the primary cause of mercury contamination in European waters. Methylation of inorganic mercury deposited from the atmosphere is thought to occur especially in low oxygen environments such as the deep sea. This is important because vertebrates assimilate a very high proportion of ingested organic mercury but only a small fraction of ingested inorganic mercury. High accumulation of mercury in mesopelagic and deep sea fish and in predators on mesopelagic animals suggests that methylation is a key process determining mercury accumulation in marine animals.