Anthropogenic use of lead in metallic from (battery casings, lead pipes) are usually recycled. But, lead used as petrol additives are largely lost to the atmosphere. This lead enters the marine ecosystem globally though rain. Coastal areas, with a lot of near shore automobile activity, can have considerably increased lead contamination. The reduction of leaded gasoline in the last decades resulted in decline of 50%, between 1981 and 1989, of the lead surface concentrations in the North Atlantic surface waters.
Compared with other heavy metals, lead in the sea isn't particularly toxic. Its toxicity is also mostly determined by its chemical form, lead bound to organic compounds is much more toxic than inorganic lead. So can some organisms accumulate high concentrations of inorganic lead without any apparent harm. In polluted areas barnacles can accumulate up to 100 ppm (parts per million) and mussels in Norway have been shown to contain up to 3000 ppm of lead. These mussels have a detoxifying mechanism for lead; they can store large quantities as granules (solid form) in their digestive gland (an organ that helps digest food). However, environmental concentrations above 10 ppm are shown to be detrimental for the growth of some organisms (some crustaceans and algae species). Other sublethal effects of too high lead concentrations include: anemia, reduced egg-hatching, fin degeneration and behavioural abnormalities.
Like most other metals lead doesn't show biomagnifying characteristics. As a consequence it is normally of little harm to fish eating mammals or birds. However, a rare incident of lead poisoning has occurred along the birds wintering on the Mersey estuary, near Liverpool. 2400 birds, mainly dunlins, died in 1979. The birds had 10 ppm (wet weight) of trialkyllead (an organic form of lead, which is more toxic) in their liver. Factory discharges caused lead to accumulate in the bivalve Macoma balthica, the primary food for these birds.
Case studiesHeavy metal content of mussels in the Western Scheldt estuary
Environmental standards and legislation
- Clark, R,B., 1999. Marine pollution. Oxford University press, Fourth edition, pp 161
- Kennish, M. J. (1996): Practical Handbook of Estuarine and Marine Pollution, CRC Press 524 pp
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