Lead

Definition of lead: Lead is a heavy metal with symbol Pb and atomic number 82. It has a bluish white color, when freshly cut, but tarnishes to dull gray when exposed to air. It is also highly malleable. This is the common definition for lead, other definitions can be discussed in the article

Notes

lead © Greg Robson

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. However coastal areas, with a lot of near shore automobile activity, can have considerably higher lead contamination. The reduction of leaded gasoline in the last decades caused the surface concentrations of lead in the North Atlantic surface waters to decline between 1981 and 1989 with 50%.

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 that have been demonstrated include: anemia, reduced egg-hatching, fin degeneration and behavioral 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 baltica, the primary food for these birds.

Case studies

Heavy metal content of mussels in the Western Scheldt estuary

Common starfish can act as a bioindicator for heavy metal pollution

Heavy metals in various Belgian benthic invertebrates

Environmental standards and legislation

Included in the OSPAR list of substances of priority action

Included in the water framework list of priority substances

See also

Lead on ED North Database

OSPAR background document on lead