Aquatic Pollution and Coastal Management

Unit 5 : Heavy metal pollution

5.5.4.Lead
Lead enters the environment from a variety of natural and anthropogenic sources. Natural processes such as soil weathering and erosion, volcanoes and forest fires contribute to significant releases of lead.

The burning of leaded fuel in automobiles was once the largest human source of lead in the environment, but industrial release now exceeds automotive emissions. Lead mining, smelting and refining operations, battery manufacture and industrial and municipal effluents are major sources of lead. Lead from batteries, tin cans and other products winds up in landfills and incinerators and can eventually enter the atmosphere and aquatic systems.

Since lead is largely insoluble in water, it is usually a minor constituent of surface and ground water. It tends to be absorbed by soil particles and organic materials, especially those near the source . Because of lead’s low solubility in water, its “uptake” in plants is usually limited. Like other heavy metals, lead dissolves more readily in acidic waters. Lead released into the atmosphere is a major source of environmental contamination. Deposited on the soil, in surface waters and on plants, lead can enter the food chain.

Most lead compounds have low solubilities in water and are not readily absorbed by most living organisms. Tetraethyl lead is much more toxic than inorganic lead compounds, but it breaks down quickly in the environment. Some aquatic species bioaccumulate lead, but there is no evidence for biomagnifications at higher levels in food chains. In general, the biodiversity and toxicity of lead compounds are greater in acidic conditions and less in alkaline or saline conditions.

Potential Hazards to Fish, Wildlife and other Non-human Biota:
Lead is a heavy metal that is very toxic to aquatic organisms, especially fish. In fish, lead deposits in active calcification areas such as scales, fin rays, vertebrae and opercula. In vertebrates, sub-lethal lead poisoning is characterized by neurological problems, kidney disfunction, enzyme inhibition and anaemia.

Potential Hazards to Humans:
Lead poisoning is particularly dangerous in young children (who may ingest lead by eating lead containing chips of paint); it may result in anorexia and –in severe cases—permanent brain damage. Women in the workplace are more likely to experience adverse effects from lead exposure than men because their hematopoietic system is more lead sensitive than men’s.
Chronic exposure – results in kidney disease “nephrites”.