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Lead in the freshwater environment | ||
| Introduction
| Why does lead occur in freshwater systems? Beside the normal changes in freshwater due to metals, lead has it own characteristics. The chemical properties of lead make it a useful material, so it is used widely in pipes, battery cases, paints, ect. and tetraethyl lead is used as a petrol additive. A total of 4 million tons of lead are mined worldwide in one year. It becomes extracted from the galena ore (PbS). The latter has been the most important source of organic lead to the environment and has been widely dispersed, with contamination increasing sharply from the 1950’s, even in remote areas, with the growth in the number of automobiles. The use of lead in ammunition has created some serious environmental problems. Organolead compounds have been used extensively for control of caterpillars on fruit crops. |
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| History of lead in freshwaters The use of lead in gasoline dates back to 1923, when tetrahyl lead was first introduced as an antiknock additive. This use was suspended during part of 1925 and 1926 pending the establishment Which organisms are most affected by lead poisoning? Scientific research has displayed that lead of several concentrations in freshwater fish Exposure of a freshwater fish to several sublethal concentrations of lead for a period of 30 days showed significant accumulation of lead in the blood and tissues. Lead bioaccumulated in the study showed organ-specific distribution, with high levels in the blood followed by the kidney, gill, liver, brain and comparatively lesser amounts in the ovary and muscle tissues. The lead accumulation in tissues was found to increase with lead in water up to concentrations of 5 mg/liter, and at concentrations of 10 and 20 mg/liter the lead accumulation in the tissues, although indicating an increase, was not proportional to the concentration in water. Exposure of the freshwater fish Anabas testudineus to a sublethal (5 ppm) concentration of lead nitrate for a period of 30 days during the preparatory phase of its annual reproductive cycle reduced the total lipids, phospholipids, and cholesterol levels in the liver and ovary tissue. Waterfowl are the group most affected by the chronic contamination of aquatic ecosystems with lead. Those wildfowl that manage to avoid being killed or maimed by hunters may nevertheless ingest large quantities of spent shot while feeding. In the United States, where the problem has been most investigated, some 6000 tons of spent shot are deposited each year and a minimum of 2.4 million waterfowl, out of a total North American population of 100 million, die annually of lead poisoning due to ingestion of shot, though the introduction of steel shot is reducing this mortality. Many other waterfowl suffer sublethal effects, making them vulnerable to disease and predation. The adverse physiological effects include anemia, muscular paralysis and damage to the nervous system, liver and kidney. Chicks of little blue herons exposed to lead in their food showed a reduced survival rate (Spahn and Sherry, 1999). Recycling of lead is getting more important and it is already good for more than 50% of all the lead that has been used. In the not too distant future, the percentage of recycling will go up further till above the 80%. Sheet lead is produced completely of old lead. It survives the lifespan of a building and is recycled then for the full 100%. Many swans also die through collisions with power lines (Brown et al., 1992). In Ireland such birds have been shown to elevate concentrations of lead in their tissues, through lower than those dying of acute lead poisoning (O’Halloran et al., 1989). Lead poisoning in children causes neurological damage leading to a reduction in intelligence, loss of short term memory, learning disabilities and problems with coordination. | ||
