Lead interferes with a variety of body and natural processes.
It is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems. It mainly affects the haematopoietic system. It also affects the sulfhydryl group containing enzymes and also thiol content of erythrocyte. It inhibits the enzyme delta amino levaminic acid dehydrogenase enzyme(ALA) which is present in the rbc.
It is therefore particularly toxic to young animals, mainly dogs and cattle.Lead, one of the leading causes of toxicity in waterfowl, has been known to cause die-offs of wild bird populations.[2] When hunters use lead shot, waterfowl such as ducks and other species (swan especially) can ingest the spent pellets later and be poisoned ; predators that eat these birds are also at risk.[3] Lead shot-related waterfowl poisonings were first documented in the US in the 1880s.[4] By 1919, the spent lead pellets from waterfowl hunting was positively identified as the source of waterfowl deaths.[5] Lead shot has been banned for hunting waterfowl in several countries,[4] including the US in 1991 and 1997 in Canada.[6] Other threats to wildlife include lead paint, sediment from lead mines and smelters, and lead weights from fishing lines.[6] Lead in some fishing gear has been banned in several countries.The critically endangered California condor has also been affected by lead poisoning. As scavengers, condors eat carcasses of game that have been shot but not retrieved, and with them the fragments from lead bullets; this increases their lead levels.[7] Among condors around the Grand Canyon, lead poisoning due to eating lead shot is the most frequently diagnosed cause of death.[7] In an effort to protect this species, in areas designated as the California condor's range the use of projectiles containing lead has been banned to hunt deer, wild pig, elk, pronghorn antelope, coyotes, ground squirrels, and other non-game wildlife.[8] Also, conservation programs exist which routinely capture condors, check their blood lead levels, and treat cases of poisoning.
Poisonous compounds may be useful either for their toxicity, or, more often, because of another chemical property, such as specific chemical reactivity. Poisons are widely used in industry and agriculture, as chemical reagents, solvents or complexing reagents, e.g. carbon monoxide, methanol and sodium cyanide, respectively. They are less common in household use, with occasional exceptions such as ammonia and methanol. For instance, phosgene is a highly reactive nucleophile acceptor, which makes it an excellent reagent for polymerizing diols and diamines to produce polycarbonate and polyurethane plastics. For this use, millions of tons are produced annually. However, the same reactivity makes it also highly reactive towards proteins in human tissue and thus highly toxic. In fact, phosgene has been used as a chemical weapon. It can be contrasted with mustard gas, which has only been produced for chemical weapons uses, as it has no particular industrial use.Biocides need not be poisonous to humans, because they can target metabolic pathways absent in humans, leaving only incidental toxicity. For instance, the herbicide 2,4-dichlorophenoxyacetic acid is a mimic of a plant growth hormone, which causes uncontrollable growth leading to the death of the plant. Humans and animals, lacking this hormone and its receptor, are unaffected by this, and need to ingest relatively large doses before any toxicity appears. Human toxicity is, however, hard to avoid with pesticides targeting mammals, such as rodenticides.The risk from toxicity is also distinct from toxicity itself. For instance, the preservative thiomersal used in vaccines is toxic, but the quantity administered in a single shot is negligible.
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