Pesticides+B

__**Why are Pesticides Harmful to Human Health?**__ Monica Williamson, Oct. 27, 2010 ● //Pesticide:// a material used for the mitigation, control or elimination of pests. ● //Pest:// plants or animals that are considered harmful to human health or economy. Examples include, weeds, some fungi, algae, birds, mice, rabbits, rats, insects, mites, ticks, eelworm, slugs, snails, etc. ● Some pesticides are obtained from plants and minerals, e.g. insecticides containing cryolite (a mineral) and nicotine (a plant extract) ● Some are obtained by the culture of microorganisms, e.g. toxin produced by //Bacillus thurgiensis// ● But most modern pesticides are chemically manufactured, e.g. DDT ● Pesticides can be “double-edged swords” (Ludvik), especially organic insecticides ○ they can be very effective in eliminating their target pests, but have long-lasting negative effects on the environment and human health ○ remember: many are chemicals used on crops and other food products to protect them from insects, bacteria, etc, but this exposes humans to them as well ○ notorious example, DDT ● Because of potential negative effects, developing new pesticides takes years, during which the producers must analyze: ○ side-effects on surrounding plants, animals and general ecosystem ○ toxicity (measured & related to potential hazard to users) ○ persistence of residues in environment ○ etc. ● Before WWII, pesticides were typically inorganic materials containing sulphur, lead, arsenic and copper, which are all biocides (i.e. toxic to biological organisms) or plant extracts ● WWII led to a technological revolution where the production of organic biocides (chemically manufactured pesticides) were first developed ● Organic biocides vary in toxicity, specificity (ability to harm one pest only), persistence & production of negative derivatives; these factors all determined use of pesticide ● Harmful effects include: ○ killing “pests” that are often useful and thought of as desirable in many contexts, such as predatory insects whose prey are harmful insects or plants that act as habitats for other organisms ○ killing organisms other than the target pest ○ high persistence, i.e. taking years to decompose and continuing to harm the environment ○ bioaccumulating, i.e. being soluble in fats and accumulating in fatty tissues of organisms that ingest it, thus rising in the food chain to other organisms (e.g. mercury in fish affecting humans) ○ drainage into water supply ● Case Study: DDT (1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane) or dichlorodiphenyl-trichloroethane – organochlorine insecticide first developed WWII ○ very effective, especially against malaria-causing mosquitoes ○ effectiveness resulted in mass spraying in the USA, now banned due to adverse effects ○ toxic effects: nervous system malfunction, reproductive abnormalities & cancer ○ insoluble in water, but soluble in fat; resulted in persistence in water & soil, entrance into food chain & accumulating in tissues of non-target organisms (i.e. caused endangerment of bald eagles) ○ mosquitoes & target insects grew resistant ○ controversy: as levels of malaria are rising, some wonder if it should be reintroduced to kill off malarial insects despite negative effects

__Sources__

Ludvik, George F., Robert W. Risebroug//h.// “Pesticide.” //AccessScience @ McGraw-Hill Companies.// 2008. 24 Oct. 2010. .

Keiner, Christine. “DDT.” //Encyclopedia of Science, Technology and Ethics.// Ed. Carl Mitcham. Vol. 2. Detroit: Macmillan Reference USA, 2005. 475-476. //Global Reference on the Environment, Energy and Natural Resources.// Web. 24 Oct. 2010. .

Atterholt, Cynthia. "Pesticides." //Chemistry: Foundations and Applications.// Ed. J. J. Lagowski. Vol. 3. New York: Macmillan Reference USA, 2004. 233-237. //Global Reference on the Environment, Energy, and Natural Resources.// Web. 24 Oct. 2010. .

Allchin, Douglas. "Background" //Advisory Committee on Pesticides.// 15 Nov. 2006. 24 Oct. 2010. .