Pesticides, environmental persistence

As a consequence of their environmental persistence, most OC pesticides have become ubiquitous pollutants therefore, these compounds are detectable in trace amounts in biological tissues of higher animal species, including... 

It turns out that most of these compounds have similar characteristics that contribute to their toxicity to both humans and other species of plants and animals. First, the compounds are environmentally persistent. Many of the early pesticides, and certainly the metals, do not break down in the environment or do so only very slowly. If persistent chemicals are released continually to the environment, the levels tend to rise ever higher. This means they are available to cause harm to other organisms, often not even the target of the pesticide. Second, the early pesticides were broad acting and toxic to many species, not just the target species. These poisons often killed beneficial insects or plants. Third, many of these compounds would bioaccumulate or concentrate in species as they moved up the food chain. The chlorinated pesticides accumulate in the fat of animals. Animals that consumed other animals accumulated more and more of these pesticides. Most species could not metabolize or break down the compounds. Lead accumulates in bone and methyl mercury in muscle. And finally, because of their persistence in the environment and accumulation in various species, the persistent toxicants spread around the world even to places that never used them. Animals at the top of the food chain, such as polar bears and beluga whales, routinely have fat PCB levels greater that 6 ppm. 

The environmental persistence of DDT and its immediate metabolite DDE is characteristic of chlorinated organic pesticides as a class. 

Hence OP pesticides are much less environmentally persistant than are the organochlorines. However their chemical reactivity frequently renders them more acutely toxic than the organochlorine pesticides. 

PCBs are industrial compounds which were widely used as organic diluents, plasticizers, pesticide extenders, adhesives, dust-reducing agents, cutting oils, flame retardants, heat transfer fluids, dielectric fluids for transformers and capacitors, hydraulic lubricants, sealants and in carbonless copy paper. PCBs have entered the environment via multiple pathways and residues of these compounds have been identified in air, water, wildlife and human adipose tissue, serum and milk.89-91 Like many other aromatic hydrocarbons, PCBs are highly lipophilic and chemically stable and this has contributed to their environmental persistence and bioconcentration in the food chain. PCBs were originally... 

In this volume of Issues we address the sources, environmental cycles, uptake, consequences and control of many of the more important chlorinated organic micropollutants. Under this heading we have included a range of semi-volatile persistent compounds, notably polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) as well as a number of chlorinated pesticides. We have not sought to include volatile species such as CFCs which cause environmental problems of an entirely different nature. The compounds included in this volume cause no threat to the stratospheric ozone layer, but have given widespread cause for concern in relation to their environmental persistence and high toxicity, and their potential for adverse effects on humans and wildlife. 

Despite the social and economic benefits of these compounds, problems developed because some of these compounds, once released, did not degrade in the environment. Because of their environmental persistence, some of these compounds have had unintended consequences for example, DDT caused egg shell thinning and thus affected the reproduction of certain types of birds. This problem was brought to the public s attention by the famous book Silent Spring Perhaps as a result, many of these early pesticides are no longer on the... 

Hamer, T., Shoeib, M., et al. (2004) Using passive air samplers to assess urban-mral trends for persistent organic pollutants. 1. Polychlorinated biphenyls and organochlorine pesticides. Environmental Science and Technology, 38(17) 4474 483. 

Moreau-Guigon, E., Motelay-Massei, A.,et al (2007) Vertical and temporal distrihution of persistent organic pollutants in Toronto. 1. Organochlorine pesticides. Environmental Science and Technology, 41(7) 2172-2177. 

Using pesticides with short environmental persistence to reduce selection pressure. 

Explanations I = number of lots II = National Status III = Codex Status (a) processed food in italics (b) N = no MRL or permitted level exist A = Residue exceeds permitted level for environmentally persistent pesticide that is no longer used X = Residue exceeds MRL or permitted level OK = Level under MRL (c) Latin America includes Caribbean Region... 

As a group, carbamates have a relatively low environmental persistence, in contrast to the organo-chlorine pesticides. Carbamates are broken down by... 

The use of pesticides in Kenya dates back to the colonial era. The major areas of application include agricultural pest control and the public health control of mosquitoes, snails, and tsetse flies. However, with the rapid development of resistance of pests to the chemicals, coupled with environmental persistence, most of the organochlorines have been banned for agricultural use and restricted in the case of public health vector control. Nevertheless, there are detectable residue levels of these compoimds in amounts that lead to concern for food chain magnification. These levels arise either fi om previous application or unscrupulous use through illegal means. 

Of the several classes of synthetic insecticides, the chlorinated hydrocarbon (CH) and organophosphate (OP) insecticides have the greatest psychiatric significance [Pesticides and Neurological Diseases 1982 Ecobichon 1996). The CH insecticides, also called organochlorine insecticides, include three chemical classes di-chlorodiphenyltrichloroethane (DDT), cyclodienes (aldrin, dieldrin, heptachlor, chlordane, endosulfan), and chlorinated benzene and cyclohexanes (lindane) (Ecobichon 1996). Their ban in the United States and Europe resulted from their high chemical stability and lipid solubility that allowed environmental persistence and magnification in the food chain (Ecobichon 1996 Kaloyanova and El Batawi 1991). 

Four international conventions are developed at present by means of which the governments execute actions for controlling the dissemination and usage of the environmentally persistent pesticides on international scale. 

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