DOI: http://dx.doi.org/10.1065/espr2001.09.084.1
The environmental problems that have arisen from the use of persistent pesticides in the past, and potential sources of further contamination have been discussed. The potential and limitations of phytoremediation for removal of pesticides in the environment have been reviewed. The enzymatic processes in plants that are known to be involved in phytodegradation of pesticides, and possibilities for enhancing them have also been discussed.
Background. The widespread use of synthetic organic pesticides started after the 1940s. A number of potent and broad-spectrum organochlorine (OC) and organophosphorus (OP) insecticides were developed between 1939 and 1950. These were followed by the development of carbamates and pyrethroids in the next decade. During this period, synthetic pesticides were widely used for protecting crops and controlling disease vectors throughout the world, especially in developing countries in the tropical region. Unfortunately, many of the early OCs and OPs were developed with little regard to problems that resulted from their large-scale use. Not only were there numerous incidents of acute toxicity in the short term, but also that residues of some persistent pesticides lingered on in the environment decades after abandoning their use. Their bioaccumulation and bioconcentration in the food chain has since posed long-term risks to non-target species, including humans. Some persistent pesticides in the environment have been linked to disruption of endocrine hormones, increased risk of cancers, dysfunction of the immune system, and reproductive and developmental abnormalities in a number of aquatic and terrestrial species. The widespread use of persistent pesticides also led to the development of new pests and diseases, and selection of resistance in a number of pest species.
By early 1970s, most uses of DDT and other persistent pesticides had been banned in many countries, although some applications continued into the mid-1980s. A limited use of some of the compounds is still allowed in many countries; for instance, DDT is used in over 20 countries in Asia and South Pacific for the control of insect vectors of tropical diseases, such as malaria. Since banning of persistent pesticides, and introduction of relatively more biodegradable ones (OPs, pyrethroids), their levels in the environment have been declining slowly. However, remnants of their former use can still be detected in virtually every environmental compartment around the world. The United Nations Environment Programme (UNEP) has identified twelve persistent organic pollutants that require urgent regulatory attention. Nine of these are pesticides (aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, HCB, mirex, and toxaphene), whilst the other three include polychlorinated biphenyls (PCBs), dioxins and furans. Traces of a number of pesticides (predominantly OCs) have even been detected in regions, such as the Arctic, where these chemicals were never used. In addition to this diffuse contamination, serious risks of further environmental pollution exist in the form of huge stockpiles of obsolete pesticides in many countries. The Food and Agriculture Organization (FAO) of the United Nations has estimated that at least 100,000 tons of unwanted pesticides are stored in developing countries, of which around 20,000 tons are in Africa.
Similar stockpiles exist in some countries of the Central and Eastern Europe, such as Poland, Latvia, and Bielarus. In many cases, pesticide containers had been stored in the open or in underground bunkers. The deterioration of containers over time led to leakage of pesticides and contamination of soil and water in the immediate vicinity, and subsequently in areas far from the storage sites. The unwanted pesticides mainly include both OCs (DDT, dieldrin, HCHs), and OPs (parathion, methylparathion, dichlorvos and monocrotophos). The FAO has estimated the cost of removing pesticide from Africa, and transporting and incinerating them in the EU at $3,500 to $4,00 |
