Environmental Problems, Their Causes, and Sustainability 1

our bodies, and we should be concerned about theirpossible long-term effects on both the environment andhuman health. Critics of pesticides contend that thebest way to reduce such risks is to prevent such chemicalsfrom reaching the environment. This would spurus to look for safer, affordable alternative chemicalsand for biological and ecological ways to control pests.In addition, since 1975 there has been growing evidencethat very low levels of chlorine-containing pesticidesand a variety of other fat-soluble chemicalsmay disrupt the human immune, endocrine, and nervoussystems by mimicking and disrupting the effectsof natural hormones in our bodies (Case Study, p. 416).The scientific jury is still out on if or how these chemicalsare harmful to humans.Critics of the ban on DDT and other chlorinatedhydrocarbon pesticides say the ban ended up increasinghuman deaths from exposure to pesticides. Why?Organophosphates that were less persistent and ecologicallydamaging replaced chlorinated hydrocarbonpesticides. But it turned out that these chemicals werehundreds and in some cases thousands of times moretoxic to humans than DDT and its chemical cousins.As a result, these replacements killed a large numberof farm workers and children playing in sprayed fieldsor otherwise coming into contact with organophosphatepesticides.This led the EPA to ban the use of many organophosphatesand then carbamates that followed them(Table 23-1). Since then new groups of pesticides suchas botanicals and microbotanicals have been developedthat are less harmful to humans and the environment.Although DDT is banned in developed countries,it has not gone away. It is manufactured legally in severalcountries and is still used to treat crops and to killdisease-carrying insects in a number of developingcountries.In 2000, delegates from 122 countries agreed on aglobal pollution prevention treaty to control, reduce,phase out, and destroy stockpiles of 12 persistent organicpollutants (POPs). This list of chemicals, calledthe dirty dozen, includes DDT and eight other chlorinecontainingpersistent pesticides.The treaty, which went into effect in 2004, allows25 countries to continue using DDT to combat malariauntil safer alternatives are available. This was allowedbecause the health benefits of using DDT to decreasemalaria far outweigh the remote possibility of harm topeople. Although DDT may prove to have some as-yetunknown harmful effects on humans, malaria killsabout 1 million people a year—most of them children—andsickens and weakens several hundred millionpeople.In addition, spraying low levels of DDT indoorsand on bed nets would not spread large amounts of thechemical into the environment compared to blanketingcrop fields with DDT. This should slow the developmentof genetic resistance to DDT in malaria-carryingmosquitoes. Also, after the ban it was discovered thateven when mosquitoes developed genetic resistance toDDT, it still acted as a repellent and irritant that drovenocturnal mosquitoes out of homes before they had achance to bite. Despite this decision the World Bankand other international aid agencies do not provideloans or funds for malaria-control projects that involvethe use of DDT.Opponents argue that a complete ban on DDT willspur research efforts to find other cost-effective pesticidesfor killing malaria-causing mosquitoes and tofind alternatives to using pesticides. They supportWHO efforts to use a variety of methods to reduce thethreat of malaria.xHOW WOULD YOU VOTE? Should DDT and other persistentchlorine-containing pesticides still be used to control malariathroughout the world? Cast your vote online at http://biology.brookscole.com/miller14.23-5 ALTERNATIVES TOCONVENTIONAL CHEMICALPESTICIDESWhat Should Be the Primary Goal of PestControl? Pest Reduction Not EradicationReducing crop damage to an economically tolerablelevel should be the primary goal of pest controlefforts.In most cases, the primary goal of spraying with conventionalpesticides is to eradicate pests in the area affected.However, critics say the primary goal of anypest control strategy should be to reduce crop damageto an economically tolerable level. The point at whichthe economic losses caused by pest damage outweighthe cost of applying a pesticide is called the economicthreshold. Because of the risk of increased genetic resistanceand other problems, continuing to spray beyondthe economic threshold can make matters worse andcan cost more than it is worth.The problem is determining when the economicthreshold has been reached. This involves carefulmonitoring of crop fields to assess crop damage anddetermine pest populations.Many farmers do not want to bother doing thisand instead are likely to use additional insurance sprayingto be on the safe side. One method used to reduceunnecessary insurance spraying is the purchase of pestlossinsurance. It pays farmers for losses caused by pestsand is usually cheaper than using excess pesticides.Another source of increased pesticide use is cosmeticspraying. Extra pesticides are used because mostconsumers often buy only the best-looking fruits andhttp://biology.brookscole.com/miller14527