Pesticides: a silent killer?

by Dushani Palliyaguru

A pesticide is defined as any substance or mixture of substances used to prevent, destroy, repel, ormitigate any pest. These include insecticides (affects insects), herbicides (affects plants and weeds)and fungicides (affects fungi). The main advantage in using pesticides is its ability to produce a highyield in crops. Adding to this trend, in the recent past, genetically modified crops (GMCs) have beendeveloped to produce an even better yield. No one can deny the uses of pesticides for protection ofcrops in the field, thereby providing us with abundant, inexpensive and attractive fruits andvegetables. Yet, there is no such thing as a completely safe pesticide; its purpose is to kill and thequestion is who?

When DDT (dichloro-diphenyl-trichloroethane) was introduced in the 1940's, it marked the beginningof a revolution.

It was used to control malaria, typhus, and other insect-borne diseases. However, asa result of overuse, many insect pest species developed resistance to DDT. Increasing concerns overhealth effects in humans and wildlife, and lessened effectiveness lead to DDT being banned in manycountries. Since the introduction of DDT, thousands of new chemicals have entered the market aspesticides, out of which many have been proven to have more risks than benefits.

Contrary to popular belief, it is not only farmers and individuals who work closely with pesticides thatare exclusively victims of pesticide exposure. In addition to accidental, suicidal and occupationalexposures (during manufacturing, mixing, loading and harvesting), bystanders can also be exposedas a result of off-target drift from spraying operations. Moreover, members of the general public who consume food items containing pesticide residues also ultimately fall prey to their unpleasant effects.

It has been thought that the biological effects are most lethal and immediate for accidental andsuicidal poisonings while they are the least for the general population that consumes pesticide-contaminated food.

However, over an average person's lifespan, chronic (long-term) exposure to agiven pesticide or several pesticides can have many adverse health effects, even if they areconsumed in minor amounts.

Extensive studies have been carried out to determine the associations between exposure topesticides and human disease.

While overdose of many pesticides can result in immediate death, aswith the case of pesticides used for suicides, pesticide toxicity in low doses over a long period of timecan also result in conditions such as organ failure, cancer and diabetes.

The risk for developing theseconditions has also been observed to be much higher amongst occupational users of pesticides, such as farmers. All pesticides are manufactured as mixtures of several chemicals and most of these individual chemicals have been shown to affect human health.

For example, the heavy metal cadmium, which is found commonly in fungicides and is also added to fertilizers, is known to be associated with the induction of chronic renal tubular disease and other kidney-related dysfunctions.

Interestingly enough, cadmium has been shown to be one of the possible causative agents of chronic kidney disease with unknown etiology, a disease that is also most prevalent amongst farmers in the North-Eastern region of Sri Lanka.

Cadmium and other heavy metals, such as arsenic, and mercury are not the only culprits.

Organochlorine insecticides such as DDT have been shown to directly and indirectly interfere with fertility and reproduction in both wildlife and laboratory species of animals.

While organochlorine insecticides are being banned from the markets of developed countries, developing countries continue to use them because they are relatively inexpensive to manufacture, highly effective and the absence of substitutes.

Sri Lanka banned its last approved organochlorine pesticide, chlordane in 1996.

However, the Sri Lankan pesticide market still carries a variety of chemicals, including but not limited to organophosphates (insecticide) and dithiocarbamates (fungicide). Organophosphate toxicity has been associated with psychological and neurological disorders while dithiocarbamates have been shown to have adverse reproductive outcomes in pregnancy rate and fetal development.

One of the biggest challenges here is the absence of sufficient data to determine associations and causality between pesticide exposure and long-term health effects. This lack of information is often exploited by agrochemical manufactures to market products that have not been amply studied for safety, especially to developing countries.

As mentioned previously, the use of pesticides has given man several advantages for agriculture andcrop management. Nevertheless, one cannot ignore the health hazard they can cause when abusedand used under improper guidelines. Despite the recent development of second-and third-generationderivatives of the early chemical pesticides, all pesticides possess an inherent degree of toxicity tosome living organism, otherwise they would be of no practical use. For farmers, emphasizing on simple handling techniques such as wearing protective masks, gloves and footwear when working in the fields, during spraying can mitigate a large proportion of the occupational exposure to pesticides.

It is important that manufactures present the minimum volume of pesticide that can be sprayed in order to obtain the highest yield, which could minimize exposures to toxic agents. An article that was published in The Lancet in 2002, Michael Eddleston and colleagues proposed introducing "a minimum pesticide list" as a measure to lessen pesticide-related suicides in developing countries. An effort of that nature could also be potentially useful to regulate pesticide imports and distribution.

Furthermore, continuing research to study the adverse health effects of pesticides that are currently in the market, imposing strict regulatory standards for those chemicals that have been shown to be associated with health conditions and using alternative pest control methods such as integrated pest management (IPM) can have a long-standing positive impact for safe food for generations to come.

Dushani Palliyaguru is a doctoral student at the Department of Environmental and Occupational Health, University of Pittsburgh, USA.