Pesticides Poison to pests or people?
By Quamrul Haider
Agricultural practices in Bangladesh and elsewhere are designed to minimise the amount of crop spoiled by insects or other pests. Hence, different pesticides are applied at different times during the growing season, directed at the pests most likely to damage the crop at that time. Wholesale use of pesticides will become evident in the coming months when litchis and mangos flood Dhakas fruit markets.
The term pesticide is somewhat general, even misleading. Insecticide, while more accurate, gives no hint of potential injury beyond insects. The most general term which avoids these overlapping difficulties is biocide.
In 1939, Swiss entomologist Paul Mller found that a synthetic organic compound called dichlorodiphenyltrichloroethane (DDT) was an extremely effective insect killer. His discovery ushered in a new era of chemical control of pests. Because of its lethal power to kill insects that destroy crops, DDT was viewed by many as savior of mankind.
The success of DDT in killing crop-destroying pests was a catalyst for synthesizing thousands of new pesticides. But we have not yet come up with any that insects cannot defeat. Moreover, one of the most troubling problems with most of the pesticides is, in addition to killing the pests, they also destroy insect predators and parasitic insects that naturally help control pests.
When an insect population is exposed to a new pesticide, by random coincidence, a few remain immune or resistant to the chemical. As a result of the elimination of their peers as well as predators, these few reproduce almost without competition. Such pests do little damage initially. However, over time they reproduce and form a sizeable population that can cause significant crop damage. Pesticide resistant pests have appeared everywhere we sprayed.
Another problem that emerged during the era of overuse was that many of the pesticides proved harmful to non-target species, such as fish, fowls and other animals. Insect and worm-eating birds perished in areas where aerial spraying of pesticide had occurred. Widespread contamination by pesticides nearly wiped out the population of predatory birds, such as peregrine falcons, brown pelicans, cormorants, bald eagles and ospreys, to name a few.
The segment of Bangladeshi population most affected from pesticide exposure is the farm workers. Safety provisions for them are non-existent or minimal, to say the least. People living near pesticide-treated fields are also affected because more than 50 percent of the sprayed material never reaches the ground but is carried away by winds.
Concern over the risks of eating fruits and vegetables sprayed with pesticides raises the broader question of whether any produce sold in the market is safe to eat. Even fruits and vegetables labeled as 100 percent organic can contain trace amounts of pesticides because, as noted above, the chemicals can drift on wind. Most experts believe that by eating the pesticide-treated produce, we have, along with just about every other organism, accumulated harmful chemicals in our body.
There is worrisome evidence that even minute levels of pesticide in food can impair human development and damage the immune system. Insomnia, nausea, headaches, dizziness and cancers are some of the many health-related effects of pesticide poisoning. Some people exposed to pesticides complain of reduced powers of concentration and nervous disorders. There are indications that certain pesticides may act as a hormone disrupter and affect fertility as well as promote premature delivery.
Pesticides contain both active and inactive chemicals. The latter, called inerts, are used as propellants to carry the active agents to the target. Although not toxic, they often act as a catalyst for some of the above-mentioned health problems.
Many of the chemicals used in pesticides are persistent environment contaminants, whose impact may endure for decades. They are contributing to enormous environmental degradation, including but not limited to soil contamination, loss of genetic diversity and destruction of ecosystems. Rain water carrying pesticides from lawns and farm lands pour into rivers and affect the fish population. They also end up in groundwater in rural communities, causing potential health risks.
While DDT is no longer used in the industrialized nations, its use continues in parts of the world where the soil is regarded as some kind of an incinerator. Since its discontinuation, concentration of DDT in the environment has decreased, but because of its persistence, residues from past use still remain. Many tropical countries still use DDT to control malaria.
The magnitude of pesticide related problems we are faced with evokes feeling of despair and helplessness. Nevertheless, we have entered a reflective stage, a period of tempered optimism about the biological and ecological repercussions of pesticides. Although odious in extreme usage, we are aware of the benefits of pesticides; we also know that the benefits come with a cost. We should, therefore, have a rational basis for determining at what point the cost becomes prohibitive in terms of human health and the environment. More importantly, we have to realize that what is poison to pests is poison to human beings, too.
The writer is Professor of Physics at Fordham University, New York.
Photos: Google Image
