Chemistry

Growing crops entails a lot of work, not to mention the time and money invested. However, farmers are often bridled with problems concerning their crops  plant pests and diseases that if unfortunately affect their crops, can decrease their production in varying degrees. The November 2009 World Summit on Food Security asserts that crop production provides about 84 percent of global food, feed, and fiber needs and virtually all human endeavors depend on food security. Crop pests, including diseases, insects and weeds, should be overcome to meet future needs. The same conference provided compelling data that insect pests are estimated to have caused the destruction of 15 percent of crops on a global scale (World Summit on Food Security 2009).

To counteract the effects of pest infestation and prevent crop losses from insects, growers resort to the use of insecticides. CropLife Foundation (2009) states in its March 2009 The Value of Insecticides in U.S. Crop Production Executive Summary that for every dollar spent on insecticides, U.S. growers gain 19 in increased production value. Such was the benefit of farmers from insecticides that variations of which exist that can kill a number of plant pests. One of such broad spectrum insecticide is chlorpyrifos.

Chlorpyrifos is a popular insecticide because it can kill a wide variety of insects cutworms, corn rootworms, cockroaches, grubs, flea beetles, flies, termites, fire ants, and lice (U.S. Environmental Protection Agency 1986). It is used to control insects that harm grain, cotton, field, fruit, nut and vegetable crops, and is used as well on lawns and ornamental plants. Chlorpyrifos (with chemical formula C9H11Cl3NO3PS) is colorless to white, crystalline solid with a mild, mercaptan-like odor. Chlorpyirifos belongs to the family of organophospates. Organophosphates are chemicals known to inhibit cholinesterase. Acetylcholinesterase is an enzyme that synthesizes acetylcholine, a chemical involved in the transmission of nerve impulses across nerve junctions of humans and animals.  Inhibiting acetylcholineterase will lead to an accumulation of acetylcholine which could cause rapid twitching of involuntary muscles, convulsions, paralysis and untimely death (Cremlyn 1991). Exposure to chlorpyrifos is mainly through skin contact and inhalation. Other means of getting it into your body is through eating fruits and vegetables which were used with chlorpyrifos-containing insecticides and drinking contaminated water.

From an ecological standpoint, chlorpyrifos can also harm several avian species and aquatic organisms. Birds are exposed to chlorpyrifos through the air and water, with different species having varying tolerance for this chemical. Its effect mainly is to lower egg production of mallards when exposed to 125 ppm of chlorpyrifos (U.S. Environmental Protection Agency 1989). Meanwhile aquatic organisms have low tolerance levels for chlorpyrifos  exposure to low concentrations already leads to cholinesterase inhibition, with the substance amassing in their tissues. Sea bottom dwellers, in particular, are in great danger of poisoning because of the persistence of chlorpyrifos as sediment (Schimmel et al 1983). For non-target species, the effect of chlorpyrifos is quite potent. Guenzi (1974) reported that all non-target species died after 0.01 to 0.02 kilogram per hectare (kgha) was applied to ricefields. It is also recommended that areas treated with chlorpyrifos be cordoned off from grazing animals or used within among honey-producing bees for extended periods of exposure again accumulated chlorpyrifos in their bodies (Thomson 1982).

The volume of pesticides used in the U.S. every year is 1.2 billion pounds but only 0.1 percent of it kills the pests it intended to kill. The remaining percentage (1.19 billion pounds to be exact) can either be washed off the plant and seep into the soil, contaminate lakes and rivers, or volatilize into the air (Pimentel 1995). According to the U.S. Environmental Protection Agency (U.S. EPA), chlorpyrifos has been widely used for 30 years and that annual application ranges from 20 to 24 million tons annually.

In 1999, a reassessment of pesticides was done by the Tolerance Reassessment Advisory Committee to ascertain whether their existing EPA registrations comply with the safety standards called for by the Food Quality Protection Act of 1996 the following year, the EPA sought the ban of chlorpyrifos use in gardens and homes as pesticide. This was due to the numerous reports about the adverse effects of chlorpyrifos use in environments where children are present. Developmental delays were seen in children and were linked to their exposure to chlorpyrifos-containing pesticides (Lovasi et al. 2010). However, the use of chlorpyrifos, marketed under the brand name Dursban, is still being used for agricultural purposes to date though restrictions were enforced reductions in application risks were to be implemented, as well as the use of protective gear and clothing when possible contact with the chemical is likely. From the U.S. EPA website (2008), the following risk mitigation measure was deemed necessary for agricultural workers
PPE (personal protective equipment) consisting of double layers, chemical resistant gloves, chemical resistant shoes plus socks, chemical resistant headgear for overhead exposure, chemical resistant apron when cleaning and mixing or loading and a dustmist respirator are required for the following scenarios mixingloading liquids for groundboom and airblast application, loading granulars for ground application, tractor drawn granular spreader, and low pressure handwand.

While for foreseen ecological risks, the manufacturers of chlorpyrifos-containing pesticides entered in an agreement with U.S. EPA (2008) to label amendments which include the use of buffer zones to protect water quality, fish and wildlife, reductions in application rates, number of applications per season, seasonal maximum amounts applied, and increases in the minimum intervals for retreatment.

On a personal level, the continued use of chlorpyrifos might be due to the sustained support of people of products grown with the use of such pesticides. In mitigating this environmental chemical threat, I suggest that we go organic. That we patronize only produce grown organically. This way, the demand for products exposed to pesticides will decline and farmers will shift to the use of other alternative methods of combating pests. Theres the use of other insects that prey on the supposed pests (Charlet 2002). The prey-predator relationship that exists in nature is a viable means to curb the population of the pests present in the crops.
I also vouch for the full ban of chlorpyrifos. Whats the use of banning chlorpyrifos in homes if it is still used in the fields Chlorpyrifos can stay on the surface for 10-14 days before it is lost through volatilization (Thomson 1982). What if the crop was harvested, brought to the market, bought then consumed within that period Then the person has actually ingested some amount of chlorpyrifos.

I would also like to urge the scientific community to continue studying and publishing the effects of chlorpyrifos in the body, as well as in animals and the environment. That way, evidences will mount referring to the hazards it imposes and further convince people of the risks they face when they still patronize or tolerate the use of chlorpyrifos in the food they eat.

Lastly, through this paper, I would like to inform and warn the public about pesticides in general, and chlorpyrifos in particular.