Pesticide Life Cycle

Introduction

The word pesticide is one which is used to denote a large group of substances which share the common property of controlling pests. As defined in the Draft Legislation for Pesticides and Toxic Chemicals Control, prepared by the Legal Unit of the Organisation of Eastern Caribbean Sates (OECS), a pesticide is “any substance which by itself, or in combination with other substances, is proposed, represented or used for destroying or controlling or repelling, mitigating plant or animal life which are considered pests but does not include any antiseptic, disinfectant, drug or preservative”. In order that this definition may have true meaning to the lay person, it necessary to define the term pest, and the aforementioned legislation fines a pest as “ any insect, bird, rodent, fish, mollusk, nematode, fungus, weed, algae, micro-organism or virus, and any other kind of plant or animal life that injurious, troublesome or undesirable to any crop, stored produce, food, feed, wood, clothes, textiles or other fabrics and any includes any ectoparasites of man, and ectoparasites and endoparasites of animals”. This briefing paper seeks to address the pesticide life cycle, and to provide general information on issues such as pesticide toxicity, the routes of entry of pesticides into the body, biochemical processes which occur internally when pesticides enter the human body, and the effects of pesticides on the environment.

The Pesticides Use Cycle has at least six distinct stages:

1. Selection and purchase,

 2. Transportation,

3. Storage,

4 Mixing or diluting,

 5. Application

 6. Disposal

During each phase of this cycle, it is essential that consideration be given to the safety and protection of (a) the user, (b) other persons who may become exposed to the pesticide, (c) non- target animals, (d) property, and (e) the environment. The ideal pesticide is one which would act quickly and specifically on the target pests, while being completely harmless to humans, domesticated animals, wildlife and the environment. The residues of this pesticide would be short lived and would last only as long as was absolutely necessary to effect the necessary pest control. The pesticide would be inexpensive and readily available in the necessary quantities, chemically stable, non-flammable and generally safe to use around homes and industrial sites .There would be no dangers associated with its preparation and application, the formulation would be non-corrosive, non-staining and would have no offensive odor. The disposal of this pesticide would represent no dangers to the environment or to animal and plant life. Unfortunately. No such pesticide exists, and although the danger of accidental death from pesticides is considerably less than that from many commonly engaged-in activities, and the risks of protracting cancer from many pesticides is less than that from hundreds of other frequently- contacted substances and foods. Due care and attention must be paid when using pesticides.

Selection and purchase

In selecting and purchasing a pesticide, it is necessary that consideration be given to factors such as the area where the pesticides will be used (commercial agriculture, home garden, domestic environment, etc.), the safety of non-target organisms such as pets, wildfire plants ( house plants if used in a home setting), and even the protection of electronic equipment, as many spray and dust formulations, if used in environments which house computers , televisions, and stereos may damage such equipment.

Transportation

The transportation of pesticides is an area where due care and attention must be exercised. Vehicles transporting pesticides over long distances should contain a separate compartment for the storage of the pesticides. The pesticides should be stored in a manner to avoid spills and container breakage, there should be adequate spill control, clean up material and first aid material on board, and the persons on board should knowledgeable of the appropriate spill control and first aid procedures.

Storage

Pesticides should always be stored in the original containers, and in an area specially designed for this purpose. The room should always be kept locked and should be labelled with the appropriate warning signs. There should be proper ventilation, and the room should contain first aid, spill control and fire fighting material. Users should be acquainted with the regulations governing the storage of pesticides, and should adhere to the requirements of these regulations.

Mixing

The safe mixing of pesticides requires that protective clothing be worn, and mixing must take place in open, well ventilated conditions. Users should always read the labels on the pesticide containers prior to mixing, and follow the instructions provided.

Application

The first step in the safe application of pesticides involves reading and understanding the directions on the label. The proper application and safety equipment should always be used. Additionally, users should always bear in mind that areas treated with pesticides are not usually safe immediately after treatment, therefore, users should heed the requirements concerning the safe period for re-entry into treated areas, as stipulated on the label of the respective pesticide.

Disposal

When possible, users should aim to use up all pesticide in the containers. The instructions on the container concerning the proper disposal of empty containers should be followed. Users should always use the recommended triple rinse method for empty containers. Used containers should never be used to store food or water, and should never be rinsed or disposed of in streams or rivers.

Toxicity

Every pesticide has an innate capacity to be poisonous at some level, and this capacity is defined as the toxicity of the pesticide. Toxicity is commonly expressed as the LD 5 0, which represents the lethal dose (usually in milligrams per kilogram of body weight of the animal – mg/kg) required to kill 50% of a population test animals. The lower the LD 50, the greater the toxicity of the pesticide.

Pesticide toxicity may either be chronic or acute. Chronic toxicity is the result of repeated or prolonged exposures, over time, to sub-lethal doses of a pesticide. Types of chronic toxicity include tumors and cancers, reproductive problems such as sterility or birth defects, damage to the nervous system, and damage or degeneration of internal organs such as the liver.

Acute toxicity is a rapid response, usually within minutes or hours, to a single or a few very closely spaced exposures to the pesticide. Hazard, on the other hand, is the degree of danger involved in exposure to the pesticide as it is used, and represents the chance that poisoning could occur under certain circumstances or use. The hazard associated with the use of a pesticide is directly related to its toxicity and the amount of exposure to the substance. Therefore, although we have no control over the toxicity of a pesticide, we can significantly reduce the hazard by minimizing or eliminating the exposure to it, and this should always be the underpinning philosophy behind the safe use of pesticides: to reduce the hazard by minimizing the exposure.

There are three routes for pesticides to enter the body, namely, through the skin (dermal absorption), through the nose and lungs (inhalation), and through the mouth (ingestion). The LD₅₀ values for a pesticide will vary according to its route of entry into the body.

Pesticide Poisoning

If pesticides are not used properly they can result in poisoning. It is essential, therefore, that users of pesticides be aware of the various warnings which the human body provides to denote that pesticide poisoning may have occurred.

There are two types of clues or warnings to pesticide poisoning. Sign are effects such as vomiting, muscle spasms, confusion, slurred speech or unconsciousness which can be noticed by other persons. Symptoms are feelings that the poisoned person can recognize, such as nausea, dizziness, stomach cramp or headache.

Organophosphorus pesticides represent one of the largest groups of pesticides presently in use. These pesticides can be absorbed dermally, orally or through inhalation. These pesticides attack cholinesterase, an enzyme in the body which is responsible for terminating the action of acetylcholine, the chemical responsible for the transmission of nerve impulses. The organophosphates inhibit the action of the cholinesterases by forming chemical bonds with them which prevent them from deactivating acetylcholine. This has the effect of causing an accumulation of acetylcholine, which leads to nerve impulse, transmission going out of control, and consequently muscle convulsions and loss of nervous system control.

Organophosphate poisoning is usually treated with atropine sulphate, which blocks action of acetylcholine by interfering with the cell’s ability to respond to this transmission chemical. Carbamates act very similarly to organophosphates, but their effects on cholinesterase are brief due to the rapid rate of breakdown of carbamates in the body. Because of the effect of these pesticides on cholinesterase the levels of this enzyme in the body are usually tested to determine the possibility of pesticide poisoning, and it is recommended that persons who use organophosphates be tested routinely for cholinesterase activity.

Environment Contamination

Mishandling or misuse of pesticides at any stage of the pesticides use cycle may have adverse effects on not only the human users who may become exposed to the pesticides, but also on the environment in which these chemicals are used. Although the proper and safe use of pesticides can be of benefit to the environment, pesticides also represent a major potential for environmental pollution. Besides humans, there are six major areas in the environment which require protection from mishandling and misuse of pesticides; soil, water, air beneficial insects, plants, and wildfire.

Soil

Pesticides may become attached to fine soil particles, and this attachment may be so strong that the pesticide does not move through the soil layers for any distance. Most pesticides that become attached to soil stay near the surface and may be broken down by bacteria and other micro-organisms. Pesticides with little or no movement in the soil may pose a threat to sensitive crops planted in the area, but do not pose a real threat to ground water. Such pesticides include Gramoxone and Ambush. However, even such technical information must be treated with caution, in the light of the highly fatal effects of the ingestion of Gramoxone. Pesticides which exhibit moderate to high movement in the soil are of great concern, and all efforts must be engaged to keep these out of ground sources. In the latter category are Furadan, Nemacur, Mocap, Temik and Lannate. Pesticides which exhibit moderate to high soil mobility should be used, very carefully near ground water sources, and every effort taken prevent ground water and surface pollution

Water

There are many different ways in which pesticides may get into water. Pesticides may be applied directly and often illegally to water for the control of aquatic plants and animals, they may get into water by accident when nearby land has been sprayed, they may enter as spray drift from nearby applications, pesticides attached to soil may wash into streams, and some pesticides may enter the water by being washed out of the air by the rain. It is, therefore, imperative that all possible precautions be employed to minimize the possibility of surface water and ground water pollution from pesticides. These precautions include avoiding mixing and loading pesticides near wells and other water sources, careful disposal of used pesticides, use of integrated pest management, and paying attention to land geology, soil characteristics and pesticide characteristics.

Air

A major source of air pollution by pesticides is ground and aerial pesticide application. Pesticide carried by the air can be harmful to human and wildlife health and safety. Pesticides in the air are difficult, if not impossible, to control. It is, therefore, important that users be cognizant of the effects of wind, temperature, climatic conditions, pesticide formulations, particle size, drift, and type of compound applied on pesticide drift.

Insects

The beneficial insect most affected by pesticide pollution is honey bee. Honey bees are important pollinators of food crops, in additions to being producers of the economically important honey and beeswax, therefore, the accidental killing of honey bees when crops are treated with pesticides is detrimental to both the bee keeper and the farmers.Bees killed by pesticides are usually the result of inappropriate or careless application of pesticides, improper timing of pesticide application, and improper disposal of unused pesticides. In the light of this, pesticide users should always try to (i) use pesticides and formulations which will have the least effect on bees, (ii) communicate with bee keepers on the timing and nature pesticide applications, ( iii) time their applications in a manner to lessen the possibility of bee kills, (iv) keep pesticide treatment to a minimum(v) avoid spraying or treating crops or fields which are in bloom and therefore likely to be visited by bees.

Plants

Plants, although usually the beneficiary of pesticide use, may also be harmed accidentally by pesticides. Plant injury from pesticides usually results from volatility and drift herbicides to sensitive non-target crops. This may be mitigated by using formulations which remain in the target area, by not using dosages in excess of those recommended, and by paying attention to long term effects of persistent pesticides.

Wildlife

Wildfire such as fish, birds and mammals are very important to human beings and to quality of life in general. Sadly, these animals may be the victims of careless and indiscriminate use of pesticides. Birds and mammals may be killed directly by insecticide use, either through dermal or inhalation entry, but also through ingesting contaminated food. Wildlife do not have to be killed directly to be affected. Pesticides may cause hatching failure in birds, reduced reproduction in mammals, and a reduction in the growth and survival rates of young animals. Pesticides users should always be careful to protect wildlife from accidental death, or harm from pesticide use and disposal, and should ensure that the crop protection practices which they employ are complimentary to, and not competitive with, coexisting wildlife species.

Persistence and Accumulation

Eventually, all pesticides will break down into simpler substances. However, the rate of chemical breakdown varies for different pesticides. Those pesticides which take a relatively long period to break down, chemically are referred to as persistent pesticides. In addition to the chemical nature of the persistent, factors such as temperature, sunlight and air influence the rate of breakdown of pesticides. Although persistent pesticides effect longer control against the target pests, they also cause greater damage to the environment, and if coupled with other factors such as environmental mobility and possibility of being stored in animal tissue, can pose serious hazards to humans and non –target animals.

Pesticide which have the property of being able to build up in the body of animals are known as accumulative pesticides. Many pesticides can accumulate in the bodies of animals, particularly in fatty tissues, and over the long term in the long term result in chronic toxicity problems. Additionally, animals higher up the food chain, such as humans, may become exposed to very high levels of pesticides by eating animals which have accumulated these pesticides in their bodies.

Conclusion

The aforementioned issues serve to highlight the need to adopt a cradle to grave approach to pesticide management. All steps in the pesticide use cycle are potential areas for pesticides poisoning to humans and pesticides contamination of the environment. Pesticide users must always be informed about the nature of the substances with which they are dealing, the recommended safe way of handling and using these pesticides and the possible hazard to themselves and the environment resulting from careless and irresponsible use. If pesticides are used in a responsible and informed manner, many of the hazards associated with their use can be eliminated, and pesticides can continue to play, their important role in increasing crop production, improving the quality of life for humans and domesticated animals and also preserving the environment.