Module 1. Background Concepts
The world population is now over seven billion people, who all need to be properly fed. This rising population rightly expects to have nutritious food that is safe to eat, and not too costly. There are many organisms that can reduce the output of farming, and could cause catastrophic food shortages unless they are controlled. Pesticides are one of the important ways that farmers can reduce these losses. Used alongside other methods of preventing damage from insects, moulds, slugs and rats, and competition from weeds, pesticides help to ensure that food is of good quality and keep the cost of production in check. Herbicides (weed-killers) in particular, save a lot of costly and sometimes tedious manual labour that would be needed to remove plants that compete with crops. A summary of the benefits of pesticides can be found at http://www.sciencedirect.com/science/article/pii/S026121940700097X
The word ‘pesticide’ is a broad term, covering a range of products that are used to control pests. A pest is usually considered to be any undesired plant or organism that is destructive, harmful or troublesome to its host, or carries disease to plants, animals, or humans. Often people only think of pesticides as chemicals, but they include a large range of different types of products. Some are natural, such as pyrethrums, obtained from chrysanthemum flowers, while others are altered versions of natural chemicals. Many of the older more toxic pesticides have been withdrawn from the market, while more recently developed pesticides include products that are very specific and generally safer to both people and the environment, than earlier generations of chemicals. This is not to say that care is not needed when using pesticides to make the most of their merits while avoiding unwanted effects.
Hazard and Risk
Hazard is the potential to cause harm. Pesticides have this potential and therefore can be hazardous if used carelessly. They are designed to kill or adversely affect living organisms, and unless they are used properly and correctly, have the potential to harm people. Similarly if used indiscriminately or incorrectly, many pesticides can damage the environment or hurt non target animals. To avoid this, we take precautions to reduce the likelihood of a harmful outcome (i.e. we reduce the risk). Risk management enables people to get the benefits of a technology without allowing it to cause harm. With pesticides, the legislators, the agrochemical industry and users, all have a role in risk management, that is, making sure that the benefits of pesticides are not at the expense of injury to people, animals or the natural environment. As part of an integrated pest management programme, pesticides can continue to be useful tools for protecting crops and helping to maintain a healthy population.
Below are links to some sites with more complete information, including reasons why we need pesticides. The next lessons will cover the potential health and environmental risks associated with irresponsible or ill-informed use of pesticides.
Further information on pesticides
Reducing Health Risks
Almost every chemical poses some risk to human health if used incorrectly. Pesticides, which are chemicals designed specifically to have an adverse effect on a target organisms, are particularly prone to create potential health risks to humans and non-target species if the instructions are ignored or if they are applied inappropriately. The good news is that the risks can be greatly minimised if proper precautions are taken. This means applying the correct product at the recommended rate, and at the right time, while making sure that the person handling the pesticide is not put at risk. When applying pesticides it is very important to avoid exposure, so precautions often include wearing protective clothing such as gloves and coveralls. The technical name for this is personal protective equipment (PPE). If PPE is required the pesticide label will usually inform the user, often using both pictorial and written information.
Not all pesticides are equally dangerous. Some hazardous pesticides are restricted to being used only by specially trained personnel, who will take special precautions and wear special apparel. Others such as domestic fly control aerosols, can be used by any adult. The degree of risk (likelihood of causing harm) associated with a pesticide is usually defined using the following equation:
R = T x E
Risk (likelihood of harm) = Toxicity (the hazard, a measure of how harmful or poisonous a pesticide is) x Exposure (contact)
Pesticide risk varies with:
- type and amount of active ingredient(s),
- type and amount of carrier or solvent ingredient(s),
- type and amount of inert ingredient(s), and
- type of formulation, such as liquid, dust, granule, powder.
The toxic effect of a pesticide exposure depends on how toxic it is, how much pesticide is involved and how long it remains in contact. Pesticide exposure occurs either when you get a pesticide in or on your body, for example when spraying and the skin is wetted with the spray liquid, or after eating food that has been recently sprayed. The pesticide label always gives a period of time between spraying and harvesting food crops. Provided that this interval is respected, the food will have a residue level that is safe.
Pesticides can cause three types of harmful effects: acute effects, chronic effects, and allergic effects. An acute effect is the toxic response that results from a single dose or exposure to a pesticide. A chronic effect is the toxic response that results from repeated exposures to small doses of a pesticide over a longer period of time. An allergic effect is suffered by people who have an abnormally high sensitivity to certain substances that do not cause the same reaction in most other people.
Reducing Environmental Risks
It is probably safe to assume that most people know what is meant by the environment – literally everything around us including air, soil, water, plants, animals, houses, restaurants, office buildings, and factories and all that they contain. Over the past few years, the public, national governments, international organizations, farmers and agricultural professionals alike have become much more concerned about how we humans are affecting the environment. The effects of agricultural pesticides on the environment are specifically worrisome to some people, and have been shown to outweigh the actual risks (Hibbitt 1990). While it is true that if used irresponsibly, pesticides have the potential to cause harm to the environment, when proper practices are observed the environmental risks are small.
This risk depends on a number of factors. Here are some of the most commonly mentioned:
- persistence – how long the pesticide remains active in the environment
- mobility – how easily the pesticide can move from where it is applied
- nontarget toxicity – how toxic the pesticide is to organisms other than the pest
- volume of use – how much of that pesticide is used in the environment
- degradation – the time it takes for a pesticide to break down in the environment
- bio-accumulation – the degree to which a pesticide accumulates in body tissues
- bio-magnification – the build up of a pesticide in the food chain
- volatility – how easily a pesticide vaporizes when exposed to air
- adsorption – the degree to which a pesticide binds onto soil particles
- absorption – the ease with which a pesticide can enter an organism or soil structures
When we apply pesticides there are three ways in which they can affect the environment:
- drift – the movement through the air of a pesticide away from the target site. Small drops are particularly prone to being carried away by wind, so we tend to use larger drops when spraying herbicides, to reduce drift.
- surface runoff – water (rain or irrigation) that runs off a treated site can carry pesticides far from the target. If we apply pesticides in too much water, and they run off the leaves it is not efficient and may damage the soil organisms.
- leaching – the movement of pesticides dissolved in water through the soil. Some pesticides do not break down quickly in the soil, and may pollute water courses.
- Environmental effects of pesticides at: http://www.epa.gov/pesticides/ecosystem/index.htm
- Environmental fate of pesticides at http://www.agf.gov.bc.ca/pesticides/c_2.htm
International Code of Conduct on the Distribution and Use of Pesticides
The International Code of Conduct on the Distribution and Use of Pesticides is an initiative by the Food and Agriculture Organization (FAO) of the United Nations to establish voluntary standards of conduct for all public and private entities engaged in or associated with the distribution and use of pesticides. The Code describes the shared responsibility of many sectors of society to work together so that the benefits to be derived from the necessary and acceptable use of pesticides are achieved without significant adverse effects on human health or the environment. The first release of this document was developed in 1985 by the FAO in consultation with United Nations agencies and other organizations. It was revised and the latest version was adopted by the Hundred and Twenty-third Session of the FAO Council in November 2002. The Code is based on internationally agreed technical guidelines and is aimed at reducing the hazards associated with the marketing and use of pesticides. It is of particular value in countries that do not yet have adequate control infrastructures. The Code sets standards for pesticide management; testing; reducing health hazards; regulatory and technical requirements; availability and use; distribution and trade; information exchange; labelling, packaging, storage and disposal and advertising. The International Code of Conduct on the Distribution and Use of Pesticides is fully supported by the international crop protection industry. Everyone concerned about the responsible use of pesticides should have at least a general understanding of what the Code advocates and what its implications are for professionals in various sectors.
The Code recognises the benefits to be derived from the necessary and acceptable use of pesticides but encourages use of integrated pest management (IPM) rather than complete reliance on pesticides. It suggests a life-cycle approach to the development, regulation, production, management, packaging, labelling, distribution, handling, application, use and control, including post registration activities and disposal of all types of pesticides, including used containers.
If you don’t have a copy available you can:
- read it at http://www.fao.org/docrep/005/Y4544E/y4544e02.htm#bm2.1
- or download a PDF copy at ftp://ftp.fao.org/docrep/fao/005/y4544e/y4544e00.pdf
The next Module (2) is A Basic Approach to Responsible Use of Pesticides
 *Hibbitt (1990). Putting pesticides into perspective. Agricultural Engineer, Summer 1990 p.61.