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Toxicity & Hazard
Exposure
Human Pesticide Exposure [top]
There are three ways in which pesticides can enter the human body:
- through the skin or eyes (dermal),
- through the mouth (oral) and
- through the lungs (respiratory or inhalation).
Dermal Exposure [top]
  In typical work situations, skin absorption is the most common route of poisoning from pesticides. Absorption will continue as long as the pesticide remains in contact with the skin. The rate at which dermal absorption occurs is different for each part of the body (Figure 1). The head (especially the scalp and ear canal) and the genital areas are particularly vulnerable. The relative absorption rates are determined by comparing each respective absorption rate with the forearm absorption rate. This absorption may occur as a result of a splash, spill or drift when mixing, loading or applying a pesticide. It may also result from exposure to residue on application equipment, protective clothing or treated surfaces after pesticide application. The dermal toxicity of a pesticide depends on the pesticide formulation, the site of contamination and the duration of the exposure. In general, pesticides formulated as wettable powders, dusts or granules are not absorbed as readily through the skin as liquid formulations. The hazard from skin absorption increases when workers are mixing pesticides because they are handling concentrated pesticides that contain a high percentage of active ingredient.
 Certain areas of the body such as the genital area and eyes absorb pesticides easily and rapidly. It is easy to transfer pesticide residues from one part of the body to another. When this occurs, the applicator increases the potential for pesticide poisoning. For example, residues can be inadvertently moved from a hand to a sweaty forehead (4.2) or to the genital area (11.8). At this very high rate, the absorption of a pesticide is more dangerous than swallowing it! A cut can greatly increase pesticide absorption. Absorption is a particular hazard through cut or abraded skin on the hands or face.
Protect yourself from dermal exposure. Follow these guidelines:
- Wear protective clothing and equipment when using pesticides or repairing contaminated equipment.
- Spray during periods when there is little or no wind.
- Do not re-enter a sprayed field without protective clothing until the re-entry time has elapsed.
- If your clothes become contaminated, change immediately. Wash affected areas of the skin.
- Change clothes as part of the clean-up after pesticide use at the end of the day.
- Wash and shower after using pesticides.
- Wear clean clothes at the start of each day during pesticide application.
The tissues of the eyes are particularly absorbent. Besides the potential for chemical injury to the eye itself, some pesticides may be absorbed in sufficient amounts through the eyes to result in serious or even fatal illness. Eye protection is needed when measuring or mixing concentrated or highly toxic pesticides. Protective face shields or goggles should be worn whenever there is a chance that pesticide sprays or dusts may come in contact with the eyes.
Protect yourself from eye exposure. Follow these guidelines:
- Always wear eye protection when you measure or mix pesticides.
- Always wear eye protection when pesticide sprays or dusts may contact your eyes.
- Do Not wipe your eyes with contaminated gloves or hands.
Oral Exposure [top]
 While skin absorption is the most common means of exposure, the most severe poisoning usually result when pesticides are taken in through the mouth. Pesticides can be ingested by accident, through carelessness, or intentionally. The most frequent cases of accidental oral exposure are those in which pesticides have been taken from their original labelled container and put into an unlabelled bottle or food container. There are many cases where people, especially children, have been poisoned by drinking pesticides from a soft drink bottle. Adults have mistakenly drunk from bottles containing pesticides or have been poisoned by drinking water stored in contaminated containers. Workers handling pesticides or application equipment can also consume excessive levels of pesticides if they do not wash their hands before eating or smoking. Applicators must never try to clear a spray line or nozzle by blowing on it while holding it to their mouth.
Protect yourself from oral exposure. Follow these guidelines:
- Always store pesticides in their original labeled containers.
- Never put pesticides in an unlabelled bottle or food container.
- Never use your mouth to clear a spray hose or nozzle, or to begin siphoning a pesticide.
- Always wash after handling pesticides and before eating, drinking, smoking, or using the toilet.
- Never leave pesticides unattended.
- Avoid splashes or dusts when mixing pesticides.
- Label your pesticide measuring containers.
Respiratory Exposure [top]
 Certain pesticides may be inhaled in sufficient amounts to cause serious damage to nose, throat and lung tissues, or to be absorbed through the lungs into the bloodstream. Vapors and very small particles pose the most serious risks. The hazard of poisoning from respiratory exposure is great because of the rapid and complete absorption of pesticides through lung tissues.
Lungs may be exposed to pesticides by inhalation of powders, airborne droplets or vapours. Working with wettable powders can be hazardous because the powder may be inhaled during mixing operations and usually contains concentrated pesticide active ingredient. The hazard from inhalation of pesticide spray droplets is fairly low when dilute sprays are being applied with conventional low pressure application equipment. This is because most droplets are too large to remain airborne and be inhaled. However, when high pressures are used or ultra low volume (ULV) or fogging equipment are used, the potential for respiratory exposure is increased. The droplets produced during these operations are in the mist or fog size-range and can be carried on air currents for a considerable distance.
Many pesticides give off a vapour when exposed to air. Fumigants are used because their toxic vapours are desirable for pest control. They also have the highest hazard with respect to worker exposure to vapours. Some non-fumigant pesticides are toxic to pests as liquid or solid formulations, but also give off vapours which could be toxic to applicators or bystanders. The Workers' Compensation Board has established maximum permissible levels in the air for approximately 100 pesticides (W.C.B., 1985. Standard Practices for Pesticide Applicators). Some pesticides emit vapours that could exceed the maximum W.C.B. permissable levels under certain still air conditions (e.g. fumigants, fensulfothion, demeton, mevinphos, diazinon, disulfoton, carbaryl, parathion and chlorpyrifos). The hazard is greatest in enclosed spaces where there is little air movement. For example, high vapour levels could result from a spill in an unventilated storage area or application in a confined space such as a greenhouse. Air currents due to wind or ventilation can substantially reduce vapour levels.
Many pesticides that produce vapours provide a warning of their presence by their smell or by causing irritation of the eyes, nose and throat. However, some pesticide vapours have little smell and provide little warning of their presence.
As temperatures increase, vapour levels of many pesticides increase. This is why it is recommended that pesticides should not be applied when air temperatures are above 30°C.
Pesticides with high vapour hazards will have label directions to use respiratory protection equipment. It is important to use respirators if required on the label or if pesticides are used or mixed in poorly-ventilated areas or if there is a possibility of inhalation of pesticide mist or powder.
Protect yourself from respiratory exposure. Follow these guidelines:
- Wear an appropriate and properly fitting respirator:
- If it is required on the label;
- If pesticides are used or mixed in poorly ventilated areas;
- If there is a possibility of inhaling spray droplets, vapour, or powder.
- Do not re-enter a treated area too soon. Follow the re-entry guidelines on the label.
- Ventilate greenhouses or enclosed structures after pesticide application, before re-entry.
- Do not apply pesticides when air temperatures are above 30°C.
Toxicity of pesticides can vary depending on the type of exposure; dermal, oral or respiratory (inhalation), but it is important to remember that, in each case, the danger usually increases as concentration and duration of exposure increases. The longer a pesticide remains on the skin or in eyes, or the longer it is inhaled, the greater the damage that is likely to result.
In addition to route of entry into the body, there are two other ways that exposure is described: short-term (acute) or long-term (chronic) exposure.
Acute exposure refers to intake of a single dose or to a series of exposures within a short time period (e.g. one day). Acute exposures may be referred to as acute dermal, acute oral or acute inhalation poisoning. Usually the effects of acute exposure, if any, occur within 24 hours.
Chronic exposure is the exposure to pesticides over an extended period of time, such as where a pesticide applicator is frequently wetted with spray during unsafe spray practices. Pesticides which have a tendency to accumulate, or which break down slowly in body tissues, usually represent the greatest chronic exposure hazard. Someone who is frequently exposed to low doses of such pesticides may develop symptoms of poisoning long after the first exposure. Chronic exposure may be referred to as chronic oral, chronic dermal or chronic inhalation poisoning.
Further informaton on acute and chronic toxicity can be found in the General Information heading of the Toxicity & Hazard section of this website.
Additional Resources [top]
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