PESTICIDES The US Environmental ProtectionAgency (EPA) defines pesticides as any materials manufactured or formulated to kill a pest.
As defined by the Federal Insecticide, Fungicide, andRodenticide Act (FIFRA), the federal low thatregulates the manufacture, sale, and use of pesticidesin USA, a pesticide is “any substance or mixture ofsubstances intended for preventing, destroying, repelling,or mitigating any insects, rodents, nematodes, fungi or anyother forms of life declared to be pests; any substance ormixture of substances intended for use as a plantregulator, defoliant or desiccant.”
The principal goal of pesticide application in commercial agriculture is to reduce crop loss or decrease growing or cultivation costs in order to enhance economic returns.
There are over 1200 chemical compounds used as pesticides andmarketed in over 30 000 formulations and under different brand names.Prior to World War II, most pesticides were inorganic chemicals. Since then, most have come to be synthetic organic chemicals.
Most of these can be divided into categories, or families, according to structure or use, with certain properties in common – including health effects on workers and othersexposed to toxic quantities by various routes.
Classification by usage:- herbicides – (weeds)- fungicides – (fungi)- rodenticides (rats and other rodents)- repellents (insects)- growth regulators (plants and insects)- bactericides (bacteria)- virucides (viruses)- acaricides or miticides (mites)- nematocides (nematodes)
Classification by chemical typeHelps to determine similarities of mode ofaction and metabolism in target organs.examples of different compounds are:- organophosphate- carbamate- thiocarbamate- chlornitrophenol derivates- pyridyl derivates- pyretroid
The Farm Chemical Handbook is a usefulsource of identification of a pesticide bycommon name, chemical name, tradename, and manufacturer or marketer.
Classification by HAZARDRecommended by IPCS (International Program on Chemical Safety) Based primarily on the acute oral anddermal toxicity in rats (LD50), four groupsare proposed. Substances with LD50 lowerthan characterized in Class III are thoughtunlikely to present acute hazard in normal use.
Distinction should be made between toxicity –innate capacity of a substance to cause damageand- hazard – the risk of poisoning arising inpractice.Hazard is based on the toxicity of the compoundand its formulation.Hazard is also a function of two variables otherthan toxicity – contamination and time.
Hazard (Risk) = Toxicity x Exposure(Contamination x Time)- Hazard = risk of poisoning- Toxicity = ability to cause damage- Contamination = prerequisite forentering the bodytime – duration of contact
In all cases the toxicity is dose-related. The aim of pesticide use is to applyan amount that is non toxic for humansand other animals but is poisonous forthe target pest. When this is impossibleadditional precautions and preventivemeasures are needed.
Toxic effects due to pesticidesexposure may result from a singleexposure (acute toxicity) or fromrepetitive exposures (chronic toxicity). LD50 values are standardmeasurements (cited in mg/kg of bodyweight), often used to compare acutetoxicity of pesticides.
LD50 values provide measures of acutetoxicity when test animals are fed withpesticide-treated feed or water (oral LD50) orin case of dermal pesticide application(dermal LD50). The toxicity of a pesticide is relatedwith the route of entry into the organism. Pesticides toxic effects vary significantlyamong species. The aim is to producepesticide with low mammalian toxicity andsufficiently toxic to the target pest.
Table 30-6. Environmental protection agency (EPA) labeling toxicity categories. Toxicity CategoriesHazard 1 II Ill IVIndicatorsOral LD50 < 50 mg/kg 50-500 mg/kg 500-5000 mg/kg > 5000 mg/kgInhalation LD50 < 0.2 mg/L 0.2-2 mg/L 2-20 mg/L > 20 mg/LDermal LD50 < 200 mg/kg 200-2000 mg/kg 2000-5000 mg/kg > 5,000 mg/kgEye effects Corrosive; corneal Corneal opacity No corneal opacity; No irritation opacity irreversible reversible in 8-21days; irritation reversible irritation in 7 daysSkin effects Corrosive Severe irritation at 72 Moderate irritation at Mild or slight hours 72 hours irritation at 72 hoursSignal word "Danger" "Warning" "Caution" "Caution"Precautionary Fatal (poisonous) if May be fatal if swal Harmful if Nostatements swallowed, inhaled, lowed, inhaled, or swallowed, inhaled, precautionary or absorbed through absorbed through or absorbed through statements skin. Do not breathe skin. Do not breathe skin. Avoid required. vapor, dust, or spray vapor, dust, or spray breathing vapor, mist. Do not get in mist. Do not get in dust, or spray mist. eyes or on skin or eyes or on skin or Avoid contact with clothing. clothing. skin, eyes, or cloth ing.
The toxicity of a pesticide product isexpressed by signal words DANGER,WARNING and CAUTION. - DANGER – highly toxic - WARNING – moderately toxic - CAUTION – slightly toxic.Signal words could also reflectformulation’s lethal effects such as skinand eye irritation.
However, a highly toxicpesticide could be speciallyformulated (microencapsulated) toreduce its toxicity if compared to asimilar, non-encapsulated product.The aim of the signal words is toalert the user about the toxicity ofthe product.
HAZARD Hazard in pesticide use should be considered on the toxicity of a given pesticide or pesticide product. Therefore, hazard (risk) depends on the toxicity of the compound and the probability of exposure. The hazard could be reduced by- use of products with lower toxicity or by - proper preventive measures.
A pesticide as applied consists of the technical grade chemical (“active”ingredient), formulated with diluents (often organic solvents), additives (“adjuvants”), and other “inert” ingredients, and thenapplied mixed or unmixed, as sprays, dusts, aerosols, granular or impregnated preparations, fumigants. "Inert" ingredients are not necessarilynontoxic; many are organic solvents such as methylene chloride.
The degree of hazard depends on the:- toxicity of the active ingradient- concentration of the active ingradient- type of formulation- rate and frequency of application- method of application- type of protective clothing worn- persistence in the environment
HEALTH EFFECTS Studies report association of pesticides use andnon-Hodgkin lymphoma, leukemia, prostate cancer, multiple myeloma, soft tissues sarcoma and other types of cancer. The application of organophosphate pesticides is associated with abdominal pain, dizziness,headache, nausea, vomiting, skin and eye problems.Long-term effects as respiratory problems, memory disorders, neurological deficits and depression, birth defects also have been reported to follow pesticide exposure.
Occupational and environmental pesticide exposure Typical occupational and no occupational pesticide exposure situations are listed below.
Occupational and environmental pesticide exposure situations. Occupational exposures Research and development Manufacturing: Technical grade material produced. Formulation: Technical grade material mixed with "inert"ingredients such as solvents, adjuvants. Transportation Pest control Mixing: Commercial material diluted with water or other material. Loading: Into tanks in planes, ground rigs, backpacks, orhand-held sprayers.
Occupational exposures Application Flagging: Standing at the end of fields to mark the rows to be sprayed by crop-dusting aircraft. Farm work: Field workers, pickers, sorters, packers, and others who come into contact with pesticide residues on leaves and fruit. Emergency and medical work: Personnel exposed to con-taminated persons and equipment in the process of responding to spills, accidents, and poisonings.
Environmental and consumer exposures Accidents and spills: Especially ingestion by children Suicide and homicide Home use: House and garden Structural use: Residents and occupants of buildings Bystanders Contamination: Food, water, air
The highest exposures and highestincidence of poisoning occur in thoseinvolved in agricultural pest control operations: - mixing, - loading and - applying.
Mixers and loaders are exposed to concentrated pesticides and large volumes, respectively.The use of closed systems for mixing and loading has reduced these exposures and poisoning considerably.
The exposure of applicators varieswith the type of application - from leaking sprayers to enclosed-cab vehicles with filtered cooled air. Exposures in formulating facilitiesmay be much higher, particularly ifdusty formulations (dusts, powders, granules) are produced in open systems.
The most important route for mostoccupational exposures is dermal, though in some occupations such as manufacturing inhalation may be equally significant.A high percentage of pesticides are absorbed across intact human skin to a significantdegree, since they must be absorbed through the coverings of insects or plants to be effective.
The ratio of dermal LD50 to oral LD50 – values that are available for most pesticides – can provide a rough indication of degree of dermal absorption.
The nature of exposure depends on whether exposure is to- commercial formulation of pesticide,as applied in a field or structure, or - only to the active ingredient, as occurs in manufacturing facility.
Environmental effects of pesticidesOver 95% of sprayed pesticides could spread to destination other than their target species, including non-target species, air, water and soil. When pesticides are suspended in the air as particles they are carried by wind to other areas, potentially contaminating them. Pesticides could be a water pollutant, andsome of them are persistent organic pollutants contributing to soil contamination.
Prevention Work Practices: Manufacturing and formulation workers, mixers, loaders, applicators are directly exposed to the concentrated or diluted product and can only be protected by - engineering controls and- personal protective clothing and devices.
Field workers are exposed primarily to residues on plants and in soil. They are protected primarily by reentry intervals – the minimum time allowed between application ofpesticide on a field and entry into that field.
The rate of degradation and the toxicity of the degradation products areimportant determinants of the extent and effect of exposure in this group. Pesticide degradation rates often vary among geographic regions, so thatreentry intervals may need to be specific to an area or climate.
Since skin contamination is the mostimportant route of most occupationalexposures, the focus of prevention is toreduce dermal exposure, though the use of respirators by manufacturing of formulation workers or pesticide applicators is often necessary.
Contamination of clothing, irritated skin, heat, and sweat are all factors common in agricultural work that promote absorption through the skin. The use of protectiveclothing in agricultural work is impeded bythe fact that most agricultural works takes place in hot and frequently humid environments. Therefore, need for skin protection, which is difficult to quantify, must be balanced against the risk of heat- related disorders.
Medical surveillanceChronic exposure to organophosphate and carbamate pesticides may suppress thelevels of acetylcholin-esterase resulting in endogenous acetylcholine poisoning.Specific medical and biologic monitoring is available for cholinesterase-inhibiting pesticides.
Different types of analytic methods areused to measure plasma cholinesterase,with results usually reported in different units.Accurate methods for express determination of both serum and erythrocyte cholynesterase activity have been used for diagnosis of acute and subacute poisoning (Colortest, Merk, Boeringer).
As the individual baseline cholinesterase activity may vary up to 22% from day to day even when measured by the same method and by the samelaboratory, these levels must be established prior the exposure. Therefore, 25-30 % inhibition of the baseline level during periodic monitoring (Kaloyanova, Izmirova) can be taken as a warming level of biological response to chronic exposure to organophosphate and carbamate pesticides, approaching a level likely to produce intoxication.
Removal of workers at this level (30 % of baseline) and prevention of further exposureuntil levels return to approximately baseline is likely to prevent the development of clinical signs and symptoms of toxicity. For most other pesticides, surveillance islimited to general and occupational histories and physical examination with available laboratory tests.
Treatment Treatment of pesticide poisoning in general proceeds in 3 steps, as described below.1. Decontamination: this is the first priority unless life-saving measures are required. In the case of acute dermal overexposure, the skin and clothing are reservoirs for continued exposure, as is the gastrointestinal tract in the case of ingestion.
All clothings should be removed and placed in double plastic bags for latter analysis, decontamination, or disposal. The skin and, if necessary,the hair should be washed with soap.Contamination should be looked for under the fingernails. If the eyes have been contaminated, they should be irrigated.
The need for gastrointestinal lavage or activated charcoal instillation should bedetermined case-by-case basis, i.e., depending on the pesticide, on whether vomiting or diarrhea has occurred, and the level of consciousness.All procedures should be done in such way as tominimize the contamination of medical personnel and equipment without compromising patient care.
2. Specific Antidotes: they are available only in the form of atropinefor cholinesterase-inhibiting pesticides, and chelating agents for heavy metalpesticides such as arsenic and mercury, which rarely result in the need fortreatment except for cases of ingestion.
3. Supportive care: it may be the only treatment indicated and may be lifesaving. Assessment of respiratory status and provision of appropriate ventilatory support are critical, since most fatal orserious poisonings are mediated at least in part through respiratory embarrassment or arrest.
REGULATION OF USE OF PESTICIDES The pesticide industry is regulateddifferently in most countries that have chemical regulatory system. - Labeling, - application to plants and soil, - training in pesticide use and - transportation are controlled.
When a pesticide is approved for use, its use isspecified as either general or restricted (many pesticides can only be spread by licensed applicators).Labels contain useful information such as use instruction, application methods, first-aid recommendations, hazard information. The use of pesticide in any way other than as specified by the label is illegal.
Another problem is the disposal of empty containers. It is not advisable,and in many places it is illegal, to reuse pesticide containers. Many advances have been made to mitigate this problem. Plastic containers have been collectedby the distributors and reprocessed into plastic pipe. Bulk, reliable containers have been used.
Triple rinsing the container into the solution tank gives the applicator amethod to decontaminate the container before landfilling or recycling. Hand lances that can pierce the container are used to assure proper cleaning and destruction of thecontainer so that it can not be reused.
Preventing pesticide exposure Select the safest formulation – granular or microencapsulated materials Reduce the rate of application to the lowest effective level Mix only enough pesticide to complete the assigned task Select a method for application to minimize the personal contact Wear all protective clothing noted on the label Avoid direct contact when mixing and filling the equipment
- - Use pesticides only in well-ventilated areas - Consider the safety of others around youduring application - Dispose the pesticide containers properly - Be attentive to the re-entry intervals specifiedon the label - Keep pesticides in their original, labeledcontainers - Avoid pesticide drift - Avoid conditions that might lead to groundwater contamination
Pesticide safety tips - Always read the label before use - Pesticides requiring special protective equipment should be used by trained, experienced applicators- Do not eat or smoke or eat during application - Never spray pesticides outdoors on a windy days - Store pesticides under lock in original containers with proper label. - Never transfer pesticide to another container (e.g. soft drinking water)
Health control in pesticide use – most important assignments of medical specialists 1. To become acquainted with the list of approved pesticides for use via the running year, with their categorization and the instructions for first aid in poisoning.2. To carry out health instructions for persons working with pesticides. 3. To supply the tractor drivers and aviators applyingpesticides with first-aid medicine chest with atropine, sodium bicarbonate, carbon medicinally, magnesiumsulfate and other antidote substances at the beginning of the campaign of pesticide use.
4. To organize and participate in the preliminary and periodical medicalexaminations and perform a dispensary system for people working with pesticides.5. To organize health control about the storage,transportation and application of pesticides and provision of workers with protective clothing and personal protective devices. 6. To render a first aid in case of poisoning.7. To carry out health education among people about prevention of pesticide poisoning.