Pesricides

PESTICIDES

The US Environmental Protection

Agency (EPA) defines pesticides as

any materials manufactured or

formulated to kill a pest.

As defined by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the federal low that regulates the manufacture, sale, and use of pesticides in USA, a pesticide is “any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any insects, rodents, nematodes, fungi or any other forms of life declared to be pests; any substance or mixture of substances intended for use as a plant regulator, 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 and

marketed 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 others exposed 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 of action and metabolism in target organs.examples of different compounds are:

- organophosphate- carbamate- thiocarbamate- chlornitrophenol derivates- pyridyl derivates- pyretroid

The Farm Chemical Handbook is a useful

source of identification of a pesticide by

common name, chemical name, trade

name, and manufacturer or marketer.

Classification by HAZARDRecommended by IPCS (International

Program on Chemical Safety)

Based primarily on the acute oral and dermal toxicity in rats (LD50), four groups are proposed. Substances with LD50 lower than characterized in Class III are thought unlikely to present acute hazard in normal

use.

Distinction should be made between toxicity – innate capacity of a substance to cause damage and - hazard – the risk of poisoning arising in practice.

Hazard is based on the toxicity of the compound and its formulation.

Hazard is also a function of two variables other than toxicity – contamination and time.

Hazard (Risk) = Toxicity x Exposure (Contamination x Time)

- Hazard = risk of poisoning- Toxicity = ability to cause damage- Contamination = prerequisite for entering the bodytime – duration of contact

In all cases the toxicity is dose-related.

The aim of pesticide use is to apply an amount that is non toxic for humans and other animals but is poisonous for the target pest. When this is impossible additional precautions and preventive measures are needed.

Toxic effects due to pesticides exposure may result from a single exposure (acute toxicity) or from repetitive exposures (chronic toxicity).

LD50 values are standard measurements (cited in mg/kg of body weight), often used to compare acute toxicity of pesticides.

LD50 values provide measures of acute toxicity when test animals are fed with pesticide-treated feed or water (oral LD50) or in case of dermal pesticide application (dermal LD50).

The toxicity of a pesticide is related with the route of entry into the organism.

Pesticides toxic effects vary significantly among species. The aim is to produce pesticide with low mammalian toxicity and sufficiently toxic to the target pest.

Table 30-6. Environmental protection agency (EPA) labeling toxicity categories.Toxicity Categories

Hazard Indicators

1 II Ill IV

Oral LD50 < 50 mg/kg 50-500 mg/kg 500-5000 mg/kg > 5000 mg/kg

Inhalation LD50

< 0.2 mg/L 0.2-2 mg/L 2-20 mg/L > 20 mg/L

Dermal LD50 < 200 mg/kg 200-2000 mg/kg 2000-5000 mg/kg > 5,000 mg/kg

Eye effects Corrosive; corneal opacity irreversible

Corneal opacity reversible in 8-21days; irritation

No corneal opacity; irritation reversible in 7 days

No irritation

Skin effects Corrosive Severe irritation at 72 hours

Moderate irritation at 72 hours

Mild or slight irritation at 72 hours

Signal word "Danger" "Warning" "Caution" "Caution"

Precautionary state­ments

Fatal (poisonous) if swallowed, inhaled, or absorbed through skin. Do not breathe vapor, dust, or spray mist. Do not get in eyes or on skin or clothing.

May be fatal if swal­lowed, inhaled, or absorbed through skin. Do not breathe vapor, dust, or spray mist. Do not get in eyes or on skin or clothing.

Harmful if swallowed, inhaled, or absorbed through skin. Avoid breathing vapor, dust, or spray mist. Avoid contact with skin, eyes, or cloth­ing.

No precautionary statements required.

The toxicity of a pesticide product is expressed by signal words DANGER, WARNING and CAUTION.

- DANGER – highly toxic- WARNING – moderately toxic- CAUTION – slightly toxic.

Signal words could also reflect formulation’s lethal effects such as skin and eye irritation.

However, a highly toxic pesticide could be specially formulated (microencapsulated) to reduce its toxicity if compared to a similar, non-encapsulated product.

The aim of the signal words is to alert the user about the toxicity of the product.

HAZARDHazard 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 then applied mixed or unmixed, as sprays, dusts,

aerosols, granular or impregnated preparations, fumigants.

"Inert" ingredients are not necessarily nontoxic; 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 and non-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, or

hand-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 homicideHome use: House and gardenStructural use: Residents and occupants

of buildingsBystandersContamination: Food, water, air

The highest exposures and highest incidence of poisoning occur in those involved 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 varies with the type of application - from leaking sprayers to enclosed-cab vehicles with filtered cooled air.

Exposures in formulating facilities may be much higher, particularly if dusty formulations (dusts, powders,

granules) are produced in open systems.

The most important route for most occupational 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 significant

degree, 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, and

some 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 of pesticide on a field and entry into that

field.

The rate of degradation and the toxicity of the degradation products are

important determinants of the extent and effect of exposure in this group.

Pesticide degradation rates often vary among geographic regions, so that

reentry intervals may need to be specific to an area or climate.

Since skin contamination is the most important route of most occupational exposures, the focus of prevention is to reduce 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 protective

clothing in agricultural work is impeded by the 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 surveillance

Chronic exposure to organophosphate and carbamate pesticides may suppress the

levels of acetylcholin-esterase resulting in endogenous acetylcholine poisoning.

Specific medical and biologic monitoring is available for cholinesterase-inhibiting

pesticides.

Different types of analytic methods are used 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 same

laboratory, 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 exposure

until levels return to approximately baseline is likely to prevent the development of clinical

signs and symptoms of toxicity.

For most other pesticides, surveillance is limited to general and occupational histories

and physical examination with available laboratory tests.

TreatmentTreatment 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 be

determined 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 to minimize the contamination of medical personnel

and equipment without compromising patient care.

2. Specific Antidotes: they are available only in the form of atropine for cholinesterase-inhibiting pesticides, and chelating agents for heavy metal

pesticides such as arsenic and mercury, which rarely result in the need for

treatment 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 or serious poisonings are mediated at least

in part through respiratory embarrassment or arrest.

REGULATION OF USE OF PESTICIDES

The pesticide industry is regulated differently 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 is specified 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 collected by the distributors and reprocessed into plastic pipe. Bulk, reliable containers

have been used.­

Triple rinsing the container into the solution tank gives the applicator a

method to decontaminate the container before landfilling or recycling.

Hand lances that can pierce the container are used to assure proper

cleaning and destruction of the container 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

-

- Use­pesticides only in well-ventilated areas - Consider the safety of others around you during application - Dispose the pesticide containers properly - Be attentive to the re-entry intervals specified on the label - Keep pesticides in their original, labeled containers - Avoid pesticide drift - Avoid conditions that might lead to ground water 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 applying pesticides with first-aid medicine chest with atropine, sodium bicarbonate, carbon medicinally, magnesium sulfate and other antidote substances at the beginning

of the campaign of pesticide use.

4. To organize and participate in the preliminary and periodical medical

examinations 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.