How are pesticides classified based on toxicity?

Author: Leonard Klein  |  Last update: Tuesday, May 13, 2025

Acute toxicity makes it possible to classify pesticides into five classes: class I - highly toxic, class II - toxic, class III - moderately toxic, class IV - slightly toxic, class V - virtually non-toxic.

What is the classification of pesticides based on toxicity?

Based on toxicity of pesticides, WHO classified them into four classes: extremely dangerous, highly dangerous, moderately dangerous and slightly dangerous. damage to the environment; the ecosystem including the mankind. Pesticides are known to control insect pests, weeds, diseases, rodents and pests in the storage.

How are pesticides classified?

Pesticides can be classified either by target pest or by chemical identity. [1] Classification by target pest is perhaps the most familiar. For example, insecticides are pesticides that target insects, and herbicides target plants.

How to determine the level of pesticide toxicity?

There are several ways to estimate to the toxicity of a pesticide. One easy way is to look at the signal word, which is an indicator of the toxicity of the product. Every registered pesticide will have the words CAUTION, WARNING, or DANGER on the label, and that word reflects the level of toxicity of the product.

What are the classification of toxicity?

Toxicity category I is highly toxic and severely irritating, Toxicity category II is moderately toxic and moderately irritating, Toxicity category III is slightly toxic and slightly irritating, Toxicity category IV is practically non-toxic and not an irritant.

Resistance101 - Insecticide classes & modes of action

What is acute and chronic toxicity of pesticides?

Others can be dangerous after small, repeated doses (chronic toxicity). Acute toxicity of a pesticide refers to the effects from a single dose or repeated exposure over a short time (e.g. one day), such as an accident during mixing or applying pesticides. Acute toxicity is measured by LD50 and LC50 values.

What is the pesticide toxicity index?

Pesticide Toxicity Index (PTI) is a tool to assess pesticide mixtures. PTI is an indicator of potential toxicity of pesticide mixtures to aquatic life.

How are pesticides with the highest toxicity labeled?

Signal words are found on pesticide product labels, and they describe the acute (short-term) toxicity of the formulated pesticide product. The signal word can be either: DANGER, WARNING or CAUTION. Products with the DANGER signal word are the most toxic. Products with the signal word CAUTION are lower in toxicity.

How to measure pesticide exposure?

A typical scenario-based approach estimates pesticide exposure by merging the following information: a) concentration of the chemical in the carrier medium, estimated by using monitoring, exposure models, or assumptions; and b) the individual's contact time with the carrier medium, estimated by using existing ...

How do you classify pesticides based on their target organisms?

Based on the targeted pest species, they are categorized into distinct types like herbicides, insecticides, fungicides, and rodenticides (Abdollahdokht et al. 2022 ).

What is legally defined as a pesticide?

Under state and federal law, a pesticide is any substance intended to control, destroy, repel, or attract a pest. Page 2 California also regulates adjuvants as pesticides.

What is the toxicity of a pesticide a measure of?

Pesticide Toxicity and Exposure. The toxicity of a pesticide is a measure of its capacity or ability to cause injury or illness. The toxicity of a particular pesticide is determined by subjecting test animals to varying dosages of the active ingredient (a.i.) and each of its formulated products.

What are the basic toxicology of pesticides?

The Science of Toxicology

Toxicological testing evaluates whether short-term exposure to a pesticide will produce acute effects (e.g., eye and skin irritation, death) and whether long-term, continual exposure will cause chronic effects (e.g., impaired liver function, reproduc- tive abnormalities, cancer).

Which group of pesticides is most toxic?

Fungicides were the most toxic from concentrations 300–600 times lower than agricultural dilutions, followed by herbicides and then insecticides, with very similar profiles in all cell types. Despite its relatively benign reputation, Roundup was among the most toxic herbicides and insecticides tested.

What is the lowest level of toxicity in pesticides?

Pesticides with a high LD50 are the least toxic to humans if used according to the directions on the product label. The chronic toxicity of a pesticide is determined by subjecting test animals to long-term exposure to the active ingredient.

What is the rating scale for phytotoxicity?

The 0-100 scale is used to rate both weed control efficacy and crop tolerance, where 0 = no plant phytotoxicity, and 100 = complete plant death. The assessment of herbicide action of a product is based on the comparison of the treated plot with an untreated control plot.

What is the most hazardous category of pesticide toxicity?

This section establishes four Toxicity Categories for acute hazards of pesticide products, Category I being the highest toxicity category. Most human hazard, precautionary statements, and human personal protective equipment statements are based upon the Toxicity Category of the pesticide product as sold or distributed.

Who does the toxicity classification of pesticides?

The World Health Organization has classified pesticides' toxic effects from class Ia to class III and a category of "active ingredients unlikely to present acute hazard”. Class-I technical-grade pesticides are banned or strictly controlled, but not in developing countries.

How to test the toxicity of pesticides?

EPA recommends using rats for subchronic, chronic, carcinogenicity, and reproduction studies; mice for carcinogenicity studies; and dogs for subchronic and chronic studies. Rats are routinely used for acute oral and inhalation studies and rabbits for eye and skin irritation studies and acute dermal studies.

What are the 5 categories of toxic chemicals?

For the purposes of this Strategy, toxic compounds have been grouped into five categories: atmospherically- deposited compounds; organic and inorganic contaminants that result from industrial, manufacturing or other point and non-point discharges from facilities; pesticides; contaminants of emerging concern (CECs); and ...

What are the categories of pesticides?

Insecticides, herbicides, fungicides and rodenticides are some of the more well-known pesticides. Others include growth regulators, plant defoliants, surface disinfectants and some swimming pool chemicals.

How long after spraying pesticides is it safe for humans?

If possible, they should stay inside or avoid the area for about 30 minutes after spraying. If pesticides are applied inside the home, windows should be opened to allow air flow. People should avoid touching sprayed areas and leave the room until the pesticide has dried.

What are the levels of toxicity?

The World Health Organization (WHO) names four toxicity classes:
  • Class I – a: extremely hazardous.
  • Class I – b: highly hazardous.
  • Class II: moderately hazardous.
  • Class III: slightly hazardous.

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