overview of pesticide classes

Over the last few years, the most commonly applied pesticides are  "modern pesticides", characterized by lower lipophilicity and limited stability making them less time persistent in the environment. Among these are organophosphorus, urea, phenoxy alkanoic, triazine, chloroacetanilide or glyphosate-based pesticides.

Organochlorine pesticides and their metabolites

(e.g. 1,2,3,4 – tetrachlorobenzene; 1,2,4,5 – tetrachlorobenzene; 1,2,3,5 - tetrachlorobenzene; aldrin; alpha – endosulfan; dieldrin; endrin; heptachlor)

Organochlorine pesticides are so-called contact insecticides. These substances have a high bioaccumulation potential (affinity for fatty tissues of organisms). They are highly persistent in the environment and for this reason, their application in most countries is prohibited. The oldest and best known of the organochlorine is the insecticide DDT, full name 1, 1, 1 - trichloro - 2,2- bis (4 -chlorophenyl) ethane. DDT was used to control insect carriers of diseases such as typhoid and malaria in tropical countries, but also in Europe (e.g. lice and mosquitoes).

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Organophosphate pesticides and their metabolites

(e.g. acephate; azinphos-methyl; bensulide; chlorethoxyfos; chlorpyrifos; chlorpyrifos-methyl; diazinon; dichlorvos, malathion)

From the point of view of chemistry, organophosphate pesticides are esters of ortho-, thio- and pyro- phosphoric acids. The class of organophosphate pesticides is characterised by its wide spectrum of application as fumigants, acaracides, but primarily as insecticides, killing moving individual pests (larvae, nymphs, and adults), but is not effective on eggs. Organophosphates act as contact pesticides and as orally ingestible poisons with time- limited residual effect. The list of EPA includes organophosphates, which are highly acutely toxic to bees, wildlife, but also to humans.

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Urea Pesticides

(e.g. chlortoluron; chlorsulfuron; diuron; fenuron; isoproturon; linuron; metoxuron)

Most of these compounds are now widely used as herbicides. They are mainly used as systematic herbicides. They act as inhibitors of photosynthesis in plants. The most commonly applicated urea pesticides are isoproturon, chlortoluron, and fluometuron.

They are used for weed control in the cultivation of potatoes, cereals, corn, poppy seeds, sugar beet, but also for treatment of the seeds before planting. They act as pre-emergent herbicides after the incorporation into the soil but some are used as post-emergent. They are rather less soluble in water and better absorbed by the soil.

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Dinitroaniline pesticides

(trifluralin; pendimethalin; oryzalin; prodiamine; ethalfluralin; benfluralin)

This is a group of selective pre-emergent herbicides. They prevent seed germination and are used for stopping development of weeds by inhibiting the growth of roots.

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Carbamates

(e.g. oxamyl; pirimicarb; carbofuran; methiocarb; fenoxycarb; mancozeb)

Carbamates are derivatives or esters of carbamic acids. There are about 25 kinds of carbamates such as dithio-, benzimidazole-, dimethyl-, oxime-, phenyl-, methyl- carbamates. They are used as selective herbicides, insecticides, acaracides, nematicides, molluscicides or fungicides in fruits, vegetables, ornamental trees, hops cultures, or for seed treatment. They are used as systematic and contact insecticides. They act on insects as contact pesticides and as oral ingestible poison. Carbamates kill moving individuals (larvae, nymphs, and adults) of pest; they are not effective on eggs.

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Pyrethroids

(e.g. cypermethrin, deltamethrin, permethrin, bifenthrin, cyhalothrin)

Pyrethroids now constitute the majority of the market of synthetic insecticides and are a normal part of commercial products, such as household insecticides and repellents. They are used as insecticides and repellents, acaracides or herbicides. They are rather lipophilic substances, which bind to the cuticle of plants and insects and resistant to rain wash off. They sorb easily to soil particles and lose their effectiveness; they do not easily flush into surface or ground waters.

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Glyphosate-based pesticides and metabolite AMPA

(glyphosate, glyphosate-IPA, glufosinate, AMPA)

Glyphosate based pesticides are herbicides characterised by their broad spectrum, systematicity, and non-selectivity. Their consumption is rapidly increasing.

The compounds are used in agriculture, forestry, but also in households and urban areas.

They cause growth cessation of plants, which first show yellowing and browning of their surface with subsequent mortality.

Glyphosate-based pesticides easily adsorb onto soil particles:

  • low probability of occurrence in groundwater
  • a frequent occurrence in surface waters

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Triazine Pesticides and their metabolites

(e.g. atrazine; cyanazine; simazine; propazine; prometryn; pymetrozine; terbuthylazine)

Triazine Pesticides are gradually being replaced by chloracetanilide pesticides.

They operate primarily as herbicides (atrazine, cyanazine, simazine), then as zoocides (pymethrozine) or fungicides (some triazine derivatives).

The compounds are used to control broad-leaved and grassy weeds in crops such as corn, sorghum and sugar beets. They influence photosynthesis of plants, causing yellowing, stopping their growth, and finally causing the total collapse of the weed.

Concerning the insecticide pymetrozine, the mechanism of action is based on blocking the food intake (aphids, whiteflies).

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Chloracetanilide pesticides and their metabolites

(e.g. metazachlor; metolachlor; alachlor; propachlor; acetochlor; dimethachlor)

Chloracetanilide pesticides belong to systematic, selective herbicides.

They kill monocots and dicotyledonous weeds and are used in the cultivation of maize, corn, potatoes, cucumbers, beets and stone fruits.

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Phenoxyalkanoic acids

(e.g. 2,4-D; 2,4-DP; 2,4,5-T; MCPA; MCPB; MCPP)

Phenoxyalkanoic acids are used as herbicides and are particularly effective on dicotyledonous weeds, thistle, chamomile, burdock, dandelion, sorrel and goosefoot.

They are applied for the treatment of cereals, pastures, but also for example, for treating roadsides as they have broad spectrum effects.

One effect of these compounds is that they cause metabolic disorders, growth retardation of overground parts and underground parts of the plant, and eventually death.

The most common symptoms are distortion of the plant (twisting of leaves, stalks).

These substances are present in the environment in the form of anions, usually absorbed by soil as they have limited solubility in water.

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Quaternary ammonium salts

(paraquat; diquat; chlormequat)

Quaternary ammonium salts have the general formula NR4+ where R is either an alkyl or aryl group. From this one can see the similarity to the ammonium ion, NH4+. Quaternary ammonium salts have predominately been used to reduce plant height by inhibiting a plant hormone called Gibberellins.

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Neonicotinoids

(e.g. acetamiprid, nitenpyram, nithiazin, imidacloprid)

It is class of neuro-active insecticides chemically similar to nicotine. These compounds represents nearly 25% of the global market for insecticides, and are in particular used to treat seeds.

Discussions are ongoing to ban these substances within the European Union as they are harmful to the bee population

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