TOXICOLOGY OF PESTICIDES Pesticides are preparations for the eradication of plant and animal pests, for the protection of plants, animals and man. About 800 compounds of active ingredients of pesticides have been registered world-wide.

Historical background: -alkaloids nicotine and anabasine contained in tobacco – insecticides -pyrethrines contained in plants of the genus Pyrethrum – insecticides Pyrethrines later became the prototype for synthetic pyrethroids -rotenon – is highly toxic to all forms of life, is from roots of lianas. Rotenon was used as a piscicide and insecticide -an important milestone was introduction of phenyl mercury in 1913 for the protection of seed – fungicide -insecticidal effect of DDT was discovered in 1939 by the Swiss Paul Müller

Classification of pesticides -fungicides -zoocides (insecticides, rodenticides, molluscocides) -herbicides – including desiccants -selective -non-selective -plant growth regulators (to shorten the straw of cereals) Desiccation – drying desiccant – drying agent Desiccants are used for alfalfa (lucern) or clover for seed: plants dry up and can be harvested.

Pesticide degradation -in abiotic environment the most important factors are light, temperature, photolysis, free radicals produced in photochemical reactions, hydrolysis -in biotic environment 1. phase 2. phase XH X – OH X – O – conjugate The final products are inactive and are excreted.

Pesticide transformation -mostly detoxicative nature -result may even be a more toxic substances (desulphuration of organophosphates) parathion paraoxon – a powerful ACHE inhibitor trichlorfondichlorvos diazinondiazooxon DDTDDE (extremely persistent and xenoestrogenic)

Pesticides: -Organochlorine pesticides -Organophosphates -Carbamate pesticides -Pyrethroids -Phenoxyacetic acid – based pesticides -Urea – based pesticides -Diazine and triazine pesticides -Bipyridil – based pesticides -Phenylpyrazoles -Metal – based pesticides

Organophosphates - insecticides - antiparasitics Mechanism of toxic action – irreversible inhibition of enzymes, particularly of acetylcholinesterase on nerve synapses (by phosphorylation of hydroxyl group of serine bound in the active centre of ACHE).

Carbamate pesticides - insecticides - herbicides - fungicides Mechanism of the toxic action – reversible inhibition of acetylcholinesterase (by carboxylation of hydroxyl group of serine bound in the active centre of ACHE). Carbofuran is very up-to-date substance in toxicology. It is used to control vermin (foxes) and is used in baits. Birds are 10 times more sensitive to carbofuran than mammals (LD50 for mammals 3 – 19 mg/kg body weight). Frequent carbofuran poisoning cases among predatory birds.

Pyrethroids - insecticides - antiparasitics Mechanism of the toxic action - -pyrethroids T (tremor) – contain no α-cyano group cause reversible block of sodium channels (e.g. permethrin) -pyrethroids CS (choreoatetosis, salivation) – contain α-cyano group cause reversible block of sodium channels and inhibition of GABA (e.g. deltamethrin)

Pyrethroids are - highly toxic for fish (LC 50 below 0,1 mg/l) - toxic for bees (LD 50 2 – 11 µg/bee) - not very toxic for mammals Cats are most sensitive mammals to pyrethroids. Why? - Pyrethroids’ detoxification, similarly to other organic toxicants, takes place in two phases. Activity of conjugation enzyme, especially of glucuronyl transferase, is very low in cats.

Phenoxyacetic acid – based pesticides (MCPA) - herbicides Mechanism of the toxic action – disruption of oxidation and phosphorylation processes (drop in the ATP production and disruption of energy metabolism). They are little toxic for mammals, fish, bees. Symptoms of poisoning: hypotermia, hypodynamia, paresis, paralysis, tympania in ruminants. But: In the production and use of those herbicides (2, 4-D; 2,4,5-T) dioxin was produced.

Urea – based pesticides - herbicides They cause damage of the thyroid gland and diuron may cause methaemoglobinemia. In mammals linuron reduces haematopoiesis In dogs triasulfuron causes cystic hyperplasia of the prostate, vacuolisation of liver cells, anaemia and accumulation of pigment in the liver

Diazine and triazine pesticides - herbicides Diazine pesticides are less toxic than triazine ones Mechanism of the toxic action – -triazines are antimetabolites of pirimidine bases - components of nucleic acids and folic acid -atrazine damages the liver detoxication functions -simazine, prometryne, terbutryne – inhibit haematopoiesis Toxicity: toxic for fish relatively harmless for bees LD 50 for mammals exceeds 1000 mg.kg -1 live weight

Serious risk of triazine – based pesticides 1.very low biodegradability (risk for drinking water) 2.triazines are secondary amines (secondary amines + nitrosation agents nitrosamines) 3.atrazine has xenoestrogenic effects (causes abnormal development of gonads, turns amphibians into hermaphrodites)

Bipyridil – based pesticides - herbicides - desiccant They are very rapidly deactivated in soil, but leave residues in plants: diquat for 3 – 5 days, paraquat for 21 days. Diquat (Reglone) LD 50 for cattle 30 – 50 mg.kg -1 l.w. for rabbit 280 mg.kg -1 l.w. Symptoms of poisoning – pulmonary oedema, damage of liver and kidneys, arthritis, periarthritis

Paraquat (Gramoxone) LD 50 for man 40 mg.kg -1 l.w. for cattle and pigs 30 – 70 mg.kg -1 l.w. for dogs and cats 25 – 50 mg.kg -1 l.w. Mechanism of toxic action – is mediated by - free oxygen radicals - proteolytic enzymes formed by active neutrophilic leucocytes Symptoms of poisoning – pulmonary oedema, fibrotic pneumonia fetotoxicity,retardation of ossification

Metal – based pesticides arsenic compounds – insecticides, rodenticides phenylmercury – fungicide for treatment of seed (1913 – 1993) tributyltin – fungicide (xenoestrogenic effect) thalium compounds – rodenticides Today Copper compounds – copper sulphate - copper oxichloride fungicides, algicides, molluscocides Toxicity for fish – LC 50 1 – 10 mg.l -1 depending on water quality

Phenylpyrazoles - insecticides - antiparasitics Mechanism of the toxic action – inhibition of GABA Fipronil is very toxic for bees (LD 50 is 5 ng/bee) It causes secondary toxicity in bees. Its residua persists for 21 days. It produces the „knock down“ effect.