TOXICOLOGY OF PESTIC I DES. 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:.
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.
Pyrethrines later became the prototype for synthetic pyrethroids
Desiccation – drying
desiccant – drying agent
Desiccants are used for alfalfa (lucern) or clover for seed:plants dry up and can be harvested.
the most important factors are light, temperature, photolysis, free radicals produced in photochemical reactions, hydrolysis
in biotic environment
1. phase2. phase
XH X – OH X – O – conjugate
The final products are inactive and are
parathion paraoxon – a powerful ACHE inhibitor
DDT DDE (extremely persistent and
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).
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 10times more sensitive to carbofuran than mammals (LD50 for mammals 3 – 19 mg/kg body weight). Frequent carbofuran poisoning cases among predatory birds.
Mechanism of the toxic action -
cause reversible block of sodium channels (e.g. permethrin)
cause reversible block of sodium channels and inhibition of GABA (e.g. deltamethrin)
Pyrethroids are- highly toxic for fish (LC50 below 0,1 mg/l)- toxic for bees (LD50 2 – 11 µg/bee)- not very toxic for mammalsCats 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.
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.
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 pesticides are less toxic than triazine ones
Mechanism of the toxic action –
Toxicity: toxic for fish
relatively harmless for bees
LD50 for mammals exceeds 1000 mg.kg-1 live weight
They are very rapidly deactivated in soil, but leave
residues in plants: diquat for 3 – 5 days, paraquat for 21 days.
LD50 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)LD50 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 leucocytesSymptoms of poisoning – pulmonary oedema, fibrotic pneumonia fetotoxicity,retardation of ossification
arsenic compounds – insecticides, rodenticides
phenylmercury – fungicide for treatment of seed (1913 – 1993)
tributyltin – fungicide (xenoestrogenic effect)
thalium compounds – rodenticides
Copper compounds – copper sulphate
- copper oxichloride
fungicides, algicides, molluscocides
Toxicity for fish – LC50 1 – 10 mg.l-1 depending on water quality
Mechanism of the toxic action – inhibition of GABA
Fipronil is very toxic for bees (LD50 is 5 ng/bee)
It causes secondary toxicity in bees.
Its residua persists for 21 days.
It produces the „knock down“ effect.