Pyraclofos

The Uses of Pyraclofos

Pyraclofos is used to control Lepidoptera, Coleoptera, mites and nematodes in fruit, vegetables, ornamentals and forestry. It has also been used in a human health application to control filarial worms.

Definition

ChEBI: Pyraclofos is an organic thiophosphate, an organothiophosphate insecticide, an organochlorine insecticide, a member of pyrazoles, a member of monochlorobenzenes and an organosulfur compound. It has a role as an EC 3.1.1.7 (acetylcholinesterase) inhibitor and an agrochemical.

Metabolic pathway

Pyraclofos is apparently subjected in insects to a metabolic activation to yield a more active acetylcholinesterase inhibitor which is possibly a thiooxidized metabolite. The compound is very rapidly degraded in mammals to inactive metabolites via P-O-aryl, P-O-alkyl and P-S-alkyl cleavage which explains its favourable selective toxicity. In both mammals and plants the principal degradative route is via P-O-aryl cleavage to give 1-(4-chlorophenyl)-4-hydroxypyrazolwe hich is rapidly conjugated.

Metabolism

Pyraclofos is metabolized to an active AChE inhibitor, probably by the oxidation of the sulfur atom in the phosphorothiolate linkage. The half-life in soil is 3–38 d, depending on soil type.

Toxicity evaluation

The acute oral LD₅₀ for rats is 237 mg/kg. The inhalation LC50 for rats is 1.69 mg/L air. NOEL (2 yr) for rats is 0.10–0.12 mg/kg diet (0.005–0.006 mg/kg/d). Pyraclofos administered to rats is rapidly degraded, and more than 90% of the dose is excreted principally in the urine within 24 h. The degradation routes are cleavages of the P?S, P?O-alkyl, and P?O-aryl bonds in both animals and plants.

Degradation

The DT₅₀ for hydrolysis in water at pH 7 (25 °C) was 29 days (PM).