Uses
Edifenphos is a foliar applied contact fungicide that provides both
protective and curative control of rice blast diseases caused by Pyricularia
oryzae. It also controls ear blight and stem rot in rice.
Definition
ChEBI: An organic thiophosphate that is the O-ethyl-S,S-diphenyl ester of phosphorodithioic acid. Used to control a variety of fungal diseases on rice including blast, ear blight and stem rot. Edifenphos i
moderately toxic to mammals and fish but poses more of a risk to aquatic invertebrates.
Metabolic pathway
Hydrolytic cleavage of the P-0 and P-S linkages affords the major
degradation and metabolic pathways of edifenphos. A unique transesterification
reaction yielded tri-S-phenyl and di-O-ethyl phosphorus
esters as minor products in soil and plant test systems (Scheme 1).
Degradation
The hydrolytic DT50 values of edifenphos (1) at pH 7 and 9 at 25 °C
were 19 and 2 days, respectively (PM). [35S]Edifenphods egraded rapidly
in aqueous solution when exposed to UV light at 25-28 °C [DT50 ca. 3 days
(light exposed) vs. 19 days (dark control)]. Cleavage of the P-S linkage is
the primary degradation pathway. Thiophenol (2) was further oxidised
to form diphenyl disulfide (3), possibly during sample extraction, isolation
and analysis. Stepwise cleavage of the P-S and P-O linkages yielded
O-ethyl S-phenyl hydrogen phosphorothioate (4), S-phenyl dihydrogen
phosphorothioate (5), benezenesulfonic acid (6) and sulfuric acid as
major 35S-containing products, whereas O-ethyl dihydrogen phosphate
(7) and phosphoric acid were recovered from the phosphorus portion of
the molecule (Murai, 1977).
Toxicity evaluation
Edifenphos shows no delayed neuropathic symptoms.
Safety intervals between spray and harvest for rice are
21 days in Japan with 0.2 mg of MRL (Maximum Residue
Limit).
