Toxicity changes in pyrethroid residues from soil, silica gel and water.

Toxicity of residues of synthetic pyrethroids (pennetbrin.
cypermetbrin, decarnethrin and fenvalerate) both in aqueous
solution and as deposits on solid surfaces like soil and
silica gel to houseflies was studied after exposure to sunlight
for 8 hr daily. The residues were extracted after liquid 4'
days Intervals and their toxicity to houseflies was determined
through topical application. Tbe persistent toxicity values
indicated a fall in toxicity of all the four pyrethroids with
time; fall in toxicity was maximum. with decametbrin and
least with pennetbrin. In general, the persistence of pyrethroids
was least in water and highest in soil.