Pb(NO3)2(aq) +H3AsO4(aq) --> PbHAsO4(s) +2HNO3(aq)
Lead arsenate was the most extensively used arsenical insecticide According to the preceding reference, two (2) principal formulations of lead arsenate were marketed; basic lead arsenate (Pb5OH(AsO4)3, CASN: 1327-31-7) and acid lead arsenate (PbHAsO4, CASN: 7784-40-9). As an insecticide, it was first used against the gypsy moth in Massachusetts, as a less soluble and less toxic alternative to then-used Paris Green. It also adhered better to the surface of the plants, further enhancing and prolonging its insecticidal effect.
Lead arsenate was widely used in Australia, Canada, New Zealand, USA, England, France, North Africa, and many other areas, principally against the codling moth. It was used mainly on apples, but also on other fruit trees, garden crops, turfgrasses, and against mosquitoes. In combination with ammonium sulfate, it was used in southern California as a winter treatment on lawns to kill crab grass seed.
Basic lead arsenate, Pb5OH(AsO4)3, was used in some areas of California.
The search for a substitute was commenced in 1919, when it was found that its residues remain in the products despite washing their surfaces. Alternatives were found to be less effective or more toxic to plants and animals, until 1947 when DDT was found. The use of lead arsenate in the USA continued until mid 1960's. It was officially banned as an insecticide on August 1, 1988.