Lead hydrogen arsenate

Lead hydrogen arsenate, also called lead arsenate, acid lead arsenate or LA, chemical formula PbHAsO4, is an inorganic insecticide used primarily against the potato beetle.

It is usually produced using the following reaction:

Pb(NO3)2(aq) +H3AsO4(aq) --> PbHAsO4(s) +2HNO3(aq)

Lead arsenate was the most extensively used arsenical insecticide. 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.

Until 1930s-1940s, lead arsenate was frequently prepared by farmers at home, by reacting soluble lead salts with sodium arsenate.

Lead arsenate was widely used in Australia, Canada, New Zealand, USA, England, France, North Africa, and many other areas, principially against the codling moth. It was used mainly on apples, but also on other fruit trees, garden crops, turfgrasses, and against mosquitoes.

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.