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.

Chemistry

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.^[1] Two 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).^[1]

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

Uses

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, US, 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.

Lead arsenate was also used in the early part of twentieth century for controlling pests of cranberry (fireworm, cranberry girdler) in Massachusetts.^{[citation needed]}

Basic lead arsenate 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 US continued until the mid-1960s. It was officially banned as an insecticide on August 1, 1988.

Morel mushrooms growing in old apple orchards that had been treated with lead arsenate may accumulate levels of toxic lead and arsenic that are unhealthy for human consumption.^[2]

See also

• Paris Green
• Calcium arsenate