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.

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 [ Peryea F.J. 1998. Historical use of lead arsenate insecticides, resulting in soil contamination and implications for soil remediation. Proceedings, 16th World Congress of Soil Science, Montpellier, France. 20-26. Aug. Available online: http://soils.tfrec.wsu.edu/leadhistory.htm] 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.

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, 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.

ee also

* Paris Green
* Calcium arsenate

References

* Sunset Western Garden Book, First Edition, 1954

External links

* [http://www.atsdr.cdc.gov/HEC/CSEM/arsenic Case Studies in Environmental Medicine - Arsenic Toxicity]
* [http://www.atsdr.cdc.gov/HEC/CSEM/lead/ Case Studies in Environmental Medicine - Lead Toxicity]
* [http://www.npi.gov.au/database/substance-info/profiles/50.html National Pollutant Inventory - Lead and Lead Compounds Fact Sheet]
* [http://soils.tfrec.wsu.edu/leadhistory.htm Lead arsenate history]