Lead hydrogen arsenate

Production and structure

It is usually produced using the following reaction, which leads to formation of the desired product as a solid precipitate: :Pb(NO3)2 + H3AsO4 → PbHAsO4 +2 HNO3 It has the same structure as the hydrogen phosphate PbHPO4. Like lead sulfate PbSO4, these salts are poorly soluble.

Uses

As an insecticide, it was introduced in 1898 used against the gypsy moth in Massachusetts. It represented a less soluble and less toxic alternative to then-used Paris Green, which is about 10x more toxic. 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 and snow-white linden 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.

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. US EPA banned use of lead arsenate on food crops in 1988.

Safety

LD50 is 1050 mg/kg (rat, oral).

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.

Lead arsenate was used as an insecticide in deciduous fruit trees from 1892 until around 1947 in Washington. Peryea et al. studied the distribution of Pb and As in these soils, concluding that these levels were above maximum tolerance levels. This indicates that these levels could be of environmental concern and potentially could be contaminating the groundwater in the area.

References

References

1. Haynes, W.M. (ed.). CRC Handbook of Chemistry and Physics. 95th Edition. CRC Press LLC, Boca Raton: FL 2014-2015, p. 4-70
2. Hertfordshire, University of. "Lead arsenate".
3. 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 {{Webarchive. link. (2008-12-07)
4. (1991). "Structure and disorder in schultenite, lead hydrogen arsenate". Journal of Crystallographic and Spectroscopic Research.
5. (2014). "Insect Control, 2. Individual Insecticides".
6. (1910). "The Snow-white Linden Moth".
7. Sunset Western Garden Book (1954), p.69
8. (2004). "Historic Arsenical Pesticide Research". US Environmental Protection Agency Office of Pesticide Programs.
9. (June 1988). "Inorganic Arsenicals; Intent to Cancel Registrations for Pesticide Products Registered for Non-Wood Preservative Use; Conclusion of Special Review. Federal Register: 53: 126". United States Environmental Protection Agency (USEPA).
10. [https://web.archive.org/web/20211028025206/https://casetext.com/case/sherwin-williams-co-v-calif-spray-chemical Sherwin-Williams Co. v. Calif. Spray Chemical], Opinion No. 5880, Appeal from the District Court of the United States for the Northern District of Ohio, Eastern Division; John M. Killits, Judge, October 14, 1932.
11. (1994-12-01). "Vertical distribution of lead and arsenic in soils contaminated with lead arsenate pesticide residues". Water, Air, and Soil Pollution.
12. (Spring 2010). "Lead and Arsenic in ''Morchella esculenta'' Fruitbodies Collected in Lead Arsenate Contaminated Apple Orchards in the Northeastern United States: A Preliminary Study". Fungi Magazine.