Lead hydrogen arsenate
Template:Chembox Lead hydrogen arsenate, also called lead arsenate, acid lead arsenate or LA, chemical formula PbHAsO4, is an inorganic insecticide formerly used to control pests including gypsy moth, potato beetle and rats.[1]
Lead arsenate was the most extensively used arsenical insecticide.[2] Two principal formulations of lead arsenate were marketed: basic lead arsenate (Pb5OH(AsO4)3, CASN: 1327-31-7) and acid lead arsenate (PbHAsO4).[2]
It is now banned for use as a pesticide in countries such as the US and UK as it is considered too toxic and persistent.
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.[3]
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.[4] 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.[5] 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.[6]
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.[7][8]
Safety
LD50 is 1050 mg/kg (rat, oral).[4]
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.[9]
Lead arsenate was used as an insecticide in deciduous fruit trees from 1892[10] 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.[11]
See also
References
External links
- Case Studies in Environmental Medicine - Arsenic Toxicity
- Case Studies in Environmental Medicine - Lead Toxicity
- National Pollutant Inventory - Lead and Lead Compounds Fact Sheet
- Lead arsenate history
Template:Lead compounds Template:Insecticides
- ↑ Script error: No such module "citation/CS1".
- ↑ a b 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 Template:Webarchive
- ↑ Script error: No such module "Citation/CS1".
- ↑ a b Template:Ullmann
- ↑ Script error: No such module "citation/CS1".
- ↑ Sunset Western Garden Book (1954), p.69
- ↑ Template:Cite report
- ↑ Template:Cite report
- ↑ Cite error: Invalid
<ref>tag; no text was provided for refs namedshav10 - ↑ 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.
- ↑ Script error: No such module "Citation/CS1".