Lead hydrogen arsenate, also called lead arsenate, acid lead arsenate or LA, chemical formula PbHAsO₄, is an inorganic

insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...

used primarily against the

potato beetle The Colorado potato beetle (''Leptinotarsa decemlineata''), also known as the Colorado beetle, the ten-striped spearman, the ten-lined potato beetle, or the potato bug, is a major pest of potato crops. It is about long, with a bright yellow/o ...

. Lead arsenate was the most extensively used

arsenical Arsenicals are chemical compounds that contain arsenic. In a military context, the term arsenical refer to toxic arsenic compounds that are used as chemical warfare agents. This include blister agents, blood agents and vomiting agents. Examples Bli ...

insecticide.Peryea F.J. 1998. Historical use of lead arsenate insecticides, resulting in

soil contamination Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...

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 Two principal formulations of lead arsenate were marketed: basic lead arsenate (Pb₅OH(AsO₄)₃, CASN: 1327-31-7) and acid lead arsenate (PbHAsO₄).

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 ''Lymantria dispar'', also known as the gypsy moth or the spongy moth, is a species of moth in the family Erebidae. ''Lymantria dispar'' is subdivided into several subspecies, with subspecies such as ''L. d. dispar'' and ''L. d. japonica'' bei ...

Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...

. 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 The codling moth (''Cydia pomonella'') is a member of the Lepidopteran family Tortricidae. They are major pests to agricultural crops, mainly fruits such as apples and pears. Because the larvae are not able to feed on leaves, they are highly d ...

and snow-white linden moth. It was used mainly on

apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...

s, but also on other fruit trees, garden crops, turfgrasses, and against

mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...

es. In combination with

ammonium sulfate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

, it was used in southern

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

as a winter treatment on lawns to kill

crab grass ''Digitaria'' is a genus of plants in the grass family native to tropical and warm temperate regions but can occur in tropical, subtropical, and cooler temperate regions as well. Common names include crabgrass, finger-grass, and fonio. They are ...

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 Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

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

Safety

LD50 In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...

is 1050 mg/kg (rat, oral).

Morel mushroom ''Morchella'', the true morels, is a genus of edible sac fungi closely related to anatomically simpler cup fungi in the order Pezizales (division Ascomycota). These distinctive fungi have a honeycomb appearance due to the network of ridges wi ...

s growing in old

orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of larg ...

s that had been treated with lead arsenate may accumulate levels of toxic

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

and

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

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. Human exposure to lead arsenate, particularly in cases of excessive or careless application of the pesticide, caused nervous system illnesses to include acute flaccid paralysis and degeneration of the anterior horns of the spinal cord resulting in symptoms similar to poliomyelitis. Sherwin-Williams brand Lime Sulphur and Arsenate of Lead advertisement 1911 Door County Democrat

Sherwin-Williams brand Lime Sulphur and Arsenate of Lead advertisement 1911 Door County Democrat

References

External links

Case Studies in Environmental Medicine - Arsenic Toxicity

Case Studies in Environmental Medicine - Lead Toxicity

* ttps://web.archive.org/web/20081207174027/http://soils.tfrec.wsu.edu/leadhistory.htm Lead arsenate history {{Insecticides Lead(II) compounds Hydrogen compounds Arsenates Inorganic insecticides

Production and structure

Uses

Safety

See also

References

External links