Lead arsenate as a pesticide

Arsenic trioxide finds major use in the preparation of other compounds, notably those used in agricultural applications, The compounds monosodium methylarsonate. disodium methylarsonate, methane arsenic acid (cacodylic acid) are used for weed control, while arsenic acid, H3ASO4, is used as a desiccant for the defoliation of cotton crops, Other compounds once widely used in agriculture are calcium arsenate for control of boll weevils, lead arsenate as a pesticide for fruit crops, and sodium arsenite as a herbicide and for cattle and sheep dip. In some areas, arsenilic acid has been used as a feed additive for swine and poultry. Restrictions on these compounds vary from one country and region to the next. 

Use of lead arsenate as a pesticide was also cancelled on most crops - the basis for the cancellation being two-fold -the irreversibility of neurological damage resulting from lead exposure of children and the potential for lead-induced renal tumors noted at high levels in rodents resulted in a requirement to reduce the total lead exposure from all soxirces, and secondly the occupational exposure data indicates the potential for human skin cancer resulting from arsenic exposure. 

Pollution with arsenic can also be due to human, industrial activity, and most of the arsenic in the atmosphere is from the burning of fossil fuels. Arsenic has been used in fruit sprays, insecticides (lead arsenate), weedkillers (sodium or copper arsenite), rat poison, sheep dips, fly papers, wood preservative, and in glass-making. It is now also used in the semiconductor industry. Apparently, it was used as a pesticide by the Chinese centuries ago. Most of the arsenic used commercially in the world is probably contained in various pesticides. This inevitably leads to contamination of the environment. 

Pesticide safety was another environmental problem that remained in the public eye through the 50s. A special committee of the House of Representatives under Rep. James Delaney of New York, established in 1950, held 46 days of public hearings around the country. The Food and Drug Administration, still supporting the precautionary principle it had backed in 1930s debates over lead arsenate, wanted new pesticides to be allowed on the market only when proven safe. Extended negotiations over new legislation led to the Miller Amendment of 1954, which allowed the FDA to limit the uses of a pesticide on fresh produce but still denied it the power to keep a substance entirely off the market. In its clear rejection of the precautionary principle, the Miller Amendment is seen by historians as a victory for the pesticide manufacturers.7... 

In some areas, soil can also be contaminated by emissions from industries such as lead smelters, lead reclamation plants, etc., or from the accumulation of lead arsenate, used as a pesticide in orchards before 1988. ... 

Pure arsenic is presently used as a component of alloys (e.g., with lead to produce hunting ammunition). Arsenic compounds are also used in the chemical, pharmaceutical, and tanning industries, in the manufacture of glass and ceramics, and as pesticides in agriculture and fruit-farming (Nriagu and Azcue, 1990). 

A second factor concerns the purity of the diet and water received by the animals. Careful chemical analysis is needed to ensure the absence of significant amounts of highly toxic chemicals, such as aflatoxin, metals such as lead, arsenic, or cadmium, or certain pesticides, that may be present in water and various feed ingredients. 

Inorganic arsenicals find limited use as pesticides. Examples include arsenious oxide in cattle dips, zinc arsenite as a wood preservative, and calcium and lead arsenates and Paris green (double salt of copper arsenite and copper acetate) as insecticides30. ... 

As discussed in Chapters 5 and 7, the use of lime to precipitate calcium arsenates is a common method for removing inorganic As(V) from water or flue gases. Calcium arsenates were also once extensively used in pesticides (Chapter 5). The compositions of some calcium arsenates, such as johnbaumite (Ca5(As04)3(0H) Table 2.5), resemble the very common phosphate mineral, apatite (Ca5(P04)3(F,Cl,0H)), where arsenate replaces phosphate. Some lead arsenates, such as mimetite (Pb5(As04)3Cl Table 2.5), also have crystalline structures that are related to apatite. Mimetite may occur in oxidized lead-rich hydrothermal deposits. 

Elemental arsenic is used in alloys of lead and copper, in semiconductors, and as an additive to the grid metal in storage batteries. Arsenic compounds have been used as pesticides and wood preservatives [4]. Although arsenic is most well known for its use as a poison, some evidence suggests that trace amounts may be essential for good health [5]. Inorganic forms of arsenic are more toxic than the organic forms arsenite, As (III), is the most toxic form of the element, followed by arsenate, As (V), monomethylarsenate, and dimethylarsenate. 

Although the predominant source of arsenic and metals to most soils and sediments in New England is sulfide-rich rock, the extensive application of arsenical pesticides and herbicides (lead arsenate, calcium arsenate, and sodium arsenate, and others) on apple, blueberry, and potato fields may have been a possible anthropogenic source of arsenic and lead. The main objective of this study was to determine the lead isotopic compositions of commonly used pesticides, such as lead arsenate, sodium metarsenite, and calcium arsenate, in order to assist in future isotopic comparisons and to better characterize this anthropogenic source of Pb. The pesticides plot along a linear trend in isotope diagrams, for example, in values of... 

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