Arsenate

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Pourbaix diagram of arsenic

Arsenate refers to a compound containing the arsenate ion, where arsenic is in the oxidation state +5. Arsenates are part of a broader class of compounds known as oxoanions, which are anions containing oxygen and another element. The chemical formula for the arsenate ion is AsO4^3-. Arsenates are analogous to phosphates, having similar chemical properties but containing arsenic in place of phosphorus.

Chemistry

Arsenate ions can form a variety of salts with different metals, such as sodium arsenate (Na3AsO4) and calcium arsenate (Ca3(AsO4)2), among others. These compounds are often soluble in water, making them potentially hazardous due to arsenic's toxicity. Arsenates can also form esters, known as organoarsenates, which include compounds like dimethyl arsenate (C2H7AsO4).

In aqueous solutions, arsenate can exist in four different forms depending on the pH: H3AsO4, H2AsO4^-, HAsO4^2-, and AsO4^3-. The distribution of these species is pH-dependent, with H3AsO4 being predominant in acidic solutions and AsO4^3- in basic solutions.

Toxicology

Arsenic, including its compounds like arsenates, is known for its toxicity. Chronic exposure to arsenate can lead to arsenic poisoning, symptoms of which include skin lesions, peripheral neuropathy, gastrointestinal symptoms, and an increased risk of developing cancer, particularly skin, lung, and bladder cancers. The toxicity of arsenates is partly due to their interference with cellular processes, including oxidative phosphorylation and the synthesis of adenosine triphosphate (ATP).

Environmental Impact

Arsenates can enter the environment through natural processes, such as volcanic activity and the weathering of arsenic-containing minerals. However, human activities, such as the use of arsenic-based pesticides, herbicides, and wood preservatives, have significantly increased the levels of arsenates in the environment. This has led to the contamination of water, soil, and food, posing health risks to humans and wildlife.

Regulation and Remediation

Due to the health risks associated with arsenic, regulatory bodies worldwide have set limits on the allowable concentrations of arsenic in drinking water and food. Remediation of arsenic-contaminated sites often involves techniques such as phytoremediation, using plants to absorb arsenic from the soil, and chemical treatments to immobilize arsenic or convert it into less toxic forms.

See Also

• Arsenic
• Phosphate
• Toxicology
• Environmental remediation