Arsenate-based
pesticides such as
lead hydrogen arsenate were commonly used until their replacement by newer pesticides such as
DDT and subsequent ban by multiple regulatory bodies due to health concerns.[8][9]
Depending on the
pH, arsenate can be found as trihydrogen arsenate (that is
arsenic acidH3AsO4), dihydrogen arsenate (H2AsO−4), hydrogen arsenate (HAsO2−4), or arsenate (AsO3−4).[18] Trihydrogen arsenate is also known as
arsenic acid. At a given
pH, the distribution of these arsenate
species can be determined from their respective
acid dissociation constants.[17]
H3AsO4 + H2O ⇌ H2AsO−4 + [H3O]+(pKa1 = 2.19)
H2AsO−4 + H2O ⇌ HAsO2−4 + [H3O]+(pKa2 = 6.94)
HAsO2−4 + H2O ⇌ AsO3−4 + [H3O]+H(pKa3 = 11.5)
These values are similar to those of
phosphoric acid. Hydrogen arsenate and dihydrogen arsenate predominate in aqueous solution near neutral pH.[17]
The
reduction potential (pe) of a solution also affects arsenate speciation. In natural waters, the
dissolved oxygen content is the main factor influencing reduction potential. Arsenates occur in oxygenated waters, which have a high pe, while arsenites are the main arsenic species in
anoxic waters with a low pe.[16]
A
Pourbaix diagram shows the combined influence of pH and pe on arsenate speciation.
Contamination
Arsenates, along with arsenites, are a significant source of
contamination in some natural
water sources and can lead to
arsenic poisoning with repeated exposure.[19][20] Countries with high levels of arsenic minerals in
sediment and rock, such as
Bangladesh, are especially at risk of arsenate contamination.[21][20]
As with other arsenic compounds, arsenate binds to
lipoic acid, inhibiting the conversion of
pyruvate into
acetyl-CoA, blocking the
Krebs cycle and therefore resulting in further loss of ATP.[23]
^Waalkes, Michael P. (2019), Baan, Robert A.; Stewart, Bernard W.; Straif, Kurt (eds.),
"Arsenic and metals", Tumour Site Concordance and Mechanisms of Carcinogenesis, IARC Scientific Publications, Lyon (FR): International Agency for Research on Cancer,
ISBN978-92-832-2217-0,
PMID33979075, retrieved 2 April 2023
^
abPollutants, National Research Council (US) Committee on Medical and Biological Effects of Environmental (1977).
Chemistry of Arsenic. National Academies Press (US).
^
abcBarton, C. (1 January 2014),
"CCA-Treated Wood", in Wexler, Philip (ed.), Encyclopedia of Toxicology (Third Edition), Oxford: Academic Press, pp. 751–752,
ISBN978-0-12-386455-0, retrieved 10 April 2023
^
abcJekel, M.; Amy, G. L. (1 January 2006), Newcombe, Gayle; Dixon, David (eds.),
"Chapter 11 - Arsenic removal during drinking water treatment", Interface Science and Technology, Interface Science in Drinking Water Treatment, vol. 10, Elsevier, pp. 193–206, retrieved 15 April 2023
^Pollutants, National Research Council (US) Committee on Medical and Biological Effects of Environmental (1977).
Chemistry of Arsenic. National Academies Press (US).