Properties & Reactions of Arsenic

Oxidation States of Arsenic
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In the environment, arsenic exists predominantly in the +3 and +5 oxidation states. The table below outlines the spoken and written nomenclature that is usually used to describe arsenic's oxidation states.

Arsenic Oxidation State
Oxidation States As3+ As5+
In speaking “arsenic three” “arsenic five”
In writing As(III) or AsIII As(V) or AsV

As(III) is usually considered to be more toxic than As(V). As(III) is usually more prevalent under reduced environmental conditions (e. g., flooded soils). As(V) is usually more prevalent under oxidized conditions (e. g., drained soils). However, both oxidation states of arsenic are often observed together in soils, because of the sometimes slow rates of transformation between oxidation states.

Oxidation state influences many properties of arsenic, including:

  • Adsorption to soil minerals
  • Solubility in soil
  • Uptake by plants
  • Toxicity to plants and animals