Knowledge about arsenic detection

Arsenic is commonly found throughout the environment in a wide array of chemical species that vary in toxicity and mobility. Many of these chemical species can be transformed due to biological activity or other changes in the environment, such as a change in oxidation-reduction potential and pH. This prospect for natural environmental change creates the possibility that a wide variety of arsenic species are constantly transforming at any time.


To determine the potential transformation and risk of arsenic in the environment for remedy decisions, the analysis of environmental samples should include identifying and quantifying both the total quantity of arsenic present and the specific chemical forms present, a procedure known as speciation.

However, speciation by a laboratory is expensive and the sample collection methods to ensure the preservation of in situ conditions are difficult and expensive.

The main species of arsenic found in the environment are the arsenic (III) and arsenic (V) oxyacids. Arsenates, arsenate anions, along with neutral arsenite constitute the main targets for field analytical assays.

In contaminated soils, inorganic arsenate is the predominant species.

In general, the arsenate and other arsenic (V) species are immobilized on geologically available surfaces, usually as iron oxides. Although arsenic (V) compounds are considered a low risk, bacterial and other environmental activities can readily convert them back into more mobile and more toxic forms of arsenic.

Groundwater and soil also contain organoarsenic species. In general organoarsenic compounds are less toxic than their corresponding oxyacids. Although usually found in lower concentrations, under the right conditions, they can be found in very high concentrations. In freshwater lakes, methylated arsenic can make up to 60% of the total arsenic. There are also arsenic sulfur species that constitute a sizable portion of arsenic geology and reducing environments in sediment and in solution. Although all of these species are not as common or currently believed to be as toxic as arsenic oxyacids they constitute a sizable fraction of the naturally occurring arsenic and should be a target in field measurements.