Arsenic

1. What is arsenic?

• 1.1 What are the properties of arsenic?
• 1.2 How are arsenic levels measured?

1.1 What are the properties of arsenic?

The source document for this Digest states:

Arsenic is a metalloid widely distributed in the earth’s crust and present at an average concentration of 2 mg/kg. Arsenic can exist in four valency states: –3, 0, +3 and +5. Under reducing conditions, arsenite (As (III)) is the dominant form; arsenate (As (V)) is generally the stable form in oxygenated environments. Elemental arsenic is not soluble in water. Arsenic salts exhibit a wide range of solubilities depending on pH and the ionic environment.

Arsenic and its compounds occur in crystalline, powder, amorphous or vitreous forms. They usually occur in trace quantities in all rock, soil, water and air. However, concentrations may be higher in certain areas as a result of weathering and anthropogenic activities including metal mining and smelting, fossil fuel combustion and pesticide use.

There are many arsenic compounds of environmental importance. Inorganic compounds include the trivalent arsenic trioxide, arsenic trichloride, arsenic trisulphide and sodium arsenite. Pentavalent ones include arsenic pentoxide, arsenic acid and sodium arsenate. Representative organic compounds are monomethyl-, dimethyl- and trimethylarsine, and arsenobetaine.

Source & ©: IPCS "Environmental Health Criteria for Arsenic and Arsenic compounds, 
EHC 224, Chapter 1: Summary, section 1, and
Chapter 2, section 2.2 Chemical and physical properties of arsenic compounds

1.2 How are arsenic levels measured?

The source document for this Digest states:

There is a variety of instrumental techniques for the determination of arsenic. These include atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and voltammetry. Some of these (e.g. ICP-MS) can serve as element-specific detectors when coupled to chromatographic separation techniques (e.g. HPLC and GC). These so-called "hyphenated" methods are used for determining individual arsenic species. Additional sensitivity for a limited range of arsenic compounds can often be achieved by the use of hydride generation techniques. A test kit based on the colour reaction of arsine with mercuric bromide is currently used for groundwater testing in Bangladesh and has a detection limit of 50–100 µg/litre under field conditions.

Source & ©: IPCS "Environmental Health Criteria for Arsenic and Arsenic compounds, 
EHC 224, Chapter 1: Summary, section 1