Arsenic Speciation Key To Poisoning Risk

Drinking or inhaling arsenic compounds may not be the only ways to be poisoned by the toxic substances: Exposure through the skin may also be a problem, report Sairoong Ouypornkochagorn and Jörg Feldmann of the University of Aberdeen, in Scotland (Environ. Sci. Technol., DOI: 10.1021/es903667y). Dermal exposure to arsenic is a particular concern for farmers working in fields irrigated with water containing naturally occurring arsenic, such as in Asian rice paddies. Historically, arsenic exposure through the skin was thought to be a low risk, but that was based on studies of arsenate (AsO₄ ^3–). Arsenite (AsO₃ ^3–), however, is the dominant species in rice paddies. Ouypornkochagorn and Feldmann used abdominal skin from a human cadaver to compare rates of transmission of arsenate, arsenite, dimethylarsinic acid [(CH₃)₂As(O)OH], and arsenosugars from seaweed through the skin. They found that arsenosugars penetrate the skin at a rate similar to arsenate’s, but that arsenite goes through 29 times faster and dimethylarsinic acid passes through 59 times faster. Although the researchers worked with a single piece of skin and arsenic species penetration might vary from person to person and between different body parts, they say the results point to the need to consider arsenic speciation when evaluating exposure risks.