Method variables affecting the bioaccessibility of arsenic in soil

Arsenic bioaccessibility tests are now being commonly used in risk assessment. However, concerns remain about the reliability of such tests because the bioaccessibility of arsenic from soil may be susceptible to soil composition (including iron concentration), as well as method considerations such as varying liquid-to-solid ratios and the chosen buffer system. In this study, arsenic-contaminated tailings and soils were tested to compare two bioaccessibility methods: one that uses glycine as a buffer, and a second that is more physiologically based. With the glycine-buffered method, arsenic and iron bioaccessibility increased in the presence of a higher buffer concentration at higher liquid-to-solid ratios, whereas the results of physiologically-based tests were unaffected by variations in these parameters. In the glycine-buffered system, interactions between iron and glycine may influence the concentration of arsenic in solution, which may not be consistent with human gastrointestinal conditions. The choice of a physiologically-based method may be more appropriate to achieve representative arsenic bioaccessibility values toward estimating risks to human health.