Assessment of arsenic and lead contamination at a mine site in Australia using a health risk approach

The National Environment Protection Measures (NEPMs) guidelines for soil contamination in Australia identify a need to undertake further assessment of the site if the Health Investigation Levels (HIL) are exceeded (NEPC 1999). It was identified (Ng et al., 2003) that the current NEPM’s do not provide accurate close out criteria for mined land. Labile metal species are considered to be more biologically active than non-labile fractions. There are a number of tests for availability of toxic materials from single components and from mixtures (Tessier et al., 1979) and arsenic species in mining wastes (Noller et al., 1997), which are generally based on the assumptions that greater solubility enhances bioavailability. Although the chemical speciation obtained by sequential extractions is often believed to relate to bioavailability, in the absence of bioavailability data it must be assumed that metals and arsenic are 100% bioavailable. In many cases it has been demonstrated that bioavailability of contaminated soil is usually a fraction of 100% (Ng et al., 2003). Absolute bioavailability is measured via animal uptake but is expensive and time consuming. A more practical approach is to use in-vitro PBET (physiologically based extraction test) to determine the bio-accessibility of individual soils. The PBET method has demonstrated good linear correlation with both Sprague-Dawley rats (lead) and with rabbits and monkeys (arsenic) (Ruby et al., 1996). This study uses a combination of bioaccessibility and bioavailability measurements to provide a site-specific human health risk assessment. It focuses on arsenic and lead soil concentrations, at a mine site in Australia after decommissioning and rehabilitation and takes into account an assessment of the reliability of using the PBET approach