Bioavailability and pharmacokinetics of arsenic are influenced by the presence of cadmium

Mine wastes contain a mixture of metals and metalloids including arsenic (As) and cadmium (Cd). This study investigated the potential interaction between As and Cd in a rat model. Sprague Dawley rats were dosed with sodium arsenate via the oral (0, 0.5, 5 and 15mg As kg-1 b.w.) or intravenous (0.5mg As kg-1 b.w.) route to establish its dose-response relationship in terms of bioavailability and pharmacokinetic parameters. Bioavailability of As reduced when the dose of As increased. For the interaction study a fixed oral dose of As at 2.5mg As kg-1 b.w. solo and in combination with Cd as cadmium chloride at 3 or 6mg Cd kg-1 b.w. were administered to rats. Bioavailability of As was decreased by 34-35% in the presence of Cd. Elimination half-life of As was also decreased from 69 days in the As solo group to 13-22days in the presence of 3 and 6mg Cd kg-1 b.w. respectively. Decreased urinary excretion of As and tissue accumulation were also observed. A probable explanation for these findings is that As co-administration with Cd could have resulted in the formation of less soluble cadmium-arsenic complexes in the guts of the rats. Nevertheless, such an interaction between As and Cd could only explained about 44-48% of the variation when mine waste materials containing both of these elements were administered to rats. This suggests other physical properties and chemical compound formation could contribute to the observed bioavailability of arsenic in complex environmental samples

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

Speciation and bioavailability of arsenic in managing health risks for mine site rehabilitation

This paper provides an overview of the rationale of using bioaccessibility to predict arsenic bioavailability for risk assessment of rehabilitated mined land and its application to develop site-specific guidelines. The physiologically based extract test (PBET) in-vitro bioaccessibility model was used to assess of arsenic bioaccessibility and validated for its potential to predict bioavailability of mine wastes derived from rat in-vivo experiments. The alternative in-vitro approach, can replace animal in-vivo experiments, which simulate human uptake of arsenic. Comparison with bioaccessibility to predict bioavailability of arsenic then enables the development of a risk-based guideline approach for mine wastes