In-vitro determination of arsenic bioavailability in contaminated soil andmineral beneficiation waste from Ron Phibun, southern Thailand: A basis for improved human risk assessment

The post-ingestion bioavailability of arsenic (As) in alluvial soil and min eral beneficiation waste from Ron Phibun, Nakhon Si Thammarat Province,Thai land has been investigated using a physiologically-based extraction test (P BET). The method utilises synthetic leaching fluids closely analogous to th ose of the human stomach and small intestine, upon which the leaching durat ion and ambient temperature of the experimental procedure are also directly based. Replicate analyses of Ron Phibun alluvium samples holding 1406 and 2123 mu g As g(-1) respectively indicated an average stomach absorption of 11.2% (of total soil As). Gross absorption increased to 18.9% following tra nslocation through a simulated small-intenstine regime. Higher gross absorp tion (35.7%) was recorded during PBET analysis of a flotation waste sample holding c. 2% total As. Within- and between-site variations of As bioavaila bility can principally be ascribed to mineralogical factors, notably the re lative abundances of sulphide, arsenide, arsenate and oxide hosts within th e soil/flotation waste matrix. The PBET provides a potentially valuable mec hanism for refining risk assessments of sites subject to natural or anthrop ogenic As contamination. Through the substitution of total soil As values w ith input data which relate specifically to bioavailable As, risk calculati ons derived using established models such as the US-EPA package Risk Assist ant may prove more realistic, thus facilitating improved cost-benefit analy sis of site remediation options. Assessment of the relative human risks ass ociated with potable water consumption and contaminated soil ingestion at R on Phibun has signified that the latter could constitute a more significant As exposure pathway than recognised previously. Further evaluation of the precise soil ingestion levels of inhabitants residing on the As-rich alluvi um which covers much of the district is, therefore, warranted.