An inhalation-ingestion bioaccessibility assay (IIBA) for the assessment of exposure to metal(loid)s in PM10

摘要

Although bioaccessibility assessment of ambient particulate matter (APM) is recently receiving increasing attention, limited research has been undertaken into standardising methodologies. The fraction of APM that is most relevant to a human inhalation scenario is PM10 (particles with <10μm in aerodynamic diameter), which may potentially enter and deposit in the lung lining fluid with a neutral pH. Contradictory suggestions exist in the literature regarding which assay parameters should be adopted, e.g. solid to liquid ratio (S/L), maximum extraction time, and the composition of simulated lung fluid (SLF). Particularly, 13 different SLF compositions have been used in the literature and their extraction efficiencies have not been investigated. Additionally, 90% of the PM10 depositing in the lung may be cleared within 24 hours by mucociliary mechanisms and pass through the gastro-intestinal (GIT) tract, with potential continuation of metal(loid) dissolution.The objective of this study was to standardise a conservative inhalation-ingestion bioaccessibility assay (IIBA) by simulating the inhalation of PM10, including its transition into the ingestion pathway. To achieve this aim, the bioaccessibility of arsenic (As) and lead (Pb) in PM10 from three Australian mining/smelting impacted regions was used to investigate the effect of S/L (1:100–1:5000), extraction time (1–120 hours), agitation (occasional, orbital, magnetic stirring and end over end rotation) and five major SLF compositions. Using the biologically relevant parameters that resulted in the most conservative bioaccessibility outcome, the IIBA was developed by leaching PM10 in SLF, followed by simulated GIT solutions.Results from this study revealed that fluid composition and solid to solution ratio most significantly (p<0.05) affected metal(loid) dissolution. The highest cumulative bioaccessibility of Pb was obtained using SLF + simulated gastric solution, while that of As was using SLF + simulated gastric + intestinal solutions. Compared to SLF alone, cumulative metal(loid) dissolution using the IIBA was significantly higher (p < 0.05) for both metal(loid)s for all PM10 samples.