Development and application of an inhalation bioaccessibility method (IBM) for lead in the PM10 size fraction of soil

Abstract

An approach for assessing the inhalation bioaccessibility of Pb in the PM10 size fraction is presented, using an in vitro simulated epithelial lung fluid to represent the extracellular environment of the lung. The developed inhalation bioaccessibility method (IBM) is applied to a range of urban surface soils and mining wastes obtained from Mitrovica, Kosovo, a site where impacts upon human health following exposure to Pb have been internationally publicised. All Pb determinations were undertaken by inductively coupled plasma mass spectrometry (ICP-MS). The pseudo-total concentration of Pb (microwave acid digestion using aqua-regia) varied between matrices: smelter (20,900-72,800mgkg(-1)), topsoil (274-13,700mgkg(-1)), and tailings (2990mgkg(-1)-25,300mgkg(-1)). The in vitro inhalation bioaccessibility was typically several orders of magnitude lower: smelter (7.0-965mgkg(-1)), topsoil (9.8-1060mgkg(-1)), and tailings (0.7mgkg(-1)-49.2mgkg(-1)). The % inhalation bioaccessibility ranged from 0.02 to 11.0%, with the higher inhalation bioaccessible Pb concentrations being observed for samples from the Bosniak Mahalla area of Mitrovica (an area proposed for the relocation of internally displaced peoples). The estimated inhalation dose (for adults) calculated from the PM10 pseudo-total Pb concentration ranged from 0.369 to 1.284μgkg(-1)BWday(-1) (smelter), 0.005-0.242μgkg(-1)BWday(-1) (topsoil), and 0.053-0.446μgkg(-1)BWday(-1) (tailings). When daily inhalation doses were calculated using the bioaccessible Pb concentration the modelled exposure doses were much lower: smelter (0.0001-0.0170μgkg(-1)BWday(-1)), topsoil (0.0002-0.0187μgkg(-1)BWday(-1)) and tailings (0.0001-0.0009μgkg(-1)BWday(-1)). Modelled for the neutral pH conditions of the interstitial lung environment, the results indicate a low potential inhalation bioaccessibility for Pb in these samples. Given the already elevated environmental Pb burden experienced by the local population, where significant prolonged dust or particulate generating activities are taking place, or where the inhaled particles are phagocytized, then inhalation exposure has the potential to significantly add to the overall Pb burden. Such data are important for local policy makers to better enable them to assess risk, especially in areas where soils/dusts have elevated levels of contamination.

Use of simulated epithelial lung fluid in assessing the human health risk of Pb in urban street dust

“…An approximate 0.3 g of five certified reference/guidance materials (in triplicate) and the 21 urban street dust samples (in duplicate) were accurately weighed into labelled 50 mL screw-cap Sarstedt tubes (extraction tubes) to which 20 mL of the SELF was added (Boisa et al, 2014). The mixture was then shaken, on an end-over-end rotator, maintained at 37°C ± 0.2 for 96 h (Boisa et al, 2014).…”

“…The mixture was then shaken, on an end-over-end rotator, maintained at 37°C ± 0.2 for 96 h (Boisa et al, 2014). The resulting solution was then centrifuged at 3000 rpm for 10 min.…”

“…The ICP-MS was operated under standard operating conditions, as previously reported (Boisa et al, 2014).…”

“…Neutral synthetic lung fluids, largely based on modifications of the original 'Gamble's solution', are widely used for the exposure assessment of humans to inhalable pollutants (Wragg and Klinck, 2007;Caboche et al, 2011;Lima et al, 2013). More recently, the crucial (though often unclear) role of high molecular mass proteins, antioxidants and surfactant lipids in determining bioaccessibility has been recognised, along with the development and application of a new generation of in vitro lung fluid formulations (Boisa et al, 2014;Gray et al, 2010;Li et al, 2014;Stebounova et al, 2011). The development of specialised fluids to mimic other parts of the human respiratory system is also required, as particles in the lung can also be phagocytized, exposing the PM to lower pH environments.…”

“…Whilst inhaled particles would have to be phagocytized before significant exposure to a more acidic environment occurs, all PM will be exposed to the neutral lung fluid. Coupled with the fact that the actual extent of phagocytosis remains unclear, in this study we utilised the neutral synthetic epithelial lung fluid (or SELF) proposed by Boisa et al (2014). Furthermore, recent testing by Li et al (2016) indicated the important role played by some of the key constituents included in the SELF in influencing bioaccessibility and highlighted the greater bioaccesssibility of Pb in the SELF when compared to the standard Gamble's-type fluid.…”