A novel two-step sequential bioaccessibility test for potentially toxic elements in inhaled particulate matter transported into the gastrointestinal tract by mucociliary clearance

A novel two-step sequential extraction has been developed to assess the bioaccessibility of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in airborne particulate matter following inhalation and transport into the human gastrointestinal tract by mucociliary clearance. A new artificial mucus fluid (AMF) was used to determine the bioaccessible potentially toxic element (PTE) fraction in the upper airways, in sequence with the simplified bioaccessibility extraction test (SBET) or the stomach phase of the unified bioaccessibility method (gastric fluid only) (UBMG). Filter dynamic measurement system TX40 filters smeared with soil reference material (BGS RM 102) were used as test samples. Analysis was performed by ICP-MS. Comparison between results obtained for soil alone and when the soil was supported on TX40 filters indicated that the presence of the substrate did not affect the extraction efficiency, although a large Zn blank was detected. The sequential AMF→SBET extraction liberated similar amounts of Fe, Mn, Ni and Zn to the SBET alone; but significantly less Cd; and significantly more As, Cr, Cu and Pb. The sequential AMF→UBMG extraction liberated similar amounts of Cd, Cr, Mn and Zn to the UBMG alone, but significantly less As, Fe and Ni; and significantly more Cu and Pb. Enhanced extractability was due to the greater quantities of exchangeable ions and complexing agents present. Adoption of a two-step sequential extraction (AMF followed by either the SBET or the UBMG) is recommended because it is more representative of biological conditions and avoids overestimation or underestimation of bioaccessible PTE concentrations

Oral bioaccessibility tests to measure potentially toxic elements in inhalable particulate matter collected during routine air quality monitoring

The simplified bioaccessibility extraction test (SBET) and the stomach phase of the unified bioaccessibility method (UBM) have been modified for use in assessing the bioaccessibility of potentially toxic elements in samples of PM10 collected during routine air quality monitoring. Arsenic, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured by inductively coupled plasma mass spectrometry in extracts of synthetic PM samples prepared by loading candidate soil reference material BGS102 onto TX40 (Teflon-coated borosilicate) filters widely used in standard commercial tapered element oscillating microbalance/filter dynamics measurement system (FDMS) ambient particulate monitors. Analysis of blanks revealed two important sources of contamination that had to be controlled in order to achieve reproducible results. The syringe filters used in the SBET released Cu and Zn into sample extracts during filtration and had to be washed with 80 mL of 0.4 M glycine at pH 1.5 immediately prior to use, whilst the FDMS filters used to collect PM10 were found to contain sufficient extractable Zn (ca. 3 μg per filter) to almost double the concentration released by the soil. The latter is a consequence of the use of Zn in filter manufacture and so could not be eliminated, but was successfully overcome by means of blank-subtraction. A ten-fold miniaturisation of the SBET and six-fold miniaturisation of the UBM allowed 0.1 g samples to be processed, with analyte recoveries generally within ±10% of those obtained when the conventional procedures were used. Comparison between results obtained when the modified procedures were applied to soil alone, and when soil was loaded onto FDMS filters, indicated that the presence of the filter had no effect on extraction efficiency, except for Fe, provided blank-correction was performed. Results obtained for As, Cd and Pb when the modified UBM was applied to BGS102 on FDMS filters were 4.40 ± 0.04, 0.224 ± 0.002 and 17.3 ± 0.8 mg kg-1, respectively (n = 3), all within recommended ranges

Extraction methods for assessing the bioaccessibility of potentially toxic elements in urban airborne particulate matter by inductively coupled plasma mass spectrometry

Inhaled particulate matter (PM), containing bioaccessible potentially toxic elements (PTE) has attracted attention due to potential human health risk. This study was to develop and assess the suitability of simplified bioaccessibility extraction test (SBET) and the stomach phase of unified bioaccessibility method (UBMSG) to measure bioaccessible PTE in PM10 collected on filter dynamic measurement system (FDMS) filters used worldwide. Analytes were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn and measured by ICP-MS.The SBET and UBMSG were miniaturised for application to PM10. Reducing sample mass and reagents volume by a factor of 10 for the SBET and by a factor of 6 for UBMSG, and presence of the FDMS filter did not affect PTE extractabilities. Bioaccessible PTE in blank FDMS filters were generally low, except for Zn. Washing acrodisc® syringe filters immediately before use with 80 mL of glycine reduced the concentration of Cu and Zn in procedural SBET blanks from 119 and 1520 to 0.129 and 14.5 μg L-1, respectively.New closed-loop and single-pass dynamic models for the SBET and UBMSG either coupled or not with ICP-MS were successfully applied to determine bioaccessible PTE in real and simulated PM10 samples. Accuracy of models was ascertained by mass balance, and verified by Z-scores, which were generally acceptable. For single-pass models, rapid mobilization was observed for PTE, except for Cr.Finally, a new artificial mucus fluid was applied sequentially with the SBET and UBMSG (gastric fluid only) to measure bioaccessible PTE in inhaled PM10. Bioaccessible PTE concentrations, which were underestimated for As, Cr, Cu, and Pb, and overestimated for Cd, Fe, Ni and Zn using ingestion route alone, were more accurately determined. Extraction methods that are more similar to real body processes were successfully created to determine bioaccessible PTE in PM10 that are inhaled and subsequently ingested.Inhaled particulate matter (PM), containing bioaccessible potentially toxic elements (PTE) has attracted attention due to potential human health risk. This study was to develop and assess the suitability of simplified bioaccessibility extraction test (SBET) and the stomach phase of unified bioaccessibility method (UBMSG) to measure bioaccessible PTE in PM10 collected on filter dynamic measurement system (FDMS) filters used worldwide. Analytes were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn and measured by ICP-MS.The SBET and UBMSG were miniaturised for application to PM10. Reducing sample mass and reagents volume by a factor of 10 for the SBET and by a factor of 6 for UBMSG, and presence of the FDMS filter did not affect PTE extractabilities. Bioaccessible PTE in blank FDMS filters were generally low, except for Zn. Washing acrodisc® syringe filters immediately before use with 80 mL of glycine reduced the concentration of Cu and Zn in procedural SBET blanks from 119 and 1520 to 0.129 and 14.5 μg L-1, respectively.New closed-loop and single-pass dynamic models for the SBET and UBMSG either coupled or not with ICP-MS were successfully applied to determine bioaccessible PTE in real and simulated PM10 samples. Accuracy of models was ascertained by mass balance, and verified by Z-scores, which were generally acceptable. For single-pass models, rapid mobilization was observed for PTE, except for Cr.Finally, a new artificial mucus fluid was applied sequentially with the SBET and UBMSG (gastric fluid only) to measure bioaccessible PTE in inhaled PM10. Bioaccessible PTE concentrations, which were underestimated for As, Cr, Cu, and Pb, and overestimated for Cd, Fe, Ni and Zn using ingestion route alone, were more accurately determined. Extraction methods that are more similar to real body processes were successfully created to determine bioaccessible PTE in PM10 that are inhaled and subsequently ingested

On- and off-line analysis by ICP-MS to measure the bioaccessible concentration of elements in PM10 using dynamic versions of the simplified bioaccessibility extraction test

Two dynamic versions of the simplified bioaccessibility extraction test (SBET) were developed—an off-line procedure and an on-line procedure coupled directly to ICP-MS. Batch, on-line, and off-line procedures were applied to simulated PM10 samples prepared by loading NIST SRM 2711A Montana II Soil and BGS RM 102 Ironstone Soil onto 45-mm TX40 filters widely used in air quality monitoring. Three real PM10 samples were also extracted. A polycarbonate filter holder was used as an extraction unit for the dynamic procedures. Arsenic, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined in the extracts using an Agilent 7700 × ICP-MS instrument. The residual simulated PM10 samples following application of the SBET were subjected to microwave-assisted aqua regia digestion and a mass balance calculation performed with respect to digestion of a separate test portion of the SRM. Leachates were collected as subfractions for the off-line analysis or continuously introduced to the nebuliser of the ICP-MS for the on-line analysis. The mass balance was generally acceptable for all versions of the SBET. Recoveries obtained with the dynamic methods were closer to pseudototal values than those obtained in batch mode. Off-line analysis performed better than on-line analysis, except for Pb. Recoveries of bioaccessible Pb relative to the certified value in NIST SRM 2711A Montana II Soil (1110 ± 49 mg kg−1) were 99, 106, and 105% for the batch, off-line, and on-line methods, respectively. The study demonstrates that dynamic SBET can be used to measure bioaccessibility of potentially toxic elements in PM10 samples