Variability of bioaccessibility results using seventeen different methods on a standard reference material, NIST 2710

Abstract

Bioaccessibility is a measurement of a substance's solubility in the human gastro-intestinal system, and is often used in the risk assessment of soils. The present study was designed to determine the variability among laboratories using different methods to measure the bioaccessibility of 24 inorganic contaminants in one standardized soil sample, the standard reference material NIST 2710. Fourteen laboratories used a total of 17 bioaccessibility extraction methods. The variability between methods was assessed by calculating the reproducibility relative standard deviations (RSDs), where reproducibility is the sum of within-laboratory and between-laboratory variability. Whereas within-laboratory repeatability was usually better than (<) 15% for most elements, reproducibility RSDs were much higher, indicating more variability, although for many elements they were comparable to typical uncertainties (e.g., 30% in commercial laboratories). For five trace elements of interest, reproducibility RSDs were: arsenic (As), 22-44%; cadmium (Cd), 11-41%; Cu, 15-30%; lead (Pb), 45-83%; and Zn, 18-56%. Only one method variable, pH, was found to correlate significantly with bioaccessibility for aluminum (Al), Cd, copper (Cu), manganese (Mn), Pb and zinc (Zn) but other method variables could not be examined systematically because of the study design. When bioaccessibility results were directly compared with bioavailability results for As (swine and mouse) and Pb (swine), four methods returned results within uncertainty ranges for both elements: two that were defined as simpler (gastric phase only, limited chemicals) and two were more complex (gastric + intestinal phases, with a mixture of chemicals).

‘Towards a unified approach for the determination of the bioaccessibility of organic pollutants’

“…However, these tests are now being used in the UK as part of a 'body of evidence' approach when determining the risks of contaminated land. This low level of adoption has two principle reasons; the lack of validation by animal trials and the wide variability seen both within and between tests (Koch et al, 2013;Oomen et al, 2002) (Supporting information, Table 1). Within this paper we focus on organic pollutants because this chemical class has received less attention than the toxic elements which have been reviewed by the regulatory agencies (Environment Agency, 2005;EPA, 2008) and there is uncertainty on which components of the test are influential.…”

Arsenic relative bioavailability from diet and airborne exposures: Implications for risk assessment

“…Studies have been conducted comparing results among one or more soil or reference material samples among multiple versions of in vitro gastro-intestinal bioaccessibility methods (Oomen et al, 2002;Juhasz et al, 2009Juhasz et al, , 2011Wragg et al, 2011;Denys et al, 2012;Koch et al, 2013b;Brattin et al, 2013;Bradham et al, 2011). In several studies, low gastric compartment pH (e.g., 1.5) was consistently found to be related to relatively higher As bioaccessibility values (Oomen et al, 2002;Wragg et al, 2011;Denys et al, 2012).…”

“…Gastric phase pH of 4.0 yielded relatively low bioaccessibility values (Alava et al, 2013a). Within laboratory repeatability across 14 laboratories for 17 different bioaccessibility extraction methods was 10%; reproducibility relative standard deviation (RSD) across laboratories ranged from 22 to 44% for As (Koch et al, 2013b).…”

Bioaccessibility of mercury in selected Ayurvedic medicines

“…One of the limitations of bioaccessibility testing is that methods can vary widely, giving large ranges of percent bioaccessibility values (Koch et al, 2013). Additionally, bioavailability values, often used to "validate" bioaccessibility methods, are not available for the majority of elements (the exceptions are lead, arsenic and cadmium, and only for soil matrices, e.g., Schroder et al, 2004;Juhasz et al, 2009Juhasz et al, , 2010Denys et al, 2012, among others).…”