Oral Bioavailability - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 314

low gastric pH and an intestinal compartment at neutral pH, indicating that pH plays
an important role in both phases of the in-vitro test.
The multi-laboratory comparison study by Van de Wiele et al. ( 2007 ) assessed the
bioaccessibility of soil-bound lead under both fed and fasted conditions in a num-
ber of in-vitro test systems. The study utilized both the soils and the resulting lead
bioavailability data (Maddaloni et al. 1998 ), as a reference point for comparison,
from a previous human in-vivo trial. As with the previous study by the BARGE
group, both static and dynamic in-vitro methodologies were included, but unlike
the previous study, all test systems were physiologically-based. The study showed
that regardless of the nutritional status of the model (fed or fasted state), the lead
bioaccessibility was significantly different ( p < 0.05) between the methods with
bioaccessible lead ranging between ca. 2 to 35%. Comparison with the available
in-vivo data indicated that the simulation of the human gastrointestinal system under
fed conditions overestimated lead bioavailability, whilst under fasted conditions
a number of the models investigated underestimated oral bioavailability (Van de
Wiele et al. 2007 ). This study and the previous study by Oomen et al. ( 2002 ) note
that differences in the measured bioaccessibilities are often due to key methodolog-
ical parameters such as gastric and intestinal pH. This further study notes that the
method of separation (centrifugation, filtration, ultrafiltration) used in the test sys-
tem is a critical factor in separating the bioaccessible from the non-bioaccessible
fraction present and in the interpretation of the results for use in Human Health
Risk Assessment.
The third inter-laboratory study initiated by the BARGE group had the goal of
progressing development of a harmonised bioaccessibility methodology in order to
carry in-vitro testing for Human Health Risk Assessment of contaminated soils. The
collective efforts of the network modified the previously published RIVM physio-
logically based in-vitro method and the trial determined the analytical performance
characteristics of the bioaccessibility measurement (repeatability and reproducibil-
ity). Modifications were made in order that the methodology was robust and
provided adequate conservatism, at least for first tier Risk Assessment, for future use
across the local geological conditions of the individual member countries (Wragg
et al. 2009 ). The study utilized slag materials, river sediments, soil material and
house dusts that had been previously investigated for their arsenic, cadmium and
lead bioaccessibility and oral bioavailability contents by Professors Nick Basta
(Basta et al. 2007 ; Rodriguez et al. 1999 ; Schroder et al. 2003 , 2004a) and/or
Professor Stan Casteel. The first inter-laboratory study showed that the harmonised
methodology had the potential to meet the benchmark criteria set by BARGE. In
addition, with the aid of further testing on soils that are representative of the local
geology to the participating countries and not just highly elevated mining and slag
waste, the method could be standardised for international use.
Health Canada has funded the BARC group to assess the variability in the
reported data across Canadian laboratories in the form of a simple inter-laboratory
comparison. This initial BARC study includes domestic commercial and research
facilities and international research laboratories from the UK, the Netherlands
and the US. Future round robin studies are planned by the group in order to