Oral Bioavailability - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 307

Cebus monkey dosing trial, consistently overpredicting the bioavailability, result-
ing in an unacceptably large uncertainty. Juhasz et al. ( 2007 ) found that they could
model the in-vitro bioaccessibility of soils contaminated by arsenic from herbicides,
pesticides and mining waste, using the total arsenic content and total or dithion-
itecitrate extractable (free) iron. However, the bioaccessible content of a naturally
mineralised site could not be modelled in this way. In a quite different approach a
self-modelling mixture algorithm was used (Cave et al. 2007 ) to convert raw Near
Infra-Red (NIR) spectra of soils, developed over Jurassic ironstones, into five under-
lying spectral components and associated coefficients. The five spectral components
were shown to be significantly correlated to the total arsenic, bioaccessible arsenic
and total Fe-contents of the soils and tentatively assigned to crystalline Fe oxides,
Fe oxyhydroxides and clay components in the soils. A linear regression model,
using the spectral component coefficients associated with the clay fraction, the Fe
oxyhydroxides and the total arsenic content of the soils as independent variables,
was shown to predict the bioaccessible arsenic content of the soils, as measured
by an in-vitro laboratory test, with a 95% confidence limit of 1.8 mg kg − 1 and a ±

median R 2 value of 0.80.

7.2.7 Soil Sampling and Preparation
for Bioaccessibility/Bioavailability Measurements

In order for the final results of bioaccessibility/bioavailability testing to be
meaningful the samples under investigation need to be representative of the
sampling location and the grain size applicable to the resulting Human Health Risk
Assessment. As such, a number of sampling and preparation considerations need to
be met as part of the underlying analytical protocol.
Prior to soil sampling, consideration should be given to:

• the history of the location - including the effect of the local geology and or

historical anthropogenic contamination and the potential effect of contaminant
'hotspots';

• the equipment to be used to collect the samples - clean, high quality sampling

tools and containers in order to avoid sample contamination;

•

the number of samples to be collected per averaging zone; Nathanail ( 2009 ) rec-
ommend a minimum of 10 samples in order to 'gain and adequate appreciation
of the variation in bioaccessibility'. However, when considering in-vivo bioavail-
ability measurements, the cost of testing may be the driving force in determining
the number of samples, per location, to be collected;

• the depth at which samples are collected - surface soil samples from 0 to 15 cm

depth, as these are representative of the material to which humans are likely to be
exposed (Cave et al. 2003 );

• the variation of soil composition and resulting bioaccessibility across site,

therefore separate bioaccessibility sampling areas will be required for each soil
type represented;