Oral Bioavailability - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 308

• the type of sample to be collected - grab or composite? Composite sampling is the

standard practice for geochemical surveying work (Kelleher 1999 ). Composite
sampling is analogous of making three replicate measurements of analytical
data and averaging the data point (Wragg 2005 ). However, 'hotspots' may be
missed or the contaminant concentration may be reduced as not all samples to be
composited have the same/similar contaminant concentration;

the preparation of the individual samples - samples should be dried at <35 ◦ C
and gently disaggregated, but never crushed, in order to break up large clasts
and homogenized. A representative portion of the bulk material should be
sub-sampled and sieved to <250

•

μ

m, as this fraction is considered to be
the upper limit of particle sizes that are likely to adhere to children's hands
(often the at risk receptor) (Duggan et al. 1985 ), and tested for its total and
bioaccessible/bioavailable contaminant content.

7.3 Considerations for the Potential Use of Site Specific
Bioaccessibility Measurements

Bioaccessibility measurements are not necessarily applicable to all contaminants, all
soil types and all Risk Assessment scenarios. The following key questions should
be considered before embarking on bioaccessibility testing:

• Is the contaminant concentration slightly above the guidance value for the soil

under consideration?
◦

Research in the UK (Cave et al. 2003 ; Nathanail and Smith 2007 ; Palumbo-
Roe and Klinck 2007 ; Palumbo-Roe et al. 2005 ; Wragg et al. 2007 ) has shown
that specific soil types have a well defined distribution of % bioaccessibility
values. Using this knowledge it is then possible to estimate the maximum total
soil concentration, for a soil type, where bioaccessibility data would assist the
assessment of risk. For example, in the Jurassic Ironstone soils in Lincolnshire
(Eastern England) the modal bioaccessible arsenic fraction is approximately
c. 10%. Working on a possible arsenic guideline value of 20 mg kg − 1 ,this
would suggest that a total arsenic soil concentration of up to 200 mg kg − 1
would be suitable for using bioaccessibility testing in a further detailed quan-
titative Risk Assessment. Whereas, dependant on the local federal guidelines
(i.e. Superfund site etc) a soil with a concentration of 1,000 mg kg − 1 arsenic
is unlikely to be suitable for bioaccessibility testing. If the concentration is
very high, this will override all subsequent points and bioaccessibility will no
longer be an option.

• Is remediation likely to be very expensive, unsustainable or not technically

feasible?
◦

For point source contamination, it is likely that remediation will only involve
a relatively small volume of contaminated material. However, for diffuse
contamination, particularly from natural geogenic sources, e.g. naturally