Oral Bioavailability - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 288

7.4 Examples of Bioaccessibility Studies ............................

309

7.4.1 Geogenic Sources .................................... 310

7.4.2 Anthropogenic Influences ............................... 311

7.5 The BARGE Network ...................................... 312

7.5.1 Inter-Laboratory Studies ................................

313

7.5.2 Utilization of Bioaccessibility Data Across Europe ................

315

References ................................................ 316

7.1 Theory of Availability

Soil ingestion (see Chapter 6 by Bierkens et al., this topic; Pausten bach 2000 )is
a key exposure pathway in Human Health Risk Assessment (HHRA) for contami-
nants in soil (see Chapter 5 by Swartjes and Cornelis, this topic). To date, research
regarding the human bioavailability of soil contaminants, via the ingestion exposure
pathway, has concentrated on inorganic contaminants, and therefore this chapter
is focussed on these contaminants. The priority inorganic contaminants have been
arsenic (Beak et al. 2006 ; Bruce et al. 2007 ; Davis et al. 1996a ; Ellickson et al.
2001 ; Juhasz et al. 2008 ; Koch et al. 2005 ; Palumbo-Roe and Klinck 2007 ;Laird
et al. 2007 ; Roberts et al. 2007b ; Wragg et al. 2007 ) and lead (Abrahams et al.
2006 ; Denys et al. 2007 ; Drexler and Brattin 2007 ; Hamel et al. 1999 ; Oomen et al.
2002 ; Ren et al. 2006 ; Ruby et al. 1993 , 1999 ; Van de Wiele et al. 2005 , 2007 ),
but work has been carried out on other metals such as cadmium (Tang et al. 2006 ),
chromium (Fendorf et al. 2004 ; Nico et al. 2006 ; Pouschat and Zagury 2006 ;Stewart
et al. 2003a , b ), nickel (Barth et al. 2007 ; Hamel et al. 1998 ; Hansen et al. 2007 )
and mercury (Cabanero et al. 2007 ; Davis et al. 1997 ). As such, the inorganic con-
taminants referred to in this chapter include metals and metalloids such as arsenic,
lead, cadmium, chromium and nickel, but not contaminants such as cyanide. For the
organic contaminants, recent insights and projects have concentrated on polyaro-
matic hydrocarbons (PAHs) (Gron 2005 ; Tilston et al. 2008 ) and dioxin and furans
(Wiettsiepe et al. 2001 ). However, for the degradable contaminants, the estimation
of the bioavailable fraction appears to be more complicated than for inorganic con-
taminants, as the metabolites and degradation products of these contaminants have
to be taken into consideration. For example, Van de Wiele et al. ( 2005 )showed
that colon microbiota plays an important role in the biodegradation of PAH, thus
influencing the outcomes of the bioaccessibility measurement undertaken.
In Risk Assessments using exposure models, it is often assumed that inorganic
contaminants ingested via soil are absorbed to the same extent as the available form
that was used during the toxicological assessment. Thus, assuming that the rate of
absorption of ingested metal is independent of the matrix in which it is included
and of its chemical form (speciation). However, the binding of inorganic contami-
nants to solid phases in soils may render them unavailable for absorption; similar
mechanisms have been extensively shown to modulate uptake of metals by plants
and metal speciation plays an important part in the uptake process (see Chapter 8 by
McLaughlin et al., this topic).