Bioavalibility in Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 722

Contents

16.1 Introduction ........................................... 722

16.2 What is Bioavailability? .................................... 723

16.3 Impact of Soil Properties on Bioavailability ........................

724

16.3.1 Metals and Metalloids ................................

725

16.3.2 Organic Contaminants ................................ 727

16.4 Measurement of Bioavailability ............................... 732

16.4.1 Extractions for Determining Bioavailability ................... 732

16.4.2 Modelling the Bioavailability of Contaminants .................

737

16.5 Concluding Remarks ..................................... 741

References ................................................

741

16.1 Introduction

The initial measurements of contaminants during site investigation are usually total
concentrations of contaminants. However, it is usually the “bioavailable” fraction
that is relevant to whether the contaminants present in a soil pose a hazard or not.
A search on the Internet based search engine Web of Knowledge for peer-reviewed
journal articles concerned with “Bioavailability” and “Soil” returns 7703 entries
with a near perfect linear increase in journal articles for over a decade ( y 55 x

- 109969, p < 0.001 as of August 2008!). Add to this the vast number of govern-
ment and agency reports that exist on the subject and the reader will appreciate
that this chapter can not be fully exhaustive on its subject! Given the large amount
of research effort and funding that has been expended on the subject it is perhaps
surprising that there is neither a universally accepted definition of bioavailability
nor a standardized means of measuring it. This deficiency reflects in part the com-
plexity and diversity of the soil system and in part the legislative requirements of
different jurisdictions. This chapter aims to summarise for organic and inorganic
substances: (1) current thoughts on what bioavailability is, (2) how soil properties
impact bioavailability and, (3) methods for measuring and predicting bioavailabil-
ity. Covered elsewhere in this topic, but of relevance to bioavailability, are chapters
on oral bioavailability to humans (see Chapter 7 by Wragg et al., this topic), uptake
of metals from soil into vegetables (see Chapter 8 by McLaughlin et al., this topic)
and uptake of organic contaminants from soil into vegetables (see Chapter 7 by
Trapp and Legind, this topic). Besides, bioavailability is relevant for site specific
ecological Risk Assessment (see Chapter 15 by Rutgers and Jensen, this topic).
From the perspective of contaminated sites and their remediation the important
question is not “How bioavailable is a particular element?” but, “Will this contami-
nant have a toxic effect at this soil concentration on this organism or other receptor?”
Clearly bioavailability is an important part of this question but for the assessment
of contaminated sites bioavailability needs to be tied to a consideration of toxic
effects or legislatively permissible concentrations of contaminants in selected target
organisms.

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