Bioavalibility in Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 721

Chapter 16
Bioavalibility in Soils

Mark E. Hodson, Martina G. Vijver, and Willie J.G.M. Peijnenburg

Abstract In this chapter we review and discuss the commonly used phrase or con-
cept “bioavailability”. This concept is key to Risk Assessment as it assesses what
proportion of a contaminant present at a contaminated site is available for uptake
by organisms and is thus potentially able to cause harm. Whilst this is a relatively
straightforward concept the reader will discover that in reality life is not that simple.
We start by reviewing the different definitions of bioavailability currently in use.
We go on to discuss how soil properties impact on the bioavailability of both metal,
metalloid and organic contaminants. Next we review the different methods people
currently use to determine bioavailability, concentrating on chemical extractions,
but also covering modelling approaches. We conclude that a precise definition of
bioavailability equally applicable to all different contaminated sites, contaminants
and organisms is unlikely to be achieved. Similarly, a single chemical extraction
is unlikely to give a universal measure of bioavailability. However, the message is
not all doom and gloom. On a contaminant by contaminant or species by species
level chemical extractions and other measurement techniques can accurately pre-
dict bioavailability. Modelling techniques are constantly improving and offer hope
for the future in terms of predicting bioavailability. At present however, the best
method of determining the amount of contaminant available for uptake by an organ-
ism is to measure the concentration of the contaminant in the organism. Even this
method, however, is open to question as organisms can and have evolved methods
of regulating metal uptake.