Bioavalibility in Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 736

Table 16.3 Outline of some principal studies that employed chemical solvents to evaluate
bioavailability of organic contaminants

Contaminant Solvent Bioassay Operation Comments

Atrazine,
Phenanthrene
(Kelsey and
Alexander 1997 )

Methanol/water,
n-Butanol

Earthworm
uptake and
degradation.

25 ml solvent
and10g
solid.
Shaking for
2h.

Methanol/water
best predictor
for atrazine
whereas
n-butanol was
best for
phenanthrene.

DDT, DDE, DDD
PAH (mixture)
(Tang et al.
( 1999 , 2002 ))

THF, Ethanol Earthworm

uptake.

15-20 ml
solvent and
1 g soil, 10 s
of mixing.

Good correlation
with earthworm
accumulation.

Anthracene,
Fluoranthene,
Pyrene (Tang
and Alexander
( 1999 ))

n-Butanol
Propanol
Ethyl acetate

Plant retention,
earthworm
uptake and
microbial
degradation.

25 ml solvent
and 1-2 g
soil, 5 s of
mixing.

Reasonable
correlation with
bioassays.

Phenanthrene,
Pyrene,
Chrysene (Liste
and Alexander
( 2002 ))

n-Butanol Earthworm

uptake and
microbial
degradation.

15 ml
extractant,
5-10 g soil,
mixing: 5 s
(worm) or
120 s (degra-
dation).

Applicable for
bioavailability
prediction.

Taken from Jensen and Mesman ( 2006 )

Non-depleting procedures measure chemical activity of a contaminant in soil,
whereas depleting procedures measure the bioaccessible fraction of a contami-
nant. Examples of equilibrium based procedures are negligibly depleting solid
phase micro extraction (nd-SPME) (see details later) and extraction with poly-
oxymethylene strips, triolein-embedded cellulose acetate membranes, and hollow
fibre supported liquid membranes. Depleting extraction procedures include, for
example, Tenax beads and

β

-cyclodextrin. The later biomimetic extractions are
based on the principle that organisms predominantly take up contaminants from the
pore water and thereby temporarily deplete the pore water, which again is rapidly
replenished with contaminants desorbing from the solid phase.
Reid et al. ( 2000 ) propose shaking soil with an aqueous solution of

hydroxypropyl- -cyclodextrin (HPCD), a large molecule with a hydrophilic exte-

rior surface and a hydrophobic cavity within the molecule. Reid et al. ( 2000 ) report
good correlation between HPCD extractable polycyclic aromatic hydrocarbons
(PAHs) and biodegradation of PAHs (and thus bioavailability) by microorganisms.
Cuypers et al. ( 2002 ) also report good correlations. An alternative approach to assess
bioavailability/bioaccessibility has been the use of C18 membrane disks, which
are placed in the soil and then removed and purged. The amounts of contaminant
extracted have shown good correlations between, for example, extractable DDT,

β