Environmental Toxicology and Chemistry, Vol. 28, No. 4, pp. 733–740, 2009
? 2009 SETAC
Printed in the USA
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A PASSIVE SAMPLER BASED ON SOLID-PHASE MICROEXTRACTION FOR
QUANTIFYING HYDROPHOBIC ORGANIC CONTAMINANTS IN SEDIMENT
KEITH A. MARUYA,*† EDDY Y. ZENG,‡ DAVID TSUKADA,† and STEVEN M. BAY†
†Southern California Coastal Water Research Project, 3535 Harbor Boulevard, Suite 110, Costa Mesa, California 92626, USA
‡State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences,
Guangzhou 510640, China
(Received 11 July 2008; Accepted 22 October 2008)
Abstract—Sediment-quality assessment often is hindered by the lack of agreementbetween chemicalandbiologicallinesofevidence.
One limitation is that the bulk sediment toxicant concentration, the most widely used chemical parameter, does not always represent
the bioavailable concentration, particularly for hydrophobic organic compounds (HOCs) in highly contaminated sediments. In the
present study, we developed and tested a pore-water sampler that uses solid-phase microextraction (SPME) to measure freely
dissolved (bioavailable) HOC concentrations. A single polydimethylsiloxane (PDMS)-coated SPME fiber is secured in a compact,
protective housing that allows aqueous exchange with whole sediment while eliminating direct contact with sediment particles.
Fibers with three PDMS coating thicknesses were first calibrated for 12 model HOCs of current regulatory concern. Precalibrated
samplers were exposed to spiked estuarine sediment in laboratory microcosms to determine the time to equilibrium and the
equilibrium concentrations across a range of sediment contamination. Time to equilibrium ranged from 14 to 110 d, with 30 d
being sufficient for more than half the target HOCs. Equilibrium SPME measurements, ranging from 0.009 to 2,400 ng/L, were
highly correlated with but, in general, lower than HOC pore-water concentrations determined independently by liquid–liquid
extraction. This concept shows promise for directly measuring the freely dissolved concentration of HOCs in sediment pore water,
a previously difficult-to-measure parameter that will improve our ability to assess the impacts of contaminated sediments.
Sediment pore water
Persistent organic pollutants BioavailabilitySolid-phase microextraction
Accumulation of hydrophobic organic compounds (HOCs)
to high levels in sediments poses a risk to both ecological and
human health via direct and indirect pathways. Some legacy
HOCs (e.g., chlordane) may be toxic to benthic organisms that
inhabit contaminated sediments, whereas marine and terrestrial
mammals (including humans) are indirectly exposed to HOCs
via food-web transfer. The biomagnification of toxicants like
DDT, polychlorinated biphenyls (PCBs), and polybrominated
diphenyl ethers can result in and/or exacerbate reproductive
and immunosuppressive impacts. The bulk sediment concen-
tration is a logical and, thus, commonly used indicator of po-
tential HOC exposure for benthic organisms. Coupled with
biological endpoints like benthic community condition and
toxicity (e.g., median lethal concentration), bulk sediment
chemistry has been widely used in sediment-quality assess-
ment [1,2]. To account for the affinity of HOCs with organic
matter , models relating aqueous- and solid-phase parti-
tioning were created to help explain differences in bioavail-
ability observed in ecotoxicological endpoints .
More recently, heterogeneity within the organic subcom-
ponent of soils and sediments has been shown to have a pro-
found effect on the partitioning and bioavailability of HOCs.
Condensed, sooty materials, known collectively as black car-
bon (BC), were shown first to reduce the bioavailability of
PAH in contaminated harbor sediments  and subsequently
to influence similarly the bioavailability of PCBs  as well
* To whom correspondence may be addressed
Published on the Web 11/20/2008.
as legacy and current-use, chlorinated pesticides . The ef-
fectiveness of BC in altering HOC bioavailability, at least in
the short term, has resulted in its consideration for remedial
strategies for highly contaminated sediments . A growing
body of evidence suggests that the freely dissolved phase of
HOCs (Cfree) represents the highly bioavailable fraction [9,10].
Determination of this parameter, however, must be made at
ultralow levels, and it is made difficult by the presence of
dissolved organic matter (DOM), a competing binding phase
for HOCs in natural waters , including sediment interstitial
or pore water . Because separation of freely dissolved from
colloidal and particulate HOC fractions is exceedingly diffi-
cult, little data are available, and measurements of total aque-
ous HOC concentrations are much more common. Unfortu-
nately, this latter parameter can be of limited utility in quan-
tifying bioavailable HOCs.
Solid-phase microextraction (SPME) is a passive sampling
technology  that senses Cfreein complex aqueous matrices
. As evidence, in situ samplers with polydimethylsiloxane
(PDMS)-coated SPME fibers  were deployed for several
weeks in coastal seawater . Subparts-per-trillion concen-
trations of DDT as determined by this sampler agreed well
with independently measured, operationally defined, dis-
solved-phase measurements. Based on this concept, a mass-
balance and partitioning model predicted that the minimum
sediment volume required to maintain nondepletive conditions
for a SPME-based, pore-water sampler was independent of
HOC concentration (both solid and aqueous phases) and that
relatively small sediment volumes (?10 ml) participated in
exchange equilibria . More importantly, that work also
demonstrated that sub-ng/L detection limits were possible for
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