Application of cosolvent  to reduce  equilibration time of passive sampling for monitoring
porewater concentrations of POPs in freshwater sediments


MICHAELA BELHÁČOVÁ^1, BRANISLAV VRANA^1, TATSIANA RUSINA^1, FOPPE SMEDES^1


^1Research Centre for Toxic Compounds in the Environment, Kamenice 753/5, 625 00 Brno, Czech
Republic, belhacova@recetox.muni.cz



The freely dissolved concentration of POPs in pore water (C[W]) has shown to be a better predictor
of internal concentration in benthic organisms and sediment toxicity than total concentrations in
sediment [1,2]. C[W] is directly proportional to chemical activity, i. e. the driving force of POPs
accumulation in organisms and spontaneous diffusive transport between environmental compartments.
Freely dissolved concentration in pore water can be determined by equilibration of a passive
sampler, (e.g. an organic polymer)  with sediment. Provided equilibrium was attained and the
sediment was not significantly depleted, the C[W] can be estimated from the  measured concentartion
in the sampler and the passive sampler-water partition coefficient [3]. Attaining equilibrium for
highly hydrophobic contaminants in a practical time span is a difficult task because the uptake
rate by nonpolar passive sampler is limited by diffusive transport through water boundary layer at
sampler surface and very low solubility of POPs in water. The uptake rate can partly be speed up by
the intensive shaking of the sediment slurry. Application of thinner sampler films, e.g. micromiter
thin, reduces the equilibrium time. Nevertherless, those actions only partly solve the problem.
Secondly, solubility of hydrophobic contaminants in water can be increased by addition of
modifiers, e.g. methanol, 2-hydroxypropyl-beta-cyclodextrin (HPCD) [4] that subsequently results in
an increased transport through the water phase.

In the present study we used silicone rubber as passive sampler known to have high permeability for
hydrophobic contaminants. Solubilty of POPs in water was increased by addition of methanol. The
results show that addition of methanol up to 40% of water content in a freshwater sediment slurry
from Morava river, Czech republic resulted indeed in faster equilibrium compared to water only for
most of POPs (PAHs, PCBs, PBDEs). The addition of methanol did not affect the sediment/sampler
distribution of the POPs. Therefore, derived porewater concentrations of POPs in a sediment with
and without addition of methanol were not significantly different.


References:


1. Burgess, R.M.; Berry, W.J.; Mount, D.R.; Di Toro, D.M. Mechanistic sediment quality guidelines
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2. Kraaij, R.; Mayer, P.; Busser, F.J.M.; Bolscher, M.V.; Seinen, W.; Tolls, J. Measured pore-water
concentrations make equilibrium partitioning work - A data analysis. Environ. Sci. Technol. 2003,
37 (2), 268-274.


3. Smedes F., van Vliet L. A., and Booij K., Multi-ratio equilibrium passive sampling method to
estimate accessible and pore water concentrations of polycyclic aromatic hydrocarbons and
polychlorinated biphenyls in sediment., Environ. Sci. Technol., Jan. 2013, 47, 510–7.


4. Gouliarmou, V. and Mayer, P. Sorptive Bioaccessibility Extraction (SBE) of Soils: Combining a
Mobilization Medium with an Absorption Sink. Environ. Sci. Technol. 2012, 46 (19), 10682-10689;
10.1021/es301515s.


Acknowledgments:

We acknowledge the SOLUTIONS Project supported by the European Union Seventh Framework Programme
(FP7-ENV-2013-two-stage Collaborative project) under grant agreement 603437 and the International
Comission for the Protection of the Danube River (ICPDR) for the financial support. The RECETOX
research infrastructure was supported by the projects of the Czech Ministry of Education (LO1214)
and (LM2011028).