Pore water and accesible concentrations of hydrophobic contaminants in Danube river sediments
estimated by multi-ratio equilibrium passive sampling


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


1Masaryk University, Research Centre for Toxic Compounds in the Environment, Kamenice 753/5, 625 00
Brno, Czech Republic

belhacova@recetox.muni.cz, vrana@recetox.muni.cz,

rusina@recetox.muni.cz, smedes@recetox.muni.cz



The information about total concentration of persistent organic pollutants (POPs) in sediment is
not adequate to assess the risks linked with sediment contamination. A fraction of POPs may be
adsorbed to sediment very firmly (amourphous organic carbon - different types of black carbon) or
cannot be released (1) while it is the concentration released to the aqueous phase, actually the
POP’s concentration, that pose the risk to the surrounding environment. (2) Freely dissolved
concentrations in pore water are directly proportional to chemical activity, i. e. also driving
force of POPs accumulation in organisms and diffusive transport. As a result of the presence of a
strongly bound POPs fraction in sediment, the contaminants concentration in pore water may be
significantly lower than estimated using equilibrium partitiong models from total concentration and
generic partition coefficients.

Freely dissolved concentrations in pore water (Cw) as well as the accessible/releasable (CAS)
concentrations in the sediment can be determined by equilibration of a partitioning passive sampler
(silicone rubber polymer with a high sorption capacity for non-polar compounds) with sediment using
various sampler−sediment ratios. (3) This method allows construct a sorption isotherm yielding the
concentration in the pore water at low sampler/sediment ratio (minor depletion of the sediment
phase) or at high sampler/sediment ratio (maximum depletion of the sediment phase) - the accesible
concentration in the sediment (3).

We demonstrated the application of the multi-ratio equilibrium passive sampling method (five
different sampler-sediment phase ratios rating from 0.0005 to 0.2) to measure freely dissolved
concentrations and accesible concentrations of polycyclic aromatic hydrocarbons (PAHs),
organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), musks and alkylphosphates and
their total concentrations in the sediments that were collected at 9 locations of the Danube
river. The comparison of obtained freely dissolved concentrations in porewater and the water column
in the river allow to assess the potential of riverbed sediments to spontaneously release or
accummulate contaminants to/from the water column. The accessible concentrations provide the
information of contaminant pool in sediment available for a spontaneous exchange with the
surrounding environment.


(1) Cornelissen G., Gustafsson Ö. ̈, Bucheli T. D., Jonker M. T. O., Koelmans A. a., and Van Noort
P. C. M., Extensive sorption of organic compounds to black carbon, coal, and kerogen in sediments
and soils: Mechanisms and consequences for distribution, bioaccumulation, and biodegradation,
Environ. Sci. Technol., 2005, 39, 6881–6895.


(2) Reichenberg F. and Mayer* P., Two Complementary Sides of Bioavailability: Accessibility and
Chemical Activity of Organic Contaminants in Sediments and Soils, Environ. Toxicol. Chem., 2006,
25,

1239.


(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.