Competition between phenanthrene, chrysene, and 2,5-dichlorobiphenyl for high-energy adsorption sites in a sediment.

We determined the maximum amounts of added phenanthrene, chrysene, and 2,5-dichlorobiphenyl sorbed onto high-energy adsorption sites in a sediment on bi-solute experiments. The bi-solute pairs were phenanthrene/chrysene and phenanthrene/2,5-dichlorobiphenyl. On the bi-solute sorption experiments, one solute was introduced and equilibrated with sediment prior to addition of the second solute.

Gibbs free energies for dual Langmuir-like adsorption onto hard carbon materials in sediment and soils.

Adsorption of organic compounds onto hard carbon constituents of soils and sediments may be described by a dual Langmuir-like equation for adsorption onto high-energy sites and low-energy sites. To describe quantitatively the sorbate-sorbent interactions on these high-energy sites and low-energy sites, Gibbs free energies for adsorption onto several soils and sediments were calculated using suitable experimental sorption data from the literature. A large part of the variation in these Gibbs free energies relative to the pure solid state appeared to be related to differences in sorbate molecular symmetry.

Estimation of polychlorinated biphenyl fugacity ratios.

On the quantitative comparison of solubilities or vapor pressures of homologous series, the variation in the effect of crystal structure on solid properties may substantially influence the outcome of the comparison. Usually, the effect of this variation is eliminated by comparing values of the liquid state. The ratio of solid to liquid properties is called the fugacity ratio.

Kinetics of adsorption and desorption of some organochlorine compounds on black carbon in a sediment.

Rate constants for adsorption and desorption of four organochlorine compounds on black carbon in a sediment were determined from measurements of the rate of removal, by gas purge, of the organochlorine compounds as single solutes from a water-sediment mixture immediately after addition of the solute to the system. The rates of removal fitted to a kinetic scheme based on Langmuir adsorption onto two types of sites in black carbon. The first-order rate constants for desorption from these sites were comparable to those for slow and very slow desorption from sediment.

Quantification of total native compounds on phenanthrene-specific adsorption sites in the very slow desorption domain of 16 sediments and soils.

We determined the maximum amount of added phenanthrene that could be adsorbed in the very slow desorption domain of 16 sediments and soils with and without native compounds present. The differences in the amount of phenanthrene taken up in this domain with and without native compounds present indicates to what extent native compounds occupy those adsorption sites in the very slow desorption domain which may accommodate phenanthrene. For the two aquifer materials, presence of native compounds was less than the uncertainty associated with the methodology.

Sorbate size-dependent maximum capacities for adsorption of organic compounds in the slowly and very slowly desorbing domains of a sediment.

Maximum capacities were determined for adsorption of six polycyclic aromatic hydrocarbons, seven polychlorinated biphenyls, and five chlorobenzenes in both the slowly desorbing domain and the very slowly desorbing domain of a sediment. For separate compound classes in the two desorption domains, log-transformed maximum adsorption capacities were linearly related to the relative magnitude of the shadow of the sorbate on an imaginary planar surface. For planar compounds, the ratio of maximum adsorption capacities for the slowly desorbing domain and the very slowly desorbing domain was approximately two.

Climate change and effects on water quality: a first impression.

A number of possible relationships between climate change and water quality of Dutch surface waters have been investigated and an indicative quantification of the impact of climate change on water quality has been established. The analysis focused on water quality during periods of low flow and extreme heat, which are assumed to increase in frequency and intensity due to climate change. The results indicate that the impact of climate change on water quality cannot be generalised and should be assessed on a case by case basis.

Maximum capacities for adsorption of phenanthrene in the slowly and very slowly desorbing domains in nineteen soils and sediments.

The maximum amounts of phenanthrene that can be taken up in both the slowly desorbing domain and the very slowly desorbing domain of 19 soils and sediments were determined by measuring the desorption of phenanthrene added at high loadings associated with equilibrium concentrations in water close to the aqueous solubility of phenanthrene. For two soils and one sediment, literature values for Langmuir phenanthrene adsorption capacities were available. These values were almost equal to the sum of the maximum amounts taken up in the slowly and in the very slowly desorbing domain.

Modeling maximum adsorption capacities of soot and soot-like materials for PAHs and PCBs.

Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van derWaals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions.

Fugacity ratio estimations for high-melting rigid aromatic compounds.

Prediction of the environmental fate of organic compounds requires knowledge of their tendency to stay in the gas and water phase. Vapor pressure and aqueous solubility are commonly used descriptors for these processes. Depending on the type of distribution process, values for either the pure solid state or the (subcooled) liquid state have to be used.

Policy development for the reduction of pollution caused by traffic experiences from The Netherlands.

Road traffic is a diffuse source of heavy metals and oil that leads to pollution of verges and surface water in areas immediately surrounding roads. The Commission for Integrated Water Management (CIW) has drawn up a policy document addressing methods for managing this type of pollution. The document is based on results from numerous studies in The Netherlands targeting pollution caused by traffic.

Removal of indigenous compounds to determine maximum capacities for adsorption of phenanthrene by sediments.

The maximum amounts of phenanthrene that can be adsorbed in both the slowly desorbing domain and the very slowly desorbing domain of two sediments were determined. To this end, native compounds were removed by mild solvent extraction, heating, or extraction by Tenax. Maximum capacities for adsorption of phenanthrene in the very slowly desorbing domain after removal of native compounds by heating the sediments at 300 degrees C for 24 h were comparable to those after extraction with Tenax at 60 degrees C for 13 days.

Tenax extraction mimics benthic and terrestrial bioavailability of organic compounds.

Biota to sediment accumulation factors (BSAFs) are widely used to describe the potential accumulation of organic contaminants in organisms. From field studies it is known that these BSAFs can vary dramatically between sediments of different origin, which is possibly explained by the variation in bioavailability of organic contaminants in sediments. In the present study it is shown that the variability in BSAF values for different sediment samples obtained at two Dutch freshwater sites could largely be explained by the variation in Tenax-extractable concentrations in these sediments.

Competition for adsorption between added phenanthrene and in situ PAHs in two sediments.

A study was performed on the influence of the addition of a relatively large amount of phenanthrene to two in situ contaminated sediments on the fractions of native PAHs in both the slowly desorbing domain and the very slowly desorbing domain in comparison to the undisturbed situation. Added phenanthrene was found to be present in both the slowly desorbing domain and the very slowly desorbing domain. The extent of removal of native PAHs from the very slowly desorbing domain induced by the presence of a large excess of phenanthrene was in line with expectations based on the incubation time and the rate constants for desorption of native PAHs from the very slowly desorbing domain.

A thermodynamics-based estimation model for adsorption of organic compounds by carbonaceous materials in environmental sorbents.

A model was developed to estimate Langmuir affinities for adsorption of low-polarity organic compounds from either water or air by carbonaceous sorbents. Sorption enthalpies and entropies provided the basic information for the description of sorption affinities in terms of the entropy of melting and either solubility in water or vapor pressure. For m-xylene, polycyclic aromatic hydrocarbons (PAHs) and chlorobenzenes on 10 different sorbents, 80% of the measured sorption affinities fall within a factor of four of the model estimates.

Slow and very slow desorption of organic compounds from sediment: influence of sorbate planarity.

The kinetics of desorption of in situ chlorobenzenes, PAHs, and PCBs from four different sediments was studied employing Tenax beads as an infinite sink for sorbates. Rate constants for slow desorption were 2.9+/-0.

Measurement of heavy metal speciation over redox gradients in natural water-sediment interfaces and implications for uptake by benthic organisms.

The sediment or fauna incubation experiment (SOFIE) is an experimental research tool that was developed to analyze concentrations and chemical speciation of heavy metals in pore waters of natural, undisturbed sediments or water-sediment interfaces over time, while simultaneously conducting exposure tests with sediment-dwelling organisms. In this way, concentrations of chemical species are directly linked to accumulation by biota. It is shown that discrete gradients of redox-sensitive metals and nutrients occur over very small intervals.

Influence of sorbate planarity on the magnitude of rapidly desorbing fractions of organic compounds in sediment.

Organic compounds in sediments are known to distribute between rapid, slowly, and very slowly desorbing sites. This distribution is relevant to bioavailability and risk assessment of organic compounds in sediment. In this study, the fraction desorbing to Tenax in 6 h was measured for a range of organic compounds in sediment differing in their extent of planarity.