Paul C.M. van Noort

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. Variations of a factor of about 50 could be explained. The ratio between concentrations in biota and Tenax-extractable concentrations in sediment varied slightly between sediments and contaminant class, but was close to the theoretically expected value of 2. This is a strong indication that Tenax-extractable concentrations of contaminants in sediments are an excellent indicator of available concentrations.

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+/-0.4 x 10(-2) x h(-1), irrespective of the extent of sorbate planarity. Rate constants for very slow desorption were 2.1+/-0.5 x 10(-4) and 6.7+/-1.4 x 10(-4) x h(-1) for planar and non-planar compounds, respectively. Comparison with literature data suggests a priori estimates for rate constants for slow desorption to be 3 x 10(-2) x h(-1), and to be 2 x 10(-4) and 7 x 10(-4) x h(-1) for very slow desorption of planar and non-planar compounds, respectively. The ratio between the fractions in the very slowly desorbing domain and the rapidly desorbing domain was 15-38 for planar compounds which is higher than for non-planar compounds for which the ratio was 2.8-5.2. The ratio between the fractions in the slowly desorbing domain and the rapidly desorbing domain was 1.3-1.8 and independent of the sorbate planarity. The difference in influence of sorbate planarity on the very slowly desorbing domain as compared to the slowly desorbing domain points to different environments for the slowly and the very slowly desorbing fractions.

Two-stage desorption kinetics and in situ partitioning of hexachlorobenzene and dichlorobenzenes in a contaminated sediment

The desorption kinetics of in situ hexachlorobenzene (HCB), 1,3-dichlorobenzene (1,3-DCB) and 1,4-dichlorobenzene (1,4-DCB) from a sediment were determined by a method in which the aqueous phase was kept solute-free with Tenax TA beads. Slowly desorbing fractions were 47–98% for HCB, 58–76% for 1,3-DCB and 36–63% for 1,4-DCB. Also, in situ partition coefficients (Kocin situ) were measured; they were 0.24–1.4 log-unit higher than literature Koc-values measured using short-term laboratory incubations Koc values for the rapid fractions (Kocrap), calculated with Kocin situ and the rapidly desorbing fractions, were similar to literature Koc values. From this, it is concluded that the slowly desorbing contaminant fractions and the fractions not available for rapid equilibrium partitioning are the same.

Estimation of amorphous organic carbon/water partition coefficients, subcooled liquid aqueous solubilities, and n-octanol/water partition coefficients of nonpolar chlorinated aromatic compounds from chlorine fragment constants

This study aims to derive the relation between the number of chlorine atoms in chlorobenzenes, polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) and logK(oc) for linear partitioning between water and average amorphous organic carbon in soils or sediments. Because reliable determinations of logK(oc) are relatively sparse for chlorobenzenes and PCBs, and are even absent for PCDDs and PCDFs, a work-around solution was developed: First, the relation of n-octanol/water partitioning (K(ow)) and (subcooled) liquid solubility (S(l)) to the number of chlorines was investigated. Slopes for the linear correlation of logK(ow) with the number of chlorines (corrected for the number of ortho-chlorines in the case of PCBs) appeared identical for chlorobenzenes, PCBs, PCDDs, and PCDFs. Such was also the case for logS(l). Slopes for the linear relation of chlorobenzenes and PCB logK(oc) values with the number of chlorines were similar for the various soils and sediments, though intercepts were different. The ortho-chlorine correction factor for PCB logK(oc) was equal to the ortho-chlorine correction factor for PCB logK(ow) and logS(l). For PCDDs and PCDFs, a relation between logK(oc) and the number of chlorine atoms was derived by combining the chlorobenzenes/PCB logK(oc)-logK(ow) and logK(oc)-logS(l) relationships with logK(ow) (or S(l))-chlorine number relations for PCDDs and PCDFs.

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. In contrast, the addition of phenanthrene did not result in a removal of native PAHs from the slowly desorbing domain. This was tentatively explained by assuming that native PAHs in the slowly desorbing domain are at adsorption sites with dimensions specific to each PAH and which are, therefore, less suited to other PAHs.

Particle size dependence of slow desorption of in situ PAHs from sediments

Abstract The desorption kinetics of in situ contaminations of phenanthrene, anthracene, pyrene, benzo(a)anthracene, benzo(b)fluoranthene, and benzo(a)pyrene have been measured for four size fractions of three sediments, with a technique in which the porous polymer Tenax serves as an infinite sink for desorbed PAH. For one of the sediments, there appears to be a slight tendency of increasing (slowly + very slowly) desorbing fractions (F slow+very slw ) and decreasing first-order rate constants of slow desorption (k d, low ) with increasing particle size. However, for the two other sediments F slow+very slow and k d, slow showed no relation with particle size. F slow+very slow values ranged from 7 to 90% of the total extracted PAH amount; k d, slow ranged from 0.23·10 −3 h −1 to 1.52·10 −3 h −1 . The present results indicate that whole-particle size and, thus, overall particle size distribution are not determinants for the slow desorption of organic chemicals. This means that it is probably not diffusion on the whole-grain scale which determines slow desorption of organic compounds from sediments.

Estimation of amorphous organic carbon/water partition coefficients, subcooled aqueous solubilities, and n-octanol/water distribution coefficients of alkylbenzenes and polycyclic aromatic hydrocarbons

The aim of this work was to derive a relation between the number of specific carbon atoms in alkylbenzenes and PAHs and the average logK(oc) for linear partitioning between amorphous organic carbon in soils and sediments and water. The relation between the number of specific carbon atoms and n-octanol/water partitioning and subcooled aqueous solubility was sought first, as the number of data for partitioning into amorphous organic carbon was relatively sparse. It turned out that linear partitioning into amorphous organic carbon could be described by a linear relation based on the number of aromatic carbons, the number of alkyl carbons and the number of alicyclic carbons in the same way as for n-octanol/water partitioning and subcooled liquid aqueous solubility. From the linear regressions for linear partitioning into the various amorphous organic carbons, an average intercept for the linear partitioning regression equation was derived to represent average organic carbon in soils and sediments.

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. The time needed to reach apparent equilibrium in the experimental setup, with 10 g sediment/L water, ranged from 13 to 166 h, depending on the sorbate and the adsorption process. These short times to equilibrium suggest no need to assume rate-limiting diffusion from and to adsorption sites in this sediment. Average Gibbs free energies for adsorption of the four organochlorine compounds from the pure solid state were -10 +/- 3 and -20 +/- 3 kJ/mol for low-energy and high-energy sites, respectively, pointing to two different adsorption mechanisms.

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. This ratio was eightfold higher for strongly nonplanar polychlorinated biphenyls, which suggests that adsorption depends on sorbate thickness in the very slow desorption domain but not in the slow desorption domain. The rates of decrease of the log-transformed sum of maximum capacities for adsorption in the slow desorption domain and the very slow desorption domain with increasing relative magnitude of the shadow of the sorbate on a planar surface were similar to those derived from literature data regarding maximum capacities for adsorption onto a soil and a sediment. It is proposed that the rates of decrease for both the slow desorption domain and the very slow desorption domain may have general applicability to soils and sediments.

Wet deposition of polycyclic aromatic hydrocarbons in The Netherlands.

The concentrations of 11 polycyclic aromatic hydrocarbons (PAH) in rainwater at four locations in the Netherlands in 1983 are reported. From literature data for these PAH in air, scavenging ratios were calculated. For PAH predominantly adsorbed on aerosols these scavenging ratios are in the range 3-13 X 10(4). For phenanthrene the scavenging ratios are in the range 0.35-2.5 X 10(4). The data for the aerosol-associated PAH at the various locations are discussed in terms of aerosol in-cloud scavenging, and are compared with reported data from Belgium and Germany. The scavenging ratios for phenanthrene are compared with those predicted on the basis of Henrys law constant and were found to be less than one order of magnitude higher than expected, possibly because of enhanced aqueous solubility.