No abstract

Pollutants in aged field sediments seem to differ from spiked sediments in their chemical and biological availability. Biphasic desorption is often used as an explanation. In the present study, desorption kinetics and partitioning of chlorobenzenes (CBs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) in long term field contaminated sediment cores and top layer sediment were measured by gas-purging. Desorption from sediment was deduced to be triphasic:  fast, slowly, and very slowly desorbing fractions were distinguished. In both the sediment core and the top layer sediment no detectable fast fractions were present for all the compounds studied, so these were estimated as upper limits from the desorption curves. This observation coincided with very high in situ distribution coefficients for several PCBs and PAHs:  10−1000 times higher than literature values for short contact time experiments. Rate constants were (3−8) × 10-3 h-1 for slow desorption and (0.16−0.5) × 10-3 h-1 for very slow desorption. In some cases only a very slowly desorbing fraction was detectable. Desorption from field contaminated sediments with extended contact times may not be readily estimated from laboratory experiments in which contaminants have contact times with the sediment in the order of weeks.

Aqueous solubilities, n-octanol/water partition coefficients (K ow s), and Henry's law constants were determined for a range of polycyclic aromatic hydrocarbons (PAHs) using a generator-column, slow-stirring, and gas-purge method, respectively. The currently obtained data were compared to available literature data. For seven of the PAHs no K ow s previously were determined with the slow-stirring method. For four of the PAHs the present study reports the first experimental Henry's law constants. Relationships between subcooled liquid solubilities, K ow s, and Henry's law constants as a function of molar volume are discussed. A consistent data set was obtained, for which an excellent correlation was found between subcooled liquid solubility and molar volume. A linear fit did not accurately describe the relationship between log K ow and molar volume. This is probably due to a decreasing solubility in n-octanol with increasing molar volume. Finally, a high correlation was found between Henry's law constant and molar volume. The presently obtained dataset can be used to predict the fate and behavior of unsubstituted homocyclic PAHs.

Henry's law constants for 11 polychlorinated biphenyls (PCBs) were measured using a gas purge system at 20 °C. The studied PCB congeners ranged from 2,4,4‘-trichlorobiphenyl to 2,2‘,3,4,4‘,5,5‘-heptachlorobiphenyl, spanning a range of hydrophobicities and solubilities, and including four mono-, and seven di-ortho-chlorinated compounds. For four PCBs, Henry's law constants have not been published before. These are 2,3,5,6-tetrachlorobiphenyl, 2,3,4,5,6-pentachlorobiphenyl, 2,2‘,3,4,4‘,5-hexachlorobiphenyl, and 2,3,3‘,4,4‘,5-hexachlorobiphenyl. For the lower chlorinated PCBs, the values are in agreement with available literature data. The values for the higher chlorinated PCBs agreed well with other partitioning data for PCBs and are lower than most available literature data. The measured Henry's law constants decreased with increasing hydrophobicity and showed a high correlation with the number and position of the chlorine atoms. The methods used are suitable for measuring reliable Henry's law constants and also for the higher chlorinated PCB congeners.

It is argued that the aspects of intergroup relations that potentially can arouse emotions in the perceiver are likely to become central and motivationally relevant elements of group stereotypes. Asking participants to report on the perceived antecedents of their emotional reactions to in-group and out-group members should therefore be an especially useful method to reveal the content of stereotypes. Native Dutch participants reported both the frequencies with which different emotions were felt in different intergroup relations and the perceived causes of these emotions. Analysis of self-reported antecedents of emotional reactions revealed that (a) despite a general in-group favourability bias, both the in-group and the two out-groups employed arouse different kinds of negative and positive emotions; and (b) differences in emotional reactions to the two out-groups are related to salient differences in perceived antecedents between these groups. Theoretical and practical implications of the present emphasis on the cognitive foundation of emotion in intergroup relations are discussed.