Agata Mechlińska

Sources and Fate of PAHs and PCBs in the Marine Environment

The assessment of a hazard resulting from the pollution of the environment by chemical compounds is in principle limited to the determination of their concentrations in its various compartments. But for solving many problems in this context, knowledge of the emission sources, transport pathways, and sites of deposition is of great benefit. By far the largest amounts of pollutants, regardless of where they were discharged, end up in the soil or the aquatic environment. By defining the source of origin of compounds like PAHs, and PCBs in the environment, especially in areas where they are emitted from different sources, it is possible to obtain information on the nature of different materials that are sources of these compounds (e.g., petroleum), or on the processes during which they are formed (e.g., combustion). In addition, the fate of toxic compounds in the environment can be tracked. This knowledge enables hypotheses to be formulated regarding the course of environmental phenomena; it also supplies a tool for taking administrative action and for resolving disputed issues concerning environmental pollution.

Polychlorinated biphenyls (PCBs) in bottom sediments: Identification of sources

Polychlorinated biphenyls (PCBs) can enter the environment from various sources. They are synthetic chemicals and as such are present in the environment mainly as mixtures containing various amounts of PCB congeners. It is therefore difficult to pinpoint the source of PCB emissions into the environment and the pathways along which they migrate there. The situation is different where locating the emission sources of polycyclic aromatic hydrocarbons (PAHs) is concerned. There is much information in the literature on the molecular markers that can be used to identify the sources of PAH emissions into the environment. Environmental samples like soil or bottom sediments are usually analysed for their contents of both groups of compounds. Therefore, with data on the origins of PAHs to hand, and seeking and comparing mutual correlations, one can attempt to define the probable sources of emission of PCBs. The purpose of this work was to identify the probable PCBs emission sources in bottom sediments using available data, that is polycyclic aromatic hydrocarbon diagnostic ratios. The numerical ratios of pairs of compounds such as fluoranthene/pyrene, phenanthrene/anthracene, fluoranthene/(fluoranthene+pyrene) and chrysene/benzo[a]anthracene are generally used as a tool for identifying and assessing pollution emission sources.

The effect of adding a standard on the result of determination of polychlorinated biphenyls in bottom sediment samples

Bottom sediments are a very important component of aquatic ecosystems. The sediment matrix is highly diverse and heterogeneous; in consequence, compounds entering the aquatic environment from different sources are considerably enriched at its surface. Bottom sediments are regarded as natural sorbents, since they accumulate many harmful substances, such as heavy metals and stable organic contaminants. Extraction is a key stage in every analytical procedure. It is during this stage that standards are added to samples. Standards are necessary not only for estimating analyte yields but also for validating the whole procedure. The question of the addition of standard substances to sediment samples has not been widely addressed in the subject literature, and yet it is of fundamental importance as regards obtaining reliable results of determinations. This paper describes the results of a study on the effect of standard addition techniques on the results of determination of polychlorinated biphenyls in sediment samples (certified reference material: METRANAL2-river sediment).

Comparison of Different Extraction Techniques of Polychlorinated Biphenyls from Sediments Samples

In this work, problems that may occur during determination of trace levels of polychlorinated biphenyls in sediment samples are described. Main error sources are connected with extraction of analytes prior to final determination. During model studies, polychlorinated biphenyls have been extracted from sediment reference material (METRANAL 2) with the use of different solvents (dichloromethane, hexsane, and toluene); the process has been enhanced by mechanical shaking or ultrasounds. Seven selected PCBs (PCB 28, 52, 101, 118, 138, 153, and 180 – according to IUPAC) were determined in extracts samples by GC–MS technique. During the studies, two calculation methods were applied to determine the amount of analytes introduced to the chromatographic column. The first approach assumes that the recovery of PCBs that contained a small amount of chlorine atoms in the molecule is similar to the recovery of 13C12PCB28 standard, whereas compounds with greater number of chlorine atoms in the molecule will be recovered from the sediment similarly to the recovery of 13C12PCB180 standard. The second approach assumes that the recovery of PCB 138 and PCB 153 is similar to the average value of 13C12PCB28 and 13C12PCB180 standards. In the case of shaking assisted extraction, 55–90% PCB recoveries were achieved when toluene was used as a solvent, while 71–86% recovery was achieved when dichloromethane was used. When hexsane was used as solvent, recovery ranged 43–107%. In the case of ultrasounds assisted extraction, PCB recoveries of 50–108% were achieved when toluene was used as solvent, while 44–101% recovery was achieved when dichloromethane was applied. When hexsane was used as solvent, recovery reached 57–95%. Studies have also shown that, when applying different isolation techniques and different solvents, the recovery of applied 13C12PCB28 and 13C12PCB180 standards is different. Recovery of 13C12PCB28 standard was from 5% (for hexane tenfold extraction assisted by shaking) to 57% (for toluene tenfold extraction assisted by shaking). However, recovery of 13C12PCB180 standard was from 9% (for hexane tenfold extraction assisted by shaking) to 82% (for toluene tenfold extraction assisted by shaking). This is due to the differences of their binding to the sludge matrix. Standard with a greater number of chlorine atoms in the molecule (13C12PCB180) is more weakly associated with sediment than 13C12PCB28 standard. In order to improve the accuracy of the results obtained, it is necessary to use labeled PCB compounds.