Spatial distribution of persistent organic pollutants (POPs) in sediments contaminated by fiber material from pulp and paper industries
Abstract: Sweden has had a long history of forestry activities together with pulp and paper operations. Historical discharges of organic-rich wastewater from pulp and paper factories have resulted in formation of large fiberbanks on the seafloor, which lately have been found to be contaminated with persistent organic pollutants (POPs). The aim of this study was to determine the levels of POPs in fiberbank sediments from two known contaminated sites (Väja and Sandviken) located in the Ångermanälven estuary in the county of Västernorrland, Sweden. The objective was to investigate the spatial distribution of POPs in these fiberbanks on both a horizontal and vertical axis. The sediment samples (n= 43) were collected on SGU’s survey vessel Ocean Surveyor in autumn 2017. The sediment samples were extracted using a Soxhlet followed by a multilayered silica gel clean-up column, prior to instrumental analysis with GC-MS/MS. The sediment’s concentration of hexachlorobenzene (HCB), 20 polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) and its transformation products (DDE and DDD) together referred to as DDX, were measured. At both locations, surface sediment samples (0-4 cm depth) generally presented low concentrations of POPs and organic carbon (TOC), likely due to recent sedimentation of fine clay material. At increased depth, contents of TOC, as well as, the levels of PCBs and DDX (sum of 6 DDT congeners) tended to increase. However, spatial distribution was found to be irregular within both fiberbank and fiber-rich sediment areas. The PCBs compositions, for each location, were found to be related to known technical grade products by using hierarchical cluster analysis. The toxicity of the target pollutants, found in the studied areas, was also assessed using the Norwegian quality standards for sediments. It was found that the HCB levels, for all the samples analyzed, were classified as having no effects on biota (Class II). In both areas, the state of the surface sediment, regarding the Ʃ p,p’-DDX and o,p’-DDT, was classified as good (Class II). However, as the sampling depth increased, many sites contained levels causing chronic effects of long-term exposure (Class III). Most of the levels of Ʃ7PCB in surface sediment samples were classified as having no toxic effects (Class II) with few samples classified as causing chronic effects of long-term exposure (Class III). For both Sandviken and Väja, the levels of Ʃ7PCB increased with sampling depth, and some sites contained levels which are classified as having acute toxic effects of short-term exposure (Class IV). To conclude, this study has contributed in generating important information about the distribution of hazardous contaminants in fiberbanks, and the risk on the immediate environments. The outcome from this study demonstrated how heterogeneous the contaminant levels can be in the vicinity of a pulp and paper factory. This should be taken into consideration when defining remediation strategies for fiber-impacted areas, like defining the site of a remediation project.
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