Purpose: Many coastal areas in the Baltic Sea are contaminated with wood fiber and pollutants from pulp and paper industries. These anthropogenic, organic-rich, sediments (fiberbanks) have not been characterized and knowledge about their role as secondary sources for dispersal of persistent organic pollutants (POPs) is limited. Hence, the aim of this study was to elucidate the fate of POPs and the relationships between sorption (K_D and K_TOC), sediment type, and compound hydrophobicity (K_OW) in fiber-contaminated sediments. Materials and methods: Paired sediment and pore water samples (n = 24 sites) from three fiber-contaminated areas, located in the Ångermanälven river estuary in northern Sweden, were analyzed for POPs (viz. PCBs, DDT, and HCB) in sediment types representing different fiber content (i.e., fiberbanks, fiber-rich sediments, and natural less fiber impacted sediments). The freely dissolved concentration in sediment pore water was determined by sediment-polyoxymethylene (POM) partitioning. Instrumental analysis was performed using gas chromatography coupled to a triple quadrupole mass spectrometer (GC-MS/MS). Results and discussion: Higher levels of total organic carbon (TOC) were found in the fiberbank sediment (range 8.6–37%) than in fiber-rich sediment (range 2.0–6.5%) and more natural sediment (range 2.0–2.9%). The sediment concentrations of POPs (dry weight basis) were also found to be significantly (p < 0.05) elevated in fiberbanks compared to the other sediment types. The fraction of DDD (48–66% of Σ₆DDX) was larger in fiberbanks than in the other sediment types, likely due to anoxic conditions favoring reductive dechlorination of DDT. When sediment levels were normalized to TOC, HCB displayed similar levels across sediment type, suggesting a more diffuse source pattern than for PCB and DDT. Although significantly higher sorption (K_D) of POPs was observed in fiberbanks, pore water levels were still elevated due to high bulk concentrations. Conclusions: This study shows that fiberbanks are coastal hot spots for POPs in the Baltic Sea and that the levels are of ecotoxicological concern. Although the POPs are more strongly sorbed (K_D) to this type of organic rich sediment, the high pore water concentrations in fiberbanks compared to the other sediment types investigated show that the risk of contaminant dispersal via pore water is elevated for fiberbanks.

Historical use of organochlorine pesticides (OCPs) in the Republic of Moldova could pose a potential risk for the aquatic environment due to the persistence, bioaccumulation and toxic properties of these environmental pollutants. However, knowledge on environmental concentrations of legacy OCPs in Moldova is limited. In this study, surface sediment from the two main rivers; Dniester (8 sites, n = 15) and Prut (6 sites, n = 12), and two tributary rivers; Bîc (11 sites, n = 11) and Răut (6 sites, n = 6), were collected during 2017-2018 and analyzed for hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs) and their transformation products (DDDs and DDEs) using gas chromatography coupled to mass spectrometry (GC-MS/MS). Sediment concentrations of Ʃ6DDX (1.9-140 ng g-1 dry weight (dw)) and Ʃ4HCHs (n.d-2.5 ng g-1 dw) were found. In the big rivers, the average Ʃ6DDX concentration (18 ng g-1 dw) were 35 times higher than Ʃ4HCHs (0.51 ng g-1 dw). Whereas, in the small rivers the average Ʃ6DDX concentration (32 ng g-1 dw) was approximately 41 times higher than Ʃ4HCHs (0.77 ng g-1 dw). Compared to previous studies from Eastern Europe, the sediment levels were generally similar as found in Moldova's neighboring countries (Romania and Ukraine). Overall, the contamination profile indicates long-term ageing of OCPs used in the past in the agricultural sector. Less than half of the sites (45%) had levels that pose a potential risk for benthic organisms. Hence, further work is needed to determine the bioaccumulation of OCPs in the aquatic food web in this region and the associated risks to ecosystems and human health.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been detected in humans and wildlife. Using in vitro models, we recently showed that OH-PBDEs disrupt oxidative phosphorylation (OXPHOS), an essential process in energy metabolism. The goal of the current study was to determine the in vivo effects of OH-PBDE reported in marine wildlife. To this end, we exposed zebrafish larvae to 17 OH-PBDEs from fertilisation to 6 days of age, and determined developmental toxicity as well as OXPHOS disruption potential with a newly developed assay of oxygen consumption in living embryos. We show here that all OH-PBDEs tested, both individually and as mixtures, resulted in a concentration-dependant delay in development in zebrafish embryos. The most potent substances were 6-OH-BDE47 and 6′-OH-BDE49 (No-Effect-Concentration: 0.1 and 0.05 µM). The first 24 h of development were the most sensitive, resulting in significant and irreversible developmental delay. All substances increased oxygen consumption, an effect indicative of OXPHOS disruption. Our results suggest that the induced developmental delay may be caused by disruption of OXPHOS. Though further studies are needed, our findings suggest that the environmental concentrations of some OH-PBDEs found in Baltic Sea wildlife in the Baltic Sea may be of toxicological concern.

Purpose: Numerous sites contaminated with fiber emissions from pulp and paper industries are found in coastal areas of the Baltic Sea, but there is limited knowledge about the magnitude of dispersal of persistent organic pollutants (POPs) from these anthropogenic, organic-rich sediments called fiberbanks. The aim of this study was to quantify and compare different POP dispersal pathways from such fiberbanks. Dispersal mechanisms studied included abiotic and biotic routes (dissolved in water, particle-bound, and bioaccumulation). Materials and methods: Contaminated fibrous sediments located in Ångermanälven River estuary in north-eastern Sweden were studied in sediment types representing different fiber content (i.e., fiberbanks, fiber-rich sediments, and less fiber impacted sediments). Sediment-to-water fluxes of dissolved contaminants (polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), and dichlorodiphenyltrichloroethane (DDT)) were measured in situ using benthic flux chambers. Particle resuspension was measured by sampling bottom water, before and after disturbing the sediment surface. Benthic biota was collected to determine the body burden of contaminants and to determine biota-pore water accumulation factors (BAF_PW) and biota-sediment accumulation factors (BSAFs). In addition, concentrations of dissolved POPs in the water column were measured in field using passive samplers. Instrumental analysis was performed using gas chromatography coupled to a triple quadrupole mass spectrometer (GC-MS/MS). Results and discussion: The flux of dissolved Σ₂₀PCBs was approximately two times higher from one of the investigated fiberbanks (3.4 ng m^− 2 day^− 1) compared to the other. The average particle burden of PCBs was also higher at this fiberbank after artificial disturbance (15 ng g⁻¹ particle), which indicates that larger amounts of contaminants are likely to disperse via particle resuspension from this site compared to the other fiberbank (4.8 ng g^− 1 particle). The difference might be associated with a layer of recently settled minerogenic material that covers one of the fiberbanks, which probably functions as a protective barrier. The lack of benthic biota implies that contaminant release by bioturbation is negligible in the studied fiberbanks. However, benthic biota from fiber-rich sediment showed bioaccumulation and biomagnification of contaminants. Conclusions: The importance of diffusive flux from fiberbanks under undisturbed conditions became apparent when the different dispersal pathways were quantified. However, no dispersal pathway could be judged as irrelevant, since even under undisturbed conditions, advective particle transport was significant. Additionally, the uptake by biota and trophic transfer can be considerable. Quantification of dispersal routes and understanding of the relative importance of various pathways is critical for proper risk assessment and management of contaminated sediments.

Deposits of contaminated wood fiber waste (fiberbanks), originating from sawmills and pulp and paper industries, have been found in the aquatic environment in boreal countries. In-situ isolation capping has been proposed as a remediation solution because it has the potential to prevent dispersal of persistent organic pollutants (POPs) from this type of sediment. However, knowledge about the performance of such caps when placed on very soft (unconsolidated), gaseous organic rich sediment is scarce. We investigated the effectiveness of conventional in-situ capping to limit POPs fluxes to the water column from contaminated fibrous sediments that produce gas. A controlled, large-scale laboratory column (40 cm diameter, 2 m height) experiment was performed over 8 months to study changes in sediment-to-water fluxes of POPs and particle resuspension before and after capping the sediment with crushed stones (≥4 mm grain size). Two different cap thicknesses were tested (20 and 45 cm) on two types of fiberbank sediment with different fiber type composition. Results showed that capping fiberbank sediment with a 45 cm gravel cap reduced the sediment-to-water flux by 91-95% for p,p'-DDD, o,p'-DDD, by 39-82% for CB-101, CB-118, CB-138, CB-153, CB-180 and by 12-18% for HCB, whereas for less hydrophobic PCBs, capping was largely ineffective (i.e. CB-28 and CB-52). Although cap application caused particle resuspension, the long-term effect of the cap was reduced particle resuspension. On the other hand, substantial sediment consolidation released large volumes of contaminated pore water into the overlying water body. Importantly, both sediment types produced large amount of gas, observed as gas voids forming inside the sediment and gas ebullition events, which increased pore water advection and affected the structural integrity of the cap. This may limit the practical applicability of this method on fiberbank sediments.