Large-scale field study on thin-layer capping of marine PCDD/F-contaminated sediments in Grenlandfjords, Norway: physicochemical effects.

A large-scale field experiment on in situ thin-layer capping was carried out in the polychlorinated dibenzodioxin and dibenzofuran (PCDD/F) contaminated Grenlandsfjords, Norway. The main focus of the trial was to test the effectiveness of active caps (targeted thickness of 2.5 cm) consisting of powdered activated carbon (AC) mixed into locally dredged clean clay. Nonactive caps (targed thickness of 5 cm) consisting of clay without AC as well as crushed limestone were also tested. Fields with areas of 10,000 to 40,000 m(2) were established at 30 to 100 m water depth. Auxiliary shaken laboratory batch experiments showed that 2% of the applied powdered AC substantially reduced PCDD/F porewater concentrations, by >90% for tetra-, penta- and hexa-clorinated congeners to 60-70% for octachlorinated ones. In-situ AC profiles revealed that the AC was mixed into the sediment to 3 to 5 cm depth in 20 months. Only around 25% of the AC was found inside the pilot fields. Sediment-to-water PCDD/F fluxes measured by in situ diffusion chambers were significantly lower at the capped fields than at reference fields in the same fjord, reductions being largest for the limestone (50-90%) followed by clay (50-70%), and the AC + clay (60%). Also reductions in overlying aqueous PCDD/F concentrations measured by passive samplers were significant in most cases (20-40% reduction), probably because of the large size of the trial fields. The AC was less effective in the field than in the laboratory, probably due to prolonged sediment-to-AC mass transfer times for PCDD/Fs and field factors such as integrity of the cap, new deposition of contaminated sediment particles, and bioturbation. The present field data indicate that slightly thicker layers of limestone and dredged clay can show as good physicochemical effectiveness as thin caps of AC mixed with clay, at least for PCDD/Fs during the first two years after cap placement.

Long-term effects of thin layer capping in the Grenland fjords, Norway: Reduced uptake of dioxins in passive samplers and sediment-dwelling organisms.

The Grenlandfjords in South East Norway are severely contaminated with dioxins from a magnesium smelter operated between 1950 and 2001. In 2009, the proposal of thin-layer capping as a potential mitigation method to reduce spreading of dioxins from the fjord sediments, resulted in the set-up of a large-scale field experiment in two fjord areas at 30 and 100 m depth. After capping, several investigations have been carried out to determine effects on benthic communities and bioavailability of dioxins. In this paper we present the results on uptake of dioxins and furans (PCDD/F) in passive samplers and two sediment-dwelling species exposed in boxcores collected from the test plots during four surveys between 2009 (after cap placement) and 2018. Sediment profile images (SPI) and analyses of dioxins revealed that the thin (1-5 cm) cap layers became buried beneath several centimeters of sediments resuspended from adjacent bottoms and deposited on the test plots after capping. Uptake reduction ratios (R) were calculated as dioxins accumulated in cores collected from capped sediments divided by dioxins accumulated in cores collected from uncapped reference sediments. Cap layers with dredged clay or crushed limestone had only short-term positive effect with R-values increasing to about 1.0 (no effect) 1-4 years after capping. In spite of the recontamination, cap layers with clay and activated carbon had significant long-term effects with R-values slowly increasing from 0.12-0.33 during the first three years to 0.39-0.46 in 2018, showing 54-61% reduced uptake of dioxins (PCDD/F-TE) nine years after capping with AC.

Levels and trends of tributyltin (TBT) and imposex in dogwhelk (Nucella lapillus) along the Norwegian coastline from 1991 to 2017.

The banning of organotin biocides, such as tributyltin (TBT), from use in marine antifouling paints is now leading to reproductive health recovery in marine gastropod populations all over the world. TBT induces so-called imposex (superimposition of male sexual characters onto females) in certain marine gastropods, such as the common dogwhelk Nucella lapillus. In this publication, the results of the Norwegian TBT and imposex monitoring in N. lapillus from the period 1991-2017 are presented. Significantly higher levels of TBT and imposex were measured in coastal areas close to shipping lanes along most of the coast prior to 2008 than afterwards. Levels started declining after restrictions were imposed on the use of TBT in all antifouling paint applications, with a total ban in 2008. In 2017, no sign of imposex was found in N. lapillus in any of the monitoring stations along the Norwegian coastline. Based on monitoring data shown herein, the importance of long-term biomonitoring and international chemical regulations, as well as the TBT and imposex story in general, are discussed.

Mercury concentration trend as a possible result of changes in cod population demography.

Mercury (Hg) in Atlantic cod (Gadus morhua) is one of many parameters that are monitored through OSPAR's Joint Assessment and Monitoring Programme. Time series for cod in the Inner Oslofjord (Norway) go back to 1984. Until 2014, annual median Hg-concentrations in cod from the Inner Oslofjord showed both significant upward long-term (whole time series) and short-term (recent 10 years) trends (when 2015 was included, the short-term trend was not significant). However, the median length of the cod sampled also showed upward trends. This may have been caused by low cod recruitment in the area since the start of the 2000s, as indicated by beach seine surveys. To investigate how length would impact the trend analysis, the Hg-concentrations in the cod were normalised to 50 cm. No significant short-term trend in Hg-concentrations could be detected for length-normalised concentrations. The results indicated that most of the upward trend in Hg-concentrations could be attributed to the sampling of larger fish. The reasons for the apparent change in the cod population demography are not conclusive, however, sampling bias must also be considered.

Petroleum oil and mercury pollution from shipwrecks in Norwegian coastal waters.

Worldwide there are tens of thousands of sunken shipwrecks lying on the coastal seabed. These potentially polluting wrecks (PPW) are estimated to hold 3-25milliont of oil. Other hazardous cargo in PPW includes ordnance, chemicals and radioactive waste. Here, we present and discuss studies on mercury (Hg) and oil pollution in coastal marine sediment caused by two of the >2100 documented PPW in Norwegian marine waters. The German World War II (WWII) submarine (U-864) lies at about 150m below the sea surface, near the Norwegian North Sea island of Fedje. The submarine is estimated to have been carrying 67t of elemental Hg, some of which has leaked on to surrounding sediment. The total Hg concentration in bottom surface sediment within a 200m radius of the wreckage decreases from 100g/kgd.w. at the wreckage hotspot to about 1mg/kgd.w. at 100m from the hotspot. The second wreck is a German WWII cargo ship (Nordvard), that lies at a depth of ca. 30m near the Norwegian harbor of Moss. Oil leakage from Nordvard has contaminated the bottom coastal sediment with polycyclic aromatic hydrocarbons (PAH). The findings from this study provide useful insight to coastal administration authorities involved in assessing and remediating wreck-borne pollution from any of the tens of thousands of sunken shipwrecks.

Genotoxicity of environmentally relevant concentrations of water-soluble oil components in cod (Gadus morhua).

Large discharges from oil and gas production platforms (produced water) have led to concerns for adverse biological effects in marine areas. The aim of this study was to investigate the development of DNA adductformation and related biomarkers in fish after chronic exposure to water-soluble components of oil. Atlantic cod (Gadus morhua) were exposed for up to 44 weeks to three treatments (low, pulsed, high) containing environmentally relevant concentrations of low-molecular-weight polycyclic aromatic hydrocarbons (PAHs) and short-chained alkylphenols (APs). A time- and dose-related pattern of DNA adduct formation (measured using 32P-postlabeling) was observed. The results suggested that an extended exposure period (more than 16 weeks) would be required for the formation of DNA adduct levels above background. Interestingly, fish receiving pulsed high exposure did not develop elevated concentrations of DNA adducts, possibly due to DNA repair processes. No obvious relationship between DNA adduct concentration and cytochrome P4501A activity (EROD) was observed. This study has demonstrated the genotoxic potential of water-soluble oil components, relevant for operational discharges (produced water) and chronic oil spills. The quantification of PAH metabolites in bile and hepatic DNA adduct formation appear to be suitable for environmental monitoring of chronic oil pollution.