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

Morten Thorne Schaanning,Bjørnar Beylich,Jonas S Gunnarsson,Espen Eek

doi:10.1016/j.chemosphere.2020.128544

Morten Thorne Schaanning, Bjørnar Beylich + Show 2 more

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https://doi.org/10.1016/j.chemosphere.2020.128544

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Abstract

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.

Highlights

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzo-furans (PCDFs), commonly referred to as dioxins, are a group of hydrophobic, persistent compounds of major environmental concern
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 and 2018
The vertical profiles of carbon, nitrogen and water content measured in the sediments in 2018 (Fig. 1), showed that the capping materials had caused long-term impacts, still observable nine years after treatment

Summary

Introduction

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzo-furans (PCDFs), commonly referred to as dioxins, are a group of hydrophobic, persistent compounds of major environmental concern. Sediments and biota in the Grenland fjords in SE Norway have elevated levels of dioxins due to emissions from a magnesium smelter located in the inner fjord area (Oehme et al, 1989). Because of remobilization from fjord sediments, another 20e50 years of natural attenuation were required before modelled dioxin levels in seafood would be compatible with safe consumption (Saloranta et al, 2008). To shorten this period of attenuation to five years or less, the model required (theoretical) elimination of the sediment source over 47% or more of the fjord area. In order to investigate the potential of alternative remediation methods a large-scale field experiment was set up in 2009 (Eek et al, 2009, 2014)

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