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