Bottom trawling resuspends sediment and releases bioavailable contaminants in a polluted fjord

Sediments are sinks for contaminants in the world's oceans. At the same time, commercial bottom trawling is estimated to affect around 15 million km2 of the world's seafloor every year. However, few studies have investigated whether this disturbance remobilises sediment-associated contaminants and, if so, whether these are bioavailable to aquatic organisms. This field study in a trawled contaminated Norwegian fjord showed that a single 1.8 km long trawl pass created a 3–5 million m3 sediment plume containing around 9 t contaminated sediment; ie. 200 g dw m−2 trawled, equivalent to c. 10% of the annual gross sedimentation rate. Substantial amounts of PCDD/Fs and non-ortho PCBs were released from the sediments, likely causing a semi-permanent contaminated sediment suspension in the bottom waters. PCDD/Fs from the sediments were also taken up by mussels which, during one month, accumulated them to levels above the EU maximum advised concentration for human consumption.

► A 1.8 km long trawl pass resuspended 9 t sediment in a 3–5 million m3 plume.
► One trawl pass resuspends the equivalent of c. 10% gross annual sedimentation.
► Substantial amounts of PCDD/Fs were released from the sediments by trawling.
► PCDD/Fs released from the sediments were taken up by blue mussels.