Exploring variations of hexabromocyclododecane concentrations in riverine sediments along the River Medway, UK

Surface riverine sediment samples were collected along the course of the River Medway, UK, between Yalding and the mouth of the estuary at 40 different sites. The samples were then analysed for hexabromocyclododecane (HBCDD) concentrations using a liquid chromatography system coupled to a high-resolution, accurate mass Orbitrap™ mass spectrometer. After normalisation to the sediment organic carbon (OC) content, average ΣHBCDD was 270 ng g-1 OC with a maximum concentration of 1006 ng g-1 OC. Spatial trend analysis revealed that industrial and residential land uses have significantly influenced HBCDD concentrations and profiles in riverine sediments. Higher concentrations of ΣHBCDD were found in sites near construction and maritime port locations, and these included freight ports, new builds and demolition sites. The HBCDD isomer profile reflected that of the commercial mixture with a comparatively high γ-HBCDD to α-HBCDD and β-HBCDD. The isomer profiles of sites located near construction activities indicate recent pollution events, with increased γ-HBCDD and decreased α-HBCDD compared to the study area's average profile. HBCDD isomer concentrations also indicated that the non-tidal portions of the river caused by locks showed a profile that was typical of older HBCDD contamination, indicating a possible sediment and HBCDD trap.