Reed, Jacqueline; (2001) Polychlorinated biphenyls in marine sediments and dredged material around England and Wales. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This study provides the first comprehensive investigation of polychlorinated biphenyl (PCB) contamination of marine sediments and dredged material in England and Wales. A geographically extensive analysis of data acquired through national monitoring programmes since 1990 is used to define 'typical' concentrations for coastal and offshore sediments. Spatial variation is investigated on a regional basis and temporal trends in PCB loadings are examined where sufficient repeat sampling has been undertaken. The nature of within-site spatial and chemical variation in contaminant loadings are investigated through an intensive case study of a known PCB 'hotspot' in the Port of Swansea. Offshore sediments around England and Wales are found to be largely uncontaminated by PCBs. Concentrations in estuarine sediments are much higher, with particular 'hotspots' being evident in the River Blyth and in Cardiff Bay. PCB concentrations in dredged material are typically an order of magnitude above those found in marine sediments, with several areas of concern being identified in North East England, South Wales and North West England. PCB concentrations in a third of all dredged material samples analysed since 1990 exceed current Sediment Quality Guidelines. Many of the most contaminated samples have been obtained from commercial dockyards in South Wales (principally Cardiff, Newport and Swansea). Multivariate and geostatistical methods are used to investigate more fully the spatial and chemical structure of PCB concentrations within King's Dock, Swansea. Principal component analysis shows that variation in PCB homologue profiles is consistent with historical contamination from the more chlorinated commercial Aroclor® mixtures. Spatial variation of the less chlorinated PCB congeners appears to be more structured than the more chlorinated CBs. This high spatial dependence of the less chlorinated PCBs is attributed to properties such as volatility and solubility. Total organic carbon influences the concentration of the more chlorinated CBs, since it encourages adsorption to sediments. Ordinary kriging is conducted to estimate PCB concentrations throughout King's Dock. The resulting inventories show that, in this case, conventional monitoring significantly overestimates the total PCB inventory. Geostatistically-based sampling and analysis is appropriate for the intensive monitoring of known PCB 'hotspots', and lessons from the Swansea case study are integrated into a new protocol for sampling and for assessment of dredging licence applications.

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