Sedimentary filters for emerging contaminants in estuarine and coastal systems

Estuarine sediments serve as critical sinks and archives for a range of contaminants, including trace metals, polycyclic aromatic hydrocarbons (PAHs), and emerging contaminants like steroidal hormones. While sequestration mechanisms for trace metals and PAHs in estuarine sediments are relatively well-studied, the behaviour and fate of steroidal hormones, especially the role of sedimentary organic matter on hormone retention, are not as well understood. This thesis integrates field investigations from two contrasting estuarine systems, Southampton Water (UK) and the Pearl River Delta (PRD) (China), with laboratory adsorption experiments to evaluate the spatial and temporal distribution of contaminants and examine how sediment properties, particularly the origin of organic matter, affect contaminant retention. Surface and core sediments were analysed to determine contaminant concentrations and historical deposition trends, and sediment properties were characterised. In Southampton Water, elevated concentrations of trace metals were observed, particularly near Southampton Port and wastewater treatment plants (WWTPs), with concentrations reaching up to 2570 mg/kg for Cu, 5560 mg/kg for Zn, and 810 mg/kg for Pb. Hormones like estrone, estradiol, and progesterone, were detected in sediments at all sites (average concentrations 3.3 - 40 ng/g). Ethinylestradiol, a synthetic hormone, was found only near WWTP discharges (average concentration 7.4 ng/g). Principal component analysis (PCA) suggests that sediment properties such as total organic carbon (TOC) and total organic nitrogen (TON) influence the retention of organic contaminants and mercury (Hg). In the PRD, spatial gradients in trace metal and PAH concentrations indicate nearshore retention, with total trace metal concentrations ranging between 124 – 435 mg/kg, and 2 – 177 ng/g for PAHs. In contrast, estrone showed no consistent spatial pattern and was present only in surface sediments, with concentrations up to 13.1 ng/g. This suggests diffuse sources or low sedimentary sequestration. Unlike Southampton Water, sediment properties in the PRD varied only slightly throughout the estuary. PCA indicated that TOC and grain size significantly influence trace metal distribution but had minimal control over PAH and hormone distribution. To better understand interactions between hormones and organic matter source, adsorption experiments were performed using sorbents derived from estuarine plant materials. The sorption behaviour of estrone varied depending on the organic matter source, with TON being a more significant driver of estrone adsorption than TOC. Additionally, salinity had minimal influence on adsorption, suggesting a threshold effect related to estuarine ionic strengths. Together, these findings demonstrate the complexity of sediment-contaminant interactions, emphasising the need to consider environmental and geochemical characteristics when assessing the fate of hormones and other contaminants in estuarine systems. This integrated approach offers new insights into contaminant dynamics in estuarine systems.