Mercury, n-alkane and unresolved complex mixture hydrocarbon pollution in surface sediment across the rural–urban–estuarine continuum of the River Clyde, Scotland, UK

Abstract

Surface sediments (n=85) from a 160-km river-estuarine transect of the Clyde, UK, were analysed for total mercury (Hg), saturated hydrocarbons and unresolved complex mixtures (UCMs) of hydrocarbons. Results show that sediment-Hg concentration ranges from 0.01 to 1.38mgkg–1 (mean 0.20mgkg–1) and a spatial trend in Hg-content low–high–low–high, from freshwater source, to Glasgow, to estuary, is evident. In summary, sediment-Hg content is low in the upper Clyde (mean of 0.05Hg mgkg–1), whereas sediments from the Clyde in urbanised Glasgow have higher Hg concentrations (0.04 to 1.26mgkg–1; mean 0.45mgkg–1), and the inner estuary sediments contain less Hg (mean 0.06mgkg–1). The highest mean sediment Hg (0.65mgkg–1) found in the outer estuary is attributed to historical anthropogenic activities. A significant positive Spearman correlation between Hg and total organic carbon is observed throughout the river estuary (0.86; P<0.001). Comparison with Marine Scotland guidelines suggests that no sites exceed the 1.5mgkg–1 criterion (Action Level 2); 22 fall between 0.25 and 1.5mgkg–1 dry wt. (Action Level 1) and 63 are of no immediate concern (<0.25mgkg–1 dry wt.). Saturated (n-alkane) hydrocarbons in the upper Clyde are of natural terrestrial origin. By contrast, the urbanised Glasgow reaches and outer estuary are characterised by pronounced and potentially toxic UCM concentrations in sediments (380–914mg/kg and 103–247mgkg–1, respectively), suggesting anthropogenic inputs such as biodegraded crude oil, sewage discharge and/or urban run-off.

Trends in heavy metals, polychlorinated biphenyls and toxicity from sediment cores of the inner River Thames estuary, London, UK

“…For example, a recent survey of persistent organic pollutants (POPs) in surface sediments from a 160 km stretch of the River Clyde, Scotland revealed the main source of PCBs were from Glasgow's urban tributaries and an earlier evaluation of sediments from the Mersey estuary showed elevated POPs concentrations at the conuence of the Manchester Ship canal at Eastham Locks. 16,25,66 Comparison of absolute PCB concentrations presented here with other UK sediment surveys suggests that the upper Thames is similarly polluted. For example, the inner Clyde reported (ICES-7) ranged 1.20 to 76.8 mg kg À1 , mean 25.8 mg kg À1 , whereas those from the inner Mersey estuary (n ¼ 22) 0.15-410 mg kg À1 and mean 33.8 mg kg À1 and Humber (n ¼ 18) varied from 1 to 84 mg kg À1 , mean 30.9 mg kg À1 .…”

“…Operating conditions were identical to those previously reported for evaluation of surface sediments of the Clyde estuary. 25 Quality assurance was accomplished by analysing high (PACS-2, 3.04 mg kg À1 ), MID (TH2-1, 0.620 mg kg À1 ) and low level (MESS3-1, 0.091 mg kg À1 ) sediment Hg reference materials. Measured values were 3.24 mg kg À1 (RSD 2.41%, n ¼ 4), and 0.66 mg kg À1 (RSD 2.1%, n ¼ 2), 0.10 mg kg À1 (11.25%, n ¼ 4) respectively and a limit of quantication of 0.005 mg kg À1 .…”

Tracking natural organic carbon in the River Clyde, UK, using glycerol dialkyl glycerol tetraethers

“…The TOC concentration of the Clyde sediments is described in Vane et al . (2018). Briefly, TOC ranges from 0.08 to 6%, with higher values in the city of Glasgow (sites 29–47) and outer estuary (sites 78–85; Figs 1, 3).…”

“…Sample collection is described in Vane et al . (2018). Briefly, surface sediments (0–10cm depth), covering a maximum deposition time of 30 years (Vane et al .…”

“…The method used to measure TOC is reported in Vane et al . (2018). δ 13 C and TN were determined using a Europa Scientific Elemental Analyser.…”