Rise and fall of mercury (Hg) pollution in sediment cores of the Thames Estuary, London, UK

Abstract

Fifty six sediment cores were collected along a 100 km longitudinal transect of the Thames estuary. Total Hg ranged from 0.01 to 12.07 mg/kg, with a mean of 2.10 mg/kg (n ¼ 351). Concentrations of the toxic metal decreased downstream from London to the outer estuary and were positively correlated to total organic carbon (TOC) content. Many Hg profiles showed a clear rise, peak and fall, reflecting changing anthropogenic input through time. Surface concentrations averaged 1.27 mg/kg, confirming the effectiveness of recent environmental legislation and improved river management. Sediments at >40 cm depth from London reaches of the river (Waterloo Bridge, Cuckolds Point (Rotherhithe), Butlers Wharf (Tower Bridge), Millwall, Deptford and Millennium Dome) were highly contaminated, with levels of Hg of >7 mg/kg. The outer Thames had lower Hg, with the exception of Rainham, Crossness and Cliffe. Benchmarking against UK guidelines for the disposal of dredged material revealed that 88 samples from 21 sites exceeded the 3 mg/kg criteria (unsuitable for disposal at sea); 173 fell between 0.3 and 3 mg/kg (further assessment required); and 90 were of no concern. Using Hg as a generic pollution marker, the tidal Thames is one of the world's most contaminated river-estuarine sediment systems.

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

“…[9][10][11] Investigation of the toxic heavy metal, mercury (Hg), in foreshore samples reported mean concentrations of 2.1 mg kg À1 (n ¼ 351) with some of the highest intertidal Hg concentrations in Europe at 7 to 12 mg kg À1 occurring at 40 to 50 cm from surface within central London sections (Waterloo Bridge, Rotherhithe, Tower Bridge, Millwall, Deptford and Greenwich peninsula). 7 Taken together these earlier studies conrm that Thames sediments retain an appreciable but spatially and temporally variable pollution legacy that accumulates as a function of: (1) current velocity, salinity and particle-contaminant behaviour controlled by physicochemical sorption to organic matter coating clay and ne silts and chemical complexation and; (2) proximity to current and historical industrial and municipal works discharge points. 7 The suspended sediment load of the tidal Thames is classi-ed into four zones.…”

“…7 Taken together these earlier studies conrm that Thames sediments retain an appreciable but spatially and temporally variable pollution legacy that accumulates as a function of: (1) current velocity, salinity and particle-contaminant behaviour controlled by physicochemical sorption to organic matter coating clay and ne silts and chemical complexation and; (2) proximity to current and historical industrial and municipal works discharge points. 7 The suspended sediment load of the tidal Thames is classi-ed into four zones. Zone 1 stretches 27 km from Teddington Lock to Lower Pool ($60 to 140 mg L À1 ); Zone 2 stretches 24 km connecting Lower Pool to Erith Reach (500 to 600 mg L À1 ); Zone 3, spans 20 km and covers Erith to Lower Gravesend Reach (200 to 400 mg L À1 ) and nally Zone 4 which extends from Gravesend to Sea Reach spanning a distance of 27 km and opens into the southern North Sea.…”

“…The tidal River Thames (UK) is an exemplar urban catchment grossly affected by atmospheric, terrestrial and uvial transported organic compounds and heavy metals originating from multiple sources including the city of London and upstream catchment inputs. [1][2][3][4][5][6][7][8] Understanding the spatial and temporal variation of sedimentary pollution in the tidal Thames is of interest to environmental scientists, marine, estuary and river managers, waste water utilities as well as the public because: (1) individually or together the compounds and elements have been implicated to have adverse effects on human health; (2) shipping and port/ harbours activities require dredging for clear navigation and berth clearance which in turn demands sediment quality evaluations for regulatory disposal compliance; (3) accelerating global climate change effects may drive an increase in intensity and frequency of uvial and coastal ooding which mobilises buried legacy contamination and potentially transports them from river back to land; (4) the outer estuary supports about 22 sh species and hosts one the largest cockle sheries in the UK.…”

“…Sedimentary pollution in the River Thames estuary has been investigated along the entire salinity gradient ($120 km) using shallow cores and or surface grabs from intertidal foreshore and assessed for brominated ame retardants, sewage input, phosphorus and mercury. 1,4,6,7 This includes specic local conservation sites or salt marshes of the outer estuary for heavy metals (copper), organo-metals (organotins) and halogenated organic compounds. [9][10][11] Investigation of the toxic heavy metal, mercury (Hg), in foreshore samples reported mean concentrations of 2.1 mg kg À1 (n ¼ 351) with some of the highest intertidal Hg concentrations in Europe at 7 to 12 mg kg À1 occurring at 40 to 50 cm from surface within central London sections (Waterloo Bridge, Rotherhithe, Tower Bridge, Millwall, Deptford and Greenwich peninsula).…”

A Model-Based Analysis of Metal Fate in the Thames Estuary

“…Its urban and estuarine reaches were so severely polluted between early 1960s and late 1970s that it was called an 'open sewer' (Attrill et al, 1996). Historical sewage sludge dumping into the estuary together with other urban and industrial activities led to a legacy of metal accumulation in the sediments (Vane et al, 2015). In turn, such interaction with sediments is influencing the environmental risk and the residence time of pollutants (Hobbie, 2000;Bianchi, 2006).…”