Editing River Mersey (section)

===Sediment pollution===
Persistent organic and [[Mercury (element)|mercury]] (Hg) pollution contained within sediments of the Mersey estuary have been evaluated by [[British Geological Survey]].<ref name="Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediments from the Mersey Estuary, U.K.">{{cite journal |last1=Vane |first1=C. H. |last2=Harrison |first2=I. |last3=Kim |first3=A. W. |title=Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediments from the Mersey Estuary, U.K. |journal=Science of the Total Environment |date=March 2007 |volume=374 |issue=1 |pages=112–126 |doi=10.1016/j.scitotenv.2006.12.036 |pmid=17258286 |bibcode=2007ScTEn.374..112V |url=http://nora.nerc.ac.uk/id/eprint/992/ |language=en |issn=0048-9697}}</ref><ref name=" Mercury contamination in surface sediments and sediment cores of the Mersey Estuary, UK. ">{{cite journal |last1=Vane |first1=C. H. |last2=Jones |first2=D. G. |last3=Lister |first3=T. R. |title=Mercury contamination in surface sediments and sediment cores of the Mersey estuary, UK |journal=Marine Pollution Bulletin |date=2009 |volume=58 |issue=6 |pages=940–946 |doi=10.1016/j.marpolbul.2009.03.006 |pmid=19356771 |bibcode=2009MarPB..58..940V |url=http://nora.nerc.ac.uk/7405/ |language=en |issn=0025-326X}}</ref> Mersey river sediments from outer to inner estuary (Alfred Dock to Widnes) contain a variety of common organic pollutants, including [[polyaromatic hydrocarbons]] (PAH) with concentrations which fall in the middle of the range of similarly industrial-urban river-estuaries.<ref name="Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediments from the Mersey Estuary, U.K."/> The distribution of individual PAH compounds suggests that the Mersey has contaminants mainly derived from combustion sources such as vehicle exhaust as well as coal burning. The distribution of the toxic heavy metal Mercury (Hg) has been assessed by measuring 203 sediments taken from shallow cores (0.4  – 1.6 m) extracted from both the main river and adjacent salt marshes.<ref name=" Mercury contamination in surface sediments and sediment cores of the Mersey Estuary, UK. "/> The average amount of Hg in the Mersey was found to be 2&nbsp;mg/kg with the highest amounts of 5&nbsp;mg/kg occurring below the surface at concentrations harmful to sediment dwelling biota. The vertical rise and fall in Hg pollution observed at four Mersey salt marshes indicated a decline in metal pollution since the 1980s.<ref name=" Mercury contamination in surface sediments and sediment cores of the Mersey Estuary, UK. "/>