19th-century London of the Thames from the City of London westwards experienced a flurry of bridge-building during the 19th century, improving overland communication to South London. At the turn of the 19th century there were only three existing bridges in Central London: Westminster Bridge, Blackfriars Bridge, and the ancient London Bridge. Beyond Westminster, the closest bridge was that of Battersea, three miles upstream from Westminster Bridge. All four were demolished and rebuilt over the course of the century (completed in 1862, 1869, 1831,and 1885 respectively). In addition, a slew of new bridges for road, pedestrian, and railway traffic were built: Southwark Bridge
River Thames in the Thames estuary occurs in the central London area between Vauxhall Bridge and Woolwich. The majority of sediment cores show a clear decrease in Hg concentrations close to the surface which is attributed to an overall reduction in polluting activities as well as improved effectiveness of recent environmental legalisation and river management (e.g. Oslo-Paris convention). Evaluation of select of lipid compounds in the Thames estuary, known as glycerol dialkyl glycerol tetraethers (GDGTs) has revealed enhanced concentrations of isoprenoid GDGT compounds (crenarchaeol) around East London. This suggests that London's pollution affects the spatial distribution of natural carbon in the river