Background wet deposition of mercury in Great Britain

Precipitation samples have been collected on a monthly basis from a network of 10 sites in Great Britain (GB) in order to estimate background mercury (Hg) deposition in the rural environment. Collection started in February 2005 and results presented here cover the period up to June 2009. The annual volume-weighted mean (AVWM) Hg concentrations range from 1.0 ng L(-1) at Cockley Beck in the Lake District in 2006 to 8.8 ng L(-1) at Heigham Holmes on the Norfolk Coast England in 2008. The largest validated solution concentrations were 33.7 ng L(-1) Hg measured at Cockley Beck in May 2008. The large difference in rainfall amount between sites means that the remote site at Cockley Beck has both the lowest long-term AVWM concentration (1.6 ng L(-1)) and the greatest annual flux is greatest at 43 mg ha(-1) yr(-1). Predicted deposition tends to be much greater in western Britain where the greater rainfall occurs. Because some observations are very close to the analytical detection limit (1.0 ng L(-1)), rigorous cleaning procedures, the use of replicate samplers to monitor contamination, and the inclusion of 'bottle blanks' are required to obtain valid measurements of Hg in the bulk deposition. Deposition in rural sites is equivalent to about 10% of the estimated magnitude of known emissions in GB.