Heavy metal deposition mapping: concentrations and deposition of heavy metals in rural areas of the UK

CEH has been monitoring the concentrations of a range of heavy metals in rural locations across the UK since 2004. This report presents the annual average concentrations and deposition of heavy metals in air and rainfall samples collected from rural locations during 2011 and it reviews the temporal and spatial trends in heavy metal concentrations and deposition between 2004 and 2011. The monitoring network was established to measure the background concentration of a range of heavy metals in samples of airborne particulate matter (the PM10 fraction), rainwater and cloudwater which have been collected at rural locations which are not unduly influenced by local sources of emissions. The data are compiled to provide information of the background concentrations of these pollutants, and are used to demonstrate compliance with relevant air quality legislation. The measured concentrations are also used to calculate annual deposition of heavy metals and to produce UK maps of concentration and deposition. The heavy metals (and metalloids) which are monitored are aluminium (Al), arsenic (As),antimony (Sb), barium (Ba), beryllium (Be), cadmium (Cd), caesium (Cs); chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), manganese (Mn), mercury (Hg), molybdenum (Mo), nickel (Ni), rubidium (Rb), scandium (Sc), selenium (Se),strontium (Sr),tin (Sn), titanium (Ti), tungsten (W), uranium (U), vanadium (V) and zinc (Zn). The concentrations of all metals measured in airborne particulate matter, rainfall and cloudwater are low, as would be expected in samples collected from rural areas. The concentrations are 1.5 to 8.5 times lower than the national average as reported in the Urban and Industrial Heavy Metals Monitoring network (see Table 5 for comparison). Although the reported emissions of heavy metals in the UK have declined considerably from their industrial peak in the 1970s,and more recently during the 1990s, the inter-year variability in measured concentrations do not allow any corresponding temporal trends in measured concentrations to be established. For the majority of metals analysed, there are also large discrepancies between the reported UK emissions and the amount of metal deposited in the UK. This discrepancy needs further investigation, including improvements being made to the way that metal emission are produced, and the quantification of the amount of re-suspended material that is being picked up by the monitoring networks.