1. Lead lability in alluvial soils of the river Trent catchment, U.K. M. Izquierdo, A.M. Tye, S.R. Chenery British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK Lead lability in alluvial soils of the river Trent catchment, U.K. M. Izquierdo, A.M. Tye, S.R. Chenery British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK SOURCE APPORTIONMENT 27 sampling sites paired topsoils (0-15cm) and subsoils (35-50cm) + extraction of pore waters Pb= 40-1280 mg/kg Extensive Pb mining since pre-Roman times Pb-rich sediments still pulse into the Trent tributaries Floodplains downstream the Orefield are a primary Pb repository ACKNOLEDGEMENTS Pb IN TRENT ALLUVIAL SOILS Overbank sediments in the river Trent floodplains act as a focus for deposition and short- to long-term storage of Pb Pb can be released back into the drainage network through bank erosion Potential for increased Pb uptake to grazing livestock, terrestrial and aquatic ecosystems AIMS & METHODOLOGY Pb SOURCES IN THE TRENT CATCMENT 2. Coal Coal mining Coal combustion emissions 3. ‘BHT’ Pb Diffuse source Petrol-derived 1. Pennine Ore Examine the sources, lability and solubility of Pb in alluvial soils from the River Trent and River Dove Pb source apportionment Pb Isotope dilution 2.350 2.370 2.390 2.410 2.430 2.450 2.470 2.490 1.0701.0901.1101.1301.1501.1701.190 208 Pb/ 207 Pb 206 Pb/ 207 Pb coal Pennine ore (galena) UK petrol lead pore water surface topsoil pore water subsoil subsoil London aerosols labile pool road dust sewage BHT (petrol) Pb UK coal Pennine Pb ore Km dowstream 0 50 100 150 200 250 0 20406080 100 Lability %E 2 3456 7 pH 8 % E 206 Pb/ 207 Pb 1.1001.200 Pennine ore Pb dominant BUT BHT (petrol) Pb contribution=0- 50% despite withdrawal in 2000 BHT Pb in subsoils post depositional vertical migration of Pb from traffic related sources Pb LABILITY -10 0 20 30 40 50 -10 3050 % petrol Pb topsoil subsoil Current UK regulations on metal contamination are based on the total concentration in soil  no indication of the chemically reactive or labile fraction of a given element in a soil system ISOTOPE DILUTION TECHNIQUES (E-value) allow the determination of the reactive pool of metal in soils i.e. pool of metal in equilibrium with soil pore water L labile: soluble+adsorbed+solubilised in pore water N fixed Pb: occluded, inert, inaccessible N N L N L N L L L L L N N L N L N L L L L L spike 204 Pb E-VALUE Isotopically exchangeable fraction: geochemically active – bioavailable for uptake LABILE Pb=9-56% over the total pool No differences in Pb lability with depth No Pb >fixation with depth  evidence of continuous bank recycling No differences in Pb contents with depth No source control on lability Strong pH control on %E This work has been funded by a Marie Curie Fellowship (Project no. 254983) to M.Izquierdo 206 Pb/ 207 Pb 208 Pb/ 207 Pb Pb isotopic ratios in total, labile and pore water pools Enrichment of ‘BHT’ Pb in the bioavailable pools possible causes BHT Pb still being deposited (dry/wet deposition + present/recent dissolution of poorly soluble traffic related Pb-bearing species BHT Pb bound to sub-micron FeO colloids in soil pore waters M.Izquierdo, A.M.Tye, S.R.Chenery Sci Total Environ 433 (2012) 110-122