In this study we present the results of a Pb isotope study to identify the sources of natural and anthropogenic Pb in the Dutch province Limburg. This area is known for its long industrial history (mine tailings, coal dumps, metal and non-metal industries), therefore many sources of Pb can be expected. For this study 10 overbank deposits were sampled. At each sample site 2 samples were taken, representing the pre-industrial (background) component and the industrial (after 1860) component of lead. In order to distinguish between the leachable component of lead (Pb sorbed to biological debris and ferromanganese films) and the more refractory component of lead (Pb within the structure of silicate minerals) two dissolution procedures have been used: 1. total destruction of the samples with HNO3, HClO4 and HF using a high-pressure microwave system and 2. dilute acid leach with 4.5% HNO3. Lead concentrations and isotopic composition were determined with ICP-MS (2s<0.8% for all ratios). Lead analyses were corrected for fractionation by repeated analysis of the NBS 981 standard. The lead isotopic component of the pre-industrial samples is substracted from the industrial samples to calculate the amount and isotopic composition of anthropogenic Pb added to the background.
According to both methods lead concentrations increase 2- to 12-fold, whereas the 206Pb/207Pb ratio generally decreases, comparing the pre-industrial sample with the anthropogenic (industrial) sample. The lead isotopic ratios of the different
pre-industrial samples vary strongly. It will be shown that this variation is due to the difference in provenance of the sediments. The lead isotopic ratios of the calculated anthropogenic lead component show at least two different anthropogenic lead sources. The main sources are presumably the Pb-Zn type mineralizations of Plombières and La Calamine and gasoline lead. This study shows that lead isotopic compositions prove to be an useful tool to distinguish between the provenance and the sources of
lead contamination of the sediments. In addition, enrichment that can occur by diagenetic 'natural' processes can easily be distinguished from enrichment caused by anthropogenic factors.