Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments

This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden. Both lead concentrations and Pb-206/Pb-207 ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia. Four of the lakes have varved (annually-laminated) sediments. Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the (2)06Pb /(2)07Pb ratio in unpolluted background sediments in Sweden was > 1.3, whil e that of lead from pollution, derived from ores and coal, was < 1.2. The s ediments show a consistent picture of past temporal changes in atmospheric lead pollution. These changes include: the first traces of pollution 3,500- 3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower le ad fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industr ial revolution; a major increase following World War II; the maximum peak i n the 1970s; and decreasing fall-out over the last decades. The four varved sediments provide high-resolution records of atmospheric pollution. They r eveal pollution peaks about 1200 and 1530 AD which match the history of met al production in Europe. According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s. The p ollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high. About 50% of the total accumulated atmospheri c lead pollution deposition through time was deposited in the pre-industria l period. The sediments also show a consistent picture of the geographic di stribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypo thesis that the main sources of pre-industrial atmospheric lead pollution i n Sweden were cultural areas in mainland Europe and Great Britain.