Stable Pb isotopes and PAHs as indicators of lead contamination sources in a lake of the Rouyn-Noranda area

摘要

We determined the depth distribution of total Pb and its stable isotope composition (~(206)Pb/~(207)Pb, ~(206)Pb/~(208)Pb, ~(206)Pb/~(204)Pb) in a dated sediment core collected at the deepest site, in the hypolimnion of a headwater Canadian Shield lake, located 25 km downstream from a metal smelter in operation since 1927. The isotopic ratios reveal the occurrence of one natural and two anthropogenic types of Pb over the last century. One of the anthropogenic Pb, predominant in the sediments accumulated in the early 20~(th) century, likely derives from coal combustion (~(206)Pb/~(207)Pb ≈ 1.185). The second anthropogenic Pb has a signature similar to that of the ore processed during several decades at the smelter (~(206)Pb/~(207)Pb ≈ 1.000); its contribution to the total Pb concentration sharply increased from 1927 to 1975 and then decreased steadily to the sediment surface.