Recent Changes in Stable Lead Isotope Ratios in Sediments of Lake Zug, Switzerland

Abstract

In Switzerland, unleaded gasoline was introduced in 1985. In order to study the effects of decreasing lead emissions from gasoline on a lake sediment, profiles of lead concentrations and 206Pb/207Pb ratios have been determined in cores from Lake Zug. Sediment samples were digested and analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Accurate dating of sediment cores was achieved using four independent methods showing the results within a range of <10%. Pb emissions in Switzerland and Pb concentrations in the sediment correlated well. Background Pb concentrations in pre-industrial sedi ments were 16 μg/g in Lake Zug and 13 μg/g in Lake Baldegg (for comparison); background 206Pb/207Pb ratios were 1.20 in both lakes. In Lake Zug, lead concentrations reached a maximum of 110 μg/g in a depth corresponding to ca. 1970, the time of highest lead emissions. The 206Pb/207Pb ratio profile provided additional information because this ratio of Pb used for gasoline additives in Europe ranges from 1.04 to 1.10, and the ratio of background Pb in central Europe is about 1.20. The ratios in the sediment had a minimum of 1.13 ca. 1980 and an increase up to 1.16 since ca. 1990. The isotope ratios reflected the frac tion of Pb emissions from gasoline.

Bacterial Chitin Hydrolysis in Two Lakes with Contrasting Trophic Statuses

“…In both seasons, the water column of LB was fully oxic. For LZ, anoxic conditions were measured below 130 m (O 2 Ͻ 0.1 mg liter Ϫ1 ), a shallower depth than reported previously (41,43).…”

“…The lake consists of two basins: a shallow (40-to 60-m depth) North Basin and a 200-m-deep South Basin. The South Basin is meromicitc, with mix-ing depths that do not exceed 100 m. Together with the eutrophic status of LZ, this leads to seasonally anoxic conditions at a depth of 140 to 160 m and permanent anoxia below that depth (41,43 Sediment cores were recovered from the two sampling sites using a gravity corer (32). The first 5 (spring) to 7 (fall) centimeters of each core were sliced at intervals of 1 centimeter.…”

Geochemical-focusing of manganese in lake sediments ? An indicator of deep-water oxygen conditions

“…The decreasing cross section at the peninsula increases current velocities according to mass conservation. The sediment composition near the channel is greatly influenced by these bottom currents: Resuspension of organic matter and clay particles leads to a 7-fold decrease of the net sedimentation rate of core 5, as was shown by 137Cs measurements and particle size distribution (Moor et al, 1996). We therefore excluded these two cores from our final analysis.…”

(Pre-) historic changes in natural and anthropogenic heavy metals deposition inferred from two contrasting Swiss Alpine lakes

“…Conversely, the isotopic composition of lead (Pb), which is unaffected by natural fluxes variability and by anthropogenic processes (e.g., smelting), consistently traces the changing sources of pollution (Sturges and Barrie, 1987;Veysseyre et al, 2001). Investigation of long-term continental records notably revealed variations in Pb accumulation and isotopic composition linked to metallurgical activities since the antiquity (Rosman et al, 1997;Cortizas et al, 2002) whereas the largest atmospheric Pb emissions occurred during the 1970s due to the extensive use of leaded gasoline (Moor et al, 1996;Weiss et al, 1999). Although automobile lead emissions subsequently decreased thanks to the policy initiatives concerning the reduction of lead in petrol, other industrial (i.e., Pb smelters, steel-metallurgy plants, waste incineration) or secondary sources (i.e., wood and coal burning) produced a global re-increase in airborne Pb pollution (Chiaradia and Cupelin, 2000;Flament et al, 2002).…”