A critical gap in the understanding of the global cycling of mercury is the limited data describing the natural background atmospheric deposition rate of mercury before the advent of pollution. Existing estimates of the natural deposition rate are typically about 2−5 μg of Hg m-2 year-1 (see, for example, Swain et al. Science 1992, 257, 784−787), based on studies that generally rely on short, 210Pb-dated lake sediment and peat cores that span the past 150 years. Analyses of mercury in long peat cores in southcentral Sweden indicate that natural mercury deposition rates in the period 4000−500 BP were lower, about 0.5−1 μg of Hg m-2 year-1. This suggests that recent mercury accumulation rates in the peat (15−25 μg of Hg m-2 year-1) and measured atmospheric deposition rates of mercury in Sweden over the past 3 decades (5−30 μg of Hg m-2 year-1) (Munthe et al. Water, Air, Soil Pollut.: Focus 2001, 1, 299−310) are at least an order of magnitude greater than the prepollution deposition rate, rather than representing only a 3−5-fold increase, as has generally been estimated.