Lead concentration profiles in lead-210 dated Lake Ontario sediment cores

Lead concentrations were measured in sediment cores from four sites distributed among the three major sedimentary basins - Niagara, Mississauga and Rochester - of Lake Ontario for which sedimentation rates had been previously determined by 210Pb dating. Around 90% of the total lead present in fine-grained surface sediments was removed by CH3CO2H/NH2OH.HCl leaching, concentrations ranging from 137 μg/g in surface sections to a constant background of 12-13 μg/g at unpolluted depths. Lead-210 dating indicated that increases in lead concentrations commenced ca. 1850-1875 with 5, 10, 35 and 50% of the total 'excess' lead inventory in the sediment column being assigned to the pre-1900 period and successive 25-year intervals during the 20th century, respectively. Anthropogenic inputs of lead from such sources as the combustion of leaded gasoline and coal are reponsible for these increases. About 10 μg/g lead remained in the sediment residue after leaching. The total natural lead flux to the sediments ranged from 0.4-1.3 μg/cm2/yr while 'excess' lead of anthropogenic origin varied from 1.2-6.7 μg/cm2/yr and totalled 0.5-1.5 g/m2 at the four sites. Various potential modes of introduction of anthropogenic lead and of 210Pb to the lake are considered in conjunction with the ratio of Pb/210Pb fluxes to the sediment. (Auth.)