--> Evaluating the Time and Source of Hydrocarbon Additions to Soils Using Lead Isotopes and Historical Changes in Industrial Lead Sources: Applications to Environmental Liability, by R. W. Hurst; #90986 (1994).

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Abstract: Evaluating the Time and Source of Hydrocarbon Additions to Soils Using Lead Isotopes and Historical Changes in Industrial Lead Sources: Applications to Environmental Liability

Richard W. Hurst

Isotopic analyses of anthropogenic Pb in well-dated, southern California coastal sediments have been integrated with historical changes in ore Pb sources to produce calibration curves (206Pb/207Pb versus time) that allow us to model the time anthropogenic Pb was added to a soil horizon. The major, historical sources of anthropogenic Pb in southern California are fossil fuels (e.g., gasoline). Hence, Pb model ages (LABILE model; Los Angeles Borderland Industrial Lead) provide time constraints on Pb deposition from fossil fuel combustion via airborne deposition, runoff, and/or sewage outfall in this region. The correlation between the LABILE model age and known times of anthropogenic Pb additions at 17 specific sites is good (r = 0.978); the accuracy of the method anges from one to five years in the post-1960 time interval. Factors influencing accuracy include analytical uncertainties in Pb isotopic measurements (less than or equal to 0.1%), the scatter in isotopic ratios of anthropogenic Pb (circa 0.2%), and the uncertainty in the sediment age used to calibrate the method (0-1.5 years). At one site, three statistically distinguishable events were identified; they correlate with residential development (1968), airborne vehicular Pb deposition (1983), and site remediation (1991). Gasoline incursions at two test sites have been dated accurately (+/-1 year). The limitations of the LABILE model and its acceptance in the legal arena are now being tested.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994