Mercury and Radionuclides in Forest Soils of Southwestern Georgia, USA: The Role of Older Anthropogenic and Naturally Occurring Mercury

摘要

Concentrations of mercury, radionuclides, and other analytes were measured in three soil profiles from relatively undisturbed, older growth forest soils of the Ichawaynochaway Creek watershed, Georgia, USA to investigate their penetration into the soil profiles and to assess how long they had been accumulating. Bomb-fallout radionuclides, cesium (~(l37)Cs), plutonium (~(239,240)Pu), deposited in the watershed in the past 50 years, and lead (~(210)Pb; half-life of 22 yrs) were measured and used as analogues for recent atmospherically deposited mercury. These radionuclides were observed to have penetrated to at least 16 cm in these soils, suggesting that accumulation of recent atmospherically deposited mercury is not limited to the top few centimeters. Mercury profiles also differed markedly from recently deposited Cs, Pu, and Pb. Based on transport modeling of radionuclides and mercury in soil profiles, it was estimated that atmospherically deposited mercury has been accumulating for at least 1,200 years and likely on the order of 6,000 years in this watershed. Time frames of this magnitude are required to produce the observed concentration profiles for mercury, given the magnitude of the experimentally determined partition coefficients (K_d) in this study.