Transformations of elemental mercury to inorganic and organic forms in mercury and hydrocarbon co-contaminated soils.

There are many industrial sites, such as gas processing plants, that are contaminated with both mercury and hydrocarbons. These sites tend to be localized but can have very high concentrations of mercury in the soil and heterogeneous distribution of hydrocarbons. The original form of mercury in many cases was elemental mercury from broken manometers. Over time the mercury has become redistributed within soil and has undergone chemical transformations into new forms. The forms of mercury will govern the chemical behavior and the availability of the mercury to biological receptors. The availability of the mercury is important as it will govern the risk associated with the contaminated soil and will also determine the effectiveness of any attempts at remediation. In the present study a chemical extraction protocol was used to determine the forms of mercury in soil originally contaminated by spillage of elemental mercury and petroleum hydrocarbons. Chemical extractions have been used in the past to determine the forms of mercury in uncontaminated soils and several researchers have used them to study contaminated soils. However, to date, no researchers have studied the forms of mercury in soils following years of weathering of elemental mercury after a spill. This study shows that decades after the original spill the elemental mercury has transformed and is dominantly (up to 85%) associated with soil organic matter, and to a lesser extent the mineral fraction of soil.

Sorption of 1-naphthol to soil and geologic samples with varying diagenetic properties.

Remediation of contaminated land requires a firm understanding of the processes that occur between xenobiotics and soil colloids. It is currently accepted that the extent of xenobiotic uptake is proportional to the carbon quantity and character of the soil or geologic sample. Previous studies have developed empirical equations to predict the extent of sorption based on the aromatic carbon content. We examined these relationships with an independent set of soil and geologic samples and 1-naphthol. The 1-naphthol sorption coefficients varied significantly (P < 0.01) among sorbents and are consistent with the diagenetic properties of the organic matter in these samples. The cross-polarization magic angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) and elemental data did not concur with the sorption data for most of the soil samples. We suggest that this contradiction may be due to a third variable, the physical organization of the organic matter. Chemical methods measure the whole sample, whereas short-term sorption occurs on the surface; therefore, only some organic matter domains in the soil are available for interaction with 1-naphthol. Hence, chemical data alone may be insufficient for predicting the sorption behavior of xenobiotics in soil and geologic samples.

Radon emanation coefficients for phosphogypsum.

Phosphogypsum is a by-product of the phosphate fertilizer industry which is stockpiled in large quantities world-wide. Phosphogypsum consists mainly of dihydrate gypsum (CaSO42H2O) but also contains elevated concentrations of 226Ra and other inorganic species which originate from the processing of phosphate rock. 222Rn gas is the first decay product of 226Ra and has been identified as one of the major environmental concerns associated with phosphogypsum. This study was conducted to determine effects of particle size, weathering, and moisture content on the 222Rn emanation coefficient (epsilon) for phosphogypsum. Average epsilon for air-dry, unfractionated phosphogypsums derived from Togo, Florida, or Idaho rock was approximately 12%. Average epsilon for fine fraction phosphogypsum (< 20 microns diameter) was greater than for unfractionated phosphogypsum by a factor of 4.6, 1.4, and 4.4 for samples derived from Idaho rock, Togo rock, and Florida rock, respectively. Phosphogypsum samples subjected to an artificial weathering procedure lost 40% mass, with no change in epsilon. Increasing water content was found to first slightly decrease, then to increase epsilon compared to air-dry samples; epsilon for 100% saturated phosphogypsum was 1.9-fold greater than in air-dry phosphogypsum. Particle size sorting could account for variability of 222Rn exhalation at repositories. Very high moisture contents could slightly increase 222Rn emanation, but exhalation would likely be reduced due to slow diffusion through porosity of saturated phosphogypsum.