Soil mobility of surface applied polyaromatic hydrocarbons in response to simulated rainfall

Polyaromatic hydrocarbons (PAHs) are emitted from a variety of sources and can accumulate on and within surface soil layers. To investigate the level of potential risk posed by surface contaminated soils, vertical soil column experiments were conducted to assess the mobility, when leached with simulated rainwater, of six selected PAHs (naphthalene, phenanthrene, fluoranthene, pyrene, benzo(e)pyrene and benzo(ghi)perylene) with contrasting hydrophobic characteristics and molecular weights/sizes. The only PAH found in the leachate within the experimental period of 26 days was naphthalene. The lack of migration of the other applied PAHs were consistent with their low mobilities within the soil columns which generally parallelled their log Koc values. Thus only 2.3% of fluoranthene, 1.8% of pyrene, 0.2% of benzo(e)pyrene and 0.4% of benzo(ghi)perylene were translocated below the surface layer. The PAH distributions in the soil columns followed decreasing power relationships with 90% reductions in the starting levels being shown to occur within a maximum average depth of 0.94 cm compared to an average starting depth of 0.5 cm. A simple predictive model identifies the extensive time periods, in excess of 10 years, required to mobilise 50% of the benzo(e)pyrene and benzo(ghi)perylene from the surface soil layer. Although this reduces to between 2 and 7 years for fluoranthene and pyrene, it is concluded that the possibility of surface applied PAHs reaching and contaminating a groundwater aquifer is unlikely

MOLECULAR MODELING AND ELECTROSTATIC POTENTIAL CALCULATIONS ON CHEMICALLY-MODIFIED CU,ZN SUPEROXIDE DISMUTASES FROM BOS-TAURUS AND SHARK PRIONACE GLAUCA - ROLE OF LYS134 IN ELECTROSTATICALLY STEERING THE SUBSTRATE TO THE ACTIVE-SITE RID A-4573-2009

The three-dimensional structure of Cu,Zn superoxide dismutase (SOD) from the shark Prionace glauca was homology modeled on the structure of the bovine enzyme used as a template. Shark SOD displays the conservative substitution of one of the residues involved in the electrostatic guidance of superoxide toward the active site of the enzyme, i.e., Lys134, which is replaced by arginine. The association rate, calculated by brownian dynamics simulations incorporating electrostatic terms, and the enzyme reaction rate, measured by the pulse radiolysis method, were found to be identical for both bovine and shark SODs. In order to quantify the role of Lys134 in electrostatically steering the superoxide to the active site, chemical modification of the lysine residues by carbamoylation was carried out on both bovine and shark. SODs. Experimental determination of the enzymatic reaction rate indicated that the charge located on the residue 134 gives 19% contribution to the guidance of superoxide anion at low ionic strength. This value matches the association rates predicted by brownian dynamics. (C) 1994 Academic Press, Inc

Sentinel Lymph Node Biopsy Accurately Stages the Regional Lymph Nodes for T1-T2 Oral Squamous Cell Carcinomas: Results of a Prospective Multi-Institutional Trial

online ahead of print at www.jco.org o

Reducibility and a New Entropic Term in Multifragment Charge Distribution

The charge distributions and their dependence on fragment multiplicity have been studied for the multifragmentation of 30 MeV/nucleon Xe+Au, Cu. For both targets, the charge distributions are approximately independent of the fragment multiplicity n. However, a residual systematic dependence on n is detectable at the largest values of the total charge multiplicity Nc. Such n dependence obeys a simple scaling law and suggests the presence of an entropic term possibly related to the mechanism of multifragmentation. Thermal scaling between the different bins of Nc seems to occur