Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and heavy metals (HMs) as well as their genotoxicity in soil after long-term wastewater irrigation

A study was carried out on the residue level of major concern pollutants (PAHs, PCBs and HMs) and the assessment of their genotoxicity in soils obtained from Shenyang, northeast of China which had been subjected to wastewater irrigation for more than 40 years. Topsoils (0-20cm) in paddy fields were sampled along the upper, middle and lower reaches of the wastewater disposal channel. Sixteen USEPA PAHs were determined by High Performance Liquid Chromatography (HPLC) with fluorescence detector, eight PCBs were detected by Gas Chromatography (GC) with electron capture detector, and six heavy metals (Cd, Cu, Pb, Zn, Ni, and Cr) were measured by Atomic Absorption Spectrophotometer (AAS). The genotoxicity effect of soils was examined by Vicia faba micronucleus (MN) test. Archived soils that had undergone a similar history of wastewater irrigation provided by Technical University of Berlin, Germany were subjected to analysis of the above pollutants and Vicia faba/MN test for comparison. Results indicated elevated residues of the studied pollutants (PAHs, especially benzo (a) pyrene, the eight PCB congeners and heavy metals) in both tested and archived soils. The MN frequencies were 2.2-48.4 times higher compared with the control. However, there was no correlation between the MN frequencies and the concentration of pollutants detected. This investigation suggested a potential ecological risk even with a lower level of residual pollutants in soil matrix after long-term wastewater irrigation.     

Travel time and trajectory moments of conservative solutes in two-dimensional convergent flows

We address advective transport of a solute traveling toward a single pumping well in a two-dimensional randomly heterogeneous aquifer. The two random variables of interest are the trajectory followed by an individual particle from the injection point to the well location and the particle travel time under steady-state conditions. Our main objective is to derive the predictors of trajectory and travel time and the associated uncertainty, in terms of their first two statistical moments (mean and variance). We consider a solute that undergoes mass transfer between a mobile and an immobile zone. Based on Lawrence et al. [Lawrence, A.E., Sánchez-Vila, X., Rubin, Y., 2002. Conditional moments of the breakthrough curves of kinetically sorbing solute in heterogeneous porous media using multirate mass transfer models for sorption and desorption. Water Resour. Res. 38 (11), 1248, doi:10.1029/2001WR001006.], travel time moments can be written in terms of those of a conservative solute times a deterministic quantity. Moreover, the moments of solute particles trajectory do not depend on mass transfer processes. The resulting mean and variance of travel time and trajectory for a conservative species can be written as functions of the first, second moments and cross-moments of trajectory and velocity components. The equations are developed from a consistent second order expansion in sigmaY (standard deviation of the natural logarithm of hydraulic conductivity). Our solution can be completely integrated with the moment equations of groundwater flow of Guadagnini and Neuman [Guadagnini, A., Neuman, S.P., 1999a. Nonlocal and localized analyses of conditional mean steady state flow in bounded, randomly non uniform domains 1. Theory and computational approach. Water Resour. Res. 35(10), 2999-3018.,Guadagnini, A., Neuman, S.P., 1999b. Nonlocal and localized analyses of conditional mean steady state flow in bounded, randomly non uniform domains 2. Computational examples. Water Resour. Res. 35(10), 3019-3039.], it is free of distributional assumptions regarding the log conductivity field, and formally includes conditioning. We present analytical expressions for the unconditional case by making use of the results of Riva et al. [Riva, M., Guadagnini, A., Neuman, S.P., Franzetti, S., 2001. Radial flow in a bounded randomly heterogeneous aquifer. Transport in Porous Media 45, 139-193.]. The quality of the solution is supported by numerical Monte Carlo simulations. Potential uses of this work include the determination of aquifer reclamation time by means of a single pumping well, and the demarcation of the region potentially affected by the presence of a contaminant in the proximity of a well, whenever the aquifer is very thin and Dupuit-Forchheimer assumption holds.     

Effects of pH, organic acids, and inorganic ions on lead desorption from soils

The desorption characteristics of lead in two variable charge soils (one developed from Arenaceous rock (RAR) and the other derived from Quaternary red earths (REQ)) were studied, and the effects of pH value, organic acid, and competitive ions were examined. Desorption of Pb(2+) decreased from nearly 100.0 to 20.0% within pH 1.0-4.0 in both soils, and then the decrease diminished at pH > 4.0. Organic ligands at relatively low concentrations (< or =10(-3) mol L(-1)) slightly inhibited Pb(2+) desorption, but enhanced Pb(2+) desorption at higher concentrations. In this study, citric acid or acetic acid at higher concentrations (>10(-3) mol L(-1)) had the greatest improvement of Pb(2+) desorption, followed by malic acid; and the smallest was oxalic acid. Desorption of the adsorbed Pb(2+) increased greatly with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Pb(2+) desorption more than Zn(2+) at the same loading.     

Uptake of vapor and particulate polycyclic aromatic hydrocarbons by cabbage

Polycyclic aromatic hydrocarbons (PAHs) in cabbage (aerial part), air (gas and particles) and soil samples collected from two sites in Tianjin, China were measured. Although the levels of PAHs in all samples from the heavily contaminated site B were higher than those from the less contaminated site A, the PAH profiles were similar, suggesting the similarity in source type. PAH concentrations in cabbages were positively correlated to either gas or particle-bound PAHs in air. A multivariate linear regression with cabbage PAH as a function of both gas and particle-bound PAHs in air was established to quantitatively characterize the relationship between them. Inclusion of soil PAH concentrations would not improve the model, indicating that the contribution of soil PAHs to cabbage (aerial part) accumulation was insignificant.     

Nitrous Oxide Emission from <Emphasis Type="Italic">Deyeuxia angustifolia</Emphasis> Freshwater Marsh in Northeast China

Here we report N₂O emission results for freshwater marshes isolated from human activities at the Sanjiang Experimental Station of Marsh Wetland Ecology in northeastern China. These results are important for us to understand N₂O emission in natural processes in undisturbed freshwater marsh. Two adjacent plots of Deyeuxia angustifolia freshwater marsh with different water regimes, i.e., seasonally waterlogged (SW) and not- waterlogged (NW), were chosen for gas sampling, and soil and biomass studies. Emissions of N₂O from NW plots were obviously higher than from the SW plots. Daily maximum N₂O flux was observed at 13 o′clock and the seasonal maximum occurred in end July to early August. The annual average N₂O emissions from the NW marsh were 4.45 μg m⁻² h⁻¹ in 2002 and 6.85 μg m⁻² h⁻¹ in 2003 during growing season. The SW marsh was overall a sink for N₂O with corresponding annual emissions of −1.00 μg m⁻² h⁻¹ for 2002 and −0.76 μg m⁻² h⁻¹ for 2003. There were significant correlations between N₂O fluxes and temperatures of both air and 5-cm-depth soil. The range of soil redox potential 200–400 mV appeared to be optimum for N₂O flux. Besides temperature and plant biomass, the freeze–thaw process is also an important factor for N₂O emission burst. Our results show that the freshwater marsh isolated from human activity in northeastern China is not a major source of N₂O.