Effect of dissolved organic matter on the stability of magnetite nanoparticles under different pH and ionic strength conditions.

Upon release of engineered nanoparticles (NPs) into the subsurface environment, their fate and transport and hence their potential environmental and public health impacts will largely depend on how stable these NPs are as suspended particles in the natural environment. In this study, we systematically examine the effect of humic acid (HA) on surface charge status and aggregation potential of magnetite (Fe(3)O(4)) NPs, selected as a model for metal oxide NPs, over a wide range of solution pH and ionic strength. Through zeta potential (ZP) measurements, we found that HA can adsorb to magnetite particles hence modifying their surface charge status. At low loadings, the presence of HA can induce a shift in the point zero of charge of due to partial neutralization of the positive charges on magnetite NPs. At high loadings, however, HA is capable of completely cover magnetite particles giving rise to a suspension ZP profile similar to its own (observed in presence of 20 mg L(-)(1) HA). These impacts on surface charge correspond well with the observed aggregation behaviors in the absence and presence of HA. From the dynamic light scattering (DLS) measurements, fast aggregation, which is independent of solution chemistry, took place when the pH is close to the point zero charge (PZC) and the ionic strength is above the critical coagulation concentration (CCC). At high ionic strength, a small dose (2 mg L(-)(1)) of HA stabilized the NPs' suspension significantly. This stabilization effect is substantially enhanced with increasing HA concentration. The calculated DLVO (Derjaguin-Landau-Verwey-Overbeek) interaction energy profiles, using experimentally determined values of Hamaker constant, adequately support the experimental observations. The DLVO analysis further reveals the possible presence of secondary energy minima and the possibility of deaggregation of magnetite agglomerates. The complexation of HA-NPs and the HA effects on NPs aggregations were confirmed by atomic force microscope (AFM) observations.

[PAH sources in road runoff system in Beijing].

In this study, road runoff, rainwater, ground sediment and roadside tree water samples were collected from three types of roads in Beijing in 2006. The samples were analyzed for polycyclic aromatic hydrocarbons (PAHs). The average PAH concentrations in each media in May-June were generally higher than those in July-August. Factor analysis indicated that PAHs in road runoff were mainly from ground sediment, and rainwater and roadside tree water also had certain influence to road runoff. Multiple regression analysis indicated that PAHs in ground sediment and road runoff mainly come from vehicular emission at the vehicle way and branch road, and at the bicycle way, the contributions of vehicular emission and coal combustion were equal. PAHs in rain were mainly from coal/oil combustion, and PAHs in roadside tree water were dominated by vehicular emission source.

Numerical simulation of PAHs sorption/desorption on soil with the influence of Tween80.

In this paper, the influences of inionic surfactant Tween80 on polycyclic aromatic hydrocarbons (PAHs) sorption/desorption on artificially contaminated soil were studied, and gamma model was applied to simulate the influences. Results showed that, with the use of Tween 80, the sorption behaviors of PAHs on soil altered significantly. Adsorbed Tween 80 increased the sorption amount of PAHs while the dissolved Tween80 increased the apparent solubility of PAHs. These two processes exert influences on the sorption coefficient of PAHs in soil-water system, which can be depicted by apparent sorption coefficient. The partition coefficients (the soil/water partition coefficient of PAHs and surfactants obtained from sorption experiments) and statistical parameters used in the amended gamma model were obtained in independent experiments. With these parameters, the gamma model could provide a satisfactory independent prediction of PAHs release from soil to aqueous phase at two surfactant concentrations.

[Desorption of polycyclic aromatic hydrocarbons from soil in presence of surfactants].

Four types of surfactant were used to study their effects on polycyclic aromatic hydrocarbons (PAHs) desorption from artificially contaminated and oil-contaminated soil. The results show that the desoption of PAHs from soil is affected by the type and concentration of surfactant and also by the character and state of PAHs. Surfactants don't improve PAHs desorption from soil when their concentrations are below or near their critical micelle concentration (CMC) values. While, surfactants could obviously enhance the desorption process when the concentrations exceeded the CMC values. The desorption ratios of PAHs were increasing with the increase of surfactant concentrations. Comparatively, lower hydrophile lipophile balance(HLB) can lead to more obvious surfactant solubilization. There were linear relationship between PAHs desorption ratio and PAHs lgKow value. The desorption ratio of PAHs in artificially contaminated soil was higher than in oil-contaminated soil.

[Effect of surfactants on biodegradation of PAHs by white-rot fungi].

The impacts of surfactants (Tween80, Trition X-100, LAS and SDS) on PAHs degradation by white-rot fungi in aqueous system and soil-water system were studied. Results show that the type and concentration of surfactants, PAHs statues, pH value of the systems and temperature have impacts on the degradation of PAHs. In aqueous system, all the four surfactants restrained the degradation of PAHs. In soil-water system, Trition X-100 and SDS restrained the degradation of PAHs, while the impacts of Tween80 and LAS on PAHs degradation were influenced by the concentration of the surfactants. Low concentration Tween80 and LAS didn't promote the degradation of PAHs, and even played minor effects of restrain. But the degradation of PAHs could be enhanced with the increasing of the concentrations of Tween80 and LAS to certain levels. However, Tween80 and LAS with significant higher concentrations didn't show higher abilities on the promotion of PAHs degradation.

[Influences of surfactant on the transport of PAHs in artificially contaminated soil columns].

The effect of anionic surfactant LAS on leaching of PAHs from artificially contaminated soil was studied. The interaction of these processes were studied in a two-layer column experiment with a base layer of uncontaminated soil(9cm) and a top layer of artificially contaminated soil(1cm). Results show that 5 critical micelle concentration (CMC) LAS enhanced the transport of PAHs. The breakthrough curves of low ring PAHs followed the normal distribution and the relative leaching ratios of 4 or more rings PAHs were low, and not more than 10%. The transport of PAHs was retarded compared with LAS, and the high ring PAHs were retarded more significantly. Linear correlation was observed between the relative leachability of the individual PAHs and the octanol/water coefficient of PAHs.