Kinetic constraints on theIn-situ remediation of soils contaminated with organic chemicals

Remediation of trapped DNAPL enhanced by SDS surfactant and silica nanoparticles in heterogeneous porous media: experimental data and empirical models

The remediation of nonaqueous phase liquids (NAPLs) enhanced by surfactant and nanoparticles (NP) has been investigated in numerous studies. However, the role of NP-assisted surfactants in the dissolution process is still not well discussed. Besides, there is a lack of empirical dissolution models considering the effects of initial residual saturation S_trap, NAPL distribution, and surfactant concentration in NAPL-aqueous phase systems. In this work, micromodel experiments are conducted to quantify mass transfer coefficients for different injected aqueous phases including deionized water, SDS surfactant solutions, and NP-assisted solutions with different levels of concentrations and flow rates. Observations reveal that silica nanoparticles (SNP) can significantly enhance interphase mass transfer, while SDS surfactant reduces the mass transfer coefficient. In addition, S_trap and intrinsic interfacial area a_i, as an indicator of dense nonaqueous phase liquids (DNAPL) distribution, influence the interphase mass transfer. The a_i is also independent of DNAPL saturation S_NAPL except for S_NAPL < 7% when ganglia breakup occurs. Based on these observations, new empirical dissolution models are proposed in the presence and the absence of SDS surfactant and SNP in which a_i, S_trap, and surfactant concentrations are introduced as new parameters. The evaluated mass transfer rate coefficients using the proposed models show a significant improvement compared to available empirical models. The finding of this study might be attractive for application in field-scale simulations of surfactant-enhanced aquifer remediation (SEAR) and NP-assisted methods.

Formation and release of non-extractable 14C-Dicamba residues in soil under sterile and non-sterile regimes

The role of native soil microorganisms in the formation and release of non-extractable (14)C-residues, previously treated with (14)C-Dicamba, was investigated to examine their significance to the longer-term environmental effects on non-extractable pesticide residues. A 90 d study compared the fate of Dicamba under sterile and non-sterile regimes. In addition, soils were aged for 30 d and repeatedly extracted with a 0.01 M CaCl(2) solution, to an extraction end point, to produce non-extractable residues. The extracted soil containing non-extractable residues was mixed with clean soil that had been freshly spiked with non-labeled Dicamba at 0.2 mg kg(-1) to increase the bulk volume of the soil and stimulate microbial activity. Sub-samples were then introduced into microcosms to compare the extent of microbially facilitated release and mineralisation with release rates in sterile microcosms. The results show that microorganisms play a significant role in the formation and release of non-extractable Dicamba residues. The release of (14)C-activity in sterile microcosms was linked to physical mixing of the extracted soil with field soil prior to the beginning of the incubations. The released (14)C-activity may be further mineralized, reincorporated into humus, or taken up by plants or other soil inhabiting biota.

Bound pesticide residues in soils: a review

This article is a review of the current state of knowledge regarding the formation and biological/environmental significance of bound pesticide residues in soils. We begin by defining various terms used in our discussions and identifying the types/classes of pesticides which may be added to soil and interact with it. We then consider various soil properties and aspects of land management which will influence the nature and degree of the soil-pesticide association and discuss the possible physical and chemical binding mechanisms. We then move on to consider the role of microorganisms and other forms of soil biota in bound residue formation and the bioavailability of soil-borne pesticide residues. The review ends with a consideration of the significance of bound pesticide residues.

The form and bioavailability of non-ionic organic chemicals in sewage sludge-amended agricultural soils

The application of sewage sludges to agricultural land may increase the concentrations of many toxic organic chemicals in soils which could have adverse effects on wildlife and human health if these compounds enter foodchains. Chlorobenzenes (CBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) are amongst those compounds currently receiving most attention. The "form' in which these, and other organic chemicals, are present in soils and their potential to be lost by various processes including leaching, volatilisation and (bio)degradation is shown to be dependent on the physicochemical characteristics of the soil and sewage sludge, environmental conditions and the properties of the chemicals themselves. The distinction is made between those compounds that are labile, reversibly sorbed and irreversibly sorbed by sewage sludge-amended soils. The implications of the form in which the chemicals are present in soil for their "availability' to transfer from the soil to bacteria, fungi, earthworms, grazing livestock and food crops followed by the potential for further transfers, metabolism or bioaccumulation are discussed. The importance of the timing and method of sewage sludge application to soil on "form' and "availability' are also considered.