In situ remediation of soils contaminated with toxic metal ions using microwave energy

Following onto our work on the in situ remediation of soils contaminated with PAH's, PCB's and other polychlorinated organic compounds using microwave energy, we now report a preliminary investigation on the in situ remediation of soils contaminated with toxic metal ions: Cd(II), Mn(II), Th(IV), Cr(III) and mainly Cr(VI). The soil is partially vitrified in the process, and extraction with hot (70 degrees C) 35% nitric acid for 4.5 h leads to the recovery of very small amounts of the metals which had been spiked into the clean soil: Cd, Mn, and Cr(III) are completely immobilized (unextractable), Th is mostly unextractable, and Cr(VI) partially extractable at very high levels of spiking, but almost completely unextractable using the US EPA Toxicity Characteristic Leaching Procedure. This suggests that contaminated soils which are not going to be used for agricultural purposes can be remediated safely to preset depths without fear of the toxic metal ions leaching out for a long time.     

Catalytic NOx reduction with simultaneous dioxin and furan oxidation

The engineering, construction, performance and running costs of a catalytic flue gas cleaning component in the low dust area of a municipal waste incinerator is discussed. For this purpose, the case study of a Flemish incineration plant is presented, covering the history, the design procedure of the catalyst, relevant process data and the financial aspects. A reliable PCDD/F-destruction by means of oxidation by the catalyst to typical values of 0.001 ng TEQ/Nm3 has been demonstrated. At the same time, NOx- and CO-emissions are reduced by 90% and 20% to about 50 mg/Nm3 and below 10 mg/Nm3, respectively.     

Dissolution rates of three high explosive compounds: TNT,RDX, and HMX

Incidental exposure to high explosive compounds can cause subtle health effects to which a population could be more susceptible than injury by detonation. Proper source characterization is a key requirement in the conduct of risk assessments. For nonvolatile solid explosives, dissolution is one of the primary mechanisms that controls fate and transport, resulting in exposure to these compounds remote from their source. To date, information describing dissolution rates of high explosives has been sparse. The objective of this study was to determine the dissolution rates of three high explosive compounds, 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), in dilute aqueous solutions as a function of temperature, surface area, and energy input. To determine each variable's impact on dissolution rate, experiments were performed where one variable was changed while the other two were held constant. TNT demonstrated the fastest dissolution rate followed by HMX and then RDX. Dissolution rate correlation equations were developed for each explosive compound incorporating the three aforementioned variables, independently, and collectively in one correlation equation.     

Photochemistry of 1-nitro-2-phenylnaphthalene available to the environment

Photolysis (254 nm, 72h) of 1-nitro-2-phenylnaphthalene $\text{1}$ in methanol gave 2-phenyl-1,4-naphthoquinone-4-monoxime $\text{2}$, 2,2′-diphenyl-4,4′-binaphth-1,1′-diol $\text{3}$ and 2,2′-diphenyl-4,4′-binaphth-1,1′-dione $\text{4}$. Straightforward reactions available to the environment account for the formation of the products: (a) isomerisation of the nitro compound into a nitrite ester followed by either (a) migration of the nitroso group and isomerisation into the oxime $\text{2}$ or (b) oxidative coupling and solvolysis into the binaphthol $\text{3}$ and followed by oxidation into the binaphthone $\text{4}$.     

The identification of three previously unreported lindane metabolites from mammals

Previously unreported metabolites from the urine of rats treated with lindane have been identified as configurational isomers of 2,4,5,6- and 2,3,4,6-tetrachloro-2-cyclohexen-1-ol. In addition, an intermediate metabolite from the incubation of lindane with liver preparations, under N₂, has been identified as the configurational isomer γ-3,4,5,6-tetrachlorocyclohex-1-ene. The pathways leading to these metabolites appear to have an important role in the metabolism of lindane by mammals.     

Identification of dimethylchloroarsine near a former herbicide factory by headspace solid-phase microextraction gas chromatography-mass spectrometry

The application of an improved method based on multidetector gas chromatography to the determination of trace levels of organoarsines in complex matrices is described. The method using headspace-mode solid-phase microextraction (SPME) was applied to a carefully sampled and preserved freshwater sediment core obtained from central Green Bay, Lake Michigan. The sediment core was collected and fractionated in an inert atmosphere. A carboxen/ polydimethylsiloxane-coated SPME fiber (85 microm film thickness) was equilibrated (n = 4) for 60 min at 25 degrees C in the headspace of the sample vessel before introduction to the chromatograph. Conventional quadrupole ion trap mass spectrometry (electron impact ionization), electron capture detection, and pulsed flame photometric detection (arsenic mode) were employed for structure elucidation. A heretofore unidentified species in this region, dimethylchloroarsine (DMCA). was identified. The mass spectrum for DMCA is interpreted based on the observed fragmentation pattern. A bimodal vertical distribution of DMCA in the sediment core sample was observed and its interpretation based on Pb-210 dating is reported.     

Molarity provides better clarity – using molar-based data when evaluating chlorinated volatile organic compound impacted sites

Abstract

Chlorinated volatile organic compounds are common constituents observed at many contaminated groundwater sites. Common industry practice has been to measure these constituents in groundwater on a weight concentration basis (e.g. µg/l, mg/l). This paper highlights the use of molar-based concentrations, especially in the case of parent-daughter degradation sequences commonly observed with the chloroethene, chloroethane, and chloromethane families of compounds. Converting to molar-based concentrations provides the practitioner greater insight into groundwater plume behavior including better evaluation of degradation processes, remedial progress, possible commingling, and/or sourcing. For example, this paper provides a tank analogy to evaluate whether the commonly misinterpreted observation of “DCE-stall” may be occurring at a site. Multiple examples of the benefits of using molar-based concentration data are also summarized in a project case study presented herein. As demonstrated in this paper, molarity does provide better clarity and can be a powerful evaluation tool in the groundwater practitioner’s toolbox.     

Modeling radium and radon transport through soil and vegetation

A one-dimensional flow and transport model was developed to describe the movement of two fluid phases, gas and water, within a porous medium and the transport of 226Ra and 222Rn within and between these two phases. Included in this model is the vegetative uptake of water and aqueous 226Ra and 222Rn that can be extracted from the soil via the transpiration stream. The mathematical model is formulated through a set of phase balance equations and a set of species balance equations. Mass exchange, sink terms and the dependence of physical properties upon phase composition couple the two sets of equations. Numerical solution of each set, with iteration between the sets, is carried out leading to a set-iterative compositional model. The Petrov-Galerkin finite element approach is used to allow for upstream weighting if required for a given simulation. Mass lumping improves solution convergence and stability behavior. The resulting numerical model was applied to four problems and was found to produce accurate, mass conservative solutions when compared to published experimental and numerical results and theoretical column experiments. Preliminary results suggest that the model can be used as an investigative tool to determine the feasibility of phytoremediating radium and radon-contaminated soil.     

Changes in water quality after addition of sea salts to fresh water: implications during toxicity testing

Sea salts (seven brands from six commercially-available sources) were dissolved in water to develop 30 g/l solutions, and selected water quality characteristics were then monitored for 96 h. One or more water quality characteristics changed significantly during the 96 h period in six of the reconstituted sea salts. Measured characteristics of sea water diluted to 30 g/l demonstrated no changes during the observation period. The sea salts from different sources also demonstrated differences in absolute concentrations of some characteristics measured. Application of the Biotic Ligand Model to predict copper toxicity to the bivalve Mytilus edulis in solutions of the salts tested yielded 96-h median-lethal concentrations that ranged from 2 to 13 μg/l. Since water quality affects toxicity of many environmental pollutants, the source of the sea salt and equilibration time should be considered when planning toxicity tests.