Pentachloronitrobenzene (PCNB) is an organochlorine fungicide used either as seed dressing or for soil treatment. Research was conducted to investigate the microbial reductive transformation of PCNB with cultures developed from a contaminated estuarine sediment. The biotransformation of PCNB to pentachloroaniline (PCA) occurred under all electron accepting conditions tested. Sequential dechlorination of PCA to di- and in some cases to mono-chlorinated anilines occurred under fermentative/methanogenic conditions. Based on the use of inhibitors, methanogens were not involved in the sequential dechlorination of PCA. Based on 16S rRNA gene analysis, among five known dechlorinating bacterial groups tested, only Dehalococcoides was detected in the mixed culture. The sequential dechlorination of PCA was simulated using a branched-chain Michaelis-Menten kinetic model. The dechlorination rate (k) of the chlorinated anilines ranged from 0.25 to 1.19 uM/day and the half-saturation coefficient (KC) ranged from 0.11 to 1.72 uM at an incubation temperature of 22C and pH 6.90.1. Incubation at different temperature and pH values resulted in significant differences in the biotransformation rate and extent of PCNB in the fermentative/methanogenic enrichment culture. Incubation at 35C resulted in significantly different product distribution. The effect of temperature on the PCA dechlorination rate was modeled using an Arrhenius relationship. Dechlorination of PCA and methanogenesis were not observed in cultures amended with completely bioavailable iron sources until all Fe3+ was reduced to Fe2+. In contrast, PCA dechlorination took place at the same time with iron reduction in the same mixed, methanogenic culture amended with a less bioavailable iron source (FeOOH). PCA was sequentially dechlorinated to dichloroanilines in cultures amended with low nitrate concentrations, whereas partial dechlorination of PCA to tetrachloroanilines was observed in cultures amended with high initial nitrate concentrations due to the accumulation of reduced nitrogen species (e.g., NO, N2O). A semi-empirical molecular model (MOPAC/AM1) was used to estimate the thermodynamic and electronic properties of all chlorinated aniline congeners. These values were used to predict the sequential PCA dechlorination pathway and compare to experimentally observed dechlorination reactions. The results of this study have significant environmental implications relative to the fate and transport of PCNB, PCA and its dechlorination products in subsurface systems.

Recent studies have demonstrated the omnipresence of antibacterial agents in the aquatic environment due to high usage and widespread applications of these compounds in medicine and agriculture, raising concerns over proliferation of antibiotic-resistant bacteria and other adverse health effects. Tetracyclines (TCs) are among the most widely used antibiotics and their fate and transformation in the soil-water environment are not yet well understood. Based on TCs' strong tendency to interact with metals, their environmental fate and transport are expected to be greatly influenced by metal species commonly present in waters and soils and thus the focus of this study. The study results show that TCs are highly susceptible to oxidative transformation mediated by dissolved Mn(II) and Cu(II) ions and manganese dioxide under environmentally relevant conditions. The oxidative transformation can occur via different TC structural moieties and reaction pathways when different metal species are involved, leading to complicated product formation patterns. It was also found that Al oxide surfaces can promote the acid-catalyzed isomeration and dehydration of TCs. To better evaluate the surface reactions of Mn oxide with TCs and other compounds, a new kinetic model was successfully developed to describe the complex reaction kinetics based on the experimental results with TCs and three other classes of antibacterial agents. Overall, this work significantly advances the fundamental understanding of the reaction mechanisms of TC compounds and provides the knowledge basis for better risk assessment of these compounds in the environment.

Abiotic transformation of compounds in the natural environment by metal oxides plays a significant a role in contaminant fate and behavior in soil. The ability of birnessite, ferrihydrite and green rust to abiotically transform insensitive munitions compounds (IMCs) parent (2,4 dinitroanisole [DNAN] and 3-nitro-1,2,4-triazol-5-one [NTO]), and daughter products (2-methoxy-5-nitro aniline [MENA], 2,4-diaminoanisole [DAAN]of DNAN; and 5-amino-1, 2, 4-triazol-3-one [ATO] of NTO) was studied in batch reactors under strictly controlled pH and ionic strength. The objectives of the study were to (i) assess the abiotic transformation potential of soluble DNAN, MENA, DAAN, NTO and ATO by birnessite, ferrihydrite and green rust, and (ii) identify inorganic reaction products. The study was carried out at metal oxide solid to IMC solution ratios (SSR) of 0.15, 1.5 and 15 g kg⁻¹ for birnessite and ferrihydrite and 10 g kg⁻¹ for green rust. Aqueous samples were collected at time intervals between 0 to 3 days after the reaction initiation and analyzed using HPLC with UV detection. Results indicated that DNAN was resistant to oxidation by birnessite and ferrihydrite at given solid to solution ratios. MENA was susceptible to rapid oxidation by birnessite (first order rate constant, 𝑘=1.36 h⁻¹ at 15 g kg⁻¹ SSR). The nitro groups from MENA largely mineralized to nitrite (NO₂⁻). In contrast, ferrihydrite did not oxidize MENA. DAAN was susceptible to oxidation by both birnessite and ferrihydrite, but about a six times higher oxidation rate was observed with birnessite (𝑘=1.18 h⁻¹) as compared to ferrihydrite (𝑘=0.22 h⁻¹) at an SSR of 1.5 g kg⁻¹. There was a complete loss of DAAN from solution after 5 min with birnessite at an SSR 15 g kg⁻¹ (𝑘≥90.5 h⁻¹). CO₂ evolution experiments indicate mineralization of 15 and 12 % of carbon associated with MENA and DAAN, respectively; under aerobic conditions with birnessite at an SSR of 15 g kg⁻¹. NTO was resistant to oxidation by birnessite and ferrihydrite at any SSR; however, there was slight initial loss from solution upon reaction with ferrihydrite at 0.15 and 1.5 g kg⁻¹ SSR and complete loss at 15 g kg⁻¹ SSR due to adsorption. ATO was susceptible to oxidation by birnessite and sorption by ferrihydrite. The first order rate constants (𝑘) for ATO with birnessite at 0.15 and 1.5 g kg⁻¹ SSR are 0.04 and 3.03 h⁻¹ respectively. There was complete loss of ATO from solution with birnessite at 15 g kg⁻¹ SSR (𝑘 ≥ 90.2 h⁻¹) within 5 min of reaction. Transformation products analysis revealed urea, CO₂ and N₂ as major reaction products with 44 % urea recovery and recovery of 51.5 % of ATO carbon as CO₂ and 47.8 % of ATO nitrogen as N₂ at 15 g kg⁻¹ SSR. The oxidation of ATO in the presence of birnessite was found to be independent of dissolved O₂. The results indicate that ATO, the major reductive (bio)transformation product of NTO, is readily oxidized by birnessite in soil. NTO was found strongly sorbed to ferrihydrite as compared to that of ATO. The results of the green rust experiment indicate rapid abiotic reduction of parent compounds NTO and DNAN to their reduced aminated daughter products. NTO was generally reductively transformed to 5-amino-1, 2, 4-triazol-3-one (ATO) within 10 min and completely reacted in 20 min. DNAN was rapidly transformed to its reduced daughter products MENA and 4-methoxy-5-nitroaniline (iMENA). The reduction occurred with a distinctive, staggered regioselectivity. Over the first 10 min, the para-nitro group of DNAN was selectively reduced, generating iMENA. Thereafter the ortho-nitro group was preferentially reduced, generating MENA. Both iMENA and MENA were subsequently transformed to the final reduction product DAAN within 1 day. X-ray absorption near edge spectroscopy data suggested oxidative transformation of green rust to lepidocrocite-like mineral forms, accounting for 94 % of the mineral products in the case of NTO reaction as compared to 62 % in the case of DNAN. The results taken as whole suggest that complete abiotic transformation of IMCs could be achieved by coupled stepwise green rust and birnessite treatments.

Le thème principal de cette recherche est la remédiation des sols contaminés par des hydrocarbures en utilisant des traitements d'oxydation chimique à pH neutre. Les minéraux à base de fer sont susceptibles de catalyser cette réaction d'oxydation. L'étude concerne donc dans un premier temps la synthèse des minéraux réactifs contenant des espèces FeII et FeIII (la magnétite et la rouille verte) et, dans un second temps, leur utilisation pour catalyser l'oxydation chimique. Les procédés d'oxydation testés incluent l'oxydation de type « Fenton-like (FL) » et de type persulfate activé (AP). La formation de la magnétite et de la rouille verte a été étudiée par des transformations abiotiques de différents oxydes ferriques (ferrihydrite, goethite, hématite et lépidocrocite) mis en présence de cations FeII. La magnétite a été utilisée pour catalyser les oxydations (FL et AP) dans la dégradation des hydrocarbures aliphatiques et aromatiques polycycliques (HAP) à pH neutre. Une dégradation importante des hydrocarbures aliphatiques a été obtenue par ces deux oxydants, aussi bien pour des pétroles dégradés naturellement que pour un pétrole brut. L'oxydation catalysée par la magnétite a également été efficace pour la remédiation de deux sols contaminés par HAP provenant d'anciens sites de cokerie. Aucun sous-produit n'a été observé dans nos expériences d'oxydation. En revanche, une très faible dégradation des hydrocarbures a été observée lorsque les espèces FeII solubles ont été utilisées comme catalyseur. Des expériences d'oxydation ont également été réalisées en colonne. Ces études d'oxydation ont révélé l'importance du type de catalyseur utilisé pour l'oxydation, la disponibilité des HAP dans les sols et l'effet de la matrice du sol. Les résultats suggèrent que la magnétite peut être utilisée comme source de fer pour activer les deux oxydations par Fenton-like et persulfate à pH neutre. Ce travail a de fortes implications sur la remédiation par oxydation chimique in situ des sols pollués par des hydrocarbures / The main theme of this research is the use of reactive iron minerals in the remediation of hydrocarbon contaminated soils via chemical oxidation treatments at circumneutral pH. The contribution of this thesis is two-fold including the abiotic synthesis of mixed FeII-FeIII oxides considered as reactive iron minerals (magnetite and green rust) and their use to catalyze chemical oxidation. Oxidation methods tested in this study include Fenton-like (FL) and activated persulfate oxidation (AP). The formation of magnetite and green rust was studied by abiotic FeII-induced transformations of various ferric oxides like ferrihydrite, goethite, hematite and lepidocrocite. Then, the ability of magnetite was tested to catalyze chemical oxidation (FL and AP) for the degradation of aliphatic and polycyclic aromatic hydrocarbons (PAHs) at circumneutral pH. Significant degradation of oil hydrocarbons occurring in weathered as well as in crude oil was obtained by both oxidants. Magnetite catalyzed oxidation was also effective for remediation of two PAHs contaminated soils from ancient coking plant sites. No by-products were observed in all batch slurry oxidation systems. Very low hydrocarbon degradation was observed when soluble FeII was used as catalyst under the same experimental conditions. Magnetite also exhibited high reactivity to catalyze chemical oxidation in column experiments under flow through conditions. Oxidation studies revealed the importance of catalyst type for oxidation, PAHs availability in soils and the soil matrix effect. Results of this study suggest that magnetite can be used as iron source to activate both Fenton-like and persulfate oxidation at circumneutral pH. This study has important implications in the remediation of hydrocarbon polluted soils through in-situ chemical oxidation