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Atrazine, a member of the s-triazine herbicides, appears on the EC Red List of chemicals that cause environmental concern, with residues occurring frequently in sub-soils and aquifers world-wide. Microbial metabolism is considered to be the major mechanism of complete removal of atrazine from the soil environment. Laboratory-based studies were carried out to investigate the microbial mineralisation of atrazine in soil, and to develop novel methods for potential acceleration of breakdown. In initial investigations, simple microcosm experiments were carried out to identify the importance of different fractions (water-soluble and water-insoluble) of plant residues to the dynamics, and extent of atrazine mineralisation. The amendment of soil with different plant residue fractions initially inhibited (for the water-soluble fraction) or enhanced (for the water-insoluble fraction) dynamics of atrazine mineralisation. However, by the end of the incubation, there was no overall effect on atrazine mineralisation. This suggested that increasing the soil organic matter content may render the herbicide less bioavailable to the degrader population. Investigations carried out to determine which component of the microbial biomass was more important in atrazine mineralisation showed that substantial removal of the fungal and Gram-negative bacterial population inhibited atrazine mineralisation in the soil. Experiments to selectively enrich the soil for fungal or bacterial atrazine degraders isolated a mixed bacterial culture able to accelerate atrazine mineralisation when inoculated into soil. The effect of the presence of the earthworm Lumbricus terrestris on the indigenous atrazine degrading microflora was investigated. Results indicated that atrazine mineralisation could be accelerated, but this was not primarily due to increases in microbial biomass, but possibly due to physio-chemical changes brought about by the earthworm and subsequent alterations in atrazine bioavailability.

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Pentachlorophenol (PCP) is a chloride-containing aromatic compound which is mostly used for preserving wood and leather, but still one can easily detect this compound present in the waste water generated by various industries such as petrifaction, oil-refining, and etc. PCP, due to its chemical property of being stable and highly toxic, would cause severe and irreparable environmental pollution once exposed to open air. This study is intended to explore the feasibility of dealing the problem of PCP with biodegradation. The examination results showed that, except for absorption, the suspension of contaminated soil (aerobic incubation), nonetheless, could effectively degrade PCP during a period of 90 days without the aid of any extra carbon source. (0.62 mg/L/day). The degradation rate was further greatly improved by adding sodium acetate, molasses, and sludge cake (sodium acetate added: 4.15 mg/L/day; molasses added: 1.05 mg/L/day; sludge cake added:0.83 mg /L/day). None of four experimental groups of aerobic sludge, anaerobic sludge, contaminated soil (anaerobic incubation), and Fe3+reaction could degrade PCP after 135 days, 174 days, 250 days, and 124 days, respectively, regardless of whether any sources of carbon were added or not. A bacterium which used PCP as the sole carbon source was isolated from the contaminated soil. After 16s rDNA sequence analysis, it had 98% degree of similarity to Pseudomonas mendocina and was designated as Pseudomonas mendocina NSYSU. The PCP (40 mg/L) degradation rate of Pseudomonas mendocina NSYSU was 9.33 mg/L/day, and the degradation rate would slow down as PCP concentration increased. At a PCP concentration of 320 mg/L, PCP degradation was completely inhibited, although an active population of Pseudomonas mendocina NSYSU was still present in these cultures. The study also indicated that the addition of various carbon sources such as sodium acetate and glucose did not facilitate the degradation of PCP with the degradation rate of 8.11 mg/L/day for sodium acetate, and that of 7.55 mg/L/day for glucose. Analysis from examining several environmental factors showed that the optimal condition for PCP degradation is that of 30¢J, pH6, and in the presence of oxygen. The end products of PCP degradation were detected by GC-MS. After 6 days of incubation, PCP was gradually disappeared and the metabolic intermediate product, acetic acid was detected. The chloride ion concentration also increased by 21.8 mg/L, which is approximately equal to the original total chloride content in PCP (66% of chloride content). In conclusion, PCP could be effectively and completely degraded by Pseudomonas mendocina NSYSU.

Des résultats récents ont montré que les podzols équatoriaux stockent d’importantes quantités de carbone dans leurs horizons Bh profonds. Cette constatation amène deux questions principales : (1) comment et à quel rythme se sont formés ces sols (2) dans quelle mesure le changement climatique pourrait induire une production par ces sols de carbone atmosphérique susceptible d’impacter le système climatique mondial.Dans ce contexte, nous avons réalisé un modèle qui permet de contraindre les flux de carbone à la fois par les stocks observés et leur âge 14C. En situation suffisamment simplifiée, nous avons établi une relation formelle entre l’évolution des stocks et l’âge 14C de celui-ci. Appliqué aux podzols amazoniens, notre modèle a apporté des résultats nouveaux et inattendus. Il a permis de montrer que ce sont les horizons de surface des aires podzolisées les plus hydromorphes qui sont les plus gros contributeurs de MOD transférée vers le réseau hydrographique et la mer. On observe que la formation des Bh n’est possible qu’en envisageant deux compartiments, rapide et lent. Une estimation basse de leur temps de formation permet de différencier des podzols relativement jeunes (temps de formation de l’ordre de 15 103 - 25 103 ans), développés sur des sédiments Holocènes relativement récents, et des podzols âgés (temps de formation de l’ordre de 180 103 - 290 103 ans), développés sur des sédiments plus anciens. Le taux d’accumulation du carbone dans les podzols étudiés varie de 0,54 à 3,17 gC m-2 an-1, ce qui correspond à une séquestration de carbone de l’ordre de 3 1011 gC an-1, faibles à l’échelle annuelle, mais significative aux échelles géologiques.Les expérimentations de percolation en colonne nous ont permis de montrer la réactivité du Bh et la présence, malgré des rapports C/N très élevés (63 en moyenne), d’une activité bactérienne significative qui modifie la nature de la MOD qui le traverse. Cette dernière a la capacité de transporter Al et Fe sous forme de complexes organo-métalliques, complexes susceptibles de migrer à travers des matériaux très kaolinitiques. Ces résultats participent à la compréhension des transferts de MOD d’origine pédologique dans les nappes profondes.Dans l’hypothèse de l’apparition d’un climat à saisons contrastées, nous avons pu montrer qu’une durée sans pluie de 90 jours après disparition de la nappe perchée ne permettrait pas d’atteindre le point d’entrée d’air par assèchement des horizons superficiels. Néanmoins, dans l’hypothèse d’une entrée d’air, l’extrapolation des taux de minéralisation mesurés expérimentalement en conditions oxiques aboutit à une production de C atmosphérique de l’ordre de 2,0 1014 g de CO2 par an, ce qui peut impliquer une rétroaction positive du système climatique mondial. / Recent results have shown that equatorial podzols store large amounts of carbon in their deep Bh horizons. This leads to two main questions: (1) how and at what kinetics these soils were formed, (2) how climate change could induce atmospheric carbon production that could impact the global climate system.In this context, we have developed a model that allows to constrain carbon fluxes both by the observed C stocks and their 14C age. In a sufficiently simplified situation, we have established a formal relationship between the C stock evolution and its 14C age. Applied to Amazonian podzols, our model has brought new and unexpected results. It has been shown that the surface horizons of the most hydromorphic podzolized areas are the largest contributors of MOD transferred to the hydrographic network then to the sea. It is observed that the formation of Bh is only possible by considering two compartments, fast and slow. The estimate of their formation time (low estimate) allowed to differentiate between relatively young podzols (formation time 15 – 25 ky) developed on relatively recent Holocene sediments and old podzols (formation 180 – 290 ky) developed on older sediments. The carbon accumulation rate in the studied podzols ranges from 0.54 to 3.17 gC m-2 y-1, which corresponds to a carbon sequestration around 3 1011 gC an-1, which is significant at the geological scales.Column percolation experiments allowed us to show the reactivity of the Bh material and the presence, despite very high C/N ratios (63 on average), of a significant bacterial activity which modifies the nature of the MOD which percolates through it. This MOD has the capacity to transport Al and Fe in the form of complex organometallic complexes capable of migrating through very kaolinitic materials. These results contribute to the understanding of the transfers of pedologically formed MOD in the deep aquifers.Under the hypothesis of the appearance of a climate with contrasting seasons, we have been able to show that a 90-day period without rain after the disappearance of the perched water-table would not allow to reach the point of entry of air by drying of superficial horizons. Nevertheless, assuming an air entry, the extrapolation of the experimentally measured mineralization rates under oxic conditions results in a production of atmospheric C around 2.0 1014 g of CO2 per year, which may involve a positive feedback from the global climate system.