Pesticide degradation

Pesticide degradation is the process by which a pesticide is transformed into a benign substance that is environmentally compatible with the site to which it was applied. Globally, an estimated 1 to 2.5 million tons of active pesticide ingredients are used each year, mainly in agriculture. Forty percent are herbicides, followed by insecticides and fungicides. Since their initial development in the 1940s, multiple chemical pesticides with different uses and modes of action have been employed. Pesticides are applied over large areas in agriculture and urban settings. Pesticide use, therefore, represents an important source of diffuse chemical environmental inputs. Persistence In principle, pesticides are registered for use only after they are demonstrated not to persist in the environment considerably beyond their intended period of use. Typically, documented soil half-lives are in the range of days to weeks. However, pesticide residues are found ubiquitously in the environm

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Le cours "Microbiologie pour l'ingénieur" couvre les processus microbiens principaux qui ont lieu dans l'environnement et dans des systèmes de traitement. Il présente les cycles des éléments qui sont catalysés par des microorganismes et qui ont un impact important sur la planète Terre.

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Phototransformation of Organic Contaminants in Aquatic Systems: Characterization of Long-Lived Photooxidants Derived from Dissolved Organic Matter

Stephanie Christa Remke

The increasing interest in the fate of organic contaminants in the aquatic environment requires the elucidation of relevant abiotic transformation processes. These processes often involve the ubiquitous dissolved organic matter (DOM), a complex mixture of organic compounds present in the aquatic environment. Upon light absorption of DOM a range of photochemically produced reactive intermediates (PPRI) form, which may induce the transformation of organic contaminants. PPRI reacting as oxidants have been proposed to consist of two pools, short-lived photooxidants, such as singlet oxygen (1O2), the hydroxyl radical (.OH) and triplet states of chromophoric DOM (3CDOM*), and long-lived photooxidants (LLPO), whose nature is still unclear. LLPO-induced transformations were hypothesized to cause a concentration-dependent enhancement effect observed for 3CDOM*-induced transformations. Thereby, pseudo-first-order phototransformation rate constants for electron-rich phenols increased when their initial concentrations were lowered from 5.0 to 0.1 mikroM. Phenolic moieties within DOM have been proposed as LLPO precursors. This thesis tests the hypothesis that LLPO are relevant PPRI, formed, concomitantly with 3CDOM* upon DOM light absorption, from phenolic DOM precursors. Experimental methods used in this thesis include steady-state irradiations, laser flash photolysis and studies with DOM surrogates and pre-oxidized DOM. The occurrence of LLPO-induced phototransformations was tested by analyzing target compound transformation kinetics for two initial concentrations, namely 5.0 and 0.1 mikroM in steady-state irradiation experiments. The aforementioned enhancement effect for the lower initial concentration was taken as an indicator for the involvement of LLPO in the phototransformation. Firstly, the relevance of LLPO in the phototransformation of various aquatic contaminants was evaluated. Electron-rich phenols, anilines and phenylureas were identified to be susceptible to LLPO-induced transformations. The LLPO reduction potential could be estimated to lie between 1.0 to 1.3 V vs. SHE. Secondly, LLPO-induced target compound transformation was mimicked by photochemically produced electron-poor phenoxyl radicals. Enhanced target compound transformation was observed for 0.1 mikroM initial concentration with any of the tested phenoxyl radicals, which were generated by the photosensitized oxidation of the parent phenols in aqueous solution. Reactivity increased proportionally with the one-electron reduction potential of the electron-poor phenoxyl radical. Finally, characterization of LLPO precursors was attempted by DOM pre-oxidation. A DOM isolate, Suwannee River fulvic acid, was pre-oxidized, by chlorine and ozone (with and without t-BuOH), characterized by measurements of UV absorbance measurements and electron donating capacity and subsequently tested for its photoreactivity. The chemical pre-oxidation lead to changes of DOM, such as decrease in aromaticity and phenol content, in accordance to previous studies. LLPO precursors were concluded to be composed of oxidant susceptible sites and to likely include phenolic DOM moieties. The results presented in this thesis corroborate the hypothesis of LLPO formed from phenolic DOM precursors upon DOM light absorption. One consequence drawn from this thesis is the recommendation to include target compound concentrations < 1 mikroM in laboratory-scale phototransformation experiments.

EPFL2021

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Analyse des pesticides dans les cheveux: une nouvelle approche pour l’évaluation de l’exposition professionnelle

Christelle Oltramare

pesticides. A high number of pesticides are known as endocrine disrupting chemicals or having a supposed or verified carcinogenic effect. These toxic compounds are found in the environment, in water or in food. Once in our organism these molecules can be metabolised or stored. GOALS. In order to measure the impact on human health of gardening activity in Burkina Faso, hair analysis will provide information on the pesticides’ exposition of operators. The evaluation of pesticides exposure risks for human health is usually over estimated when there is only the analysis of environmental matrices (air, water, soil…) As the aim of this project is to understand the impact of gardening activity, the volunteers who participate in this project will be classified into two groups. First, the exposed population considers the operators. Then, the reference population regroups people living in the same area that the population studied, but without being in direct contact with pesticides. This population will be our baseline. In this way, contaminations due to other vectors such as food, water, vector control etc. will not be considered to evaluate the exposition due to gardening. An inovative protocole. The protocol developed, optimised and used for natural samples is inspired from the existing method QuEChERS AOAC 2007.01. This method is used to analyse pesticides in fruits, vegetables or soils samples. The main principle is simple and based on the salting-out effect. Hair pesticides residue analysis are made in GC/MS and LC/MS-MS. REsults. Analysis over 73 volunteers shows a 100% contamination of imidaclorprid in hair. The professional activity impact is observable on the acetamiprid concentration (10 times more in gardener’s population than in the reference population). The exposed population has a mean sum of 2469.3 ng pesticides/ g hair whereas the reference population has a mean sum of 1709.5 ng pesticides/g of hair.

2016

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Chlorinated ethene plume evolution after source thermal remediation: Determination of degradation rates and mechanisms

Christof Holliger, Julien Maillard, Alexandra Marie Murray, Jérémy Zimmermann

The extent, mechanism(s), and rate of chlorinated ethene degradation in a large tetrachloroethene (PCE) plume were investigated in an extensive sampling campaign. Multiple lines of evidence for this degradation were explored, including compound-specific isotope analysis (CSIA), dual C-Cl isotope analysis, and quantitative realtime polymerase chain reaction (qPCR) analysis targeting the genera Dehalococcoides and Dehalogenimonas and the genes vcrA, bvcA, and cerA. A decade prior to this sampling campaign, the plume source was thermally remediated by steam injection. This released dissolved organic carbon (DOC) that stimulated microbial activity and created reduced conditions within the plume. Based on an inclusive analysis of minor and major sampling campaigns since the initial site characterization, it was estimated that reduced conditions peaked 4 years after the remediation event. At the time of this study, 11 years after the remediation event, the redox conditions in the aquifer are returning to their original state. However, the DOC released from the remediated source zone matches levels measured 3 years prior and plume conditions are still suitable for biotic reductive dechlorination. Dehalococcoides spp., Dehalogenimonas spp., and vcrA, bvcA, and cerA reductive dehalogenase genes were detected close to the source, and suggest that complete, biotic PCE degradation occurs here. Further downgradient, qPCR analysis and enriched delta C-13 values for cis-dichloroethene (cDCE) suggest that cDCE is biodegraded in a sulfate-reducing zone in the plume. In the most downgradient portion of the plume, lower levels of specific degraders supported by dual C-CI analysis indicate that the biodegradation occurs in combination with abiotic degradation. Additionally, 16S rRNA gene amplicon sequencing shows that organizational taxonomic units known to contain organohalide-respiring bacteria are relatively abundant throughout the plume. Hydraulic conductivity testing was also conducted, and local degradation rates for PCE and cDCE were determined at various locations throughout the plume. PCE degradation rates from sampling campaigns after the thermal remediation event range from 0.11 to 0.35 yr(-1). PCE and cDCE degradation rates from the second to the third sampling campaigns ranged from 0.08 to 0.10 yr(-1) and 0.01 to 0.07 yr(-1), respectively. This is consistent with cDCE as the dominant daughter product in the majority of the plume and cDCE degradation as the time-limiting step. The extensive temporal and spatial analysis allowed for tracking the evolution of the plume and the lasting impact of the source remediation and illustrates that the multiple lines of evidence approach is essential to elucidate the primary degradation mechanisms in a plume of such size and complexity.

ELSEVIER2019

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