Laure Joly

Cette thèse présente une étude des propriétés optiques et de la photofragmentation de biomolécules en phase gazeuse. Les expériences sont effectuées sur un piège ionique quadripolaire couplé avec des lasers UV-Visible accordables en longueur d'onde. Les molécules sont isolées en phase gazeuse au centre du piège puis irradiées par le faisceau laser. Pour les molécules polyanioniques, le canal de relaxation principal après excitation laser est l'émission d'électron. Cette perte d'un électron conduit à la formation d'un ion radicalaire. Une partie de ce travail est consacrée à l'étude de la relaxation de molécules polyanioniques après excitation laser et notamment aux mécanismes conduisant à la perte d'électron. Les expériences de photodétachement réalisées à Lyon ont été complétées par des expériences de spectroscopie de photoélectron effectuées à Karlsruhe (Pr. Kappes). La production d'anions radicalaires a un potentiel analytique important. L'un des objectifs de ce travail de thèse a été d'étudier la réactivité de ces ions radicalaires et de montrer l'intérêt de leur fragmentation pour l'analyse structurelle de peptides. L'autre objectif était de sonder les propriétés électroniques de protéines et de peptides en phase gazeuse. Pour cela, le taux de détachement d'électron a été enregistré en fonction de la longueur d'onde du laser. Nous avons notamment pu déterminer des signatures optiques pour des chromophores neutres, déprotonnés ou radicalaires au sein des protéines. Ces résultats ont été comparés à des calculs théoriques (TD DFT).

Over the last decade, the consumption of tea and herbal tea has gained more and more popularity across the globe, but the potential presence of chemical contaminants (e.g. pesticides, trace elements, synthetic drugs) may raise health concerns. This study analysed selected teas available in Belgian retail stores and performed a risk assessment for these samples. No chemical adulteration could be detected in dry tea material. More than 38% of the dry leaves samples contained at least one pesticide exceeding the maximal residue level (MRL) set by the EU. However, further risk assessment, based on the values of pesticide residues and the toxic trace elements encountered in the brew, demonstrate that the consumption of these teas will not give rise to health concerns. Nonetheless, attention should be given to the leaching potential of nickel from teas and the presence of arsenic in brews from algae containing teas.

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A total of 120 spices and herbs bought on the Belgian market have been analysed for occurrence of the four EU regulated polycyclic aromatic hydrocarbons (ΣPAH4). Samples were sorted in three groups according to their use: traditional spices, exotic spices, and herbs. Benzo[a]pyrene has been detected in 56% of samples, while ΣPAH4 were found in 96% of samples. ΣPAH4 were evenly distributed among the three groups with a median content of 7.2 for traditional spices, 5.5 for exotic spices and 6.0 µg kg⁻¹ for herbs. According to the EU legislation, three samples were exceeding maximal limits, with a maximum ΣPAH4 content of 164 µg kg⁻¹. The ΣPAH4 dietary intake has been estimated at 1.4 and 27.8 ng day⁻¹ for average and high consumption, respectively. The risk for the consumer was evaluated by using the margin of exposure (MOE). In all cases, MOE were >20 000, indicating a low concern for the population.

Pesticides are commonly applied in market gardening to improve productivity and pest control. Pesticide residues could be persistent in vegetables and generate a potential health hazard for consumers. This study has been carried out in Tunisia to assess the perceived risk of consumers exposed to pesticide residues remaining in vegetables. Two surveys with different questionnaires were conducted among 30 market gardeners and 50 households located in the Djebeniana delegation (Sfax governorate, Tunisia) in order to analyze the phytosanitary practices of farmers on the one hand, and to better understand the attitude related to vegetable consumption and awareness on pesticide residues, on the other hand. The results revealed that various phytosanitary products have been used by market gardeners (43 commercial products containing 39 different active substances (AS)). Among these AS, abamectin and methomyl are considered as highly hazardous according the WHO classification. According to the behavior of pesticides in plants, more than half of the AS. (54%) are systemic and can be absorbed by the plant and moved around in its tissues. Furthermore, the majority of the surveyed farmers had never undergone agricultural training, which is a real handicap with respect to good phytosanitary practices. After applying pesticides, the pre-harvest interval was regularly not respected by almost half of the interviewed market gardeners. In addition, the study showed that all consumers washed their vegetables before consumption, but more than half of the respondents (54%) wash their vegetables for less than a minute (simply passing them under running water). In the light of these results, it appears that consumers may be exposed to pesticide residues from vegetables on the Tunisian market, with potential effects on their health.

Many pesticides applied in cut flowers can be readily absorbed through the skin of florists during preparing bouquets and handling contaminated flowers. A study was conducted among volunteer Belgian florists in order to assess their total exposure by measuring concentrations of pesticides (parent compounds and metabolites) in their urines. A total of 42 urine samples (24-h urines) were collected from florists during their professional activities, on the three most important commercial periods. The concentrations of pesticide residues and metabolites in urine samples were analyzed with a multiresidue liquid chromatography tandem mass spectrometry method, after an ethyl acetate extraction. The results are compared with those of a control group of 42 subjects not occupationally exposed to pesticides, collected in the same periods. A total of 70 residues (56 pesticides and 14 metabolites) were identified, with an average of about eight pesticide residues and metabolites per florist’s urine sample and an average total concentration per sample of 4.3 µg/g creatinine, ranging from 0.2 to 67 µg/g creatinine. Significantly higher urinary excretion of metabolites (t-test) was found in florists than in control group. These results demonstrate that Belgian florists are exposed daily to pesticide residues with a potential effect on their health.

Sixty-four table grape samples from different regions of Tunisia were collected during three consecutive years (2015–2017). The presence of 96 pesticides, including dithiocarbamates, was assessed. Pesticides identification and quantification were performed by liquid or gas chromatography, coupled to tandem mass spectrometry. All samples contained multiple residues (4 to 24 residues), with an average of 11.6 residues per sample. Individual concentrations of pesticides in grapes ranged from 0.01 to 5.86 mg kg⁻¹. For at least one chemical compound, exceedances of the European Maximum Residue Limits were found in 94% of the samples. To assess the potential risk of pesticides through consumption of grapes, the acute exposure was estimated by the determination of predicted short term intake which is expressed as a percentage of Acute Reference Dose (ARfD), for non-compliances of pesticides. The exceedance of ARfD was associated with carbofuran, carbendazim, chlorpyrifos, deltamethrin, dimethoate and omethoate. Consequently, these pesticides could present a risk for consumer’s health.