Abstracts
Résumé
Les oeufs de nématodes sont présents dans les eaux usées et dans les boues résiduaires. Suite à ce constat, l'objectif de ce travail est la mise en évidence d'une éventuelle capacité d'adhésion par contact et fixation des oeufs sur différentes surfaces. L'oeuf d'Ascaris a été utilisé comme modèle et divers paramètres sus- ceptibles d'intervenir ou de modifier les interactions ont été testés. Sur les matériaux de laboratoire, 32,5 % des oeufs se fixent sur les tubes de verre contre respectivement 15,7 % et 9,1 % sur des tubes en polystyrène et en polypropylène. En eau désionisée, les oeufs montrent une forte capacité d'adhésion sur le support hydrophile avec 75 % d'oeufs fixés sur les particules de poudre de verre contre uniquement 1,3 % sur les feuillets hydrophobes de talc. L'adhésion sur la poudre de verre est très rapide avec 55 % des oeufs fixés après 30 secondes. En présence d'une charge en adsorbant de 10 g/l, pour une valeur de pH égale à 9 et pour les concentrations ioniques (CaCl2 et NaCl 0,9M), l'adhésion des oeufs sur la poudre de verre atteint 99 %. Cependant, des températures égales à 2 °C et 3 60 °C ou l'utilisation de solutions éluantes (hypochlorite de sodium, formaldéhyde, détergents an ionique et caffonique) diminuent les phénomènes d'adhésion avec en particulier l'hypochlorite de sodium à 2° chl qui les supprime totalement. Toutes ces informations indiquent que l'adhésion intervient de manière importante. En effet, lors du traitement des effluents, ce phénomène favorise l'épuration par adhésion des oeufs au floc de matière organique avec cependant transfert de contaminants dans les boues.
Dans les sols et sur les végétaux, l'adhésion favorise la contamination parasitaire des surfaces. L'utilisation d'effluents ou de boues contaminées devra impérativement respecter les normes ou les recommandations destinées à protéger des risques de transmission à l'homme et aux animaux.
Les techniques destinées à évaluer la contamination parasitaire d'échantillons de l'environnement sont dépendantes de ces phénomènes d'adhésion. L'utilisation de solutions éluantes et notamment d'hypochlorite de sodium est indispensable.
Mots-clés:
- Adhésion,
- oeufs d'helminthes,
- Ascaris,
- environnement,
- eau usée
Abstract
The intestinal nematodes use the environmental medium to realize their infestation cycle with eggs. In this study, the ability of helminth eggs to create binding in laboratory conditions is evaluated. This information will allow a better knowledge of the characteristics and the behaviour of the eggs in the environment and will give beginning of answer to the main question: are the nematodes eggs bound to sufaces and particulary to suspended matterin the environment or free particles?
For this study, the model used is the Ascaris eggs collected in the end of the womb in order to work with fertile coated eggs. They seem to be the most common form found when the eggs are quantified in the water or wastewater medium. However, the aggregate in the suspension create difficulties for the counting and give a protect effect of the outer layer for the eggs into the aggregate. Physically, the aggregate properties are also different from the properties of one isolated egg. To spread out the eggs without bringing modifications of the egg coating, one filtration is performed on l00 µm filter to eliminate the aggregate higher or equal to 4 eggs. Before the study, a possible adhesion on the laboratory materials is performed.
On glass materials, a strong adhesion is observed with 32.5% of eggs on the surfaces; on the other hand, on polypropylen and on polystyren, the adhesion is less important, respectively 9.1 and l5.7 % are adsorbed with a significant difference between these two results. Then for this work, polypropylen and polystyren materials are used. In deionised water (pH 6) with one 15 min stirring at 15 rpm, the behavior of the Ascaris eggs is studied on two surf'aces glass powder which is hydrophil particles with electronegative charges and talc which is hydrophob flakes with electronegative charges too. The results show a small adhesion on the hydrophob surfaces (l.3%) for a percentage of 75% on the hydrophil particles with the glass powder. In the same experimental conditions, the adhesion on hydrophil surfaces is confirmed with two other adhesion media: the muscovite and the glass wool which show a significant adsorption (96 and 98.5%). Onglass powder, the adhesion characteristics are developed with the study of 5 parameters: the contact time, the adhesion medium concentration, the pH, the temperature and the ionic concentration. For a low glass powder concentration (1g/l), a good adhesion is obtained with 65% of egg bound. The adsorption is obtained rapidly, 55% are already bound after 30 sec. The pH increase significanty the adhesion at the value 9 and an important decrease is observed atthe low and high temperatures (2 and 60°c). To complete this study, reagents used as desorption solution in the analytical techniques for the research of the helminth eggs in wastewater are tested. The eluting solutions as formalin and detergents increase in a considerable proportion the percentage of eggs non adsorbed, the outer layer properties could be modified by these reagents. For the sodium hypochlorite solution, the activity is stronger.This reagent eliminates the egg adhesion with only 0.1 percent of eggs bound. The action on the outer layer could be a destruction and then the loss of the adhesion properties. The practical implications of these adhesion properties are considerable: the wastewater depuration by physico-chemical treatments with the possibility of adhesion on floc particles for the eggs; the adhesion to the soil particles avoiding percolation and then the eggs accumulation in depth; on vegetables irrigated with wastewater the adsorption can improve the contamination and for the analytical techniques used to quantify parasite eggs in aqueous medium, we have to overcome the problem of the adhesion to the supports, with the use of eluting solution like sodium hypochlorite.
Keywords:
- Adhesion,
- helminth eggs,
- Ascaris,
- environment,
- wastewater
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