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Résumé: Ce projet avait pour objectif de préciser le risque environnemental associé à l'usage agronomique de composts de fumier de chevaux ayant reçu des traitements vétérinaires par une approche couplant l'évaluation de l'écotoxicité et la quantification des résidus médicamenteux. Le bilan détaillé des usages vétérinaires sur quatre années au sein d'une station expérimentale a permis de définir un protocole autour de deux événements entraînant un usage intensif de substances pharmaceutiques : la castration des jeunes chevaux et le traitement antiparasitaire annuel. Les résultats ont montré que sur six molécules utilisées pour ces opérations (un antiparasitaire, deux antibiotiques, un anesthésique, un anti-inflammatoire et un diurétique), quatre ont fait l'objet d'une quantification et seules l'ivermectine (antiparasitaire) et la pénicilline G (antibiotique administré après la castration) ont pu être quantifiées de manière significative au moment de la mise en compostage du fumier. Des bioessais sur deux organismes aquatiques (daphnie et microalgue verte) et quatre organismes terrestres ont été réalisés avec les molécules seules ou en mélange ainsi qu'avec les composts et leurs lixiviats. Les plus fortes concentrations auxquelles aucun effet n'a été observé (NOEC) à 72 heures ont été déterminées pour les deux organismes aquatiques. Les valeurs obtenues sont toutes supérieures à 1 μg/l et donc largement au-delà des concentrations environnementales, excepté pour l'ivermectine dont la NOEC est de 100 ng/l. La procaïne ne semble pas affecter les capacités de reproduction de la daphnie, mais une diminution de 52 % de la production de nouveau-nés est observée pour l'ivermectine à 10 ng/l. Une toxicité aquatique a cependant été observée lorsque les six molécules sont en mélange. En ce qui concerne les effets phytotoxiques, l'ivermectine, la dihydrostreptomycine et l'hydrochlorotiazide, pris séparément, engendrent une inhibition de la croissance racinaire sur les trois végétaux testés. Ces résultats peuvent expliquer la toxicité de certains échantillons de fumiers issus des boxes juste après traitement des chevaux. La convergence des essais de toxicité pour le compost préparé à partir du fumier ayant reçu l'ensemble des rejets des traitements ou à partir du fumier de référence permet de conclure à une absence d'effets significatifs sur le sol d'un amendement par du compost de chevaux ayant subi les traitements vétérinaires étudiés. This project uses a mixed approach — assessment of ecotoxicity and quantification of drug residues — to evaluate more accurately the environmental risk of soil amendment by horse manure compost including these veterinary drug residues. Use of veterinary drugs was assessed over 4 years and we defined an experimental protocol with two events involving intensive use of veterinary substances: the castration of young horses coupled with annual antiparasite treatment. The results showed that of the six substances used for these events (one antiparasite, two antibiotics, one anesthetic, one anti-inflammatory, and one diuretic), only ivermectin (a pesticide) and penicillin G (one of the two antibiotics given after castration) could be quantified before manure composting. Bioassays were carried out on two aquatic organisms (daphnia and green microalgae) and three terrestrial plants. The highest concentrations tested for which no effect on the organism was observed (NOEC) at 72 h were determined for the green microalgae and for the daphnia. Values were all above 1 μg/L and therefore well above the observed environmental concentrations, except for ivermectin with an NOEC of 100 ng/l. Procaine did not affect the reproductive capacity of daphnia but 10 ng/l of ivermectin led to a 52% decline in offspring. However, when the six molecules were used in "combination", aquatic toxicity was observed. Ivermectin, dihydrostreptomycin, and hydrochlorothiazide were all found to have phytotoxic effects, causing inhibition of root growth in all three plants. These results may explain the toxicity of some manure samples from stalls after veterinary treatment of horses. Overall, ecotoxicity tests on composts were similar for manure that received any or all of these treatments and control manure. No significant effect is observed on soil amended by horse manure compost following veterinary treatments. [ABSTRACT FROM AUTHOR]

Diagnosis of periurban Dakar (Senegal) agrosystem contamination by trace elements. Description of the subject. Urban and periurban market gardening is widespread in the Dakar area of Senegal. Repeated long-term application of organic matter results in high inputs of trace elements (TE). Objectives. The aim is to assess TE contamination in suburban agrosystems. Method. At four sites, we compared the Cu, Zn, Pb and Cd content in the surface layers and sublayers of plots cultivated over a long period with the content found in adjacent uncultivated plots. Results. The two prevailing soil types (Arenosol and Fluvisol) were characterized by significantly different background soil geochemical TE content. In the 0 – 20 and 20 – 40 cm soil layers at the four studied sites, TE content was significantly higher (p < 0.05) in the cultivated plots than in the non-cultivated plots. Arenosols showed a significantly higher (p < 0.05) TE content than Fluvisols. An exception to these results was found in cultivated Arenosols, where Cd, Cu, Zn and Pb contamination was observed. This could be explained by the frequent input into these soils of sewage sludge, poultry droppings, and irrigation with only partially treated wastewater. Cadmium contamination of cultivated Fluvisols was the result of regular natural phosphate inputs, as observed throughout the soil profile. Conclusions. Analysis of soils and organic matters would enable adjustment of the quantities of organic matter applied and could lead to a reduction in TE contamination within these agroecosystems.

Effect of the depth of brown mustard amendments in soil on wheat take-all disease. Description of the subject. The intercrop period is opportune for reducing the severity of soilborne diseases. Objectives. The aim was to evaluate the effectiveness of a biofumigant amendment according to its location in the soil. Method. An experiment combining different locations of wheat take-all inoculum and of ground brown mustard amendment was conducted under semi-controlled conditions. Results. At the early plant development stage (GS22), an inoculum localized in superficial soil horizons caused more disease than a deeper inoculum. However, it was possible to reduce significantly the level of infection through the addition of a brown mustard amendment, particularly when located in the top soil. At a later plant development stage (GS32), the location of the inoculum had no further visible effect on the severity of root infections but wheat growth increased when ground mustard was incorporated at the surface layer of the soil or at the same level as the inoculum. Conclusions. These results suggest firstly, that ground mustard amendment can reduce necrosis caused by wheat take-all and can allow increased plant growth, and secondly, that the effect depends on the relative locations of the amendment and of the inoculum.

Metals can be stabilized by soil amendments that increase metals adsorption or alter their chemical forms. Such treatments may limit the risk related to the contamination through reduction of metal transfer to the food chain (reduction of metal uptake by plants and its availability to soil organisms) and metals migration within the environment. There is a need for experiments comparing various soil amendments available at reasonable amounts under similar environmental conditions. The other question is whether all components of soil environment or soil functions are similarly protected after remediation treatment. We conducted a series of pot studies to test some traditional and novel amendments and their combinations. The treatments were tested for several highly Zn/Cd/Pb contaminated soils. Among traditional amendments composts were the most effective – they ensured plant growth, increased soil microbial activity, reduced Cd in earthworms, reduced Pb bioaccessibility and increased share of unavailable forms of Cd and Pb.