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Bioavailability - A concept to unravel the antibiotic effects on soil microbial functioning ?
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Edité par CCSD -
The intensive uses of antibiotics (AB) inhuman and veterinary medicines contributed to widespreadenvironmental contaminations, through the wastewater discharges andthe recycling of organic wastes (OW) as soil amendments. While theoccurrence and persistence of AB in the environment have becomemajor environmental and human health issues, their ecotoxicologicalimpacts are not well understood. AB inhibit active microorganisms andtherefore can represent an important risk for the environment, especiallyfor soil microbial functions (organic matter degradation, nutrientrecycling). However, these side-effects depend on the bioavailability ofAB. Organic matter quality is a key environmental factor influencingsoil dissipation processes of AB which can control the bioavailability.Our objectives were to investigate the effects of the sulfamethoxazole(SMX) on microbial nitrogen transformations in relation with ABbioavailability in soil. A dose-effect approach was performed withdifferent doses of SMX supplied to two different OW (compost ofsewage sludge / green waste (SGW), farmyard manure (FYM)) beforetheir application to soil. The final doses of SMX in soil microcosmsranged from 0,022 to 2,22 mg kg-1dw, with control soils amended withOW without SMX. Nitrogen forms, potential nitrification anddenitrification activities were determined in soils, after 7, 28 and 84 daysfollowing amendments. Also, the total amount of SMX and thechemically available fraction were extracted respectively with organicand aqueous solutions and then quantified by UPLC-MS/MS. At theselow doses, only nitrification activity was adversely impaired by SMX,following a dose-response pattern, in soils amended by SGW. Actually,as the SMX is a bacteriostatic antibiotic, the effects were stronger forgrowing microbial populations, such as the nitrifiers which are largelypromoted by the high levels of NH4+ in SGW amended soils comparedto FYM amended soils. The chemical assessment of SMX availabilitydid not show strong differences between the SGW or FYM amendedsoils. However, throughout the experiment, the decrease of SMXavailability was in accordance with a partial recovery of soil nitrificationin SGW amended soils. Nitrification is a sensitive indicator of ABeffects on soil microbial functioning. Its recovery after AB exposuremay be explained by a strong decrease in the chemical availability andconsequently in the bioavailable fraction of AB for microorganisms
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