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Résumé :
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Microbial extracellular polymeric substances (EPS) are ubiquitous features in aquatic environments. Produced by surface-adherent bacteria and microalgae, EPS are often present as coatings on surfaces of sediment particles and exhibit high affinities for divalent cationic metals. Thus, EPS sediment coatings may participate in the fate of potentially toxic metals. We coated particulate silica (8-10 µm) with EPS produced by NISC1, a bacterium isolated from estuarine sediments, in order to measure the metal binding characteristics of these coatings. We used the radioisotope Cd-109 to measure effects of salinity (salinity = 2.5, 7.5, and 25 parts per thousand), Cd concentration ([Cd] = 0.038, 5, and 50 mg/L), and pH (pH = 5, Ci, 7, 8, and 9) on Cd sorption to EPS-coated (EPS silica) silica and to noncoated silica (NC-silica). Also, Cd sorption by NISC1 EPS coatings was compared to coatings of polymers formed by the bacterium Alteromonas atlantica and the alga Macrocystis porifera. Under all circumstances, EPS coatings increased the affinity of silica for Cd. Extracellular polymeric substance-particulate aggregates rapidly sorbed up to 90% of Cd from aqueous solution.
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