RESUMEN
Selenite(IV) and selenate(VI) are the major species of Se in the seleniferous aquatic ecosystem. The redistribution of Se in the water/sediment microcosm by bioturbation remains largely unknown. In this study, the redistribution of Se in the water/sediment microcosm by the benthic oligochaete Limnodrilus hoffmeisteri was assessed. The worms were exposed to 2-40⯵g/g dry weight of Se(IV) or Se(VI) in the sediment (diet) for 2â¯months. The changes in the Se levels in different compartments of the microcosm (sediment, overlying water, and worms) were quantified after 2â¯weeks and 2â¯months. The subcellular distribution of Se in the worms were also evaluated. Finally, the volatilization of Se from the two Se sources was estimated. The results showed that Se concentration in the overlying water and Se bioaccumulation in the worms were increased with Se levels in the sediments. Approximately 1.6-9.8% of Se was volatilized in the absence of the worms and was intensified in the presence of the worms (2.1-25.7%). The subcellular distribution witnessed high levels of Se in the cell debris (>60%). Se(IV) and Se(VI) differ in their bioaccumulation, redistribution and the effects on the growth of the worms. Our results suggest that the bioturbation by benthos play an essential role in the redistribution of Se in the water/sediment microcosm.
Asunto(s)
Oligoquetos/fisiología , Selenio/análisis , Contaminantes Químicos del Agua/análisis , Animales , Ecosistema , Agua Dulce/química , Sedimentos Geológicos/químicaRESUMEN
The aim of this study was to examine bioremediation strategies for BDE-209 contaminated sediments. Sediment microcosms were established to observe anaerobic debromination of BDE-209 under conditions representing three bioremediation strategies: biostimulation, bioaugmentation and natural attenuation. To simulate biostimulation, a defined mineral medium containing both a carbon source (sodium formate) and electron donor (ethanol) was added into sediments. Bioaugmentation was established by enrichment of the sediments using a culture of Dehalobium chlorocoercia strain DF-1, previously shown to dechlorinate polychlorinated biphenyls, to sediments. No amendments were made to the third set in order to represent natural attenuation. The biostimulation, bioaugmentation and natural attenuation strategies resulted in 55.3%, 40.2% and 30.9% reductions in BDE-209, respectively, after 180 days. Nona- through tri-BDEs were observed as products, with 17 PBDE congeners detected in 25 different proposed debromination pathways. At the end of the 180 day incubation period, the products for bioaugmentation, biostimulation and natural attenuation were tri-BDEs, tetra-BDEs and penta-BDEs, respectively. The proposed pathways revealed that meta- and ortho-Br removal were favored in sediments, and that debromination regiospecificity varied with each bioremediation strategy applied. Lastly, pseudo-first-order rate constants for BDE-209 reduction were calculated as 0.0049 d-1, 0.0028 d-1, 0.0025 d-1 for biostimulation, bioaugmentation and natural attenuation, respectively.
Asunto(s)
Sedimentos Geológicos , Éteres Difenilos Halogenados , Biodegradación AmbientalRESUMEN
The environmental behavior and stereoselectivity of the chiral fungicide benalaxyl and its chiral metabolite benalaxyl acid in water, sediment, and water-sediment microcosms were studied. The microcosms were incubated at 25 °C with light or under darkness. The influencing factors such as light and microorganism were investigated. The results showed that benalaxyl had half-lives of >21 days in the microcosm system and that the metabolite benalaxyl acid could exist in the microcosm for >70 days. Benalaxyl was mainly transformed through microbial degradation, and thus sediment microorganisms played a major role in the dissipation of benalaxyl in the aquatic microcosm. The stereoselective behavior of benalaxyl and benalaxyl acid was also investigated. (-)-Benalaxyl was preferentially degraded in the microcosm, resulting in an enrichment of the more toxic enantiomer (+)-benalaxyl, which may cause higher risk to the aquatic system. Moreover, (-)-benalaxyl acid was preferentially formed in the microcosm. The enantioselectivity of the enantiomers in the microcosm should be taken into consideration for an accurate risk assessment.
Asunto(s)
Alanina/análogos & derivados , Fungicidas Industriales/química , Sedimentos Geológicos/química , Alanina/química , Cinética , Estereoisomerismo , Agua/química , Contaminantes Químicos del Agua/químicaRESUMEN
A detailed quantitative analysis of anaerobic dechlorination (AD) pathways of polychlorinated biphenyls (PCBs) in sediment microcosms was performed by applying an anaerobic dechlorination model (ADM). The purpose of ADM is to systematically analyze changes in a contaminant profile that result from microbial reductive dechlorination according to empirically determined dechlorination pathways. In contrast to prior studies that utilized modeling tools to predict dechlorination pathways, ADM also provides quantification of individual pathways. As only microbial reductive dechlorination of PCBs occurred in the modeled laboratory microcosms, extensive analysis of AD pathways was possible without the complicating effect of concurrent physico-chemical or other weathering mechanisms. The results from this study showed: (1) ninety three AD pathways are active; (2) tetra- to hepta-chlorobiphenyl (CB) congeners were common intermediates in several AD pathways, penta-CBs being the most frequently observed; (3) the highest rates of dechlorination were for penta-CB homologs during the initial 185 days; (4) the dominant terminal products of AD were PCB 32(26-4), 49(24-25), 51(24-26), 52(25-25), 72(25-35), 73(26-35) and 100(246-24), (5) potential toxicity of the sediment was reduced. ADM serves as a powerful tool not only for a thorough analysis of AD pathways, but also for providing necessary input for numerical fate models (as a degradation term) that investigate dechlorination products or outcome of natural attenuation, or bioremediation/bioaugmentation of PCB-impacted sediments.