| 1. |
- Achermann, Stefan, et al.
(author)
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Trends in Micropollutant Biotransformation along a Solids Retention Time Gradient
- 2018
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 52:20, s. 11601-11611
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Journal article (peer-reviewed)abstract
- For many polar organic micropollutants, biotransformation by activated sludge microorganisms is a major removal process during wastewater treatment. However, our current understanding of how wastewater treatment operations influence microbial communities and their micropollutant biotransformation potential is limited, leaving major parts of observed variability in biotransformation rates across treatment facilities unexplained. Here, we present biotransformation rate constants for 42 micropollutants belonging to different chemical classes along a gradient of solids retention time (SRT). The geometric mean of biomass-normalized first-order rate constants shows a clear increase between 3 and 15 d SRT by 160% and 87%, respectively, in two experiments. However, individual micropollutants show a variety of trends. Rate constants of oxidative biotransformation reactions mostly increased with SRT. Yet, nitrifying activity could be excluded as primary driver. For substances undergoing other than oxidative reactions, i.e., mostly substitution-type reactions, more diverse dependencies on SRT were observed. Most remarkably, characteristic trends were observed for groups of substances undergoing similar types of initial transformation reaction, suggesting that shared enzymes or enzyme systems that are conjointly regulated catalyze biotransformation reactions within such groups. These findings open up opportunities for correlating rate constants with measures of enzyme abundance such as genes or gene products, which in turn should help to identify enzymes associated with the respective biotransformation reactions.
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| 2. |
- Fenner, Kathrin, et al.
(author)
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Methodological Advances to Study Contaminant Biotransformation : New Prospects for Understanding and Reducing Environmental Persistence?
- 2021
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In: ACS - ES & T Water. - : American Chemical Society (ACS). - 2690-0637. ; 1:7, s. 1541-1554
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Journal article (peer-reviewed)abstract
- Complex microbial communities in environmental systems play a key role in the detoxification of chemical contaminants by transforming them into less active metabolites or by complete mineralization. Biotransformation, i.e., transformation by microbes, is well understood for a number of priority pollutants, but a similar level of understanding is lacking for many emerging contaminants encountered at low concentrations and in complex mixtures across natural and engineered systems. Any advanced approaches aiming to reduce environmental exposure to such contaminants (e.g., novel engineered biological water treatment systems, design of readily degradable chemicals, or improved regulatory assessment strategies to determine contaminant persistence a priori) will depend on understanding the causal links among contaminant removal, the key driving agents of biotransformation at low concentrations (i.e., relevant microbes and their metabolic activities), and how their presence and activity depend on environmental conditions. In this Perspective, we present the current understanding and recent methodological advances that can help to identify such links, even in complex environmental microbiomes and for contaminants present at low concentrations in complex chemical mixtures. We discuss the ensuing insights into contaminant biotransformation across varying environments and conditions and ask how much closer we have come to designing improved approaches to reducing environmental exposure to contaminants.
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| 3. |
- Li, Zhe, 1987-
(author)
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Fate of Pharmaceuticals and Their Transformation Products in Rivers : An integration of target analysis and screening methods to study attenuation processes
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Pharmaceuticals are environmental contaminants causing steadily increasing concern due to their high usage, ubiquitous distribution in the aquatic environment, and potential to exert adverse effects on the ecosystems. After being discharged from wastewater treatment plants (WWTPs), pharmaceuticals can undergo transformation processes in surface waters, of which microbial degradation in river sediments is considered highly significant. In spite of a substantial number of studies on the occurrence of pharmaceuticals in aquatic systems, a comprehensive understanding of their environmental fate is still limited. First of all, very few consistent datasets from lab-based experiments to field studies exist to allow for a straightforward comparison of observations. Secondly, data on the identity and occurrence of transformation products (TPs) is insufficient and the relation of the behavior of TPs to that of their parent compounds (PCs) is poorly understood. In this thesis, these knowledge gaps were addressed by integrating the TP identification using suspect/non-target screening approaches and PC/TP fate determination. The overarching objective was to improve the understanding of the fate of pharmaceuticals in rivers, with a specific focus on water-sediment interactions, and formation and behavior of TPs. In paper I, 11 pharmaceutical TPs were identified in water-sediment incubation experiments using non-target screening. Bench-scale flume experiments were conducted in paper II to simultaneously investigate the behavior of PCs and TPs in both water and sediment compartments under more complex and realistic hydraulic conditions. The results illustrate that water-sediment interactions play a significant role for efficient attenuation of PCs, and demonstrate that TPs are formed in sediment and released back to surface water. In paper III the environmental behavior of PCs along stretches of four wastewater-impacted rivers was related to that of their TPs. The attenuation of PCs is highly compound and site specific. The highest attenuation rates of the PCs were observed in the river with the most efficient river water-pore water exchange. This research also indicates that WWTPs can be a major source of TPs to the receiving waters. In paper IV, suspect screening with a case-control concept was applied on water samples collected at both ends of the river stretches, which led to the identification of several key TPs formed along the stretches. The process-oriented strategies applied in this thesis provide a basis for prioritizing and identifying the critical PCs and TPs with respect to environmental relevance in future fate studies.
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| 4. |
- Tian, Run, 1994-, et al.
(author)
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Increasing the Environmental Relevance of Biodegradation Testing by Focusing on Initial Biodegradation Kinetics and Employing Low-Level Spiking
- 2023
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In: Environmental Science and Technology Letters. - : American Chemical Society (ACS). - 2328-8930. ; 10:1, s. 40-45
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Journal article (peer-reviewed)abstract
- The environmental relevance of standard biodegradation tests such as OECD 309 has been questioned. Challenges include the interpretation of changing degradation kinetics over the 60–90 incubation days and the effects of chemical spiking on the microbial community. To ameliorate these weaknesses, we evaluated a modified OECD 309 test using water and sediment from three Swedish rivers. For each river, we had three treatments (no spiking, 0.5 μg L–1 spiking, and 5 μg L–1 spiking). The dissipation of a mixture of 56–80 spiked chemicals was followed over 14 days. Changes in dissipation kinetics during the incubation were interpreted as a departure of the microbial community from its initial (natural) state. The biodegradation kinetics were first-order throughout the incubation in the no spiking and 0.5 μg L–1 spiking treatments for almost all chemicals, but for the 5 μg L–1 treatment, more chemicals showed changes in kinetics. The rate constants in the no spiking and 0.5 μg L–1 treatments agreed within a factor of 2 for 35 of 37 cases. We conclude that the environmental relevance of OECD 309 is improved by considering only the initial biodegradation phase and that it is not compromised by spiking multiple chemicals at 0.5 μg L–1.
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| 5. |
- Tian, Run, 1994-, et al.
(author)
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Influence of Season on Biodegradation Rates in Rivers
- 2024
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In: Environmental Science and Technology. - 0013-936X .- 1520-5851.
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Journal article (peer-reviewed)abstract
- Biodegradation plays a key role in the fate of chemicals in the environment. The variability of biodegradation in time can cause uncertainty in evaluating the environmental persistence and risk of chemicals. However, the seasonality of biodegradation in rivers has not yet been the subject of environmentally relevant testing and systematic investigation for large numbers of chemicals. In this work, we studied the biodegradation of 96 compounds during four seasons at four locations (up- and downstream of WWTPs located on two Swedish rivers). Significant seasonality (ANOVA, p < 0.05) of the first-order rate constant for primary biodegradation was observed for most compounds. Variations in pH and total bacterial cell count were not the major factors explaining the seasonality of biodegradation. Deviation from the classical Arrhenius-type behavior was observed for most of the studied compounds, which calls into question the application of this relationship to correct biodegradation rate constants for differences in environmental temperature. Similarities in magnitude and seasonality of biodegradation rate constants were observed for some groups of chemicals possessing the same functional groups. Moreover, reduced seasonality of biodegradation was observed downstream of WWTPs, while biodegradation rates of most compounds were not significantly different between up- and downstream.
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| 6. |
- Undeman, Emma, 1981-
(author)
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Simplifying complex models : Application of modeling tools in exposure assessment of organic pollutants
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Thousands of chemicals are used in society, but the exposure to humans and other organisms has been measured only for a small number of compounds. Modeling tools constitute low-cost and effective alternatives to measurements for the assessment of exposure. In this thesis, the prerequisites for the application of modeling tools in environmental exposure assessment of organic pollutants were explored. The first aspect discussed was emission estimates, which are crucial for any quantitative modeling study. In Paper I, the only currently existing high throughput tool for ranking emissions was evaluated and found to have limited predictive power, suggesting that further research is necessary to enable exposure based screening. The second aspect was the model’s treatment of dynamic processes. A strategy for deciding on the temporal resolution required for the description of dynamic processes was proposed in Paper II, which involved identification of major transport routes and time to approach steady state. The third aspect was prediction of partition coefficients for use in bioaccumulation models. The traditional single parameter regressions (spLFER) employed for this purpose were compared to the more mechanistically sound ppLFER equations in Paper III. The two methods had a similar accuracy when compared to measured data, implying that the choice of approach should be based on other factors than methodology (e.g. availability of accurate input data). The fourth aspect was the influence of system characteristics on human exposure. The susceptibilities of several ecosystems with diverging characteristics to exposure to organic chemicals were compared in Paper IV. The strong variation in exposure susceptibilities found suggests that the choice of model system can be relevant for exposure assessment and that models may have to be tailored to the ecosystem of interest. In the broader context, this work provides methodologies for handling model complexity in exposure modeling.
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