Title: "Pollutant profile complexity governs wastewater removal of recalcitrant pharmaceuticals."
Abstract:
Organic pollutants are an increasing threat for wildlife and humans. Managing their removal is however complicated by the difficulties in predicting degradation rates. In this work, we demonstrate that the complexity of the pollutant profile, the set of co-existing contaminants, is a major driver of biodegradation in wastewater. We built representative assemblages out of one to five common pharmaceuticals (caffeine, atenolol, paracetamol, ibuprofen, and enalapril) selected along a gradient of biodegradability. We followed their individual removal by wastewater microbial communities. The presence of multichemical background pollution was essential for the removal of recalcitrant molecules such as ibuprofen. High-order interactions between multiple pollutants drove removal efficiency. We explain these interactions by shifts in the microbiome, with degradable molecules such as paracetamol enriching species and pathways involved in the removal of several organic pollutants. We conclude that pollutants should be treated as part of a complex system, with emerging pollutants potentially showing cascading effects and offering leverage to promote bioremediation.
Discussion:
Efficient pollutant removal from wastewater is essential for environmental safety, yet current water treatment facilities fail to remove organic pollutants such as pharmaceuticals. Steering microbial communities within these unique ecosystems may be key to designing better removal strategies. The composition and function of microbial communities can rapidly change depending on the incoming water composition. Therefore, these wastewater treatment plants can be seen as a model system for studying multiple drivers on microbial communities and their degradation capacity of pollutants. Pollutant removal has been extensively studied in isolation, providing detailed insights into the molecular mechanisms underlying biodegradation. However, these findings only marginally translate to real-world scenario, where multiple drivers co-occur.
In this work, we shed light on the interactive effects of pollutants within the pollutant profile, using mixtures of pharmaceutical varying in biodegradability as a model. We demonstrate that the complexity of the pollutant profile is a major driver of biodegradation and that the presence of multichemical background pollution was essential for the removal rates of recalcitrant molecules. We found in particular the degradation of recalcitrant pollutants to be strongly modulated by the presence of other pollutants. Easily degradable pharmaceuticals such as paracetamol, atenolol, and caffeine enable the degradation of the more recalcitrant ibuprofen and enalapril. In addition, some pollutants may hinder the biodegradation of other. This was particularly striking for atenolol, which degradation was inhibited in the presence of ibuprofen. These two chemicals show strong structural similarities (e.g. benzene ring and alkyl chain), which might inhibit enzymatic activity. Ibuprofen deserves special attention, as it proved to be only degradable when incubated alongside other pharmaceutical compounds. This observation underscores the significance of studying the environmental fate of pharmaceuticals as a collective group rather than at single compound level.
Interactions between pollutants are likely due to shifts in microbial community composition and function. We identified a range of potential key players (based on high relative abundances) involved in pharmaceutical removal, namely Achromobacter, Pseudomonas, Acinetobacter, Comamonas, and Trichococcus. All of them have already been shown to be associated with pollutant degradation. These genera strongly respond to the composition of the pollutant mix, potentially explaining previous observations of their fluctuations in wastewater treatment systems. In particular, paracetamol had a strong effect on the microbial community composition. This may be ascribed to the release of aminophenol, a broad-spectrum antimicrobial molecule, during the breakdown of paracetamol. In line with this hypothesis, paracetamol-treated cultures showed an increased abundance of the paracetamol degradation pathway and turned to a brownish color typical for aminophenol. Despite of potential toxicity, paracetamol addition led to an increase degradation of other pharmaceuticals. The paracetamol degradation pathway encompasses a high enzymatic diversity and may also be involved in the degradation of other recalcitrant pharmaceuticals. One caveat to mention here is the fact that due to the comparatively high concentration used in this study, it is possible that the microbial community was not able to degrade fast enough the formed aminophenol, which might have accumulated transiently.
The major question which needs to be tackled in future studies is the reason for this observation. Potential mechanisms may include cross-feeding, elevated enzyme activity, increased energy levels, and the induced expression of genes encoding promiscuous enzymes catalyzing the degradation of more than one class of pollutant. As a guideline for further studies, the presented results likely rule out increased biomass as a contributing factor given the fact that ibuprofen-degrading cultures did not yield more biomass than other treatments. Co-metabolic effect related to enzyme that fortuitously accept various chemically related substrate could play a role, since the chemical structures of the used pharmaceuticals show some chemical similarities, such as aromatic rings (Supplementary Fig. 1). Therefore, it could be possible that, e.g. specific dioxygenases that play a role in paracetamol degradation, could potentially also show (low) activity against ibuprofen and enalapril.
All tested pharmaceuticals are globally detectable in wastewater influents and effluents and occur worldwide in ng/l to μg/l scale, which is significantly lower compared with the high concentration we used in this study. However, the CODs used in this study can occur in wastewater of industrial production sites of pharmaceuticals. In this work, we opted for an additive design to reflect that in a real-world situation, the concentration of individual pollutants does not directly depend on the presence of other pollutants. However, we would like to stress that this design may entangle the effects of pollutant concentration and the number of pollutants present in a sample. To rule out concentration effects, we re-ran the experiment with selected batch cultures and an individual pollutant concentration of 1 mg/l. We observed a similar interaction pattern between the recalcitrant Enalapril and the easily degraded Paracetamol.
This study indicates that the presence of easily degradable micropollutants, such as caffeine, atenolol, and paracetamol, promoted the degradation of recalcitrant substrates such as ibuprofen and enalapril. In contrast, these latter compounds were not degraded when present as the sole pollutant. The significance of these discoveries is noteworthy, as they can serve as potential starting points for the development of future applications aimed at the effective removal of pharmaceuticals: the study demonstrated that the addition of specific compounds at specific time points can enhance the degradation of a target pollutant. Addition of non-toxic functional mimics of existing pollutants may thus improve the microbial removal of persistent pollutants, contributing to safe water, ecosystems, and food supply. We conclude that pollutants should be treated as part of a complex system, with emerging pollutants potentially showing cascading effects and offering leverage to promote bioremediation.
Funding:
The work has been funded by the European Union’s Horizon Europe framework program for research and innovation under grant ID 10106625 (project NYMPHE). This work has also received funding from the Swiss State Secretariat for Education, Research and Innovation (SERI).
Cite:
Marcel Suleiman, Natalie Le Lay, Francesca Demaria, Boris A Kolvenbach, Mariana S Cretoiu, Owen L Petchey, Alexandre Jousset, Philippe F-X Corvini, Pollutant profile complexity governs wastewater removal of recalcitrant pharmaceuticals, The ISME Journal, Volume 18, Issue 1, January 2024, wrae033, https://doi.org/10.1093/ismejo/wrae033
Institute for Ecopreneurship, FHNW University of Applied Sciences and Arts Northwestern Switzerland, 4132 Muttenz, Switzerland.
Blossom Microbial Technologies B.V., Utrecht Science Park, Padualaan 8, 3584 Utrecht, The Netherlands.
Department of Evolutionary Biology and Environmental studies, University of Zurich, 8057 Zurich, Switzerland .
College of Resources and Environmental Science, Key Lab of Organic-Based Fertilizers of China and Jiangsu Provincial Key Lab for Solid Organic Waste Utilization, Nanjing Agricultural University, 210095 Nanjing, China.
Opmerkingen