Fate and effects of triclosan in subtropical river biofilms

Accumulation of polyethylene microplastics in river biofilms and effect on the uptake, biotransformation and toxicity of the antimicrobial triclosan

The interaction of multiple stressors in freshwater ecosystems may lead to adverse effects on aquatic communities and their ecological functions. Microplastics (MPs) are a class of contaminants of emerging concern that can exert both direct and indirect ecotoxicological effects. A growing number of studies have investigated MPs-attached microbial communities, but the interaction between MPs and substrate-associated biofilm (i.e., on natural river substrates, such as stones and sediments) remains poorly studied. In this work, the combined effects of polyethylene MPs (PE-MPs) with a particle size of 10-45 μm (2 mg/L) and the antimicrobial triclosan (TCS) (20 μg/L) were investigated on river biofilms through a short-term exposure experiment (72 h). To the best of authors' knowledge, this is the first time that the combined effects of MPs and chemical contaminants in substrate-associated river biofilms were assessed. Different response parameters were evaluated, including (i) exposure assessment and ii) contaminants effects at different levels: bacterial community composition, antibiotic resistance, extracellular polymeric substances (EPS), photosynthetic efficiency (Yeff), and leucine aminopeptidase activity (LAPA). Triclosan was accumulated in river biofilms (1189-1513 ng/g dw) alongside its biotransformation product methyl-triclosan (20-29 ng/g dw). Also, PE-MPs were detected on biofilms (168-292 MP/cm2), but they had no significant influence on the bioaccumulation and biotransformation of TCS. A moderate shift in bacterial community composition was driven by TCS, regardless of PE-MPs co-exposure (e.g., increased relative abundance of Sphingomonadaceae family). Additionally, Yeff and EPS content were significantly disrupted in TCS-exposed biofilms. Therefore, the most remarkable effects on river biofilms were related to the antimicrobial TCS, whereas single PE-MPs exposure did not alter any of the evaluated parameters. These results demonstrate that biofilms might act as environmental sink of MPs. Although no interaction between PE-MPs and TCS was observed, the possible indirect impact of other MPs-adsorbed contaminants on biofilms should be further assessed.

Insight into the evolution of microbial communities and resistance genes induced by sucralose in partial nitrification system with triclosan pre-exposure

Sucralose (SUC), an artificial sweetener widely used in food, beverages and pharmaceuticals, is frequently detected in various environmental matrices. Triclosan (TCS) is commonly used as a disinfectant and often co-exists with SUC in sewage environments. This study investigated the effects of SUC (0.1-10 mg/L) on the transmission of intracellular and extracellular antibiotic resistance genes (ARGs) in the partial nitrification systems with and without TCS pre-exposure. The reactors operated for 150 days, and SUC did not affect ammonia oxidation performance, while TCS led to the maintenance of partial nitrification. The types and abundances of extracellular ARGs in sludge and free ARGs in water increased significantly after TCS pre-exposure when faced SUC stress, which might be caused by a decrease in α-Helix/(β-Sheet + Random coil). SUC was more easily to enrich ARGs in partial nitrification systems with TCS pre-exposure, exacerbating the risk of ARGs transmission. The microbial community showed stronger relationships to cope with the direct stress of SUC, and the functional bacteria (Thauera and Nitrosomonas) in TCS pre-exposure system might be potential hosts of ARGs. This study might provide insights for better understanding the fates of SUC in partial nitrification systems and the ecological risks in wastewater containing TCS and SUC. ENVIRONMENTAL IMPLICATION: Sucralose (SUC) is often detected in the environment and considered as an emerging contaminant due to its soaring consumption and environmental persistence. Triclosan (TCS) is an antibacterial agent that often co-exists with SUC in personal care products and sewage environments. During 150 d, two partial nitrification reactors with and without TCS pre-exposure were established to study the effects of SUC on nitrification performance, antibiotic resistance genes (ARGs) and microbial communities. This study showed the refractory nature of SUC, and SUC led to the transmission of extracellular ARGs in partial nitrification system with TCS pre-exposure, exacerbating the risk of ARGs dissemination.

Nanomaterials for Removal of Phenolic Derivatives from Water Systems: Progress and Future Outlooks

Environmental pollution remains one of the most challenging problems facing society worldwide. Much of the problem has been caused by human activities and increased usage of various useful chemical agents that inadvertently find their way into the environment. Triclosan (TCS) and related phenolic compounds and derivatives belong to one class of such chemical agents. In this work, we provide a mini review of these emerging pollutants and an outlook on the state-of-the-art in nanostructured adsorbents and photocatalysts, especially nanostructured materials, that are being developed to address the problems associated with these environmental pollutants worldwide. Of note, the unique properties, structures, and compositions of mesoporous nanomaterials for the removal and decontamination of phenolic compounds and derivatives are discussed. These materials have a great ability to scavenge, adsorb, and even photocatalyze the decomposition of these compounds to mitigate/prevent their possible harmful effects on the environment. By designing and synthesizing them using silica and titania, which are easier to produce, effective adsorbents and photocatalysts that can mitigate the problems caused by TCS and its related phenolic derivatives in the environment could be fabricated. These topics, along with the authors' remarks, are also discussed in this review.

Research trends and hotspots of aquatic biofilms in freshwater environment during the last three decades: a critical review and bibliometric analysis

Freshwater periphytic biofilms (FPBs), existing widely in various aquatic environments, have attracted extensive attention for many years. In the present study, a bibliometric analysis based on Web of Science Core Collection (WoSCC) was used to understand the research progress, trends, and hot topics of FPBs qualitatively and quantitatively. The results indicated that publications on FPBs have increased from 1991 to 2020 rapidly, and researchers have focused more on the areas of environmental sciences, microbiology, and marine freshwater biology. The most influential countries were mainly the USA, Spain, France, and Germany. Cooperation network analysis reflected that the USA and its affiliated institutions played crucial roles in the research of FPB cooperation, but the collaboration between core author groups still fell short. Based on the analysis of top 20 high-cited FPB documents over the last 30 years, research hotspots mainly included micro-observation and assembly mechanisms of FPBs; interactions of FPBs and pollutants including heavy metals, antibiotic resistance genes, pathogens, organic pollutants, and nanoparticles; and the role of FPBs for biogeochemical cycling, especially nitrogen cycling. Additionally, future research directions were proposed. Overall, this study provides a comprehensive and systematic overview of FPBs, which is useful for research development and researchers who are interested in this area.

Influence of temperature on CODMn and Mn2+ removal and microbial community structure in pilot-scale biofilter

Test water temperature (TWT) is a significant operational parameter in biofilter. In this study, a pilot-scale biofilter was established to investigate the removal efficiency of COD_Mn and Mn²⁺ and the microbial community structure at different TWT. When COD_Mn and Mn²⁺ in the influent were 6-8 and 0.9-1.2 mg/L, respectively, the removal rates were 22.61% and 94.28% at the low TWT, while 69.42% and 97.85% at the high TWT, respectively. Biological COD_Mn and Mn²⁺ removal followed the first-order reaction, and at the low and high TWT, the k value was 0.00704 and 0.0738 and 0.0313 and 0.113 min^-1, respectively. Organic matter oxidizing bacteria (OMOB, Sphingopyxis, Sphingomonas, Amphiplicatus, Novosphingobium, Gemmatimonas, Chryseolinea and Sphingobium) and manganese oxidizing bacteria (MnOB, Hyphomicrobium, Pedomicrobium and Pseudomonas) were coexisted in 0-1.5 m of the biofilter bed at the low and high TWT, and the abundances were not the main factor affecting the removal efficiency, however the activity.

Bacterial ecotoxicity and shifts in bacterial communities associated with the removal of ibuprofen, diclofenac and triclosan in biopurification systems

The proliferation and possible adverse effects of emerging contaminants such as pharmaceutical and personal care products (PPCPs) in waters and the environment is a cause for increasing concern. We investigated the dissipation of three PPCPs: ibuprofen (IBP), diclofenac (DCF) and triclosan (TCS), separately and in mixtures, in the ppm range in biopurification system (BPS) microcosms, paying special attention to their effect on bacterial ecotoxicity, as well as bacterial community structure and composition. The results reveal that BPS microcosms efficiently dissipate IBP and DCF with 90% removed after 45 and 84 days of incubation, respectively. However, removal of TCS required a longer incubation period of 127 days for 90% removal. Furthermore, dissipation of the PPCPs was slower when a mixture of all three was applied to BPS microcosms. TCS had an initial negative effect on bacterial viability by a decrease of 34-43% as measured by live bacterial cell counts using LIVE/DEAD® microscopy; however, this effect was mitigated when the three PPCPs were present simultaneously. The bacterial communities in BPS microcosms were more affected by incubation time than by the PPCPs used. Nonetheless, the PPCPs differentially affected the composition and relative abundance of bacterial taxa. IBP and DCF initially increased bacterial diversity and richness, while exposure to TCS generally provoked an opposite effect without full recovery at the end of the incubation period. TCS, which negatively affected the relative abundance of Acidobacteria, Methylophilales, and Legionellales, had the largest impact on bacterial groups. Biomarker OTUs were identified in the BPS microcosms which were constrained to higher concentrations of the PPCPs and thus are likely to harbour degradation and/or detoxification mechanisms. This study reveals for the first time the effect of PPCPs on bacterial ecotoxicity and diversity in biopurification system microcosms and also facilitates the design of further applications of biomixtures to eliminate PPCPs.

Occurrence and Safety Evaluation of Antimicrobial Compounds Triclosan and Triclocarban in Water and Fishes of the Multitrophic Niche of River Torsa, India

Personal care product (PCP) chemicals have a greater chance of accumulation in the aquatic environments because of their volume of use. PCPs are biologically active substances that can exert an adverse effect on the ecology and food safety. Information on the status of these substances in Indian open water ecosystems is scarce. In this paper, we report the incidence of two synthetic antimicrobials, triclosan (TCS), including its metabolite methyl-triclosan (Me-TCS) and triclocarban (TCC) in Torsa, a transboundary river flowing through India. In water TCS and TCC were detected at levels exceeding their respective PNEC (Predictive No Effect Concentration). Both the compounds were found to be bioaccumulative in fish. TCS concentration (91.1-589 µg/kg) in fish was higher than that of TCC (29.1-285.5 µg/kg). The accumulation of residues of the biocides varied widely among fishes of different species, ecological niche, and feeding habits. Me-TCS could be detected in fishes and not in water. The environmental hazard quotient of both TCS and TCC in water indicated a moderate risk. However, the health risk analysis revealed that fishes of the river would not pose any direct hazard to human when consumed. This is the first report of the occurrence of these PCP chemicals in a torrential river system of the eastern Himalayan region.

Triclosan induces PC12 cells injury is accompanied by inhibition of AKT/mTOR and activation of p38 pathway

Triclosan (TCS) has been widely used as a disinfectant and antiseptic in multiple consumer and healthcare products due to its clinical effectiveness against various bacteria, fungi and protozoa. Recently, several studies have reported the adverse effects of TCS on various nerve cells, arousing concerns about its potential neurotoxicity. The present study aimed to investigate the neurotoxicity of TCS in rat pheochromocytoma PC12 cells. After differentiation, the stabilized PC12 cells were treated with 1, 10, 50 μM TCS for 12 h. At the end of the treatment, the generation of reactive oxygen species (ROS), protein expression of apoptotic-related genes, AMPK-AKT/mTOR, as well as p38 in PC12 cells were determined. The concentrations were chosen based on the results of cell viability and lactic dehydrogenase (LDH) assays in response to TCS treatment (ranging from 0.001 to 100 μM) for varied time periods. The results showed that TCS is cytotoxic to PC12 cells, causing decreased cell viability accompanied by increased LDH release. TCS treatment at 10 and 50 μM for 12 h increased the mRNA and protein expression of the pro-apoptotic gene Bax, while Bcl-2 levels remained unchanged. Moreover, an increase in the generation of reactive oxygen species (ROS) was found in TCS-treated PC12 cells at the concentrations of 1 and 10 μM. Pretreatment with 100 μM N-acetyl cysteine (NAC- ROS scavenger) for 1 h normalized the ROS generations in TCS-treated PC12 cells. Additionally, the suppression of the phosphorylation of Akt and mTOR was observed in TCS-treated PC12 cells at 10 and 50 μM for 12 h, concomitant with the activation of p38 MAPK pathway at 50 μM TCS. However, there were no effects of TCS on the phosphorylation of AMPK in these cells. Taken together, these results suggest that TCS may cause adverse effects and oxidative stress in PC12 cells accompanied by inhibition of Akt/mTOR and activation of p38.