Biofilm formation strongly influences the vector transport of triclosan-loaded polyethylene microplastics

The potential of microplastics acting as vector for triclosan in aquatic environments

There is increased evidence of the co-occurrence of microplastics (MPs) with other co-pollutants in surface water globally, leading to ecological and environmental concerns. The risks and toxicity of co-occurring pollutants largely depend on the mechanisms controlling the activation of their various sources, their fate and transport in different environmental media. Due to their size-specific surface area, MPs in the environment can have a strong affinity for interactions with hydrophobic compounds and have a high sorption capacity for various emerging contaminants (ECs). ECs like the antibacterial and antifungal agent such as Triclosan (TCS) are persistent in the environment. Moreover, TCS in aquatic environments has a low solubility, and high octanol-water partitioning co-efficient which raises the possibility of TCS to interact with other environmental pollutants such as MPs. The interactions of TCS with MPs in the environment are controlled by a range of mechanism such as hydrogen bonding, hydrophobic interactions, π-π interactions as well as electrostatic interactions. The interacting behaviour of these driving forces needs to be fully understood to determine how the co-occurrence of TCS and MPs may lead to adverse effects on the biological functioning of aquatic ecosystems. Hence, here we conduct a systematic review of the current state-of-the-art and synthesize the available knowledge of how MPs can act as vectors for TCS in aquatic environments. This review reveals MP and TCS interactions in aquatic ecosystems, their individual and collective fate, and toxicological impacts on aquatic organisms, evidencing that MPs can act as potential vectors for transporting TCS across different trophic levels. This review also reveals critical limitations in the research of the combined toxicity and interactions of co-occurring MPs and TCS. Based on the rigorous review of the current knowledge base, we propose that multifactorious investigations along with long-terms monitoring are crucial to fully understand the impacts of co-occurring MPs and TCS in aquatic systems to underline future mitigation policies and management plans.

The threat of microplastics and microbial degradation potential; a current perspective

Microplastics in marine environments come from various sources, and over the years, their buildup in marine environments suggests an inevitable need for the safe mitigation of plastic pollution. Microplastics are one of the chief and hazardous components of marine pollution, as they are transferred through the food chain to different trophic levels, affecting living organisms. They are also a source of transfer for pathogenic organisms. Upon transfer to humans, several toxic effects can occur. This review aims to assess the accumulation of microplastics in marine environments globally, the threat posed to humans, and the biodegradation potential of bacteria and fungi for future mitigation strategies. The versatility of bacteria and fungi in the biodegradation of different types of plastics has been discussed, with a focus on the microbial majority that has been cultivated in labs from the marine environment. We also propose that the exploration of yet-to-be-cultivated microbial majority can be a way forward for employing future strategies to mitigate microplastics.

Comparison of biofilm-covered microplastics and sand particles as vectors of PCB-153 to Paracentrotus lividus

The microplastics (MPs) vector effect of environmental contaminants (such as polychlorinated biphenyls-PCBs) to organism tissues is currently one of the major concerns regarding MPs pollution in the marine environment. The relative importance of MPs as vectors for the bioaccumulation of contaminants to marine organisms compared to other naturally occurring particles has been poorly investigated and never by using biofilm-covered particles. The present study compares the role of biofilm-covered microplastics and sand particles as vectors for the transfer and bioaccumulation of ¹⁴C-PCB-153 into various body compartments of the sea urchin Paracentrotus lividus. After 14 days of exposure, similar transfer efficiency of ¹⁴C-PCB-153 from both types of biofilm-covered particles was obtained (t-test, p-val = 0.43). The particle type was not found to affect the concentration (two-way ANOVA, p-valper dry weight = 0.92, p-valper lipid weight = 0.80) and distribution (two-way ANOVA, p-val = 0.85) of ¹⁴C-PCB-153 among the different body compartments of sea urchins. These findings suggest that biofilm-covered MPs located on the seafloor may act as similar vectors for the bioaccumulation of PCB-153 in sea urchin tissues compared to other biofouled natural particles such as sand. Overall, the outcomes of this present work align with the growing consensus among various research groups that MPs-mediated bioaccumulation of co-contaminants would be negligible compared to natural bioaccumulation pathways in relation to their abundance in the ocean.

Microplastics-biofilm in aquatic ecosystem: Formation, pollutants complexation, greenhouse gas emission and ecotoxicology

The omnipresent microplastics (MPs) have gradually become a significant environmental problem due to its adverse consequences for ecological systems. MPs serve as substrates for biofilms colonization, which enhances adsorption of harmful contaminants on MPs surface in the aquatic ecosystem. The present study provides a critical discussion on the mechanism involved in MPs-biofilm formation, microbial colonization and the robust factors influencing the process in the aquatic ecosystem. Subsequently, the impact of MPs-biofilm on adsorption of inorganic and organic contaminants is explored. The ecological significance of MPs-biofilm associated pollutant complex for promoting greenhouse gases (GHGs) emissions from aquatic ecosystem is extensively discussed for understanding the climatic risk. Furthermore, the discussion is extended over ecotoxicological impact of MPs-biofilm on aquatic biodiversity and humans. The protective extracellular polymeric substances secreted by colonised bacteria over MPs during biofilm formation creates sticky MPs surface for heteroaggregates formation with swift adsorption of chemical compounds and microorganisms. MPs with functional aromatic groups facilitate the bacterial adhesion on the surface, but affect formation of biofilm. Alternatively, MPs-biofilm promotes the Mn and Fe hydrous oxides formation that can co-precipitate with heavy metal ions and facilitate in remediation measures. However, MPs biodegradation generates GHGs emission per unit mass, comparably more from freshwater than marine ecosystem. Considering the toxicity, MPs-biofilm induces the oxidative response in fishes, causing painful death and thus, destroys aquatic biodiversity. This study will be useful to address MPs-biofilm associated pollution scenario via trace, test and treat strategy involving future engineering research framework for ecological restoration.

Colonization characteristics and surface effects of microplastic biofilms: Implications for environmental behavior of typical pollutants

This paper summarizes the colonization dynamics of biofilms on microplastics (MPs) surfaces in aquatic environments, encompassing bacterial characteristics, environmental factors affecting biofilm formation, and matrix types and characteristics. The interaction between biofilm and MPs was also discussed. Through summarizing recent literatures, it was found that MPs surfaces offer numerous benefits to microorganisms, including nutrient enrichment and enhanced resistance to environmental stress. Biofilm colonization changes the surface physical and chemical properties as well as the transport behavior of MPs. At the same time, biofilms also play an important role in the fragmentation and degradation of MPs. In addition, we also investigated the coexistence level, adsorption mechanism, enrichment, and transformation of MPs by environmental pollutants mediated by biofilms. Moreover, an interesting aspect about the colonization of biofilms was discussed. Biofilm colonization not only had a great effect on the accumulation of heavy metals by MPs, but also affects the interaction between particles and environmental pollutants, thereby changing their toxic effects and increasing the difficulty of MPs treatment. Consequently, further attention and research are warranted to delve into the internal mechanisms, environmental risks, and the control of the coexistence of MPs and 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.

Exaggerated interaction of biofilm-developed microplastics and contaminants in aquatic environments

Biofilm-developed microplastics (MPs) may serve as important vectors for contaminants in aquatic environments. Elucidating the interactions between biofilm-developed MPs and coexisting contaminants is crucial for understanding the vector capacities of MPs. However, little is known about how the adverse effects of contaminants on MP surface-colonized biofilms influence their vector capacity. In this study, we aimed to investigate the interaction mechanism of biofilms colonizing the surface of MPs with coexisting contaminants using microcosm experiments and biofilm characterization techniques. The results indicated that the biofilm biomass on polystyrene increased over time, providing an additional abundance of oxygen-containing functional groups and promoting Cd accumulation by biofilm-developed polystyrene. Moreover, as a coexisting contaminant, Cd exerted adverse effects such as additional mortality of microorganisms and senescence and MP-colonized biofilm shedding. Consequently, the contaminant vector capacity of biofilm-developed MPs could be mitigated. Thus, the adverse effects of coexisting contaminants on biofilms influenced the ability of MPs to act as vectors in aquatic environments. Neglecting the negative effects of contaminants on biofilms may lead to an overestimation of the contaminant vector capacity of biofilm-developed MPs. This study provides support for more accurate assessment of the interactions between biofilm-developed MPs as vectors and contaminants in aquatic environments.

When microplastics meet electroanalysis: future analytical trends for an emerging threat

Microplastics are a major modern challenge that must be addressed to protect the environment, particularly the marine environment. Microplastics, defined as particles ≤5 mm, are ubiquitous in the environment. Their small size for a relatively large surface area, high persistence and easy distribution in water, soil and air require the development of new analytical methods to monitor their presence. At present, the availability of analytical techniques that are easy to use, automated, inexpensive and based on new approaches to improve detection remains an open challenge. This review aims to outline the evolution and novelties of classical and advanced methods, in particular the recently reported electroanalytical detectors, methods and devices. Among all the studies reviewed here, we highlight the great advantages of electroanalytical tools over spectroscopic and thermal analysis, especially for the rapid and accurate detection of microplastics in the sub-micron range. Finally, the challenges faced in the development of automated analytical methods are discussed, highlighting recent trends in artificial intelligence (AI) in microplastics analysis.

Microplastics exhibit lower carrying effects on the bioaccessibility and cytotoxicity of lead than montmorillonite clay particles

Microplastics (MPs) in the environment are always colonized by microbes, which may have implications for carrying effect of pollutants and exposure risk in organisms. We present the crucial impacts and mechanisms of microbial colonization on the bioaccessibility and toxicity of Pb(II) loaded in disposable box-derived polypropylene (PP) and polystyrene (PS) MPs and montmorillonite (MMT) clay particles. After 45 d incubation, higher biomass measured by crystal violet staining were detected in MMT (1.23) than in PP and PS (0.400 and 0.721) indicating preferential colonization of microbes in clay particles. Microbial colonization further enhanced the sorption ability toward Pb(II), but inhibited the desorption and bioaccessibility of enriched Pb(II) in zebrafish and decreased the toxicity to gastric epithelial cells in an order of MMT > PS ≈ PP. The crucial effects were mainly because microbe-colonized substrates possessed higher oxygen functional groups and specific surface area and exhibited stronger interactions with Pb(II) and digestive component (i.e., pepsin) than pure substrates. This decreased the available soluble pepsin for complexing with sorbed Pb(II). The findings highlight the role of microbial colonization in modulating the exposure risks of artificial and natural substrate-associated pollutants and suggest that the risks of MPs may be overestimated compared to clay particles.

A review on the occurrence, analytical methods, and impact of microplastics in the environment

Nowadays, microplastic pollution is one of the globally urgent concerns as a result of discharging plastic products into the atmosphere, aquatic and soil environments. Microplastics have average size of less than 5 mm, are non-biodegradable, accumulative, and highly persistent substances. Thousands of tons of microplastics are still accumulated in various environments, posing an enormous threat to human health and living creatures. Here, we review the occurrence and analytical methods, and impact of microplastics in the environments including soil, aquatic media, and atmosphere. Analytical methods including visual observation, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and pyrolysis-gas chromatography-mass spectrometry were evaluated. We elucidated the environmental and human health impacts of microplastics with emphasis on life malfunction, immune disruption, neurotoxicity, diseases and other tangible health risks. This review also found some shortages of analytical equivalence and/or standardization, inconsistence in sampling collection and limited knowledge of microplastic toxicity. It is hopeful that the present work not only affords a more insight into the potential dangers of microplastics on human health but also urges future researches to establish new standardizations in analytical methods.

Adsorption behavior of triclosan on microplastics and their combined acute toxicity to D. magna

Microplastics (MP) have been recently identified as emerging water contaminants in worldwide. Owing to its physicochemical properties, MP have been considered as a vector of other micropollutants and may affect their fate and ecological toxicity in the water environment. In this study, triclosan (TCS), which is a widely-used bactericide, and three frequently found types of MP (PS-MP, PE-MP, and PP-MP) were investigated. The adsorption behavior of TCS on MP was investigated by the effect of reaction time, initial concentration of TCS, and other water chemistry factors. Elovich model and Temkin model are the most fitted well with kinetics and adsorption isotherms, respectively. The maximum TCS adsorption capacities were calculated for PS-MP (9.36 mg/g), PP-MP (8.23 mg/g), and PE-MP (6.47 mg/g). PS-MP had higher affinity to TCS owing to hydrophobic and π-π interaction. The TCS adsorption on PS-MP was inhibited by decreasing concentrations of cations, and increasing concentration of anion, pH, and NOM concentration. At pH 10, only 0.22 mg/g of adsorption capacity was obtained because of the isoelectric point (3.75) of PS-MP and pKa (7.9) of TCS. And almost no TCS adsorption occurred at NOM concentration of 11.8 mg/L. Only PS-MP had no acute toxic effect on D. magna, whereas TCS showed acute toxicity (EC_50,24h of TCS = 0.36 ± 0.4 mg/L). Although survival rate increased when TCS with PS-MP due to lower the TCS concentration in solution via adsorption, PS-MP was observed in intestine and body surface of D. magna. Our findings can contribute to understanding the combined potential effects of MP fragment and TCS to aquatic biota.