Characterization of dynamic plastisphere and their underlying effects on the aging of biodegradable and traditional plastics in freshwater ecosystems

Dynamic changes of leachates of aged plastic debris under different suspended sand concentrations and their toxicity

Plastic pollution in aquatic environments poses significant ecological risks, particularly through released leachates. While traditional or non-biodegradable plastics (non-BPs) are well-studied, biodegradable plastics (BPs) have emerged as alternatives that are designed to degrade more rapidly within the environment. However, research on the ecological risks of the leachates from aged BPs in aquatic environments is scarce. This controlled laboratory study investigated the leachate release processes and associated toxicity of traditional non-BPs, i.e., polyethylene terephthalate (PET) and polypropylene (PP) and BPs, i.e., polylactic acid (PLA) combined with polybutylene adipate terephthalate (PBAT) and starch-based plastic (SBP) under different aging time and suspended sand concentrations (0, 50, 100, 250, and 500 mg/L). The results indicated that BPs release significantly higher levels of dissolved organic carbon (DOC) than those of non-BPs, particularly at elevated suspended sand concentrations. The DOC concentrations in PLA+PBAT leachate reached 2.69 mg/L, surpassing those of PET and PP. Additionally, BPs released organic matter of larger molecular weight and protein-like substances. Toxicity tests showed that leachates from BPs inhibited the activity of Daphnia magna more than those from non-BPs. At a suspended sand concentration of 500 mg/L, PLA+PBAT leachate caused a 30 % inhibitory rate of Daphnia magna. Despite enhanced degradability, leachates from BPs may pose increased environmental risks in ecosystems with high suspended sand concentrations. Comprehensive ecological risk assessments are essential for effectively managing and mitigating these hazards of plastic pollution.

Uncovering the toxic effects and adaptive mechanisms of aminated polystyrene nanoplastics on microbes in sludge anaerobic digestion system: Insight from extracellular to intracellular

The impacts of polystyrene nanoplastics (PS NPs) with amino functional groups on sludge anaerobic digestion process and the underlying microbial feedbacks remains unclear. Herein, PS NPs coated with and without amino functional groups were employed to explore their impacts on the sludge digestion performance. Experimental results showed that aminated PS NPs (PS-NH2) deteriorated the methane yield and hydrolysis rate. The Derjaguin-Landau-Verwey-Overbeek theory analysis suggested that the PS-NH2 decreased the interaction energy barrier, making it easier to contact with sludge and disrupting the structure of extracellular polymeric substances. Metagenomic analysis showed that the abundance of functional microbes (e.g., Longilinea, Leptolinea, and Methanosarcina) decreased, accompanied with lower network complexity and fewer keystone taxa. Molecular docking revealed that PS-NH2 occupy the antioxidant enzyme active binding sites through hydrogen bonding and hydrophobic interactions, impairing degradation of reactive oxygen species. The severe intracellular oxidative stress up-regulated genes associated with quorum sensing (e.g., luxI and luxR) and protein biosynthesis (e.g., algA, trpG and trpE), and further inducing compact tryptophan-like proteins as a defense against NPs. These findings provide new understanding of the toxic effects from PS-NH2 in biological systems and offer valuable insights into the regulation strategies aimed at alleviating NPs inhibition.

High-altitude aquatic ecosystems offer faster aging rate of plastics

While research on the aging behavior of plastics in aquatic systems is extensive, studies focusing on high-altitude ecosystems, characterized by higher solar radiation and lower temperatures, remain limited. This study investigated the long-term aging behavior of non-biodegradable plastics (non-BPs), namely polyethylene terephthalate (PET) and polypropylene (PP) and biodegradable plastics (BPs), specifically polylactic acid plus polybutylene adipate-co-terephthalate (PLA + PBAT) and starch-based plastic (SBP), in a tributary of the Yarlung Zangbo River on the high-altitude Tibetan Plateau. Over 84 days of field aging, all four types of plastics exhibited initial rapid aging followed by deceleration. This aging process can be divided into two phases: rapid surface oxidation aging and an aging plateau phase. Notably, PP aged at a rate comparable to BPs, contrary to expectations of faster aging for BPs. Compared to low-altitude aquatic ecosystems, plastics in this study showed a faster aging rate. This was primarily due to intense ultraviolet radiation causing severe photoaging. Furthermore, the lower temperatures contributed to the formation of thinner biofilms. These thinner biofilms exhibited a reduced capacity to block light, further exacerbating the photoaging process of plastics. Statistical analysis results indicated that temperature, total nitrogen TN, and total phosphorus TP were likely the main water quality parameters influencing plastic aging. The varying effects of water properties and nutrients underscore the complex interaction of water quality parameters in high-altitude environments. Given the delicate nature of the high-altitude environment, the environmental impact of plastics, especially BPs, warrants careful consideration.

Microbial carbon metabolism patterns of microplastic biofilm in the vertical profile of urban rivers

Microplastics (MPs) can provide a unique niche for microbiota in waters, thus regulating the nutrients and carbon cycling. Following the vertical transport of MPs in waters, the compositions of attached biofilm may be dramatically changed. However, few studies have focused on the related ecological function response, including the carbon metabolism. In this study, we investigated the microbial carbon metabolism patterns of attached biofilm on different MPs in the vertical profile of urban rivers. The results showed that the carbon metabolism capacity of biofilm on the degradable polylactic acid (PLA) MPs was higher than that in the non-degradable polyethylene terephthalate (PET) MPs. In the vertical profile, the carbon metabolism rates of biofilm on two MPs both decreased with water depth, being 0.74 and 0.91 folds in bottom waters of that in surface waters. Specifically, the utilization of polymers, carbohydrate, and amine of PLA biofilm was significantly inhibited in the bottom waters, which were not altered on the PET. Compared with surface waters, the microbial metabolism function index of PLA biofilm was inhibited in deep waters, but elevated in the PET biofilm. In addition, the water quality parameters (e.g., nutrients) in the vertical profile largely shaped carbon metabolism patterns. These findings highlight the distinct carbon metabolism patterns in aquatic environments in the vertical profile, providing new insights into the effects of MPs on global carbon cycle.

High levels of cadmium altered soil archaeal activity, assembly, and co-occurrence network in volcanic areas

Soil microbial communities are essential to biogeochemical cycles. However, the responses of microorganisms in volcanic soil with high heavy metal levels remain poorly understood. Here, two areas with high levels of cadmium (Cd) from the same volcano were investigated to determine their archaeal composition and assembly. In this study, the Cd concentrations (0.32-0.38 mg/ kg) in the volcanic soils exceeded the standard risk screening values (GB15618-2018) and correlated with archaeal communities strongly (P < 0.05). Moreover, the area with elevated levels of Cd (periphery) exhibited a greater diversity of archaeal species, albeit with reduced archaeal activity, compared to the area with lower levels of Cd (center). Besides, stochastic processes mainly governed the archaeal communities. Furthermore, the co-occurrence network was simplest in the periphery. The proportion of positive links between taxa increased positively with Cd concentration. Moreover, four keystone taxa (all from the family Nitrososphaeraceae) were identified from the archaeal networks. In its entirety, this study has expanded our comprehension of the variations of soil archaeal communities in volcanic areas with elevated cadmium levels and serves as a point of reference for the agricultural development of volcanic soils in China.

Freshwater plastisphere: a review on biodiversity, risks, and biodegradation potential with implications for the aquatic ecosystem health

The plastisphere, a unique microbial biofilm community colonizing plastic debris and microplastics (MPs) in aquatic environments, has attracted increasing attention owing to its ecological and public health implications. This review consolidates current state of knowledge on freshwater plastisphere, focussing on its biodiversity, community assembly, and interactions with environmental factors. Current biomolecular approaches revealed a variety of prokaryotic and eukaryotic taxa associated with plastic surfaces. Despite their ecological importance, the presence of potentially pathogenic bacteria and mobile genetic elements (i.e., antibiotic resistance genes) raises concerns for ecosystem and human health. However, the extent of these risks and their implications remain unclear. Advanced sequencing technologies are promising for elucidating the functions of plastisphere, particularly in plastic biodegradation processes. Overall, this review emphasizes the need for comprehensive studies to understand plastisphere dynamics in freshwater and to support effective management strategies to mitigate the impact of plastic pollution on freshwater resources.

Effects of photoaging on structure and characteristics of biofilms on microplastic in soil: Biomass and microbial community

Understanding of the environmental behaviors of microplastics is limited by a lack of knowledge about how photoaging influences biofilm formation on microplastics in soil. Here, original microplastics (OMPs) and photoaged-microplastics (AMPs) were incubated in soil to study the effect of photoaging on formation and characteristics of biofilm on the poly (butylene succinate) microplastics. Because photoaging decreased the hydrophobicity of the microplastic, the biomass of biofilm on the OMPs was nearly twice that on the AMPs in the early stage of incubation. However, the significance of the substrate on biomass in the biofilm declined as the plastisphere developed. The bacterial communities in the plastisphere were distinct from, and less diverse than, those in surrounding soil. The dominant genera in the OMPs and AMPs plastispheres were Achromobacter and Burkholderia, respectively, indicating that photoaging changed the composition of the bacterial community of biofilm at the genus level. Meantime, photoaging decreased the complexity and stability of the plastisphere bacterial community network. Results of Biolog ECO-microplate assays and functional prediction from amplicons showed that photoaging treatment enhanced the carbon metabolic capacity of the microplastic biofilm. This study provides new insights into the formation of plastispheres in soil.

Dynamic evolution of antibiotic resistance genes in plastisphere in the vertical profile of urban rivers

Microplastics (MPs) can vertically transport in the aquatic environment due to their aging and biofouling, forming distinct plastisphere in different water layers. However, even though MPs have been regarded as hotspots for antibiotic resistance genes (ARGs), little is known about the propagation and transfer of ARGs in plastisphere in waters, especially in the vertical profile. Therefore, this study investigated the dynamic responses and evolution of ARGs in different plastisphere distributed vertically in an urbanized river. The biofilm biomass in the polylactic acid (PLA) plastisphere was relatively higher than that in the polyethylene terephthalate (PET), showing depth-decay variations. The ARGs abundance in plastisphere were much higher than that in the surrounding waters, especially for the PLA. In the vertical profiles, the ARGs abundance in the PET plastisphere increased with water depths, while the highest abundance of ARGs in the PLA mostly appeared at intermediate waters. In the temporal dynamic, the ARGs abundance in plastisphere increased and then decreased, which may be dominated by the MP types at the initial periods. After long-term exposure, the influences of water depths seemed to be strengthened, especially in the PET plastisphere. Compared with surface waters, the microbiota attached in plastisphere in deep waters showed high species richness, strong diversity, and complex interactions, which was basically consistent with the changes of nutrient contents in different water layers. These vertical variations in microbiota and nutrients (e.g., nitrogen) may be responsible for the propagation of ARGs in plastisphere in deep waters. The host bacteria for ARGs in plastisphere was also developed as water depth increased, leading to an enrichment of ARGs in deep waters. In addition, the abundance of ARGs in plastisphere in bottom waters was positively correlated with the mobile genetic elements (MGEs) of intI1 and tnpA05, indicative of a frequent horizontal gene transfer of ARGs. Overall, water depth played a critical role in the propagation of ARGs in plastisphere, which should not be ignored in a long time series. This study provides new insights into the dynamic evolution of ARGs propagation in plastisphere under increasing global MPs pollution, especially in the vertical profile.

Characterization of the dynamic aging and leached dissolved organic carbon from biodegradable and conventional plastics under photooxidation

Biodegradable plastics have been regarded as promising candidates in the struggle against plastic pollution. However, the aging and dynamic leaching process of biodegradable and conventional plastics under photooxidation is still unclear. Herein, three types of non-biodegradable plastics (polypropylene, polyethylene, and polyethylene terephthalate), and two types of biodegradable plastics (polylactic acid and cornstarch-based plastics) were treated with 21 days of photooxidation followed by 13 days of dark conditions. Scanning electron microscopy was applied to display the morphological changes. Also, the carbonyl index, oxygen-to-carbon ratio, and contact angle were utilized to characterize the aging degree of the plastic surface. Unexpectedly, biodegradable plastics did not always display a greater aging degree than non-biodegradable plastics. Moreover, the dissolved organic carbon during the leaching process was identified using excitation-emission matrix fluorescence spectroscopy. The findings suggested that biodegradable plastics showed the potential to release more dissolved organic carbon. Particularly, the polylactic acid plastic displayed higher concentrations and more types of dissolved organic carbon release than that of conventional plastics in our experiment. This research highlights the necessity for monitoring the aging process of both biodegradable and non-biodegradable plastics and the non-negligible ecological risk of leached organic pollutants due to plastic degradation.

Microbial colonization patterns and biodegradation of petrochemical and biodegradable plastics in lake waters: insights from a field experiment

Introduction

Once dispersed in water, plastic materials become promptly colonized by biofilm-forming microorganisms, commonly known as plastisphere.

Methods

By combining DNA sequencing and Confocal Laser Scanning Microscopy (CLSM), we investigated the plastisphere colonization patterns following exposure to natural lake waters (up to 77 days) of either petrochemical or biodegradable plastic materials (low density polyethylene - LDPE, polyethylene terephthalate - PET, polylactic acid - PLA, and the starch-based MaterBi® - Mb) in comparison to planktonic community composition. Chemical composition, water wettability, and morphology of plastic surfaces were evaluated, through Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and static contact angle analysis, to assess the possible effects of microbial colonization and biodegradation activity.

Results and Discussion

The phylogenetic composition of plastisphere and planktonic communities was notably different. Pioneering microbial colonisers, likely selected from lake waters, were found associated with all plastic materials, along with a core of more than 30 abundant bacterial families associated with all polymers. The different plastic materials, either derived from petrochemical hydrocarbons (i.e., LDPE and PET) or biodegradable (PLA and Mb), were used by opportunistic aquatic microorganisms as adhesion surfaces rather than carbon sources. The Mb-associated microorganisms (i.e. mostly members of the family Burkholderiaceae) were likely able to degrade the starch residues on the polymer surfaces, although the Mb matrix maintained its original chemical structure and morphology. Overall, our findings provide insights into the complex interactions between aquatic microorganisms and plastic materials found in lake waters, highlighting the importance of understanding the plastisphere dynamics to better manage the fate of plastic debris in the environment.