The spatial distribution and abundance of microplastics in lake waters and ice during ice-free and ice-covered periods

Significant spatiotemporal pattern of nitrous oxide emission and its influencing factors from a shallow eutropic lake in Inner Mongolia, China

Eutrophic shallow lakes are generally considered as a contributor to the emission of nitrous oxide (N2O), while regional and global estimates have remained imprecise. This due to a lack of data and insufficient understanding of the multiple contributing factors. This study characterized the spatiotemporal variability in N2O concentrations and N2O diffusive fluxes and the contributing factors in Lake Wuliangsuhai, a typical shallow eutrophic and seasonally frozen lake in Inner Mongolia with cold and arid climate. Dissolved N2O concentrations of the lake exhibited a range of 4.5 to 101.2 nmol/L, displaying significant spatiotemporal variations. The lowest and highest concentrations were measured in summer and winter, respectively. The spatial distribution of N2O flux was consistent with that of N2O concentrations. Additionally, the hotspots of N2O emissions were detected within close to the main inflow of lake. The wide spatial and temporal variation in N2O emissions indicate the complexity and its relative importance of factors influencing emissions. N2O emissions in different lake zones and seasons were regulated by diverse factors. Factors influencing the spatial and temporal distribution of N2O concentrations and fluxes were identified as WT, WD, DO, Chl-a, SD and COD. Interestingly, the same factor demonstrated opposing effects on N2O emission in various seasons or zones. This research improves our understanding of N2O emissions in shallow eutrophic lakes in cold and arid areas.

Molecular weight-dependent differences in spectral properties and metal-binding behaviors of dissolved organic matter from different lakes

Dissolved organic matter (DOM) plays an important role in governing metal speciation and migration in aquatic systems. In this study, various DOM samples were collected from Lakes Erhai, Kokonor, and Chaka, and size-fractionated into high molecular weight (HMW, 1 kDa-0.7 μm) and low molecular weight (LMW, <1 kDa) fractions for measurements of dissolved organic carbon (DOC), spectral properties, and metal binding behaviors. Our results demonstrated that samples from Lake Chaka exhibited the highest DOC concentration and fluorescence indices but the lowest percentage of carbohydrates. Regardless of sampling locations, the HMW-DOM fractions contained higher abundances of aromatic DOM, carbohydrates and protein-like substances, but lower abundance of fulvic acid-like substances compared to those in the LMW fractions. Metal titration experiments coupled with the excitation-emission matrix (EEM)-parallel factor (PARAFAC) modeling revealed that the quenching of the PARAFAC-derived fluorescent components was more pronounced in the presence of Cu(II) compared to Pb(II). Humic-like components emerged as a superior model, exhibiting higher binding affinities for Cu(II) than protein-like substances, while the opposite trend was observed for Pb(II). In samples obtained from Lakes Erhai and Kokonor, the condition stability constants (Log KM) for the binding of both Cu(II) and Pb(II) with the HMW-DOM fraction were higher than those with the LMW-DOM fraction. Conversely, a contrasting trend was observed for Lake Chaka. This study highlighted the heterogeneity in spectral properties and metal-binding behaviors of natural DOMs, contributing to an improved understanding of the molecular interactions between DOM components and metal ions and their environmental fate in aquatic ecosystems.

Vertical Distribution Characteristics and Ecological Risk Assessment of Mercury and Arsenic in Ice, Water, and Sediment at a Cold-Arid Lake

Mercury and arsenic are two highly toxic pollutants, and many researchers have explored the effects of the two substances on the environment. However, the research content of toxic substances in frozen periods is relatively small. To explore the spatial and vertical distribution of mercury and arsenic in the ice, water, and sediments of Wuliangsuhai Lake under ice conditions, and to assess the harm degree of the two toxic substances to human beings. We collected the ice, water, and sediments of the lake in December 2020, and tested the contents of Hg and As. The single-factor pollution index method, the local cumulative index method, and the ecological risk coding method were used to assess the pollution status in these three environmental media, and the Monte Carlo simulation combined with the quantitative model recommended by USEPA was used to assess the population health risk. The results showed that (1) The average single-factor pollution values of Hg and As in water were 0.367 and 0.114, both pollutants were at clean levels during the frozen period. (2) The mean Igeo values of Hg and As were 0.657 and -0.948. The bioavailability of Hg in the sediments of Wuliangsuhai Lake during the frozen period was high, and its average value was 7.8%, which belonged to the low-risk grade. The bioavailability of As ranged from 0.2% to 3.7%, with an average value of 1.3%. (3) Monte Carlo simulation results indicate acceptable levels of health risks in both water and ice. This study preliminarily investigated the distribution characteristics of toxic substances and their potential effects on human health in lakes in cold and arid regions during the frozen period. It not only clarified the pollution characteristics of lakes in cold and arid regions during the frozen period, but also provided beneficial supplements for the ecological protection of lake basins. This study lays a foundation for further environmental science research in the region in the future.

Revealing the Freezing-Induced Alteration in Microplastic Behavior and Its Implication for the Microplastics Released from Seasonal Ice

Ice can serve as a significant temporary repository and conveyance mechanism for microplastics (MPs). MPs present in the water column can become entrapped within developing ice formations, subsequently being sequestered and transported by ice floes. With changing temperatures, MPs stored in ice can be released back into the environment, while freezing conditions can alter the properties of MPs, ultimately affecting the fate of MPs in the environment. Freezing of MPs in freshwater ice results in the aggregation of MP particles due to physical compression, leading to an increase in particle size once the MPs are released from the ice. The freezing-induced aggregation enhances buoyancy effects, accelerating the settling/rising velocity of MPs in water. Additionally, freezing can lead to enhanced surface wetting alterations, thus improving the dispersion of hydrophobic MPs. The presence of salt in the water can mitigate the effect of freezing on MPs due to the formation of a brine network within the ice structure, which reduces the pressure on MPs entrapped by ice. In cold regions, numerous MPs undergo freezing and thawing, re-entering the water column.

Micro/nano-plastics and microalgae in aquatic environment: Influence factor, interaction, and molecular mechanisms

Micro/nano-plastics, as emerging persistent pollutant, are frequently detected in aquatic environments together with other environmental pollutants. Microalgae are the major primary producers and bear an important responsibility for maintaining the balance of aquatic ecosystems. Numerous studies have been conducted on the influence of micro/nano-plastics on the growth, photosynthesis, oxidative stress, gene expression and metabolites of microalgae in laboratory studies. However, it is difficult to comprehensively evaluate the toxic effects of micro/nano-plastics on microalgae due to different experimental designs. Moreover, there is a lack of effective analysis of the aforementioned multi-omics data and reports on shared biological patterns. Therefore, the purpose of this review is to compare the acute, chronic, pulsed, and combined effect of micro/nano-plastics on microalgae and explore hidden rules in the molecular mechanisms of the interaction between them. Results showed that the effect of micro/nano-plastics on microalgae was related to exposure mode, exposure duration, exposure size, concentration, and type of micro/nano-plastics. Meanwhile, the phenomenon of poisoning and detoxification between micro/nano-plastics and microalgae was found. The inhibitory mechanism of micro/nano-plastics on algal growth was due to the micro/nano-plastics affected the photosynthesis, oxidative phosphorylation, and ribosome pathways of algal cells. This brought the disruption of the functions of chloroplasts, mitochondria, and ribosome, as well as impacted on energy metabolism and translation pathways, eventually leading to impairment of cell function. Besides, algae resisted this inhibitory effect by regulating the alanine, aspartate, and glutamate metabolism and purine metabolism pathways, thereby increasing the chlorophyll synthesis, inhibiting the increase of reactive oxygen species, delaying the process of lipid peroxidation, balancing the osmotic pressure of cell membrane.

Non-negligible impact of microplastics on wetland ecosystems

There has been much concern about microplastic (MP) pollution in marine and soil environments, but attention is gradually shifting towards wetland ecosystems, which are a transitional zone between aquatic and terrestrial ecosystems. This paper comprehensively reviews the sources of MPs in wetland ecosystems, as well as their occurrence characteristics, factors influencing their migration, and their effects on animals, plants, microorganisms, and greenhouse gas (GHG) emissions. It was found that MPs in wetland ecosystems originate mainly from anthropogenic sources (sewage discharge, and agricultural and industrial production) and natural sources (rainfall-runoff, atmospheric deposition, and tidal effects). The most common types and forms of MPs identified in the literature were polyethylene and polypropylene, fibers, and fragments. The migration of MPs in wetlands is influenced by both non-biological factors (the physicochemical properties of MPs, sediment characteristics, and hydrodynamic conditions) and biological factors (the adsorption and growth interception by plant roots, ingestion, and animal excretion). Furthermore, once MPs enter wetland ecosystems, they can impact the resident microorganisms, animals, and plants. They also have a role in global warming because MPs act as unique exogenous carbon sources, and can also influence GHG emissions in wetland ecosystems by affecting the microbial community structure in wetland sediments and abundance of genes associated with GHG emissions. However, further investigation is needed into the influence of MP type, size, and concentration on the GHG emissions in wetlands and the underlying mechanisms. Overall, the accumulation of MPs in wetland ecosystems can have far-reaching consequences for the local ecosystem, human health, and global climate regulation. Understanding the effects of MPs on wetland ecosystems is essential for developing effective management and mitigation strategies to safeguard these valuable and vulnerable environments.

Distribution, sources, partition behavior and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the waters and sediments of Lake Ulansuhai, China

This study represents the first comprehensive investigation of 16 polycyclic aromatic hydrocarbons (PAHs) in the waters and sediments of Lake Ulansuhai. It explores their occurrence, sources, transport behavior, and associated risks to human health and ecosystems. The results revealed that concentrations of ∑PAHs in dissolved phase and sediment with no significant seasonal differences. In contrast, ∑PAHs concentrations in suspended particulate matter were significantly higher during the ice-free period compared to the ice period. Spatially, the northern part of Lake Ulansuhai displayed higher PAHs content. Diagnostic isomeric ratios and PMF models indicated that the PAHs were primarily derived from combustion sources. The distribution of PAHs within water-sediment demonstrated that non-equilibrium status. Fugacity calculations indicated that 2-4 rings PAHs acted as secondary sources of sediment emissions. Toxicity assessment, indicated that PAHs posed no significant carcinogenic risk to humans. Risk quotient values showed that PAHs as low to high ecological risk.

Characterization and traceability analysis of dry deposition of atmospheric microplastics (MPs) in Wuliangsuhai Lake

Microplastics (MPs) represent a contaminant of emerging concern that may negatively impact lacustrine ecosystems. It is important, then, to manage and reduce the influx of MPs to lakes, a process that requires the identification of MP sources. In this study, atmospheric MP samples were collected and analyzed from 6 sampling sites in the Wuliangsuhai Lake area from March to June 2021, and used to determine atmospheric depositional fluxes of MPs to the lake surface. The sources of MPs were also explored on the basis of MP characteristics and by determining atmospheric flow patterns to the sampling sites using a backward trajectory model (HYSPLIT). The average atmospheric depositional flux of MPs to the Wuliangsuhai Lake area (3371 ± 1423 n/d·m2) is several times higher than rates measured in other areas. MPs were predominately composed of small (0.05-0.5 mm), transparent fibers; a small percentage of particles consisted of fragments, thin films, or lumpy MPs. Compositionally, most MPs were composed of polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS). The former polymer types are indicative of fibers from textiles, including those from textile plants in adjacent cites. The latter (PS) type is presumably derived from degraded food containers and other items associated with tourism. PE was also identified in association with thin films, which were likely derived from bags and/or agricultural plastics. MP characteristics, combined with spatial variations in depositional rates and the results of the backward trajectory model, suggest most atmospherically deposited MPs in the Wuliangsuhai Lake area were transported to the sampling sites from large cities external to the basin, and, to a much lesser degree, areas of tourism within the lake environment. The results of the study provide a theoretical basis for assessing atmospheric MP deposition within inland lake areas as well as for the prevention and control of MP pollution.

Spatiotemporal variability and environmental effects of greenhouse gases, nutrients, and dissolved carbons in an ice-covered reservoir

Ice cover restructures the distribution of substances in ice and underlying water and poses non-negligible environmental effects. This study aimed to clarify the spatiotemporal variability and environmental effects of methane (CH4), nitrous oxide (N2O), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) in ice and water columns during different ice-covered periods. We surveyed the ice-growth, ice-stability, and ice-melt periods in an ice-covered reservoir located in Northeast China. The results showed that underlying water (CH4: 1218.9 ± 2678.9 nmol L-1 and N2O: 19.3 ± 7.3 nmol L-1) and ice (CH4: 535.2 ± 2373.1 nmol L-1 and N2O: 9.9 ± 1.5 nmol L-1) were sources of atmospheric greenhouse gases. N2O concentrations were the highest in the bottom water of the reservoir while CH4 accumulated the most below the ice in the riverine zone. These can be attributed to differences in the solubilities and relative molecular masses of the two gases. Higher concentrations of N2O, TN, TP, DOC, and DIC were recorded in the underlying water than those in the ice due to the preferential redistribution of these substances in the aqueous phase during ice formation. Additionally, we distinguished between bubble and no-bubble areas in the riverine zone and found that the higher CH4 concentrations in the underlying water than those in the ice were due to CH4 bubbles. In addition, we reviewed various substances in ice-water systems and found that the substances in ice-water systems can be divided into solute exclusion and particle entrapment, which are attributed to differences between dissolved and particulate states. These findings are important for a comprehensive understanding of substances dynamics during ice-covered periods.

Investigation on microfiber release from elastane blended fabrics and its environmental significance

Elastane blended apparel is one of the most preferred items by consumers with fashion interest due to its enhanced comfort and fit. The environmental impact and microfiber release due to elastane usage is often ignored due to its lower percentage in apparel. To address such a gap, this study aimed to quantify and characterize the microfiber release behavior of cotton/elastane knitted fabric. Cotton/Elastane blended knitted fabrics with three different proportions of Cotton/Elastane (98/2, 95/5, and 92/8) were considered for this analysis. Upon laundry and quantification, the results of the study showed that 98/2 Cotton/Elastane fabric released 21.04 ± 12.46 microfibers/sq.cm, whereas, 92/8 Cotton/Elastane fabric released 46.56 ± 6.21 microfibers/sq.cm. An increase in elastane proportion increased the overall emission of microfibers per unit area of fabric. The results also showed a higher contribution of elastane fibers in the total microfibers released. 13.40% of the total fibers released were elastane microfibers in the case of 98/2 Cotton/Elastane fabric, whereas, 92/8 Cotton/Elastane fabric released 19.60% of elastane microfibers. The elastane percentage of the fabric showed a significant positive correlation with total microfiber emission (r = 63%) and elastane microfiber emission (r = 62%). Repeated laundering results showed an overall reduction in microfiber emissions in subsequent washes. However, interestingly, an increase in the wash cycle increased the proportion of elastane microfibers in the total microfibers released. 92/8 Cotton/Elastane fabric released 20% of elastane microfibers in the first wash and the proportion increased to 36% in the 4th wash. In contrast to that, the release of cotton microfibers is noted to decrease with the number of laundry cycles. As far as the length of microfiber is considered, elastane microfibers are shorter than cotton microfibers. The length of elastane microfibers was higher in the initial wash (98/2 Cotton/Elastane fabric - 352.5 μm; 95/5 Cotton/Elastane fabric - 920 μm; 92/8 Cotton/Elastane fabric - 695 μm) and it is reduced with increment in the number of washes with a strong negative correlation of -0.88. A higher proportion of emissions and lower fiber length are the alarming negative impacts of elastane fibers in apparel. Based on this analysis, it is estimated that one square meter of fabric with a lower elastane percentage (2%) can release up to 2.81 × 104 microfibers into the environment at the first wash. The threatening issues of microfibers on aquatic life, particularly in terms of bioaccumulation and biomagnification, are alarming. Elastane blended fabrics should be given special attention because they can make the problem more serious by posing a risk of chemical leachates, such as bisphenols.