Photo-aged non-biodegradable and biodegradable mulching film microplastics alter the interfacial behaviors between agricultural soil and inorganic arsenic

Polylactic acid microplastics before and after aging induced neurotoxicity in zebrafish by disrupting the microbiota-gut-brain axis

Polylactic acid (PLA) is a biodegradable alternative to traditional plastics due to its excellent biocompatibility. However, PLA is challenging to fully degrade and can easily become microplastics (MPs) in surface water, a process accompanied by aging. This study found that aged PLA (APLA) MPs exhibited increased surface roughness, decreased surface potential, and more oxygen-containing functional groups compared to PLA. Acute exposure to PLA/APLA in zebrafish larvae resulted in sluggish behavior and inhibited neuronal development. Chronic exposure to PLA/APLA in adult zebrafish led to reduced exploratory behavior, poor memory, increased aggression, and neuron loss. Overall, PLA/APLA induced dose-dependent neurotoxicity, with APLA exhibiting greater toxicity than PLA, potentially due to its higher rate of uptake. Additionally, exposure to PLA/APLA led to thinning of the intestinal wall, shortening of villi, and suppression of intestinal neurotransmitter levels, accompanied by alterations in microbial abundance and gut dysbiosis. Meanwhile, supplementation with bile acid, considered as the key regulator in the gut-brain axis, significantly mitigated the neurotoxicity induced by PLA/APLA. These findings confirm that PLA/APLA MPs indeed elicit neurotoxicity via the gut-brain axis and provide scientific evidence for targeted environmental interventions to minimize the adverse ecological impacts of biodegradable MPs.

Conventional and biodegradable microplastics affected arsenic mobility and methylation in paddy soils through distinct chemical-microbial pathways

The presence of microplastics (MPs) in paddy soil has become a growing concern, yet the influence of MPs on arsenic (As) dynamics in paddy soil remains largely unexplored. A 98-day microcosm experiment was conducted to investigate the impact of MPs on As behavior in As-contaminated paddy soil. The results revealed that conventional microplastics (CMPs) reduced As concentration in porewater by 25-38 %, but substantially increased the percentage of methylated As (% MeAs) in soil by 8-23 times under 5 % dosages after 98-day incubation. In contrast, at the end of incubation, biodegradable microplastics (BMPs) at 5 % dosages notably increased As concentration in porewater and % MeAs in soil by 2-9 times and 11-395 times, respectively. The combination of network analysis and Random-Forest analysis implied that CMPs might inhibit As mobility through enhancing microbial As(III) oxidation and promote As methylation by enriching arsM-carrying microbes. However, BMPs promoted As release mainly accompanying with microbial iron reduction, and enhanced As methylation through enriching fermenting bacteria (i.e., Clostridiaceae) and arsM-carrying organic matter degrading bacteria (i.e., Gemmatimonas and Nocardia). These findings might provide broaden insights into As cycling induced by MPs and contribute to the prevention of combined pollution from As and MPs in paddy soil.

Effects of naturally aged microplastics on arsenic and cadmium accumulation in lettuce: Insights into rhizosphere microecology

Naturally aged microplastics (NAMPs) are commonly found in farmland soils contaminated with heavy metals (HMs), such as arsenic (As) and cadmium (Cd); yet their combined effects on soil-plant ecosystems remain poorly understood. In this study, we investigated the toxic effects of NAMPs and As-Cd on lettuce, considering the influence of earthworm activity, and examined changes in As-Cd bioavailability in the rhizosphere. Four experimental systems were established: soil-only, soil-lettuce, soil-earthworms, and soil-lettuce-earthworms systems, with four NAMPs concentrations (0, 0.1, 0.5, 1 %). Our results showed that exposure to 0.1 % NAMPs reduced As accumulation in lettuce shoots (0.17-0.25 mg kg-1) and roots (1.13-1.72 mg kg-1), while increasing biomass and enhancing root growth by alleviating toxicity. In contrast, the combined stress of higher NAMPs concentration (0.5 %/1 %) and As-Cd caused a 28.4-58.4 % reduction in root activity, which stimulated low-molecular-weight organic acid (LMWOA) secretion in the rhizosphere, increasing the bioavailability of As and Cd and enhancing their absorption by lettuce. Partial least squares path modeling (PLS-PM) revealed that co-exposure altered LMWOA content, soil enzyme activity, and microbial community stability in the rhizosphere, ultimately influencing the bioavailability and uptake of As and Cd by lettuce.

Response of sedimentary microbial community and antibiotic resistance genes to aged Micro(Nano)plastics exposure under high hydrostatic pressure

Several studies reported that the presence of microplastics (MPs)/nanoplastics (NPs) in marine environments can alter microbial community and function. Yet, the impact of aged MPs/NPs on deep sea sedimentary ecosystems under high hydrostatic pressure remains insufficiently explored. Herein, the sedimentary microbial community composition, co-occurrence network, assembly, and transfer of antibiotic resistance genes (ARGs) in response to aged MPs/NPs were investigated. Compared with the control, NPs addition significantly reduced bacterial alpha diversity (p < 0.05), whereas MPs showed no significant impact (p > 0.05). Moreover, networks under NPs exhibited decreased complexity than that under MPs and the control, including edges, average degree, and the number of keystone. The assembly of the microbial community was primarily governed by stochastic processes, and aged MPs/NPs increased the importance of stochastic processes. Moreover, exposure to MPs/NPs for one month decreased the abundance of antibiotic resistance genes (ARGs) (from 94.8 to 36.2 TPM), while exposure for four months increased the abundance (from 40.6 to 88.1 TPM), and the shift of ARGs in sediment was driven by both functional modules and microbial community. This study is crucial for understanding the stress imposed by aged MPs/NPs on sedimentary ecosystems under high hydrostatic pressure.

Deciphering the role of nonylphenol adsorption in soil by microplastics with different polarities and ageing processes

In the soil environment, microplastics (MPs) commonly coexist with organic pollutants such as nonylphenol (NP), affecting the migration of NP through adsorption/desorption. However, few studies have focused on the interaction between NP and MPs in soil, especially for MPs of different types and ageing characteristics. In this study, non-polar polypropylene (PP) and polar polyamide (PA) MPs were aged either photochemically (144 h) or within soil (60 days), then used to determine the effect of 5 % MPs on the adsorption behaviour of NP (0.1-4.0 mg/L) in soil. Results showed that both ageing processes significantly promoted the conversion of -CH3 groups to C-O and CO on the surface of PPMPs, while PAMPs exhibited amide groups changes and a reduction in average particle size due to ageing. Additionally, both ageing processes promoted the adsorption of NP by soil containing PPMPs, due to an increase in oxygen-containing functional groups and specific surface area. In contrast, the NP adsorption capacity of soil containing PAMPs decreased by 15.4 % following photochemical ageing due to hydrolysis of amide groups, but increased by 21.15 % after soil ageing due to reorganization of amide groups, respectively. The soil-PAMPs systems exhibited a stronger affinity for NP compared to the soil-PPMPs systems, which was primarily attributed to the dominant role of hydrogen bonding. NP was found to be distributed mainly on soil particles in the soil-PPMPs systems, while it tended to be adsorbed by MPs in the soil-PAMPs systems, especially in the soil aged MPs system. This study provides a comprehensive analysis of the complex effects of MPs on coexisting pollutants in soil environments, highlighting the effect of MP characteristics on the adsorption of organic pollutants, which is essential for understanding the transport behaviour of organic pollutants.

Single and combined effect of polyethylene microplastics (virgin and naturally aged) and cadmium on pakchoi (Brassica rapa subsp. chinensis) under different growth stages

To protect agro-systems and food security, study on the effect of microplastics and heavy metals on edible plants is of great significance. Existing studies mostly used virgin microplastics to evaluate their effects on plants, effects of naturally aged microplastics and their combined effects with heavy metals are rarely explored. In this study, single and combined effect of polyethylene microplastics (PE, both virgin and naturally aged) and cadmium (Cd) on pakchoi under seedling and mature stages were analyzed from perspectives of growth inhibition, oxidative damage, nutrition content and soil enzyme activities. Results showed that inhibiting effects of naturally aged PE (PEa) on the growth of pakchoi were stronger than virgin PE (PEv), whereas co-contamination of PEa and Cd was less toxic than that of PEv and Cd. The co-contamination of PE and Cd could inhibit pakchoi dry biomass by over 85 %. Both single and combined contamination of PE and Cd promoted soil fluorescein diacetate hydrolase (FDA) activities, which were 1.11 to 2.04 times of that in control group. Soluble sugar contents under co-contamination of PEa and Cd were 14 % to 22 % higher than those in control group. PEa and PEv showed different effects on oxidative damage of pakchoi. Compared with PEv, catalase (CAT) activities were more sensitive with PEa, whereas PEa had lower effect on superoxide dismutase (SOD) activities. The response of pakchoi to PE and Cd changed with growth stage. Chlorophyll contents in pakchoi under seedling stage were generally higher than those under mature stage. For Cd contaminated soils, PE benefited pakchoi growth under seedling stage, i.e. antagonistic effect between Cd and PE but hindered their growth under mature stage, i.e. synergistic effect. The results unraveled here emphasized PE, especially PEa, could trigger negative effects on agro-systems, whereas PE could be beneficial for heavy metal contaminated agro-systems under specific situations.

Biodegradable plastics: mechanisms of degradation and generated bio microplastic impact on soil health

Conventional petroleum-derived polymers are valued for their versatility and are widely used, owing to their characteristics such as cost-effectiveness, diverse physical and chemical qualities, lower molecular weight, and easy processability for large-scale production. However, the extensive accumulation of such plastics leads to serious environmental issues. To combat this existing situation, an alternative lies in the production of bioplastics from natural and renewable sources such as plants, animals, microbes, etc. Bioplastics obtained from renewable sources are compostable and susceptible to degradation caused by microbes hydrolyzing to CO2, CH4, and biomass. Also, certain additives are reinforced into the bioplastic films to improve their physicochemical properties and degradation rate. However, on degradation, the bio-microplastic (BM) produced could have positive as well as negative impact on the soil health. This article thus focuses on the degradation of various fossil based as well as bio based biodegradable plastics such as polyhydroxyalkanoates (PHA), polyhydroxy butyrate (PHB), polylactic acid (PLA), polybutylene succinate (PBS), polycaprolactone (PCL), and polysaccharide derived bioplastics by mechanical, thermal, photodegradation and microbial approaches. The degradation mechanism of each approach has been discussed in detailed for different bioplastics. How the incorporation or reinforcement of various additives in the biodegradable plastics effects their degradation rates has also been discussed. In addition to that, the impact of generated bio-microplastic on physicochemical properties of soil such as pH, bulk density, carbon, nitrogen content etc. and biological properties such as on genome of native soil microbes and on plant nutritional health have been discussed in detailed.

Water-dependent effects of biodegradable microplastics on arsenic fractionation in soil: Insights from enzyme degradation and synchrotron-based X-ray analysis

The abundance of biodegradable microplastics (BMPs) is increasing in soil due to the widespread use of biodegradable plastics. However, the influence of BMPs on soil metal biogeochemistry, especially arsenic (As), under different water regimes is still unclear. In this study, we investigated the effects of two types of BMPs (PLA-MPs and PBAT-MPs) on As fractionation in two types of soils (black soil and fluvo-aquic soil) under three water regimes including drying (Dry), flooding (FL), and alternate wetting and drying (AWD). The results show that BMPs had limited indirect effects on As fractionation by altering soil properties, but had direct effects by adsorbing and releasing As during their degradation. Enzyme degradation experiments show that the degradation of PLA-MPs led to an increased desorption of 4.76 % for As(III) and 15.74 % for As(V). Synchrotron-based X-ray fluorescence (μ-XRF) combined with micro-X-ray absorption near edge structure (μ-XANES) analysis show that under Dry and AWD conditions, As on the BMPs primarily bind with Fe hydrated oxides in the form of As(V). Conversely, 71.57 % of As on PBAT-MP under FL conditions is in the form of As(III) and is primarily directly adsorbed onto its surface. This study highlights the role of BMPs in soil metal biogeochemistry.

Microplastics emerge as a hotspot for dibutyl phthalate sources in rivers and oceans: Leaching behavior and potential risks

Dibutyl phthalate (DBP) as a plasticizer has been widely used in the processing of plastic products. Nevertheless, these DBP additives have the potential to be released into the environment throughout the entire life cycle of plastic products. Herein, the leaching behavior of DBP from PVC microplastics (MPs) in freshwater and seawater and its potential risks were investigated. The results show that the plasticizer content, UV irradiation, and hydrochemical conditions have a great influence on the leaching of DBP from the MPs. The release of DBP into the environment increases proportionally with higher concentrations of additive DBP in MPs, particularly when it exceeds 15 %. The surface of MPs undergoes accelerated oxidation and increased hydrophilicity under UV radiation, thereby facilitating the leaching of DBP. Through 30 continuous leaching experiments, the leaching of DBP from MPs in freshwater and seawater can reach up to 12.28 and 5.42 mg g-1, respectively, indicating that MPs are a continuous source of DBP pollution in the aquatic environment. Moreover, phthalate pollution index (PPI) indicates that MPs can significantly increase DBP pollution in marine environment through land and sea transport processes. Therefore, we advocate that the management of MPs waste containing DBP be prioritized in coastal sustainable development.

How do polystyrene microplastics affect the adsorption of copper in soil?

Microplastics (MPs) commonly coexist with heavy metals in the soil environment. MPs can influence the activity of heavy metals, and the specific mechanisms need to be further explored. Here, different contents of polystyrene (PS) MPs were added to soil to explore their effects on the adsorption and desorption characteristics of copper (Cu2+) in soil. The adsorption process was mainly chemical adsorption and belonged to a spontaneous, endothermic reaction. The hydrophobicity of MPs slowed down the adsorption and desorption rates. The main adsorption mechanisms included complexation by oxygen-containing functional groups, ion exchange (accounting for 33.97-36.04 % of the total adsorption amounts), and electrostatic interactions. MPs lacked oxygen-containing functional groups and were predominantly engaged in ion exchange and electrostatic interactions. MPs diluted, blocked the soil, and covered the active sites of soil, which reduced adsorption (3.56-16.18 %) and increased desorption (0.90-2.07 %) of Cu2+ in soil samples, thus increasing the activity and mobility of Cu2+. These findings provide new insights into the effects of MPs on the fate and risk of heavy metals in soil. ENVIRONMENTAL IMPLICATION: The existing literature concerning the effects of microplastics on the adsorption of heavy metals in soil is insufficient. Our investigation unveiled that the main adsorption mechanisms of different soil samples included complexation by oxygen-containing functional groups, ion exchange (accounting for 33.97-36.04 % of the total adsorption amounts), and electrostatic interactions. MPs lacked oxygen-containing functional groups and were predominantly engaged in ion exchange and electrostatic interactions. MPs diluted, blocked the soil, and covered the active sites of soil, which reduced adsorption (3.56-16.18 %) and increased desorption (0.90-2.07 %) of Cu2+ in soil samples, thus increasing the activity and mobility of Cu2+.

Interaction mechanism of water-soluble inorganic arsenic onto pristine nanoplastics

Nanoplastics (NPLs) persist in aquatic habitats, leading to incremental research on their interaction mechanisms with metalloids in the environment. In this regard, it is known that plastic debris can reduce the number of water-soluble arsenicals in contaminated environments. Here, the arsenic interaction mechanism with pure NPLs, such as polyethylene terephthalate (PET), aliphatic polyamide (PA), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), and polystyrene (PS) is evaluated using computational chemistry tools. Our results show that arsenic forms stable monolayers on NPLs through surface adsorption, with adsorption energies of 9-24 kcal/mol comparable to those on minerals and composite materials. NPLs exhibit varying affinity towards arsenic based on their composition, with As(V) adsorption showing higher stability than As(III). The adsorption mechanism results from a balance between electrostatics and dispersion forces (physisorption), with an average combined contribution of 87%. PA, PET, PVC, and PS maximize the electrostatic effects over dispersion forces, while PE and PP maximize the dispersion forces over electrostatic effects. The electrostatic contribution is attributed to hydrogen bonding and the activation of terminal O-C, C-H, and C-Cl groups of NPLs, resulting in several pairwise interactions with arsenic. Moreover, NPLs polarity enables high mobility in aqueous environments and fast mass transfer. Upon adsorption, As(III) keeps the NPLs polarity, while As(V) limits subsequent uptake but ensures high mobility in water. The solvation process is destabilizing, and the higher the NPL polarity, the higher the solvation energy penalty. Finally, the mechanistic understanding explains how temperature, pressure, pH, salinity, and aging affect arsenic adsorption. This study provides reliable quantitative data for sorption and kinetic experiments on plastic pollution and enhances our understanding of interactions between water contaminants.

Natural aging and adsorption/desorption behaviors of polyethylene mulch films: Roles of film types and exposure patterns

Polyethylene (PE) mulch films are an important source of microplastics (MPs) in agricultural soils, which may further affect the bioavailability of coexisting pollutants. In this study, white (WM), black (BM), and silver-black (SM) PE mulch films were aged on the soil surface and under soil burial to simulate the two exposure patterns of abandoned mulch films in the field. Results indicated that the soil-surface exposure induced more pronounced aging characteristics, and WM seemed the most susceptible. Serious surface deterioration by aging led to a drastic decrease in the tensile properties of the films, suggesting the tendency to fragment. Oxygen-containing functional groups were generated on the film surfaces, with oxygen/carbon ratios increasing by up to 29 times, which contributed to the prominent increase in Pb adsorption on the film-derived MPs. Additionally, the film surface became more hydrophobic when exposed to the soil surface but more hydrophilic in the soil-burial exposure, which was in agreement with the change in triclosan adsorption, i.e., promotion and suppression, respectively. Aging generally decreased the desorption potential of the adsorbed pollutants in simulated gastrointestinal solutions due to increased interactions. By comparison, exposure patterns were revealed to be the critical factor for these changes, regardless of film types.

A case on source to soil to solutions: Distribution characteristics of microplastics in farmland soil of the largest vegetable base in Northwest China

The wide application of facility agriculture accelerated the rapid development of agriculture. However, microplastics pollution in the soil caused by long-term residual agricultural film posed a significant threat to the soil ecosystem and human health. Jingyang County of Shaanxi Province was the largest vegetable planting base in northwest China. Soil samples of facility agriculture and non-facility agriculture were collected to investigate the distribution characteristics and risks of microplastics. The abundance of microplastics in Jingyang County ranged from 200.00 to 4733.33 n·kg-1, and the mean abundance was 1955.00 n·kg-1. Microplastics abundance in facility agriculture soil was higher than that in non-facility agriculture soil, and it increased with the growth of planting years. In general, the size of soil microplastics was mainly <100 μm and the abundance was negatively correlated with particle size. There were 30 types of chemical constituents in the microplastics detected, and PE (47.03 %) and PET (11.48 %) were the main ones. In addition, the types of microplastics in soil were identical with those detected in irrigation water and fertilizer, which provided another source of soil microplastics. All the sampling sites were ecological risk category I, and there was no carcinogenic risk to human health at present. In the future, the government should advocated and encouraged farmers to improve mulch recycling efficiency. Correspondingly, more positive action should be taken to the management on mulch recycling and the standards on placement of waste agricultural inputs. This study would provide foundation data for the research of microplastics pollution in farmland and the risk assessment of ecosystem and human health.

Iron plaque formation and its influences on the properties of polyethylene plastic surfaces in coastal wetlands: Abiotic factors and bacterial community

Iron (Fe) plaques in coastal wetlands are widely recognized because of their strong adsorption affinity for natural particles, but their interaction behaviors and mechanisms with plastics remain unknown. Through laboratory incubation experiments, paired with multiple characterization methods and microbial analysis, this work focused on the characteristics of Fe plaques on low-density polyethylene plastic surfaces and their relationship with environmental factors in coastal wetlands (Mangrove and Spartina alterniflora soil). The results showed that iron plaques increased the adhesive force of the plastic surface from 65.25 to 300 nN and promoted the oxidation of the plastic surface. Fe plaque formation was stimulated by salinity, anaerobic conditions, natural organic matter, and a weak alkaline scenario (pH 8.0-8.3). The Fe content showed a stable positive correlation with heavy metals loading (i.e., As, Mn, Co, Cr, Pb, and Zn). Furthermore, we revealed that Fe plaque was positively regulated by Nitrospirae through 16S rRNA high-throughput sequencing analysis. Meanwhile, Verrucomicrobia and Kiritimatiellaeota. may act as depressants by consuming salt. This work illustrated that iron plaques could enhance the role of plastics in contaminant migration by altering their adsorption performance, providing new insights into plastic interface behavior and potential ecological effects in coastal wetlands.

Physicochemical properties of environmental media can affect the adsorption of arsenic (As) by microplastics

Microplastics are emerging pollutants that can adsorb heavy metals and threaten human health through food chain. Recently, there has been increasing interest in understanding the adsorption behavior of heavy metals by microplastics in farmland soil. In particular, arsenic (As), as a carcinogen, has the potential to be adsorbed by soil microplastics. However, the mechanisms and controlling factors of As adsorption by microplastics in farmland soil under natural conditions are still unknown. Here, microplastics and As were respectively added to farmland soils with different physicochemical properties from twelve provinces of China for adsorption experiment. We performed surface analysis of microplastics, quantified As accumulation through quasi-first-order kinetic equation and developed regression models to screen the factors controlling As adsorption. The results showed that the adsorption of As by soil microplastics was a chemical process accompanied by the loss of electrons from oxygen-containing functional groups. Soil cation exchange capacity (CEC) was the main factor controlling the adsorption rate, while soil organic matter (SOM), total nitrogen (TN) and CEC mainly influenced the equilibrium adsorption capacity. This is the first report on microplastic-As adsorption in natural soil, which allows deeper insights into risk assessment, prediction and control of microplastic-As pollution in agricultural soil.