Co-occurrence of co-contaminants: Cyanotoxins and microplastics, in soil system and their health impacts on plant - A comprehensive review

Microplastic contamination in Ashtamudi Lake, India: Insights from a Ramsar wetland

Estuaries function as temporary storage sites for plastic debris, influencing the distribution of microplastics (MPs) across ecosystems. This research delves into the presence of MPs in the water, sediment, fish, and shellfish of Ashtamudi Lake, a Ramsar wetland with brackish water located on the southwest coast of India. Given the lake's significance in supporting the livelihoods of numerous fishers and acting as a vital source of fishery resources for both local consumption and export, examining the contamination of the system by MPs becomes particularly pertinent. The highest percentage composition of MPs was found in macrofauna at 60.6% (with fish at 19.6% and shellfish at 40.9%), followed by sediment (22.8%) and water (16.7%). The primary types of MPs identified in all samples were fibers (35.6%), fragments (33.3%), and films (28%), with beads being the least represented at 3.03%. ATR-FTIR and Raman spectra analysis identified five polymers from shellfish (polypropylene, polyethylene, polystyrene, nylon, and polyvinyl chloride), five from fish guts (nylon, polypropylene, polyethylene, polyurethane, and polysiloxane), four in sediment (polypropylene, polyethylene, nylon, rayon), and four in water samples (polypropylene, polyethylene, nylon, and polystyrene). SEM-EDAX analysis of MPs obtained from the samples revealed degradation and the presence of inorganic elements such as Na, Mg, Al, Si, S, K, Cl, P, and Ca, as well as heavy metals like Pb, Mo, Rh, Pd, Ti, and Fe. The existence of these plastic polymers and heavy metals in microplastic samples poses a threat to vulnerable biota; people consume contaminated fish and shellfish, underscoring the importance of monitoring MPs in lake water. This investigation of MPs in Ashtamudi Lake highlights the system's susceptibility to plastic pollution and the bioavailability of smaller MPs to aquatic organisms. Identified sources of MPs in the lake include fishing and aquaculture activities, sewage pollution, improper solid waste management in lake watersheds, and unsustainable tourism. Upstream and downstream management interventions are recommended to address MP pollution in Ashtamudi Lake.

Micro (nano)plastics and phthalate esters drive endophytic bacteria alteration and inhibit wheat root growth

Endophytes play an important role in plant growth and stress tolerance, but limited information is available on the complex effects of micro (nano)plastics and phthalate esters (PAEs) on endophytes in terrestrial plants. To better elucidate the ecological response of endophytic bacteria on exogenous pollutants, a hydroponic experiment was conducted to examine the combined impact of polystyrene (PS) and PAEs on endophyte community structure, diversity, and wheat growth. The findings revealed that wheat roots were capable of absorbing and accumulating PS nanoparticles (PS-NPs, 0.1 μm), whereas PS microparticles (PS-MPs, 1 and 10 μm) merely adhered to the root surface. The addition of PAEs resulted in a stronger accumulation of fluorescent signal from PS-NPs in the roots. The dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) were identified in wheat roots, and they could be metabolized to form minobutyl phthalate and phthalic acid, and mono-(2-ethylhexyl) phthalate, respectively. Compared to single PAEs, the concentration of PAEs and their metabolites in the roots treated with PS-NPs showed a great increase, while they exhibited a significant decline in the presence of PS-MPs. Principal coordinate analysis and permutational multivariate analysis of variance demonstrated that PS size were the major factor that induced oxidative damage, and altered the endogenous homeostasis of wheat roots. The increase in PS size positively promoted the relative abundance of dominant endophytes. Specifically, Proteobacteria. Proteobacteria were the most important in the symbiosis survival, which had a great impact on the microbial community and diversity. Therefore, PS and PAEs could affect the endophytes directly and indirectly. Structural equation modeling further implied that these endophytic bacteria, along with antioxidant enzymes such as superoxide dismutase which were regulated by non-enzymatic mechanisms, promoted root biomass increase. These results indicated a synergistic resistance mechanism between antioxidant enzymes and endophytic bacteria in response to environmental stress.

Dynamic fluctuations in plant leaf interception of airborne microplastics

Plant leaves have been demonstrated to be a crucial sink of airborne microplastics (MPs). However, because of the particular shape of MPs and their relatively weak forces with leaves, the traditional accumulation model used for the adsorption of particulate matter and persistent organic pollutants may not be appropriate for describing the interception of MPs by leaves. Here, we performed a 7-day exploration of the interception of MPs by leaves in downtown Nanning. The abundances and characteristics of leaf-intercepted MPs showed dramatic diurnal fluctuations and interspecies differences (conifers > arbors > shrubs). The fluctuation (Coefficient of Variation (CV) = 0.459; abundances 0.003 ± 0.002 to 0.047 ± 0.005 n·cm-2) was even more drastic than that measured across species (CV = 0.353; 0.06 ± 0.01 to 0.40 ± 0.04 n·cm-2). Further analysis using partial least-squares path modeling demonstrated that stomatal variation and divergence largely dominated diurnal fluctuations and interspecies differences in microplastic interception by leaves, respectively. Our results highlight that the leaf-intercepted MPs is characterized by dynamic fluctuations rather than static equilibrium and reveal the important regulatory roles played by leaf micromorphological structures in intercepting MPs, thus enhancing our understanding of the interactions between terrestrial plants and airborne pollution.

Adsorption behaviors and bioavailability of tetrabromobisphenol A in the presence of polystyrene microplastic in soil: Effect of microplastics aging

Microplastics, a kind of emerging pollutant, have become a global environmental research hotspot in recent years due to its wide distribution in soil and its impact on soil ecosystems. However, little information is available on the interactions between microplastics and organic contaminants in soil, especially after microplastic aging. The impact of polystyrene (PS) microplastic aging on the sorption of tetrabromobisphenol A (TBBPA) in soil and the desorption characteristics of TBBPA-loaded microplastics in different environments were studied. The results showed a significant increase of 76.3% in adsorption capacity of TBBPA onto PS microplastics after aging for 96 h. Based on the results of characterization analysis and density functional theory (DFT) calculation, the mechanisms of TBBPA adsorption changed mainly from hydrophobic and π-π interactions on pristine PS microplastics to hydrogen bond and π-π interactions on aged PS microplastics. The presence of PS microplastics increased the TBBPA sorption capacity onto soil-PS microplastics system and significantly altered the distribution of TBBPA on soil particles and PS microplastics. The high TBBPA desorption over 50% from aged PS microplastics in simulated earthworm gut environment suggested that TBBPA contamination combined with PS microplastics might pose a higher risk to macroinvertebrates in soil. Overall, these findings contribute to the understanding of impact of PS microplastic aging in soil on the environmental behaviors of TBBPA, and provide valuable reference for evaluating the potential risk posed by the co-existence of microplastics with organic contaminants in soil ecosystems.

Microcystin bound on microplastics in eutrophic waters: A potential threat to zooplankton revealed by adsorption-desorption processes

The presence of microplastics (MPs) in eutrophic waters (both freshwaters and coastal waters) is increasingly reported globally, as has the occurrence of cyanotoxins, including microcystins (MCs). MPs have the potential to act as vectors for MCs in freshwater environments, but the transportation mechanisms and associated risks remain poorly understood. In this study, we investigated how aging process and water conditions influenced the adsorption behavior of the microcystin-leucine-arginine (MC-LR) onto polyethylene (PE) and polypropylene (PP). Adsorption kinetics and isotherms showed that the MC-LR sorption capacity in descending order was aged PP > pristine PP > aged PE > pristine PE. The aging process increased the MC-LR sorption amount by 25.1% and 6.5% for PP and PE, respectively. The increase in sorption affinity of aged MPs may be attributed to the significant surface oxidation and the formation of the hydrogen bonding between MPs and MC-LR. Furthermore, MC-LR sorption can be largely influenced by the aqueous conditions. MC-LR preferred to be much adsorbed onto different MPs in brackish water than in freshwater owing to the cation bridging effect and complexation of high levels of cations. The usual alkalescent pH in eutrophic waters did not favor MC-LR sorption to MPs. Finally, based on the desorption results, assuming a worst-case scenario, MC-LR bound on MPs may have a high risk to daphnids. The findings obtained in this study have improved our knowledge in the interaction of MPs with hydrophilic cyanotoxins in aqueous ecosystems, as well as the risks associated with their coexistence.

Chemicals/materials of emerging concern in farmlands: sources, crop uptake and potential human health risks

Certain chemicals/materials that are contaminants of emerging concern (CECs) have been widely detected in water bodies and terrestrial systems worldwide while other CECs occur at undetectable concentrations. The primary sources of CECs in farmlands are agricultural inputs, such as wastewater, biosolids, sewage sludge, and agricultural mulching films. The percent increase in cropland area during 1950-2016 was 30 and the rise in land use for food crops during 1960-2018 was 100-500%, implying that there could be a significant CEC burden in farmlands in the future. In fact, the alarming concentrations (μg kg^-1) of certain CECs such as PBDEs, PAEs, and PFOS that occur in farmlands are 383, 35 400 and 483, respectively. Also, metal nanoparticles are reported even at the mg kg^-1 level. Chronic root accumulation followed by translocation of CECs into plants results in their detectable concentrations in the final plant produce. Thus, there is a continuous flow of CECs from farmlands to agricultural produce, causing a serious threat to the terrestrial food chain. Consequently, CECs find their way to the human body directly through CEC-laden plant produce or indirectly via the meat of grazing animals. Thus, human health could be at the most critical risk since several CECs have been shown to cause cancers, disruption of endocrine and cognitive systems, maternal-foetal transfer, neurotoxicity, and genotoxicity. Overall, this comprehensive review provides updated information on contamination of chemicals/materials of concern in farmlands globally, sources for their entry, uptake by crop plants, and their likely impact on the terrestrial food chain and human health.

Soil microplastic characteristics and the effects on soil properties and biota: A systematic review and meta-analysis

The soil environment serves as an assembling area for microplastics, and is an important secondary source of microplastics in other environmental media. Recently, soil microplastics have been extensively studied; however, high variability is observed among the research results owing to different soil properties, and the complexity of soil microplastic composition. The present study amassed the findings of 2886 experimental groups, across 38 studies from 2016 to 2022, and used meta-analysis to quantitatively analyze the differences in the effects of microplastic exposure on soil physicochemical properties and biota. The results showed that among the existing soil microplastic research, agricultural soils maintained a higher environmental exposure distribution than other environments. Microplastic fibers and fragments were the predominant shapes, indicating that the extensive use of agricultural films are the primary influencing factor of soil microplastic pollution at present. The results of the meta-analysis found that microplastic exposure had a significant negative effect on soil bulk density (lnRR = -0.04) and aggregate stability (lnRR = -0.085), indicating that microplastics may damage the integrity of soil structure or damage the soil surface. The significant changes in plant root biomass and soil phosphatase further signified the potential impact of microplastics on soil nutrient and geochemical element cycling. We further constructed species sensitivity distribution curves, revealing that invertebrates had a higher species sensitivity to microplastics, as they can pass through the gut wall of soil nematodes, causing oxidative stress and affecting gene expression. In general, soil is an interconnected complex, and microplastic exposure can directly or indirectly interact with environmental chemical processes in the soil environment, potentially harming the soil ecosystem; however, current research remains insufficient with respect to breadth and depth in terms of the comprehensive "source-sink" mechanism of soil microplastics, the hazard of exposure, and the overall toxic effects.

A critical review on interaction of microplastics with organic contaminants in soil and their ecological risks on soil organisms

The pollution of microplastics (MPs) in soil has become a global environmental problem. Due to high sorption capacity and persistence in environment, the MPs exhibit combined effects with organic pollutants in soil, thereby posing a potential risk to soil ecology and human health. However, limited reviews are available on this subject. Therefore, in response to this issue, this review provides an in-depth account of interaction of MPs with organic contaminants in soil and the combined risks to soil environment. The sorption of organic contaminants onto MPs is mainly through hydrophobic and π-π interactions, hydrogen bonding, pore filling and electrostatic and van der Waals forces. The intrinsic characteristics of MPs, organic contaminants and soil are the key factors influencing the sorption of organic pollutants onto MPs. Importantly, the presence of MPs changes the sorption, degradation and transport behaviors of organic contaminants in soil, and affects the toxic effects of organic contaminants on soil organisms including animals, plants and soil microorganisms through synergistic or antagonistic effects. Source control, policy implementation and plastic removal are the main preventive and control measures to reduce soil MPs pollution. Finally, priorities for future research are proposed, such as field investigations of co-pollution, contribution of plastisphere to organic contaminant degradation, and mechanisms of MPs effects on organic contaminant toxicity.

Trojan horse in the intestine: A review on the biotoxicity of microplastics combined environmental contaminants

With the reported ability of microplastics (MPs) to act as "Trojan horses" carrying other environmental contaminants, the focus of researches has shifted from their ubiquitous occurrence to interactive toxicity. In this review, we provided the latest knowledge on the processes and mechanisms of interaction between MPs and co-contaminants (heavy metals, persistent organic pollutants, pathogens, nanomaterials and other contaminants) and discussed the influencing factors (environmental conditions and characteristics of polymer and contaminants) that affect the adsorption/desorption process. In addition, the bio-toxicological outcomes of mixtures are elaborated based on the damaging effects on the intestinal barrier. Our review showed that the interaction processes and toxicological outcomes of mixture are complex and variable, and the intestinal barrier should receive more attention as the first line of defensing against MPs and environmental contaminants invasion. Moreover, we pointed out several knowledge gaps in this new research area and suggested directions for future studies in order to understand the multiple factors involved, such as epidemiological assessment, nanoplastics, mechanisms for toxic alteration and the fate of mixtures after desorption.

Co-occurence of antibiotics and micro(nano)plastics: a systematic review between 2016-2021

Pollution by plastics and antibiotics are emerging issues in the areas of the environment and human health. In recent years, several studies have documented the widespread occurrence of plastic particles in various environmental, as well as human, systems, and much research has focused on possible interactions of contaminants with microplastics. Thus, the co-occurrence of plastics and antibiotics has caused another global problem for the environment and human health. Therefore, we focused on the current knowledge in the field of the co-occurrence of plastics and antibiotics to summarize the available studies. In this review, categorization of the topics, contaminants details, such as polymer type, size and source, antibiotic type, and other experimental parameters were summarized and discussed. This study indicated that the sorption of antibiotics on plastics, antibiotic susceptibility in the presence of plastics, and antibiotic resistance gene onto plastics were the most frequently examined categories in this field. Moreover, the variability in the procedures and the processes, and the heterogeneity data of reporting between different studies on similar topic make it difficult to bring all results together and produce a comprehensive picture of the current knowledge. Therefore, it is suggested that further research should be done using this systematic study.