Identification of organic pollutants and heavy metals in natural rubber wastewater and evaluation its phytotoxicity and cytogenotoxicity.

The natural rubber industry consumes large volumes of water and annually releases wastewater with rich organic and inorganic loads. This wastewater is allowed for soil irrigation in developing countries. However, the pollutant composition in wastewater and its environmental effects remain unclear. Therefore, we aimed to assess the wastewater's physicochemical parameters, toxic organic pollutants, heavy metals, and phytotoxic and cytogenotoxic. The result revealed that values of comprehensive wastewater parameters were recorded as chemical oxygen demand (187432.1 mg/L), pH (4.23), total nitrogen (1157.1 mg/L), ammonia nitrogen (1113.0 mg/L), total phosphorus (1181.2 mg/L), Zn (593.3 mg/L), Cr (0.6127 mg/L), and Ni (0.2986 mg/L). The organic compounds detected by LC-MS were salbostatin, sirolimus, Gibberellin A34-catabolite, 1-(sn-glycero-3-phospho)-1D-myo-inositol, and methyldiphenylsilane. The toxicity of the identified toxic chemicals and heavy metals was confirmed by onion and mung bean phytotoxicity characterization tests. The wastewater affected the germination of mung bean seeds, reduced or inhibited the growth of onions, and induced various chromosomal aberrations in root apical meristems. Our study shows that the treatment of natural rubber wastewater needs to be improved, and the feasibility of irrigating soil with wastewater needs to be reconsidered.

Effects of polypropylene films and leached dissolved organic matters on bacterial community structure in mangrove sediments.

Over the past decades, the accumulation of plastics in mangrove ecosystems has emerged as a significant environmental concern, primarily due to anthropogenic activities. Polypropylene (PP) films, one of the plastic types with the highest detection rate, tend to undergo intricate aging processes in mangrove ecosystems, leading to the release of dissolved organic matter (DOM) that may further influence the local bacterial communities. Yet, the specific effects of new and weathered (aged) plastic films and the associated leached DOM on bacterial consortia in mangrove sediments remain poorly understood. In this study, an incubation experiment was conducted to elucidate the immediate effects and mechanisms of the new and relatively short-term (45 or 90 days) aged PP films, as well as their leached DOM (PDOM), on characteristics of DOM and the bacterial community structure in mangrove sediments under different tidal conditions. Surface morphology and functional group analyses showed that both new and aged PP films exhibited comparable degradation profiles under different tidal conditions over the incubation period. As compared to the new PP film treatments, the introduction of the short-term aged PP films significantly affected the content of humic-like compounds in sediments, and such effects were partially ascribed to the release of PDOM during the incubation. Although the addition of PP films and PDOM showed minor effects on the overall diversity and composition of bacterial communities in the sediments, the abundance of some dominant phyla exhibited a growth or reduction tendency, possibly changing their ecological functions. This study was an effective attempt to investigate the relationship among plastic surface characteristics, sedimentary physicochemical properties, and bacterial communities in mangrove sediments. It revealed the ecological ramifications of new and short-term plastic pollution and its leachates in mangrove seedtimes, enhancing our understating of their potential impacts on the health of mangrove ecosystems.

Response of earthworms to microplastics in soil under biogas slurry irrigation: Toxicity comparison of conventional and biodegradable microplastics.

As a reliable environment-friendly alternative, biodegradable plastic mulching films have been introduced into agricultural practice to reduce the adverse threats posed by conventional plastic products. Information regarding whether potential untoward effects of biodegradable plastics exist in soil and how strong are such effects on terrestrial organisms, however, still remains unknown. This study examined differences in the responses of earthworm, represented by Eisenia fetida, to exposure to biodegradable (PLA: polylactic acid) and conventional microplastics (PVC: polyvinylchloride, LDPE: low-density polyethylene) in soil with biogas slurry irrigation. Mortality, growth, histopathology and biochemical enzymes of the earthworms exposed to different concentrations of microplastics (5, 20 and 50 g/kg wet weight of soil, respectively) were investigated after 28 days of incubation in the experiment. The obtained results showed that the ecotoxicity of microplastics (MPs) to earthworms was time-dependent. Regardless of MPs type, continuous exposure to MPs at the concentration of 50 g/kg induced mucous vacuolization, longitude muscle disorder, and granular lipofuscin-like deposits generation in the epithelium. Moreover, tissue fibrosis and cavity formation were also observed in intestinal tissue. The presence of MPs stimulated the oxidative stress system of the earthworms, as indicated by the enhancement of malonaldehyde (MDA) content in vivo. The antioxidative defense system in earthworms was supposed to collapse at the MPs concentration of 50 g/kg after 28 days of exposure. Interestingly, PLA exhibited similar ecotoxicity effects with LDPE, which might violate the original intention of biodegradable plastics with less harmful or nontoxic influence on the terrestrial biotas. Thus, knowledge regarding the molecular and genetic mechanisms of the earthworms in soil containing biodegradable plastics should be further explored to better understand the risk posed by biodegradable plastics in the agroecosystem.

Mangrove degradation retarded microplastics weathering and affected metabolic activities of microplastics-associated microbes.

Currently, information on microplastics (MPs) weathering characteristics and ecological functions driven by MPs-associated microbes in mangrove ecosystems remains unclear, especially in the degraded areas. Herein, we compared the weathering characteristics of MPs in both undegraded and degraded mangrove sediments, and then explored the potential interactions between their weathering characteristics and microbially-driven functions. After 70 days of incubation, different MPs (including polyethylene PE, polystyrene PS, and polylactic acid PLA) were strongly weathered in mangrove sediments, with significant erosion features. Interestingly, more obvious weathering characteristics were found for MPs in the undegraded mangrove sediments. O/C ratio value of MPs in the undegraded sediments was 2.3-3.0 times greater than that in the degraded ones. Besides, mangrove degradation reduced network complexity among MPs-associated microorganisms and affected their metabolic activities. Bacteria involved in carbon cycle process enriched on nondegradable MPs, whereas abundant bacteria responsible for sulphur cycle were observed on PLA-MPs. Moreover, these relevant bacteria were more abundant on MPs in the undegraded mangrove sediments. Mangrove degradation could directly and indirectly affect MPs weathering process and microbially-driven functions through regulating sediment properties and MPs-associated microbes. During weathering, contact angle and roughness of MPs were key factors influencing the colonisation of hydrocarbon degradation bacteria on MPs.

Bioremediation of tetramethyl thiuram disulfide and resource utilization of natural rubber wastewater by WR-2 Bacillus-dominated microbial community.

Tetramethyl thiuram disulfide (TMTD), an emerging pollutant with ecotoxicity and accumulation in rubber wastewater, is directly discharged by factories into the surrounding soil to save costs, and this disrupts the nearby ecosystem. In this study, an efficient bioremediation microbial community (WR-2) dominated by Bacillus was acclimatized and isolated from soil contaminated by rubber wastewater. After passing through the metabolic process of WR-2, the ecotoxic TMTD decomposes within 14 days. In the pot experiment, WR-2 not only completed the bioremediation of contaminated soil but also significantly improved the crop growth conditions and the product quality. These results show that WR-2 has broad application prospects in the bioremediation of soil contaminated by rubber wastewater. It also provides a theoretical framework for the resource utilization of the effluent at the end of the initial rubber processing.

Addition of biodegradable microplastics alters the quantity and chemodiversity of dissolved organic matter in latosol.

Dissolved organic matter (DOM) chemodiversity plays an important role in regulating nutrient cycles and contaminant behavior in soil. However, how biodegradable microplastic (MPs) affect the DOM chemodiversity is still unknown, although developing biodegradable plastics are regarded as a promising strategy to minimize the risks of MPs residues in soil. Here, with the common poly (butylene adipate-co-terephthalate) (PBAT) as the model, the molecular effect of biodegradable MPs on soil DOM was explored by adding 0%, 5% and 10% (w/w) of PBAT to tropical latosol, respectively. The results showed that PBAT addition increased microbial activity and exoenzyme activity (e.g., rhizopus oryzae lipase, invertase and cellulose). As a result, the quantity and chemodiversity of soil DOM were changed. The multispectroscopic characterization showed that PBAT addition significantly increased the DOC molecules in soil, including condensed aromatic-like substances and carbohydrates. In contrast, the TDN molecules with high bioavailability and low aromaticity, such as amino acids, were decreased. The multivariate statistical analysis indicated that there were three mechanisms that drove the shift in DOM chemodiversity. Firstly, the degradation of PBAT by rhizopus oryzae lipase facilitated the release of exogenous aromatic molecules. Secondly, PBAT decomposition stimulated the selective consumption of native N-rich molecules by soil microbes. Thirdly, PBAT accelerated the enzymatic transformation of native aliphatic CHx and cellulose toward humic substances. In addition, concentration effect was also observed in the study that high-concentration PBAT were more likely to trigger the molecular shift in DOM chemodiversity. These findings provided a new insight into the impact of biodegradable MPs on soil DOM chemodiversity at molecular level, which will be beneficial to understanding the fate and biochemical reactivity of DOM in MPs-polluted soil.

Changes in bacterial community structures in soil caused by migration and aging of microplastics.

Microplastics (MPs) are classified as emerging pollutants and greatly threatens soil ecosystems. To determine the impact of microplastic migration on soil bacterial diversity, we conducted a 90-day indoor soil column simulation test. Soil and microplastic (granular polystyrene, polypropylene MPs) samples were collected from different soil layers on days 30, 60, and 90. The downward migration trend of MPs was obvious, and its surface functional groups, hydrophobic properties, and crystallinity changed. Bacterial diversity was significantly higher in the surrounding soil than on microplastic surfaces. Also, the topsoil has more bacterial diversity than the middle soil. A higher number of OTUs were detected on microplastic surfaces for the middle soil than in the topsoil. Proteobacteria abundance on microplastic surfaces in the topsoil gradually increased over the course of the experiment, while an opposite trend was observed for the middle soil. Nevertheless, Proteobacteria abundances in both layers were higher than in the surrounding soils. MPs alters the bacterial community composition of soils and provides unique substrates for colonization. The impacts of MPs on soil bacterial communities were better understood in this study. Our findings highlighted the relevance of MPs in soil ecosystems as well as the potential threats they pose.

Occurrence and spatial distribution of microplastics, and their correlation with petroleum in coastal waters of Hainan Island, China.

In this study, the distribution, abundance, morphology, and composition of microplastics (MPs) in surface seawater and sediment of Hainan Island were systematically investigated. Seawater and sediment samples were collected from six functional zones, including harbor, industrial district, sparsely populated area, tourist area, residential area, and aquaculture area. The abundance of MPs in seawater was 0.46-19.32 items/L, with an average of 2.59 ± 0.43 items/L, which were similar to those detected in the South China Sea (e.g., Nansha (1.25-3.20 items/L) and Xisha (2.57 ± 1.78 items/L)). The highest level was detected in Qinglan Bay Estuary, and the lowest was in Sanya West Island. The abundance of MPs in sediment was 41.18-750.63 items/kg, with an average of 372.47 ± 62.10 items/kg; the highest concentration was detected at Tanmen Port, and the lowest was in Lingao sea area. It was detected that the MPs with smaller size exhibited a higher concentration in seawater. MPs were commonly black and white, and predominantly linear and fragmented in shape. Polyethylene terephthalate (PET) was the dominant polymer, which might be derived from laundry wastewater. The petroleum concentration was 0.02-0.21 mg/L in the investigated area, with harbors being the most severely polluted areas. Furthermore, this study also found that MPs pollution was positively correlated with petroleum in seawater, indicating similarities between MPs and petroleum-based sources of pollution. This study identifies the contamination and characteristics of MPs and their correlation with petroleum in Hainan Island, the biggest island in the South China Sea, providing important data for further research on protecting marine ecosystems.

Microplastic pollution in water, sediment, and specific tissues of crayfish (Procambarus clarkii) within two different breeding modes in Jianli, Hubei province, China.

This study investigates the occurrence and distribution of microplastics in water, sediment, and crayfish samples within pond and rice-crayfish co-culture breeding modes in Jianli prefecture, China. Microplastics in environmental and biological samples were systematically extracted by CaCl2 solution, digested by H2O2 and KOH, and identified by µ-FTIR. A cleansing treatment for crayfish was performed in pure water before dissection and microplastic accumulation in different tissues (gill, stomach, gut, and flesh) of non-cleansed and cleansed crayfish were compared. The average microplastic abundances were 1.3 ± 0.1-2.5 ± 0.1 particles/L, 0.03 ± 0.01-0.04 ± 0.02 particles/g, and 0.17 ± 0.07-0.92 ± 0.19 particles/individual in water, sediment, and crayfish samples, respectively. Microplastics were detected in all studied crayfish tissues, except the flesh. There were no significant differences in microplastic abundances in water (P = 0.82), sediment (P = 0.90), and crayfish (P = 0.47 for non-cleansed samples; P = 0.30 for cleansed samples) between two breeding modes despite the detection of relatively higher microplastic abundances in the samples from the pond breeding mode. Microplastic accumulation in non-cleansed crayfish stomachs and guts (0.71 ± 0.18 particles/individual) was higher (P < 0.01) than that recorded in their gills (0.13 ± 0.06 particles/individual). Moreover, microplastics present in the stomachs and guts of cleansed crayfish were significantly less abundant (P < 0.01) than in non-cleansed crayfish, although this was not observed in the gills (P = 0.99). The majority of microplastic particles in this study had fiber-like shapes, blue and transparent colors, a size smaller than 1 mm, and polymer types of PP:PE and PE. The results demonstrate that microplastics in the environment can accumulate in the internal tissues of crayfish, which may pose a potential risk to humans through food consumption without the removal of the gills, stomach, and guts. This study provides valuable information for understanding microplastic accumulation in the different tissues of crayfish and the potential risk of human exposure to microplastics from crayfish as a food supplement.

Micro- and nano-plastics in marine environment: Source, distribution and threats - A review.

Plastic litters have become the predominant components of marine debris due to extensive consumption plastics and mismanagement of plastic wastes. As part of the problem, microplastics (MPs) and nanoplastics (NPs) have generated special concerns due to their unique features that make them easy to transfer among oceans in the marine ecosystem, across different trophic levels inside the food web, and even across different tissues inside contaminated animals. Studies have demonstrated the almost omnipresence of MPs in the marine ecosystem, which present serious threats to the health of marine animals, causing symptoms such as malnutrition, inflammation, chemical poisoning, growth thwarting, decrease of fecundity, and death due to damages at individual, organ, tissue, cell, and molecule levels. The information on NPs in the marine ecosystem has been scarce due to the challenges in sampling and detecting these nano-scaled entities. In vitro and in vivo experiments have demonstrated that NPs have the potential to penetrate different biological barriers including the gastrointestinal barrier and the brain blood barrier and have been detected in many important organs such as brains, the circulation system and livers of sampled animals.