Waste rubber - Black pollution reframed as a global issue: Ecological challenges and sustainability initiatives.

In contrast to "white pollution" originating from waste plastics, waste rubber is often referred to as "black pollution." The quantity and variety of waste rubber are increasing at an alarming rate, with a considerable fraction entering the global ecosystem via various pathways. This study presents the first critical review of waste rubber research with a focus on the risks associated with toxicant discharge and existing problems in waste rubber disposal, management, and recycling practices. We aim to obtain a comprehensive understanding of current research, particularly regarding the ecological impacts of these wastes, highlight major gaps, and propose the most significant research directions. A total of 192 studies published in journals were critically analysed. The importance of conducting long-term and large-scale experiments and developing efficient waste rubber recycling systems is also emphasised. This study highlights the need to address the challenges posed by waste rubber pollution and offers insights and references for undertaking ecological risk assessments and understanding the mechanisms underlying toxicant behaviour. Suggestions and countermeasures are proposed with ecosystem sustainability as the ultimate goal. Further long-term, comprehensive, and systematic research in this area is required.

Graphene oxide affects the symbiosis of legume-rhizobium and associated rhizosphere rhizobial communities.

The large-scale production and utilization of graphene oxide (GO) have raised concerns regarding its environmental exposure and potential risks. However, existing research on GO toxicity has primarily focused on individual organisms. Little attention has been given to the interaction between GO and the nitrogen-fixing symbiosis of legume-rhizobium. In this study, we focused on alfalfa (Medicago sativa L.), a typical leguminous nitrogen-fixing plant, to investigate the effects of GO on various aspects of this symbiotic relationship, including root nodulation, rhizobial viability, nodule nitrogen fixation, DNA damage, and the composition of the rhizobial community in the rhizosphere. As the dosage of GO increased, a significant inhibition in nodulation development was observed. Exposure to GO resulted in decreased growth and viability of rhizobia, as well as induced DNA damage in nodule cells. Furthermore, with increasing GO dosage, there were significant reductions in nitrogenase activity, leghemoglobin level, and cytoplasmic ammonia content within the root nodules. Additionally, the presence of GO led to notable changes in the rhizobial community in the rhizosphere. Our findings support the existence of the damage promoted by GO in the symbiosis of nitrogen fixing rhizobia with legumes. This underscores the importance of careful soil GO management.

Graphene oxide affected root growth, anatomy, and nutrient uptake in alfalfa.

The increasing application of carbon nanomaterials has resulted in their inevitable release into the environment. Their toxic effects on plant roots require careful investigation. In the present study, alfalfa (Medicago sativa L.) was exposed to graphene oxide (GO) at levels of 0.2 %, 0.4 %, and 0.6 % (w/w) in potting soil. This study aims to better understand the impact of GO on the root growth, structure, and physiology of alfalfa in the soil matrix. The results demonstrated that GO significantly affected the development and structure of alfalfa roots, and the effect varied with GO level. The highest level of GO (0.6 %) reduced the root length, diameter, volume, dry weight, number of lateral roots, and root activity by 36.1 %, 31.3 %, 60.0 %, 89.6 %, 55.8 %, and 72.3 % (p < 0.05), respectively, and the vascular cylinder diameter, periderm thickness, vessel diameter, and phellem thickness decreased by 51.5 %, 50.7 %, 80.9 %, and 49.1 % (p < 0.05), respectively. These observations might be associated with GO-induced oxidative stress, which was indicated by the activity of antioxidant enzymes. Furthermore, high GO levels (0.4 % and 0.6 %) inhibited the uptake of N, P, K, Mg, Zn, Fe, Mo, Si, and B in roots. Our findings indicate that GO at high levels has a negative impact on root growth and development by inducing oxidative stress, structural impairment, and nutritional imbalance. Careful soil GO management should be emphasized.

Assessment of graphene oxide toxicity on the growth and nutrient levels of white clover (Trifolium repens L.).

Carbon nanomaterials (CNMs) are novel engineered nanomaterials and have been used widely. Their toxic effects on terrestrial plants in soil matrix require careful investigation. In this study, white clover (Trifolium repens L.) was grown in a potted soil with graphene oxide (GO) at levels of 0.2%, 0.4% and 0.6% and the effects of GO on the growth and nutrient uptake of white clover were evaluated after 50 and 100 days of exposure. GO exposure showed adverse effects on seedling growth, photosynthetic parameters and nutrient uptake in shoots, and the effect was more significant with increasing concentration and exposure time. Compared with the control, GO at the highest level of 0.6% decreased plant height, leaf and stem dry weights, total chlorophyll content and net photosynthetic rate by 43.7%, 45.7%, 43.4%, 32% and 85.7%, respectively, after 100 d of exposure, and N, K, Cu, Zn, Fe, Mo, B, Si contents decreased by 19.5%, 20.1%, 12.6%, 25.0%, 12.9%, 26.0%, 18.9%, 23.0%, respectively. Furthermore, the electrolyte leakage, lipid peroxidation, reactive oxygen species, antioxidant enzyme activities were all increased by GO, especially at high dose and long exposure. These results indicate that GO can suppress plant growth by oxidative stress, photosynthesis inhibition, and nutrient imbalance.

Individual and histopathological responses of the earthworm (Eisenia fetida) to graphene oxide exposure.

The increasing production and applications of graphene oxide (GO) inevitably lead to its entry into the environment. However, its potential toxicity to soil invertebrates is not yet completely known. Herein, the harmful effects of GO on the growth, survival, reproduction, and ultrastructure of earthworms were thoroughly evaluated through acute and chronic toxicity experiments. In the acute toxicity experiments, earthworms were exposed to different concentrations of GO using two test methods: filter paper contact test and natural soil contact test. The lethal concentrations (LC50) for GO at 24-h and 48-h exposure were 2.52 and 2.36 mg mL-1, respectively, in the filter paper contact test and the LC50 on day 14 was 68.8 g kg-1 in the natural soil test. Histopathological observation demonstrated that serious skin and intestinal damage occurred with increasing GO concentrations. In the chronic toxicity test, earthworm growth rate and reproduction were investigated after exposure to 0, 5, 10, 20 and 30 g kg-1 GO in natural soil for 28 and 56 d. Earthworm growth was significantly inhibited after 7, 14, 21 and 28 d of GO exposure. The effect was more significant with increasing GO concentrations and exposure days. Moreover, GO exposure significantly decreased the reproductive capacity of earthworms. When earthworms were exposed to 20 g kg-1 GO for 56 d, the number and hatching rate of cocoons and the number of juveniles decreased by approximately half compared with the control. These findings indicate the potential health risk of GO to E. fetida under high concentrations and long exposure times in soil. Thus, the potential risks associated with the application of GO should receive considerable attention. This study can provide valuable information for assessing the toxicity of carbon nanomaterials in terrestrial ecosystems.

Effects of vegetation management on the composition and diversity of the insect community at Tianjin Binhai International Airport, China.

The vegetation community affects the composition and diversity of the insect community in grasslands. To explore the effects of vegetation management on insect community abundance and diversity, regular mowing of the vegetation was conducted, and tall fescue (Festuca arundinacea) and ryegrass (Lolium perenne) were exclusively planted at Tianjin Binhai International Airport. A total of 1886 insects were collected, representing 8 orders, 23 families, and 29 species; Acrididae (Orthoptera), Coccinellidae (Coleoptera), and Chironomidae (Diptera) were the dominant taxa. The abundance and biomass of insects in the turf areas were significantly lower than those in the control area and were reduced by 45.8 and 48.5% in the ryegrass area, respectively. In all areas, insect abundance and biomass peaked in summer, and the abundance of individuals and taxa decreased as the temperature decreased. Greater diversity and richness were found in summer compared with the other two seasons, and the turf areas had lower diversity and richness indices than the control areas in spring and summer. Our results suggest that the abundance, biomass and diversity of insects can be effectively decreased by artificial regulation of grassland vegetation at the airport, the planting of a single turfgrass - specifically ryegrass had the greatest effect. The present study provides a theoretical basis for the ecological control of insects at the airport.

Biochemical toxicity, lysosomal membrane stability and DNA damage induced by graphene oxide in earthworms.

With the growing production and use of carbon nanomaterials (CNMs), the risk of their releases to the environment has drawn much attention. However, their potential effect on soil invertebrates has not yet been systematically assessed. Herein, the toxic effects of graphene oxide (GO) on earthworms (Eisenia fetida) were thoroughly investigated. Exposure to different doses of GO (0, 5, 10, 20, and 30 g kg-1) was conducted for 7, 14, 21, and 28 days. The results showed that enzymatic activity was stimulated at the early stages of exposure (7 days and 14 days) and inhibited after 14 days for catalase (CAT) and after 21 days for peroxidase (POD) and superoxide dismutase (SOD), especially at high GO doses. The content of MDA showed an increasing trend over the whole exposure period and was significantly elevated by GO from 21 days except at the dose of 5 g kg-1on day 21. Lysosomal membrane stability and DNA damage presented dose- and time-dependent relationships. Graphene oxide remarkably decreased lysosomal membrane stability except at the dose of 5 g kg-1 on day 7. The tail DNA%, tail length and olive tail moment increased with increasing GO dose throughout the exposure duration, reaching maximum values at the end of exposure (28 days). These findings suggest that GO induces oxidative stress and genotoxicity in Eisenia fetida, resulting in lipid peroxidation, decreased lysosomal membrane stability and DNA damage. Therefore, attention should be paid to the potential pollution and risk associated with graphene oxide application. The results can provide valuable information for environmental safety assessment of graphene nanomaterials in soil.

Ecotoxicological responses of the earthworm Eisenia fetida to EDTA addition under turfgrass growing conditions.

As a commonly used chelator, ethylenediaminetetraacetic acid (EDTA) enters soil environment inevitably and has the potential to cause negative effects on soil organisms. The objective of the current study was to investigate the effects of EDTA on earthworm growth, survival and activities of antioxidant enzymes. The assessment for EDTA toxicity toward earthworms (Eisenia fetida) was conducted on day 14 and 35 after exposure to four concentrations (0, 5, 10, 15 mmol kg-1) of EDTA under turfgrass growing conditions. Exposure to EDTA resulted in a significant decrease of earthworm growth and survival. The toxicity of EDTA increased with the increase in concentration and exposure duration. The activities of antioxidant enzymes increased at low concentration and decreased at high concentration, which indicates that oxidative stress was induced by EDTA addition. These results suggest EDTA is highly toxic and ecologically dangerous to earthworms.

The impact of modified nano-carbon black on the earthworm Eisenia fetida under turfgrass growing conditions: Assessment of survival, biomass, and antioxidant enzymatic activities.

Modified nano-carbon adsorbents have been employed in the immobilization of heavy metals in soil due to their good adsorption capabilities regarding metal ions. However, an assessment of their risks has not been extensively performed with soil organisms. To assess the toxic effects of three types of modified nano-carbon black (CB) on soil organisms, a laboratory test was conducted to expose the earthworm Eisenia fetida to artificial soil supplemented with 5% H2SO4-, HNO3- and KMnO4-modified nano-CB (SCB, NCB and KCB, respectively) under turfgrass growing conditions. The tested earthworms were systematically investigated for survival, biomass and the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). SCB and NCB were found to be more toxic and ecologically dangerous to E. fetida because significant decreases in biomass and survival were observed after 35- and 60-d exposures and the survival rate showed a tendency to decrease with exposure duration. The activities of SOD, CAT and POD were inhibited in all treatments with modified nano-CBs at 35- and 60-d, which indicated that oxidative stress was induced by modified nano-CBs. The results suggest that there is potential harm to earthworms in soil with 5% modified nano-CB and that it deserves special attention.

Impacts of carbon nanomaterials on the diversity of microarthropods in turfgrass soil.

Nanoscale materials have been produced with unprecedented speed due to their widespread use, and they may eventually be released into the environment. As effective adsorbents for heavy metals, carbon nanomaterials can be used to immobilize metals in contaminated soil, but little information is available regarding their effects on soil microarthropods. This study was designed to investigate the influence of three types of carbon nanomaterials, graphene (G), graphene oxide (GO) and carbon nanotubes (CNTs) on soil microarthropod communities under turfgrass growth conditions. The application of carbon nanomaterials resulted in increased abundance of all soil microarthropods, especially in the GO and CNT treatments. GO also significantly increased the abundances of multiple trophic functional groups, including predators, detritivores, herbivores and fungivores. Further, the dominant genera varied among the treatments. Herbivorous microarthropods predominated in the control, whereas predatory species predominated in the carbon nanomaterial treatments. Carbon nanomaterials also increased the total taxonomic richness, Shannon diversity index, and dominance index of the microarthropod community, but they decreased the evenness index. Higher diversity of soil microarthropods indicates an environment suitable for soil mesofauna and for enhanced decomposition and nutrient cycling in the soil food web.

Combining Nitrilotriacetic Acid and Permeable Barriers for Enhanced Phytoextraction of Heavy Metals from Municipal Solid Waste Compost by and Reduced Metal Leaching.

Phytoextraction has the potential to remove heavy metals from contaminated soil, and chelants can be used to improve the capabilities of phytoextraction. However, environmentally persistent chelants can cause metal leaching and groundwater pollution. A column experiment was conducted to evaluate the viability of biodegradable nitrilotriacetic acid (NTA) to increase the uptake of heavy metals (Cd, Cr, Ni, Pb, Cu, and Zn) by L. in municipal solid waste (MSW) compost and to evaluate the effect of two permeable barrier materials, bone meal and crab shell, on metal leaching. The application of NTA significantly increased the concentrations and uptake of heavy metals in . The enhancement was more pronounced at higher dosages of NTA. In the 15 mmol kg NTA treatment using a crab shell barrier, the Cr and Ni concentrations in the plant shoots increased by approximately 8- and 10-fold, respectively, relative to the control. However, the addition of NTA also caused significant heavy metal leaching from the MSW compost. Bone meal and crab shell barriers positioned between the compost and the subsoil were effective in preventing metal leaching down through the soil profile by the retention of metals in the barrier. The application of a biodegradable chelant and the use of permeable barriers is a viable form of enhanced phytoextraction to increase the removal of metals and to reduce possible leaching.

Heavy metal uptake and leaching from polluted soil using permeable barrier in DTPA-assisted phytoextraction.

Application of sewage sludge (SS) in agriculture is an alternative technique of disposing this waste. But unreasonable application of SS leads to excessive accumulation of heavy metals in soils. A column experiment was conducted to test the availability of heavy metals to Lolium perenne grown in SS-treated soils following diethylene triamine penta acetic acid (DTPA) application at rates of 0, 10 and 20 mmol kg(-1) soil. In order to prevent metal leaching in DTPA-assisted phytoextraction process, a horizontal permeable barrier was placed below the treated soil, and its effectiveness was also assessed. Results showed that DTPA addition significantly increased metal uptake by L. perenne shoots and metal leaching. Permeable barriers increased metal concentrations in plant shoots and effectively decreased metal leaching from the treated soil. Heavy metals in SS-treated soils could be gradually removed by harvesting L. perenne many times in 1 year and adding low dosage of DTPA days before each harvest.

[Determination of methyl propyl ketone in air of workplace by capillary gas chromatography].

OBJECTIVE: To establish a gas chromatography method for determination of methyl propyl ketone in the air of workplace. METHODS: Methyl propyl ketone in the air of workplace was collected with activated carbon tubes and desorbed with carbon disulfide before sample loading. The target toxicant was separated with the capillary column and detected with a hydrogen flame ionization detector, identified by retention time, and quantified by peak area. RESULTS: The linear range of methyl propyl ketone in the air of workplace was 202.5∼4 860.0 µg/ml, with a correlation coefficient of 0.999 98. The limit of detection was 1.5 µg/ml. The lower limit of quantification was 5.0 µg/ml. The minimum detectable concentration was 1.0 mg/m(3) under 1.5 L sampling volume and 1.0 ml desorption solution volume. The relative standard deviation of different methyl propyl ketone concentrations was 1.42%∼1.65%, and the recovery rate was 94.9%∼ 97.9%. CONCLUSION: This method has high sensitivity, precision, and accuracy, and it is applicable for determination of methyl propyl ketone in the air of workplace.

[Influence of ethylbenzene on oxidative damage and apoptosis in rat renal epithelial cells NRK-52e].

OBJECTIVE: To study the oxidative damage and apoptosis of renal tubular epithelial cells (NRK-52e cell line) induced by ethylbenzene. METHODS: NRK-52e cells were exposed to 30, 60, 90, 120 µmol/L ethylbenzene for 24 hours. Cell viability were measured using MTT, the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT), the contents of malondialdehyde (MDA) and glutathione (GSH) were detected respectively. PI fluorescent staining assay was applied to detect percentage of apoptosis in ethylbenzene-treated groups. RESULTS: Compared with control group, cell outline became clear, cell diopter increased, cell became smaller and shrinkage, some cells broke in 60 µmol/L ethylbenzene-treated group. Plenty of cells died, suspension cells increased significantly in 90 µmol/L ethylbenzene-treated group. Compared with control group, cell viability the activities of SOD and CAT and the content of GSH were significantly decreased in 60 and 90 µmol/L ethylbenzene-treated groups (P<0.05). The MDA content were remarkably elevated in 90 µmol/L ethylbenzene-treated groups (P<0.05). CONCLUSION: Ethylbenzene can induce oxidative stress and apoptosis in NRK-52e cells (P<0.05).

Accumulation and spatial distribution of Cd, Cr, and Pb in mulberry from municipal solid waste compost following application of EDTA and (NH4)2SO4.

Municipal solid waste compost can be used to cropland as soil amendment to supply nutrients and improve soil physical properties. But long-term application of municipal solid waste (MSW) compost may result in accumulation of toxic metals in amended soil. Phytoremediation, especially phytoextraction, is a novel, cost-effective, and environmentally friendly approach that uses metal-accumulating plants to concentrate and remove metals from contaminated soils. Ethylenediaminetetraacetate (EDTA) was applied to metal-contaminated soil to increase the mobility and phytoavailability of metals in soil, thereby increasing the amount of toxic metals accumulated in the upper parts of phytoextracting plants. The objectives of this study were (1) to investigate the accumulation and spatial distribution of toxic metals (Cd, Cr, and Pb) in mulberry from MSW compost with the application of EDTA and (NH(4))(2)SO(4), (2) to examine the effectiveness of EDTA and (NH(4))(2)SO(4) applied together on toxic metals (Cd, Cr, and Pb) removal by mulberry under field conditions, and (3) to evaluate the potential of mulberry for phytoextraction of toxic metals from MSW compost. The tested plant-mulberry had been grown in MSW compost field for 4 years. EDTA solution at five rates (0, 50, 100, 50 mmol L(-1) + 1 g L(-1) (NH(4))(2)SO(4), and 100 mmol L(-1) + 1 g L(-1) (NH(4))(2)SO(4)) was added into mulberry root medium in September 2009. Twenty days later, the plants were harvested and separated into six parts according to plant height. Cd, Cr, and Pb contents in plant samples and MSW compost were analyzed using an atomic absorption spectrophotometer. In the same treatment, Cd, Cr, and Pb concentrations in mulberry shoot were all higher than those in root, and Cd and Pb concentrations in shoot increased from lower to upper parts, reaching the highest in leaves. Significant increases were found in toxic metal concentration in different parts of mulberry with increasing EDTA concentration, especially when combined with (NH(4))(2)SO(4). Mulberry exhibited high ability to accumulate Cd with bioconcentration factors (BCFs) higher than 1. EDTA application also significantly increased Cd BCFs. More than 30 % of metal uptake was concentrated in mulberry branches (stem of above 100 cm height) and leaves. Results presented here show that mulberry is a woody plant that has the potential of Cd phytoextraction from MSW compost by removing leaves and cutting branches. The application of EDTA combined with (NH(4))(2)SO(4) significantly enhanced the efficiency of mulberry in removing Cd from the compost medium. Adding (NH(4))(2)SO(4) into the compost will lower the risk of the exposure of environment to excessive non-biodegradable EDTA in a large-scale EDTA-assisted phytoextraction by reducing the dosage of EDTA. In China, the need for sod is increasing day by day. Sod is often produced on arable soil and sold together with soils. This would lead to the soil being infertile and the soil layer thin. After several times' production, the soil can no longer be used for cultivating crops and be destroyed. In order to fully utilize MSW compost resources and save valuable soil resources, MSW compost can be used to replace arable soil to produce sod after extraction of toxic metals in it.

The use of a biodegradable chelator for enhanced phytoextraction of heavy metals by Festuca arundinacea from municipal solid waste compost and associated heavy metal leaching.

In a column experiment with horizontal permeable barriers, the effects of a biodegradable chelator-nitrilotriacetic acid (NTA) on the uptake of heavy metals from municipal solid waste (MSW) compost by Festuca arundinacea and metal leaching were investigated. The use of NTA was effective in increasing Cu, Pb, and Zn uptakes in shoots of two crops of F. arundinacea. In columns with barriers and treated with 20 mmol NTA per kg MSW compost, metal uptakes by the first and second crop of F. arundinacea were, respectively, 3.8 and 4.0 times for Pb, and 1.8 and 1.7 times for Zn greater with the added NTA than without it. Though NTA application mobilized metals, it caused only slight leaching of metals from MSW compost. Permeable barriers positioned between compost and soil effectively reduced metal leaching. NTA-assisted phytoextraction by turfgrass with permeable barriers to cleanup heavy metal contaminated MSW compost should be environmentally safe.

[Detecting 2-butoxy ethanol in the air of workplaces by gas chromatography].

OBJECTIVE: To establish a gas chromatographic method for detecting 2-butoxy ethanol in the air of workplaces. METHODS: After the air samples were collected with activated carbon tubes and desorbed with methylene chloride/methanol, the target toxicant was separated with FFAP capillary columns and detected with flame ionization detector, qualified by retention time and quantified by peak area. RESULTS: The linear range of 2-butoxy ethanol in air of workplace was 56.3 ∼ 901.0 µg/ml, the correlation coefficient was 09999. The limit of detection was 2.0 µg/ml. The limit of quantity was 5.0 µg/ml. The minimal detecting concentration was 0.27 mg/m(3) in the condition of 7.5L sampling volume and 1ml desorbed volume. Relative standard deviation was 3.04% ∼ 7.93% and the recovery was 92.7% ∼ 95.5%. CONCLUSION: In present study the detecting method with high sensitivity, precision and accuracy can be used to determine 2-butoxy ethanol in the air of workplaces.