Tolerance, uptake and removal of nitrobenzene by a newly-found remediation species Mirabilis jalapa L

Phytotoxicity of nitrobenzene bioaccumulation in rice seedlings: Nitrobenzene inhibits growth, induces oxidative stress, and reduces photosynthetic pigment synthesis

Nitrobenzene (NB) has been used in numerous industrial and agricultural fields as an organic compound intermediate. NB has mutagenicity and acute toxicity, and is typically a toxic pollutant in industrial wastewater worldwide. To evaluate its phytotoxicity, we treated rice (Oryza sativa) with different concentrations of NB (0, 5, 25, 50, 75, and 100 mg L-1). NB inhibited growth indices of rice (shoot and root length, fresh shoot and root weight, and dry shoot and root weight) as NB treatment concentrations increased. High concentrations (>25 mg L-1) of NB significantly inhibited rice root and shoot growth; root growth was more susceptible to NB. NB treatment could damage the structure and reduce the activity of rice seedling roots. The result of high performance liquid chromatography (HPLC) indicated that the bioaccumulation of NB in rice seedlings had a dose-dependent effect on the growth inhibition. NB reduced the photosynthetic pigment content and the expression levels of chlorophyll synthesis genes. NB treatment increased active oxygen radicals, electrical conductivity, malondialdehyde (MDA), proline, and soluble sugar contents. The expressions of antioxidant enzyme genes were induced by NB stress, and exhibited a phenomenon of initial increase followed by decrease. When the NB concentration was higher than 50 mg L-1, the gene expression levels decreased rapidly. This study provides insight into the association between exposure to NB and its phytotoxic effects on rice seedlings, and assesses the potential risk of NB bioaccumulation for crops that require a large amount of irrigation water.

Optimistic effects of galaxolide and polystyrene microplastic stress on the physio-biochemical characteristics and metabolic profiles of an ornamental plant

Galaxolide (HHCB) and polystyrene (PS) microplastics or nanoplastics have been widely recognized as emerging pollutants. However, very few efforts have been made to remove these contaminants from the environment using eco-friendly materials such as plant materials. Therefore, this study sought to investigate the physiological and biochemical effects and tolerance mechanisms of Mirabilis jalapa L. upon exposure to HHCB and PS. Our findings demonstrated that this ornamental plant was tolerant to HHCB and PS exposure. HHCB treatment increased antioxidant enzyme activity. However, superoxide dismutase (SOD) activity increased by 206.85% when the plants were treated with 0.5 mg L^-1 HHCB alone, whereas co-exposure to 0.5 mg L^-1 HHCB and 500 nm PS increased SOD activity by 93.82%. Contaminant exposure also affected photosynthetic parameters such as stomatal conductance and transpiration rate. In contrast, net photosynthetic rate and photosynthetic pigment content were not significantly affected. HHCB aggregated heavily in the roots of the plant. Moreover, 500 nm PS could be absorbed by the root and transported to the shoot, and 5 μm PS would be transferred to the shoot under the carrying effect of HHCB. Co-exposure to HHCB and PS significantly changed the glyoxylate and dicarboxylate metabolism, alanine, aspartate, and glutamate metabolism, and glycine, serine, and threonine metabolism pathways, thus affecting carbohydrate synthesis and energy metabolism in M. jalapa. These results provide a basis for the development of HHCB and PS remediation strategies using M. jalapa, an ornamental plant that is not only tolerant to organic contaminants but can also beautify the environment.

Recent advances in biological removal of nitroaromatics from wastewater

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.

Re-investigation of cadmium accumulation in Mirabilis jalapa L.: evidences from field and laboratory

Mirabilis jalapa L. was identified as a cadmium (Cd) hyperaccumulator, but data were mainly from laboratory conditions. The main aim of the present study was to confirm whether M. jalapa is a Cd hyperaccumulator by field survey and laboratory experiment. The field survey was conducted at 3 sites and 66 samples were collected, and the results showed that although M. jalapa did not exhibit any visible damage when growing on soil containing 139 mg Cd kg^-1, a low concentration of Cd (11.85 ± 3.45 mg kg^-1) in its leaves was observed. Although the translocation factor (TF) was up to 3.24 ± 0.42, the bioconcentration factor (BCF) was only 0.13 ± 0.07. The Cd accumulation in leaves of Lanping (LP, contaminated site) and Kunming (KM, clean site) populations reached 93.88 and 81.76 mg kg^-1 when artificially spiked soil Cd was 175 mg kg^-1, respectively. The BCFs of LP and KM populations were 0.55 and 0.48, and the TFs of the two populations were 3.98 and 4.15, respectively. Under hydroponic condition, the Cd concentration in young leaves of LP and KM populations was 78.5 ± 0.8 and 46.3 ± 1.2 mg kg^-1 at 5 mg L^-1 Cd treatment, respectively. Furthermore, a significantly positive correlation between tissue Cd concentration and total Cd, CaCl₂-extractable Cd, and TCLP-Cd (toxicity characteristic leaching procedure) in soil was established. Therefore, M. jalapa had constitutional characteristics for Cd tolerance and accumulation, but it was not a Cd hyperaccumulator.

Effects of glucose and starch on the toxicity of nitrobenzene to plants and microbes in constructed wetlands

Photosynthetic pigment content, antioxidant enzyme activities of plants, microbial enzyme activities and community structure were analyzed to investigate the effects of glucose and starch on the toxicity of nitrobenzene (NB) to plants and microbes in constructed wetlands (CWs). As the influent NB concentration increased from 10 mg/L to 100 mg/L, the NB removal efficiency of the blank group decreased from 97.1% to 75.02%. However, the NB removal efficiencies of the external carbon source groups were maintained at nearly 100%. External carbon sources accelerated the transformation process of NB to aniline (AN), thus decreasing NB toxicity to the microbes and plants. When the influent NB concentration reached 100 mg/L, the NB removal rates and NB reductase activities of the external carbon source groups were 2.4 times and 4 times higher, respectively, than those of the blank group. Most of the dominant genera found in the three CWs could reduce nitroaromatics to the corresponding aromatic amines according to the results of high-throughput sequencing. The performance of NB removal in the CWs indicated the potential of CWs for NB treatment and the necessity of external carbon sources under high NB concentrations.

Toxicological sensitivity of Pennisetum americanum (L.) K. Schum to atrazine exposure

The tolerance of Pennisetum americanum (L.) K Schum (P. americanum) to the herbicide atrazine, as well as the atrazine accumulation in exposed plants, was investigated in this study. The germination of P. americanum seeds was not significantly inhibited by exposure to atrazine at concentrations below 100 mg·L^-1. The roots of the seedlings were much more sensitive to atrazine than the shoots were, as shown by observations that shoot and root elongation were significantly inhibited by treatment with 100 and 50 mg·kg^-1 of atrazine, respectively. In addition, significant differences were found in the dry weights of the seedling shoots and roots after exposure to 50 and 20 mg·kg^-1 of atrazine, respectively. Atrazine accumulated readily in the roots of exposed seedlings, and the root ultrastructure was visibly damaged by exposure to lower levels of atrazine compared to the ultrastructure of the shoot. The contents of chlorophyll a and chlorophyll b and the transcription of psbA were inhibited by exposure to atrazine at concentrations above 20 mg·kg^-1. Finally, the tolerance threshold of P. americanum to atrazine was about 20 mg·kg^-1, indicating that the test plant exhibited some atrazine tolerance.

Uptake and translocation of benzo[a]pyrene (B[a]P) in two ornamental plants and dissipation in soil

Pot experiments were conducted to evaluate the phytoremediation of B[a]P contaminated soil using two ornamental plants (Tagetes patula and Mirabilis jalapa). The results showed that the dry biomass of two plants was increased at low B[a]P contaminated soil and then inhibited with increasing B[a]P concentrations. It exhibited a significantly positive linear relationship between B[a]P absorption in roots, stems, leaves and shoots of the tested plants and the concentration of B[a]P in soils (P<0.01). Meanwhile, the contents of B[a]P in different tissues of the plants increased with growing time. After planting T. patula and M. jalapa, plant-promoted biodegradation of B[a]P was account for 79.5-99.8% and 71.1-99.9%, respectively, whereas the amount of B[a]P dissipation enhancement was only 0.2-20.5% and 0.1-28.9%, respectively. Moreover, low bioaccumulation factor (BF) and translocation factor (TF) values indicated that T. patula and M. jalapa took up B[a]P from contaminated soil and transferred them to the aerial parts with low efficiency. The B[a]P removal rates in rhizosphere soils at different growing stages of T. patula and M. jalapa were 2.7-26.8% and 0.4%-33.9%, respectively, higher than those of non-rhizopshere soils. Therefore, the presence of T. patula and M. jalapa roots was effective in promoting the phytoremediation of B[a]P contaminated soils.

Identification and characterization of a cold-adapted and halotolerant nitrobenzene-degrading bacterium

According to strain X7's morphological, physiological and biochemical characteristics and 16S rDNA gene sequence, the result showed that strain X7 was Myroides odoratus.

Degradation of nitrobenzene in aqueous solution by dual-pulse ultrasound enhanced electrochemical process

The present work reports a novel dual-pulse ultrasound enhanced electrochemical degradation (US-ECD) process that synchronizes alternatively ultrasound pulses and potential pulses to degrade nitrobenzene in aqueous solution with a high percentage degradation and low energy consumption. In comparison to the test results generated from the conventional US-ECD and original electrochemical degradation (ECD) process, the dual-pulse US-ECD process increased degradation percentages to nitrobenzene by 2% and 17%, respectively, while energy used in the pulse process was only about 46.5% of that was used in the conventional US-ECD process. Test results demonstrated a superior performance of the dual-pulse US-ECD process over those of other conventional ones. Impacts of pulse mode, initial pH value, cell voltage, supporting electrolyte concentration and ultrasonic power on the process performances were investigated. With operation conditions optimized in the study at pH=3.0, cell voltage=10 V, ultrasonic power=48.84 W, electrolyte concentration=0.1M and an experiment running time of 30 min, the percentage degradation of nitrobenzene could reach 80% (US pulse time=50 ms and ECD pulse time=50 ms). This process provided a reliable and effective technical approach to degrade nitrobenzene in aqueous solution and significantly reduced energy consumption in comparison to the conventional US-ECD or original ECD treatment.

Application of Nanoscale Zero Valent Iron Combined with Impatiens Balsamina to Remediation of E-Waste Contaminated Soils

E-waste contamination is of major environmental concern on a world scale, with the rapid development of electric industry. The recycling and disposal methods of e-wastes remain rudimentary, and pose a serious environmental threat and have adverse influences on human health, because toxic pollutants such as polychlorinated biphenyls (PCBs), and heavy metals are released into the environment during crude recycling. nanophytoremediation is a combined technology between nanotechnology and phytotechnology for remediation of contaminated environments. This work was aimed to investigate the tolerance and accumulation characteristics of e-waste pollution, as well as the effect of nanoscale zero valent iron (nZVI) on their phytoremediation capacity. Results showed that nZVI could facilitate the growth of plants both under clean soil and the high pollution, with increased by 30.3% and 53.5% respectively. This may be attributed to the improvement of soil quality and adjustment of soil pH by nZVI. Especially, all the nZVI adding treatments had significantly higher PCBs accumulation efficiency compared with that without addition of nZVI, thus indicating nZVI-phytroremediation would be a very promising method in the future.