Accumulation of typical persistent organic pollutants and heavy metals in bioretention facilities: Distribution, risk assessment, and microbial community impact.

Bioretention facilities have proven highly effective in removing pollutants from runoff. However, there is a concerning paucity of research on the contamination characteristics and associated risks posed by refractory pollutants in these facilities following long-term operation. This research focuses on the distribution, sources, microbial community impact, and human health risks of pollutants in eight bioretention facilities that have been operational for 5-11 years. The results showed that the distribution of Cu, Zn, and Cd was closely related to anti-seepage measures. PAHs, PCBs, and OCPs primarily accumulated in the surface, with concentrations ranging from 7.42 to 20.34 mg/kg, 31.8-77.3 µg/kg, and 60.5-163.6 µg/kg, respectively. Their concentrations inversely correlate with the depth of the media. Although the majority of contaminants remained below their respective risk thresholds, their concentrations typically exceeded those of background soil values, indicating an enrichment phenomenon. Source analysis revealed that PAHs primarily originate from oil combustion, PCBs were linked to their related industrial products, DDTs had their main sources in technical DDx and residues from the use of dicofol, while HCHs were traced back to historical residues from agricultural activities. Microbial α-diversity (Chao 1 and Shannon) decreased by 8.3-23.4% and 0.8-4.4%, respectively, in different facilities after long-term operation. The most dominant microbial phylum in the facilities was Proteobacteria (all relative abundances >48%). The total relative abundance of dominant genera was 6.7-34.3% higher than the control site, and Pseudomonas, a typical POPs-heavy metal degrading bacterium, had the highest relative abundance (>1.2%). Cu, Zn, and Cd present no non-carcinogenic risks and have low potential ecological risks. However, the lifetime cancer risk for PAHs is 10-6 ∼10-4 in most facilities and is of concern. The cancer risk for PCBs is acceptable, while OCPs pose a low cancer risk only for children.

Removal, accumulation, and micro-ecosystem impacts of typical POPs in bioretention systems with different media: A runoff infiltration study.

Bioretention systems prove effective in purifying common persistent organic pollutants (POPs) found in urban rainfall runoff. However, the response process of the microecosystem in the media becomes unclear when POPs accumulate in bioretention systems. In this study, we constructed bioretention systems and conducted simulated rainfall tests to elucidate the evolution of micro-ecosystems within the media under typical POPs pollution. The results showed all POPs in runoff were effectively removed by surface adsorption in different media, with load reduction rates of >85 % for PCBs and OCPs and > 80 % for PAHs. Bioretention soil media (BSM) + water treatment residuals (WTR) media exhibited greater stability in response to POPs contamination compared to BSM and pure soil (PS) media. POPs contamination significantly impacted the microecology of the media, reducing the number of microbial species by >52.6 % and reducing diversity by >27.6 % at the peak of their accumulation. Enzyme activities were significantly inhibited, with reductions ranging from 44.42 % to 60.33 %. Meanwhile, in terms of ecological functions, the metabolism of exogenous carbon sources significantly increased (p < 0.05), while nitrogen and sulfur cycling processes were suppressed. Microbial diversity and enzyme activities showed some recovery during the dissipation of POPs but did not reach the level observed before the experiment. Dominant bacterial species and abundance changed significantly during the experiment. Proteobacteria were suppressed, but remained the dominant phylum (all relative abundances >41 %). Bacteroidota, Firmicutes, and Actinobacteria adapted well to the contamination. Pseudomonas, a typical POPs-degrading bacterium, displayed a positive correlation between its relative abundance and POPs levels (mean > 10 %). Additionally, POPs and media properties, including TN and pH, are crucial factors that collectively shape the microbial community. This study provides new insights into the impacts of POPs contamination on the microbial community of the media, which can improve media design and operation efficiency.

The fate of three typical persistent organic pollutants in bioretention columns as revealed by stable carbon isotopes.

There is a lack of simple and effective methods to quantify the fate processes of persistent organic pollutants (POPs) in bioretention systems. In this study, the fate and elimination processes of three typical 13C-labeled POPs in regularly added bioretention columns were quantified using stable carbon isotope analysis techniques. The results showed that the modified media bioretention column removed more than 90% of Pyrene, PCB169 and p,p'-DDT. Media adsorption was the dominant removal mechanism for the reduction of the three exogenous organic compounds (59.1-71.8% of the input) although plant uptake (5.9-18.0%) was also important. Mineralization was effective in degrading pyrene (13.1%) but had a very limited effect on p,p'-DDT and PCB169 removal (<2.0%), the reason for which may be related to the aerobic conditions of the filter column. Volatilization was relatively weak and negligible (<1.5%). The presence of heavy metals inhibited the removal of POPs to some extent: media adsorption, mineralization and plant uptake were reduced by 4.3-6.4%, 1.8-8.3% and 1.5-3.6% respectively. This study suggests that bioretention systems are an effective measure for the sustainable removal of POPs from stormwater and that heavy metals can inhibit the overall performance of the system. Stable carbon isotope analysis techniques can help to investigate the migration and transformation of POPs in bioretention systems.

Ginger (Zingiber officinale) extract mediated green synthesis of silver nanoparticles and evaluation of their antioxidant activity and potential catalytic reduction activities with Direct Blue 15 or Direct Orange 26.

The green synthesis of silver nanoparticles (AgNPs) using a water extract of Ginger (Zingiber officinale) root by microwave irradiation and its antibacterial activities have been reported. However, AgNPs prepared from different parts of ginger root water or ethanol extract by ultrasound synthesis and their antioxidant activity and whether the biogenic could be used to catalyze the reduction of hazardous dye are unknown. This study concentrated on the facile green synthesis of AgNPs prepared from different parts (unpeeled ginger, peeled ginger, and ginger peel) of ginger root water or ethanol extract by the ultrasound-assisted method. We studied their antioxidant activity and catalytic degradation of hazardous dye Direct Orange 26 (DO26) and Direct Blue 15 (DB15). The surface plasmon resonance (SPR) peak of AgNPs was at 428-443 nm. The biogenic AgNPs were approximately 2 nm in size with a regular spherical shape identified from TEM analysis. The ethanol extracts of dried unpeeled ginger and peeled ginger, fresh peeled ginger and ginger peel. The Z. officinale AgNPs synthesized by dried unpeeled ginger ethanol extract showed the best antioxidant activity. Their scavenging activities were significantly better than BHT (p <0.05). The different parts of ginger extracts showed no catalytic degradation activities of DB15 and DO26. Still, the synthesized Z. officinale AgNPs exhibited good catalytic degradation activities, while their ability to catalytic degradation to DB15 was better than DO26. In the additive ratio of 3 mL DB15, 0.1 mL NaBH4 and 0.1 mL AgNPs, the degradation rates of DB15 (or DO26) at 15 min, 30 min and 60 min were only 1.8% (0.9%), 2.8% (1.4%) and 3.5% (1.6%) in the absence of AgNPs. When adding Z. officinale AgNPs prepared from dried ginger peel ethanol extract or fresh ginger peel water extract, the degradation rates of DB15 sharply increased to 97% and 93% after 30 min, respectively. In conclusion, ginger extract has good antioxidant properties. Z. officinale AgNPs biosynthesis from ginger extract exhibit excellent catalytic degradation activities, especially for the ginger peel extract. They have application value in the treatment of textile effluents and provide a new idea and method for the comprehensive development and utilization of ginger resources.

Study on Fabrication and UV Photoelectric Property of TiO2 Nanotube Array Electrodes.

Highly ordered TiO2 nanotube array electrodes were successfully fabricated by a two-step anodization method on Ti sheet substrates in an electrolyte composed of ammonium fluoride, deionized water, and glycol. The tube wall was smooth, and the average internal and external diameters, wall thickness, and tube length achieved were 80 nm, 90 nm, 10 nm, and 9 µm, respectively. X-ray diffraction and field emission scanning electron microscopy results revealed that the TiO2 nanotube arrays presented an amorphous structure. When calcined at 300 °C, the arrays crystallized into the anatase phase, and the crystallization degree of the oxide layer increased as the temperature rose. Calcinating at 400 °C did not obviously disrupt the porous structure of the highly ordered arrays. However, higher temperature enlarged the diameter of the nanotube array and roughened the tube wall. When the temperature reached 600 °C, the nanotube mouth broke because of the excessive stress, causing the oxide layer's thinness and nanotube mouth clogging. The photoelectric test showed that the electrode presented obvious photoresponse under 300-400 nm UV excitation (maximized at 360 nm). The degree of crystallization and the micro-structure of the oxide layer can significantly affect the photoelectric properties of the electrode. After calcination at 400 °C, the TiO2 nanotube arrays, with highly ordered tubular structure directly connected to the Ti substrate, can ensure the rapid transportation of photo-induced electrons to the Ti substrate, while the high crystallinity of the arrays can help reduce the defect density of the nanotube and extend the lifetime of the photo-induced carriers. The electrode showed the best photoelectric property, and the photocurrent intensity was maximized (29.6 µA). However, the calcination process with over-temperature resulted in substantial loss of the TiO2 oxide layer, mouth clogging, and a severe decline in the photoelectric properties.