In this study, Bacillus sp. strain AVPP64 was isolated from diuron-contaminated soil. It showed 4-nitroaniline (4-NA) degradation, pesticide tolerance, and self-nutrient integration via nitrogen (N)-fixation and phosphate (P)-solubilization. The rate constant (k) and half-life period (t₁/₂) of 4-NA degradation in the aqueous medium inoculated with strain AVPP64 were observed to be 0.445 d⁻¹ and 1.55 d, respectively. Nevertheless, in the presence of chlorpyrifos, profenofos, atrazine and diuron pesticides, strain AVPP64 degraded 4-NA with t₁/₂ values of 2.55 d, 2.26 d, 2.31 d and 3.54 d, respectively. The strain AVPP64 fixed 140 μg mL⁻¹ of N and solubilized 103 μg mL⁻¹ of P during the presence of 4-NA. In addition, strain AVPP64 produced significant amounts of plant growth-promoting metabolites like indole 3-acetic acid, siderophores, exo-polysaccharides and ammonia. In the presence of 4-NA and various pesticides, strain AVPP64 greatly increased the growth and biomass of Vigna radiata and Crotalaria juncea plants. These results revealed that Bacillus sp. strain AVPP64 can be used as an inoculum for bioremediation of 4-NA contaminated soil and sustainable crop production even when pesticides are present.

In this study, two proficient Cadmium (Cd) resistant and plant growth-promoting actinobacterial strains were isolated from metal-polluted soils and identified as Streptomyces sp. strain RA04 and Nocardiopsis sp. strain RA07. Multiple abiotic stress tolerances were found in these two actinobacterial strains, including Cd stress (CdS), drought stress (DS) and high-temperature stress (HTS). Both actinobacterial strains exhibited multifarious plant growth-promoting (PGP) traits such as phosphate solubilization, and production of indole-3-acetic acid, siderophores and 1-aminocyclopropane-1-carboxylate deaminase under CdS, DS and HTS conditions. The inoculation of strains RA04 and RA07 significantly increased Sorghum bicolor growth and photosynthetic pigments under CdS, DS, HTS, CdS + DS and CdS + HTS conditions as compared to their respective uninoculated plants. The actinobacterial inoculants reduced malondialdehyde concentration and enhanced antioxidant enzymes in plants cultivated under various abiotic stress conditions, indicating that actinobacterial inoculants reduced oxidative damage. Furthermore, strains RA04 and RA07 enhanced the accumulation of Cd in plant tissues and the translocation of Cd from root to shoot under CdS, CdS + DS and CdS + HTS treatments as compared to their respective uninoculated plants. These findings suggest that RA04 and RA07 strains could be effective bio-inoculants to accelerate phytoremediation of Cd polluted soil even in DS and HTS conditions.

Pollution in soil by petroleum hydrocarbon has become a global environmental problem. The bioremediation of petroleum hydrocarbon-contaminated soil was enhanced with the combination of an isolated indigenous bacterial consortium and biosurfactant. The biodegradation efficiency of total petroleum hydrocarbon (TPH) was increased from 12.2% in the contaminated soil to 44.5% and 57.7% in isolated consortium and isolated consortium & 1.5 g sophorolipid (SL)/kg dry soil, respectively. The half-life of TPH degradation process was decreased from 32.5 d in the isolated consortium reactor to 20.4 d in the isolated consortium & 1.5 g SL/kg dry soil. The addition of biosurfactant into contaminated soils improved the TPH desorption from solid matrix to the aqueous solution and the subsequent solubilization, which ultimately improved the bioavailability of TPH in contaminated soils. Biosurfactant also served as carbon sources which contributed to the stimulation of cell growth and microbial activity and accelerated the biodegradation process via co-metabolism. The enzyme activities and quantities of functional genes were demonstrated to be incremented in SL reactors. The biosurfactant improved the TPH bioavailability, stimulated the microbial activities and participated in the co-metabolism. The combination of bioaugmentation and SL benefitted the bioremediation of petroleum hydrocarbon-contaminated soil.

Due to ecologically unsustainable mining strategies, there remain large areas of phosphate mining wasteland contaminated with accumulated lead (Pb). In this study, a Pb-resistant phosphate-solubilizing strain of Pseudomonas sp., LA, isolated from phosphate mining wasteland, was coupled with two species of native plants, ryegrass (Lolium perenne L.) and sonchus (Sonchus oleraceus L.), for use in enhancing the reduction of bioavailable Pb in soil from a phosphate mining wasteland. The effect of PbCO₃ solubilization by Pseudomonas sp. strain LA was evaluated in solution culture. It was found that strain LA could attain the best solubilization effect on insoluble Pb when the PbCO₃ concentration was 1% (w/v). Pot experiments were carried out to investigate the potential of remediation by ryegrass and sonchus in phosphate mining wastelands with phosphate rock application and phosphate-solubilizing bacteria inoculation. Compared to the control group without strain LA inoculation, the biomass and length of ryegrass and sonchus were markedly increased, available P and Pb in roots increased by 22.2%–325% and 23.3%–368%, respectively, and available P and Pb in above-ground parts increased by 4.44%–388% and 1.67%–303%, respectively, whereas available Pb in soil decreased by 14.1%–27.3%. These results suggest that the combination of strain LA and plants is a bioremediation strategy with considerable potential and could help solve the Pb-contamination problem in phosphate mining wastelands.

Marine deposit feeders are of ecological significance in transferring sedimentary Cd along aquatic food chains. A key process for this transfer is these organisms’ dietary uptake of Cd via solubilization of Cd present in ingested contaminated sediment. To better understand the bioavailability of sedimentary Cd to deposit feeders, the present study used in vitro extraction experiments to explore the contribution of different digestive agents (proteins, amino acids and surfactants) to the solubilization of Cd from sediment collected in a highly-contaminated Chinese bay. This was done for various commercially-available mimetic digestive agents (the protein BSA, a mixture of amino acids, and the surfactants rhamnolipid and SDS), and for proteins and surfactants collected from the gut juice of a sipunculan worm. The Cd mobilization capacity of BSA was significantly higher than that of the amino acids and the commercial surfactants. In the presence of BSA, > 70% of the released Cd became associated with this protein. In contrast, the digestive proteins from the sipunculan had a lower Cd mobilization capacity than was the case for the other digestive agents and the majority of the released Cd (∼80%) was associated with small molecular weight fractions. The differences in Cd mobilization between the BSA and the digestive proteins were attributed to differences in their sediment-adsorption tendencies and their Cd-complexing capacities. While the digestive surfactants had minor effects on the release of sedimentary Cd, they significantly enhanced Cd mobilization by the digestive proteins when both were present simultaneously. Our results suggest that the characteristics of proteins should be considered when using commercially-available mimetic digestive agents to explore Cd bioavailability in sediments. Furthermore, digestive surfactants seem to have important effects on the solubilization of Cd during gut passage by reducing the adsorption of the digestive proteins to the sediments.

Marine oil spill often causes contamination of drinking water sources in coastal areas. As the use of oil dispersants has become one of the main practices in remediation of oil spill, the effect of oil dispersants on the treatment effectiveness remains unexplored. Specifically, little is known on the removal of dispersed oil from contaminated water using conventional adsorbents. This study investigated sorption behavior of three prototype activated charcoals (ACs) of different particle sizes (4–12, 12–20 and 100 mesh) for removal of dispersed oil hydrocarbons, and effects of two model oil dispersants (Corexit EC9500A and Corexit EC9527A). The oil content was measured as n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and total petroleum hydrocarbons (TPHs). Characterization results showed that the smallest AC (PAC100) offered the highest BET surface area of 889 m2/g and pore volume of 0.95 cm3/g (pHPZC = 6.1). Sorption kinetic data revealed that all three ACs can efficiently adsorb Corexit EC9500A and oil dispersed by the two dispersants (DWAO-I and DWAO-II), and the adsorption capacity followed the trend: PAC100 > GAC12 × 20 > GAC4 × 12. Sorption isotherms confirmed PAC100 showed the highest adsorption capacity for dispersed oil in DWAO-I with a Freundlich KF value of 10.90 mg/g∙(L/mg)1/n (n = 1.38). Furthermore, the presence of Corexit EC9500A showed two contrasting effects on the oil sorption, i.e., adsolubilization and solubilization depending on the dispersant concentration. Increasing solution pH from 6.0 to 9.0 and salinity from 2 to 8 wt% showed only modest effect on the sorption. The results are useful for effective treatment of dispersed oil in contaminated water and for understanding roles of oil dispersants.

Water availability is paramount in the response of soil invertebrates towards stress situations. This study aimed to evaluate the effects of forecasted soil moisture scenarios on the avoidance behavior of two invertebrate species (the arthropod Folsomia candida and the soft-bodied oligochaete Enchytraeus crypticus) in soils degraded by different types of anthropogenic metal(loid) contamination (mining soil and agricultural soil affected by industrial chemical wastes). Different soil moisture contents (expressed as % of the soil water holding capacity, WHC) were evaluated: 50% (standard soil moisture conditions for soil invertebrates' tests); 75% (to simulate increasing soil water availability after intense rainfalls and/or floods); 40%, 30%, 25% and 20% (to simulate decreasing soil water availability during droughts). Invertebrates’ avoidance behavior and changes in soil porewater major ions and metal(loid)s were assessed after 48 h exposure. Soil incubations induced a general solubilization/mobilization of porewater major ions, while higher soil acidity favored the solubilization/mobilization of porewater metal(loid)s, especially at 75% WHC. Folsomia candida preferred soils moistened at 50% WHC, regardless the soils were contaminated or not and the changing soil porewater characteristics. Enchytraeus crypticus avoided metal(loid) contamination, but this depended on the soil moisture conditions and the corresponding changes in porewater characteristics: enchytraeids lost their capacity to avoid contaminated soils under water stress situations (75% and 20–25% WHC), but also when contaminated soils had greater water availability than control soils. Therefore, forecasted soil moisture scenarios induced by global warming changed soil porewater composition and invertebrates capacity to avoid metal(loid)-contaminated soils.

Solvent stabilizer 1,4-dioxane, an emerging recalcitrant groundwater contaminant, was commonly added to chlorinated solvents such as trichloroethene (TCE), and the impact of co-disposal on contaminant transport processes remains uncertain. A series of batch equilibrium experiments was conducted with variations of 1,4-dioxane and TCE composition to evaluate aqueous dissolution of the two components and their sorption to aquifer sediments. The solubility of TCE increased with increasing amounts of 1,4-dioxane, indicating that 1,4-dioxane acts as a cosolvent causing solubility enhancement of co-contaminants. The solubilization results compared favorably with predictions using the log-linear cosolvency model. Equilibrium sorption coefficients (Kd and Kf) were also measured for different 1,4-dioxane and TCE compositions, and the findings indicate that both contaminants adsorb to aquifer sediments and TCE Kd values increased with increasing organic matter content. However, the Kd for TCE decreased with increases in 1,4-dioxane concentration, which was attributed to cosolvency impacts on TCE solubility. These findings further advance our understanding of the mass-transfer processes controlling groundwater plumes containing 1,4-dioxane, and also have implications for the remediation of 1,4-dioxane contamination.

Hexabromocyclododecanes (HBCDDs) are common chemical additives in expanded polystyrene foam (EPS). To evaluate the bioaccumulation potential of endogenous HBCDDs in EPS microparticles by earthworms, two ecologically different species of earthworms (Eisenia fetida and Metaphire guillelmi) were exposed to soil added with EPS microparticles of different particle sizes (EPS2000, 830–2000 μm and EPS830, <830 μm). To clarify the accumulation mechanisms, leaching experiments using EPS microparticles in different solutions were conducted. After exposure to EPS microparticles-amended soils (S-EPS) for 28 d, the total concentrations of HBCDDs reached 307–371 ng g−1 dw in E. fetida and 90–133 ng g−1 dw in M. guillelmi, which were higher than those in earthworms exposed to the soil that was artificially contaminated with a similar level of HBCDDs directly (ACS). The accumulation of HBCDDs in earthworms was significantly influenced by EPS microparticles' size and earthworms' species. The total concentrations of HBCDDs in earthworms' cast were significantly higher than the theoretical concentration of HBCDDs in S-EPS, which suggested that EPS microparticles can be ingested by earthworms. The release rate of HBCDDs from EPS5000 (2000–5000 μm) into water-based solutions (<1%) after a 3.5-h incubation was far lower than that into earthworm digestive fluid (7%). These results illustrated that the ingestion of EPS microparticles and consequent solubilization of HBCDDs by digestive fluid play an important role in the accumulation of HBCDDs contained in EPS microparticles in earthworms. After a 28-d incubation with the soil solution, 4.9% of the HBCDDs was accumulatively leached from the EPS5000, which indicated that HBCDDs can be released from EPS microparticles to soil environment, and then accumulated by earthworms. Moreover, similar to those exposed to ACS, the diastereoisomer- and enantiomer-specific accumulation of HBCDDs in earthworms occurred when exposed to S-EPS. This study provides more evidence for the risk of microplastics to the soil ecosystem.

Arsenic (As) in soils is of major environmental concern due to its ubiquity and carcinogenicity. Pteris vittata (Chinese brake fern) is the first known As-hyperaccumulator, which is highly efficient in extracting As from soils and translocating it to the fronds, making it possible to be used for phytoremediation of As-contaminated soils. In addition, P. vittata has served as a model plant to study As metabolisms in plants. Based on the recent advances, we reviewed the mechanisms of efficient As solubilization and transformation in rhizosphere soils of P. vittata and effective As uptake, translocation and detoxification in P. vittata. We also provided future research perspectives to further improve As hyperaccumulation by P. vittata.