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Wastewater generation and treatment is an ever-increasing concern in the current century due to increased urbanization and industrialization. To tackle the situation of increasing environmental hazards, numerous wastewater treatment approaches are used—i.e., physical, chemical, and biological (primary to tertiary treatment) methods. Various treatment techniques being used have the risks of producing secondary pollutants. The most promising technique is the use of different materials as adsorbents that have a higher efficacy in treating wastewater, with a minimal production of secondary pollutants. Biosorption is a key process that is highly efficient and cost-effective. This method majorly uses the adsorption process/mechanism for toxicant removal from wastewater. This review elaborates the major agricultural and non-agricultural materials-based sorbents that have been used with their possible mechanisms of pollutant removal. Moreover, this creates a better understanding of how the efficacy of these sorbents can be enhanced by modification or treatments with other substances. This review also explains the re-usability and mechanisms of the used adsorbents and/or their disposal in a safe and environmentally friendly way, along with highlighting the major research gaps and potential future research directions. Additionally, the cost benefit ratio of adsorbents is elucidated.

PurposeSoil microbial biomass (SMB), as the source and sink of soil nutrients, and its stoichiometry play a key role in soil organic carbon (SOC) and nitrogen (N) mineralization. The objective of this study was to investigate the responses of SOC and N mineralization to changes in microbial biomass and SOC, N, and phosphorus (P) stoichiometry resulted from long-term fertilization regimes.Materials and methodsSoil was sampled from a rice-wheat rotation system subjected to 37 years of nine fertilization treatments with different nutrient input amounts: control (CK), N alone, N combined with mineral phosphorus (NP), NP plus potassium (NPK), manure alone (M), and M combined with N (MN), NP (MNP), NPK (MNPK), and a higher rate of M with NPK (hMNPK). The sampled soil was incubated for the determination of SOC and N mineralization, C, N, and P stoichiometry of soil and SMB, and associated soil enzymes related to C and N cycling.Results and discussionRelative to the CK and treatments with mineral fertilizers, treatments with manure (M, MN, MNP, MNPK, and hMNPK) significantly increased SOC and N mineralization by 48–78% and 54–97%, respectively. Microbial metabolic quotient (qCO2) decreased by 32–55% in treatments with manure compared to the N and NP treatments, but showed no effect on the qCO2 when compared to the NPK treatment. The leucine amino peptidase (LAP) enzyme showed significant positive correlation with SOC and N mineralization, and negatively related to the qCO2. Significantly negative correlations were also observed between SOC and N mineralization and soil C:P and N:P ratio, as well as microbial biomass SMBC:SMBP and SMBN:SMBP stoichiometry, respectively. However, the availability of N and P had limited effects on the qCO2 after reaching a certain value (0.69–0.72 mg CO2-C g−1 MBC h−1).ConclusionsLower soil elemental (C:P and N:P) and microbial biomass stoichiometry (SMBC:SMBP and SMBN:SMBP) and increase of LAP resulted from combined application of manure and mineral fertilizers, accelerated SOC, and N mineralization. Mineral nutrient input with manure amendments could be an optimal strategy to meet the microbial stoichiometric demands and enhance nutrient availability for crops in agricultural ecosystems.

Salinity and water stress are serious environmental issues that reduced crop production worldwide. The current research was initiated (2012) in the wirehouse of the Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan to investigate the growth, stress tolerance, and physiological responses of guava to salinity and water shortage. Guava was grown for one year in pots containing soil with Eight treatments (control, 10 dS m −1 , 20 dS m −1 , 40 dS m −1 , control + water stress (WS), 10 dS m −1  + WS, 20 dS m −1  + WS, 40 dS m −1  + WS) in a completely randomized design. The results indicated that plant growth, stress tolerance, and physiological parameters declined at higher salinity and water stress and could not survive at 40 dS m −1 . The 20 dS m −1  + WS caused a > 70% decline in dry weights of shoot and root regarding control. Similarly, the highest decrease in stress tolerance was noticed in 20 dS m −1  + WS followed by the 20 dS m −1 treatment than control. Our findings validated that guava can be cultivated on soils having salinity ≤ 10 dS m −1 but it could not be cultivated on soils having salinity ≥ 20 dS m −1 with limited water supply.

Soil contamination with readily soluble salts and heavy metals is a major challenge concerning sustainable crop production. The use of organic wastes in agriculture not only helps in waste reduction but also acts as a soil conditioner and bio-stimulant for enhancing crop growth. In this regard, a pot experiment was conducted to investigate the effect of raw and processed animal manure (AM) on the growth, yield, and physicochemical parameters of Brassica napus L. developed under salinity and Ni stress. The experiment comprised two salinity levels (1.05 and 8 dS m −1 ), two Ni levels (0 and 50 mg kg −1 ), and two types of AMs (raw and processed at a rate of 2% w/w). A control treatment without AM incorporation was also included. In results, the application of AM markedly increased the growth and yield of B. napus under Ni and salinity stress; at the same time, it improved the physiological and chemical parameters of the said crop. Similarly, incorporation of processed AM significantly improved nutrient uptake and decreased Na/K ratios in the shoot and grain under the different stress conditions, as compared to the control. Likewise, Ni uptake in the grain, shoot, and root samples was also significantly reduced under the AM treatment. Also, the application of AM significantly reduced the daily intake of metal (DIM) index and the health risk index (HRI) values under the different stress conditions, as compared to the control. In conclusion, the application of processed AM constitutes an effective agricultural strategy to alleviate the adverse effects of Ni and salinity stress on growth, physiology, and yield of B. napus , thus resulting in enhanced productivity, as well as reduced risks associated with human health.

PurposePlant growth and grain yield of most of the crops are reduced on saline-sodic soils. Different organic and inorganic amendments have been used to increase plant growth and productivity on salt-affected soils. However, the role of cotton shell biochar (CSBC) for increasing salt tolerance of plants grown on saline-sodic soils has not been investigated yet. Therefore, the current study was intended to estimate the impact of cotton shell biochar (CSBC) addition @1 and 2% for ameliorating Na-induced phytotoxicity in quinoa grown on saline-sodic soil.Materials and methodsQuinoa plants were grown on saline-sodic soil with and without CSBC addition. Different physiological attributes were measured at vegetative stage. Plants were harvested at maturity when growth and grain yield were recorded.Results and discussionResults revealed that plant biomass, grain yield, stomatal conductance, relative water contents, and chlorophyll contents of quinoa were declined by > 20%, 18%, 23%, 27%, and 16%, respectively under salt stress. Excessive uptake of Na decreased the uptake of K and K:Na, and caused the overproduction of H2O2 (62%) and lipid peroxidation (58%) in quinoa. The CSBC addition @2% was more effective than 1% in ameliorating the negative impacts of Na toxicity on plant growth and physiology. Amendment of saline-sodic soil with 2% CSBC increased plant growth, water contents, stomatal conductance, and chlorophyll contents by 60%, 36%, 41%, and 43%, respectively as compared to saline-sodic soil without CSBC. There was a slight increase in soil EC after the addition of CSBC. Additionally, 2% CSBC limited the uptake of Na and caused a 43%, 48%, and 75% increase in superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities to ameliorate the oxidative stress.ConclusionsIt was concluded through multivariate analysis that 2% CSBC was very promising in reducing Na toxicity and increasing plant biomass and grain yield of quinoa in saline-sodic soils.

The effects of salt stress on the growth, nodulation, and nitrogen (N) fixation of legumes are well known, but the relationship between symbiotic nitrogen fixation (SNF) driven by rhizobium–legume symbiosis and salt tolerance in Medicago truncatula is not well studied. The effects of the active nodulation process on salt stress tolerance of Medicago truncatula were evaluated by quantifying the compatible solutes, soluble sugars, and antioxidants enzymes, as well as growth and survival rate of plants. Eight weeks old plants, divided in three groups: (i) no nodules (NN), (ii) inactive nodules (IN), and (iii) active nodules (AN), were exposed to 150 mM of NaCl salt stress for 0, 8, 16, 24, 32, 40, and 48 h in hydroponic system. AN plants showed a higher survival rate (30.83% and 38.35%), chlorophyll contents (37.18% and 44.51%), and photosynthesis compared to IN and NN plants, respectively. Improved salt tolerance in AN plants was linked with higher activities of enzymatic and nonenzymatic antioxidants and higher K+ (20.45% and 39.21%) and lower Na+ accumulations (17.54% and 24.51%) when compared with IN and NN plants, respectively. Additionally, higher generation of reactive oxygen species (ROS) was indicative of salt stress, causing membrane damage as revealed by higher electrolyte leakage and lipid peroxidation. All such effects were significantly ameliorated in AN plants, showing higher compatible solutes (proline, free amino acids, glycine betaine, soluble sugars, and proteins) and maintaining higher relative water contents (61.34%). This study advocates positive role of Rhizobium meliloti inoculation against salt stress through upregulation of antioxidant system and a higher concentration of compatible solutes.

PurposeSoil organic carbon (SOC) is an important parameter determining soil fertility and sustaining soil health. How C, N, and P contents and their stoichiometric ratios (C/N/P) regulate the nutrient availability, and SOC stabilization mechanisms have not been comprehensively explored, especially in response to long-term fertilization. The present study aimed to determine how the long-term mineral and manure fertilization influenced soil C/N/P ratios and various protection mechanisms underlying the stabilization of OC along with profile in a cropland soil.Materials and methodsThe soil was sampled from five depths, viz., 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm, from plots comprising wheat-maize-soybean rotation system subjected to the long-term (35 years) manure and mineral fertilizer applications.Results and discussionResults revealed that the soil C, N, P stoichiometry and their contents in topsoil depths (0–20 and 20–40 cm) and subsoil depths (40–60, 60–80, and 80–100 cm) varied significantly (p < 0.01) among the soil layers. Compared with CK, the C, N, and P contents were significantly higher (p < 0.05) in NPKM in the topsoil layers, while M alone increased these contents throughout the subsoil. Overall, the C, N, and P contents and their stoichiometry decreased with the increase in depth. Regression analysis showed that C/N, C/P, and N/P ratios associated significantly with the OC fractions in the topsoil layers only. These negative correlations indicated that these ratios significantly influence the C stabilization in the surface layers. However, the results warrant further investigations to study the relationship between soil and microbial stoichiometry and SOC at various depths.ConclusionsLong-term manure applications improved the C sequestration not only in the topsoil but also in the deep layers; hence, these facts can be considered relevant for fertilizer recommendations in cropping systems across China.

PurposeLong-term fertilization is a widely accepted strategy to enhance soil organic (SOC). However, fertilization effects on the stability of aggregate-associated OC remained largely unknown. Thus, stability of aggregate-associated OC was studied through aggregate fractionation, C-mineralization, and 13C NMR analyses.Materials and methodsThree aggregates (macro-aggregates, micro-aggregates, and silt + clay) were separated and analyzed for SOC contents, C-mineralization, and 13C NMR analysis, for the following fertilization modes: control (CK), inorganic (NPK), and NPK combined with manure (NPKM).Results and discussionHighest contents (12.3–15.4 g kg−1 aggregate) for SOC were obtained in macro-aggregates under NPK and NPKM application which were 47 and 85% higher than CK. Under the applied treatments, the highest CO2-C mineralization (mg kg−1 soil) was observed for macro-aggregates and least for silt + clay fractions indicating high stability of OC associated with silt + clay fraction. Moreover, manure combined with inorganic fertilizer (NPKM) considerably lowered C-mineralization (per unit SOC) in aggregates and bulk soil suggesting high potential of manure addition to stabilize SOC through minimizing proportional to total aggregate or bulk soil OC decomposition. Furthermore, 13C NMR analysis revealed carbonyl-C as the chief C-functional group sequestered. Manure application greatly enhanced SOC stability indices AI, HI, and A/OA which further indicates high SOC stability under manure addition.ConclusionSilt + clay fraction was more capable of protecting SOC against decomposition and manure combined with inorganic fertilizer not only had the potential to sequester more C but could also improve the stability of sequestered SOC associated with different aggregates.

Toxic metals and particle pollutants in urbanized cities have significantly increased over the past few decades mainly due to rapid urbanization and unplanned infrastructure. This research aimed at estimating the concentration of toxic metals and particle pollutants and the associated risks to public health across different land-use settings including commercial area (CA), urban area (UA), residential area (RA), and industrial area (IA). A total of 47 samples for both soil and air were collected from different land-use settings of Faisalabad city in Pakistan. Mean concentrations of toxic metals such as Mn, Zn, Pb, Ni, Cr, Co, and Cd in all land-use settings were 92.68, 4.06, 1.34, 0.16, 0.07, 0.03, and 0.02 mg kg −1 , respectively. Mean values of PM 10 , PM 2.5 , and Mn in all land-use settings were found 5.14, 1.34, and 1.9 times higher than the World Health Organization (WHO) guidelines. Mn was found as the most hazardous metal in terms of pollution load index (PLI) and contamination factor (CF) in the studied area. Health risk analysis for particle pollutants using air quality index (AQI) and geoinformation was found in the range between good to very critical for all the land-use settings. The hazard quotient (HQ) and hazard index (HI) were higher for children in comparison to adults, suggesting that children may be susceptible to potentially higher health risks. However, the cancer risk (CR) value for Pb ingestion (1.21 × 10 −6 ) in children was lower than the permissible limit (1 × 10 −4 to 1 × 10 −6 ). Nonetheless, for Cr inhalation, CR value (1.09 × 10 −8 ) was close to tolerable limits. Our findings can be of valuable assistance toward advancing our understanding of soil and air pollutions concerning public health in different land-use settings of the urbanized cities of Pakistan.

Since open biomass burning (OBB) and open crop straw burning (OCSB) could pose a great risk to human health via altering the air quality, these practices have grabbed considerable attention from the scientific community and policymakers in recent years. In order to have a greater and deeper understanding of the contributions of both OBB and OCSB on air quality, a bibliometric analysis was performed using the Web of Science core collection to understand the research developments and future perspectives of these issues between 1991 and 2021. VOSviewer software 1.6.15 and R version 4.0.3 were employed to determine the annual scientific production trend and the role of countries, institutions, authors, and journal metrics network analysis. The findings showed that the interest in the study of OBB and OCSB pollution related to air quality has increased significantly over the last decade. A total of 1,021 publications were retrieved, with English as the most preferably used language. Among all documents, research articles were the most commonly appearing document type, and the researchers mainly emphasized environmental science, meteorology, atmospheric sciences, energy fuels, and environmental engineering fields. In terms of article analysis, Atmospheric Chemistry Physics , followed by Atmospheric Environment , was found to be the leading journal in this research domain, whereas the most frequently utilized keywords in the documents were biomass, biomass burning, and PM 2.5 . In terms of countries, the United States emerged as the leader with the highest publication rate, followed by China and India. The Chinese Academy of Sciences was ranked first in the list of most productive institutions, followed by the University of Montana and the US Forest Service. Based on the analysis, the finer spatial and temporal resolution and the characterization and understanding of the complex processes that are occurring in the atmosphere, such as clustering, oxidation, surface chemistry, and their impact on air quality, need to be explored in depth. Our research analysis can provide a baseline for future studies in air quality.