Effects of micro(nano)plastics on soil nutrient cycling: State of the knowledge.

The ecological impacts of micro(nano)plastics (MNPs) have attracted attention worldwide because of their global occurrence, persistence, and environmental risks. Increasing evidence shows that MNPs can affect soil nutrient cycling, but the latest advances on this topic have not systematically reviewed. Here, we aim to present the state of knowledge about the effects of MNPs on soil nutrient cycling, particularly of C, N, and P. Using the latest data, the present review mainly focuses on three aspects, including (1) the effects and underlying mechanisms of MNPs on soil nutrient cycling, particularly of C, N and P, (2) the factors influencing the effects of MNPs on soil nutrient cycling, and (3) the knowledge gaps and future directions. We conclude that MNPs can alter soil nutrient cycling via mediating soil nutrient availability, soil enzyme activities, functional microbial communities, and their potential ecological functions. Furthermore, the effects of MNPs vary with MNPs characteristics (i.e., polymeric type, size, dosage, and shape), chemical additives, soil physicochemical conditions, and soil biota. Considering the complexity of MNP-soil interactions, multi-scale experiments using environmental relevant MNPs are required to shed light on the effects of MNPs on soil nutrients. By learning how MNPs influence soil nutrients cycles, this review can guide policy and management decisions to safeguard soil health and ensure sustainable agriculture and land use practices.

Immobilization and phytoavailability of antimony (Sb) in contaminated agricultural soils amended with composted manure.

A pot experiment was conducted to assess the Sb phytoavailability and its accumulation in the wheat before and after remediation, using the composted manure of poultry and sheep, and a chemical amendment (limestone). The present study evaluates the effects of amendments on Sb bioavailability in different soils and investigates the relationship between bioaccumulated Sb and its availability in spiked soils using two different single extraction methods. Furthermore, a sequential extraction procedure was used to measure different fractions of Sb in soil, in order to assess the effect of remediation. The results revealed that bioavailability of Sb were highly affected by the three soil amendments on plant height, uptake of Sb by wheat. Poultry compost (Pc) and Sheep compost (Sc) increased the residual fraction of Sb in soils, and decreased the Sb uptake by wheat, enhanced the height, biomass and dry yield of the wheat crop. While the residual fraction of Sb in soils didn't obviously increased by adding Chemical (limestone) in the four soils. It is concluded that uptake of Sb in the soils significantly decreased with the addition of amended materials in the Sb spiked soils, and poultry compost is the most effective. In the lower level of Sb contaminated soils remediated by poultry compost (Pc), the uptake of Sb in wheat decreased 63.1-74.4 %, 68.7-79.0 %, 68.9-76.9 % and 66.3-82.6 % in S1, S2, S3, S4, compared to the contaminated soils without amendments, respectively.

Biomonitoring of mercury in water, sediments, and fish (brown and rainbow trout) from remote alpine lakes located in the Himalayas, Pakistan.

Mercury (Hg) contamination of aquatic ecological units and subsequent bioaccumulation are major environmental problems of international scope. Moreover, the biogeochemistry of Hg in the remote alpine lakes aquatic ecosystem in the Himalayas remains largely unexplored. The current study investigated Hg concentrations in different environmental compartments such as water, fish, and sediments in the remote alpine lakes (RALs) including Glacial-fed Lake, Ice melting-fed Lake, and Rain-fed Lake in northern areas of Pakistan. The mean concentration of Hg in Rain-fed Lake water was (1.07 µg L-1), Ice melting-fed Lake (1.16 µg L-1), and Glacial-fed Lake (1.95 µg L-1). For fish muscle tissues, mean concentration of Hg was 1.02 mg kg-1 in the Rain-fed Lake, and 1.2 mg kg-1 for the Ice melting-fed Lake, and 1.51 mg kg-1 in the Glacial-fed Lake. Meanwhile, 0.27 mg kg-1 was observed for sediments in the Rain-fed Lake, 0.33 mg kg-1 for the Ice melting-fed Lake, and 0.38 mg kg-1 for the Glacial-fed Lake, respectively. Chronic daily intake (CDI) and potential health quotient (PHQ) for water showed high health risk in Glacial-fed Lake and low in Rain-fed Lake (PHQ < 1). The target hazard quotient (THQ) values for both the Brown and Rainbow trout in all the studied lakes water were less than 1, indicating no health risk. Furthermore, the Hg level showed high level of contamination in the sediments of all the studied lakes (190 ≤ RI < 380). Overall, Glacial-fed Lake water was more polluted with Hg, as compared to Rain-fed Lake and Ice melting-fed Lake. In the light of the abovementioned results, further research work is urgently needed to shed light on the biological and geochemical monitoring of Hg in arid high-altitude ecosystems along with source identification, mercury speciation, and other potential pollutants.

Challenges and opportunities in functional carbon nanotubes for membrane-based water treatment and desalination.

Environmental applications of carbon nanotubes (CNTs) have grabbed worldwide attentions due to their excellent adsorption capacities and promising physical, chemical and mechanical properties. The functionalization of CNTs, which involves chemical/physical modification of pristine CNTs with different types of functional groups, improves the capabilities of CNT for desalination and/or removals of waterborne contaminants. This paper intends to provide a comprehensive review of functional CNT materials (f-CNT) and their existing and potential applications in membrane-based water treatment and desalination processes, with focuses on critical evaluation of advances, knowledge gaps and future research directions. CNT nanocomposite membranes have been studied at bench scale to efficiently remove a variety of waterborne contaminants and salts, while future improvement is under way with development in CNT functionalization techniques. The CNT-based membrane applications are found to possess a variety of advantages, including improve water permeability, high selectivity and antifouling capability. However, their applications at full scale are still limited by their high cost. Finally, we highlight that f-CNT membranes with promising removal efficiencies for respective contaminants be considered for commercialization and to achieve holistic performance for the purpose of water treatment and desalination.

Efficient removal of zinc from water and wastewater effluents by hydroxylated and carboxylated carbon nanotube membranes: Behaviors and mechanisms of dynamic filtration.

In this work, a bench scale study was designed to investigate the removal of zinc (Zn2+) and regeneration efficiencies of functionalized-MWCNT (f-MWCNT) membranes. The f-MWCNTs were incorporated into polyvinylchloride (PVC) hollow fiber membranes (HFMs), which acted as a substrate and a barrier for MWCNTs leaching to water. The results revealed that the removal capacity of Zn2+ through f-CNT membranes were above 98% for the synthetic water and over 70% for real wastewater effluents; predominantly involved surface complexation reaction. The acquired removal efficiency of CNT membrane is attributed to high absolute zeta potential followed by the hydrophilicity of the nanotubes coated the inside surface of HFMs and high concentration of oxygen functional groups on CNT surfaces. Later on, different regenerating solutions were used to desorb Zn2+ ions repeatedly from the inner surface of membranes and to recycle the CNT membranes for continuous removal of Zn2+ from water. The XPS analysis revealed that, Zn2+ ions were completely recovered owing to the ion exchange interactions. The results further confirmed that f-CNT membranes retained their original removal capacity after several successive cycles. Therefore, we recommend that, f-CNTs-based membranes have the potential to be used for large-scale removal and recovery of heavy metal ions from water or wastewater.