Sorption mechanisms of zinc in different clay minerals and soil systems as influenced by various natural ligands

The bioavailability and fate of Zinc (Zn) in soils is influenced by reactions occurring at the water-mineral interface. Understanding Zn interaction with mineral surfaces is essential to the understanding of Zn fate and toxicity. In this study, adsorption experiments investigated the impact of ligands and pH on the adsorption of Zn to mineral surfaces. X-Ray Absorption Fine Structure Spectroscopy (XAFS) was used to elucidate the adsorption mechanisms of Zn to mineral surfaces as impacted by ligands. Impact of ligands on Zn adsorption was dependent on mineral type and pH of the system. XAFS analysis showed that adsorption mechanisms of Zn were impacted by pH and ligand presence. In the ferrihydrite system, Zn adsorption was enhanced in presence of citrate and phosphate (PO4), reduced in presence desferrioxamine (DFO-B), and reduced in presence of humic acid (HA) at pH\u3e6.0. XAFS analysis showed that Zn formed strong linkages with high affinity edge sites of ferrihydrite in the control and in presence of enhancing ligands (citrate and PO4), whereas formed weaker, low affinity linkages in presence of supressing ligands (DFO-B and HA). From an environmental perspective, Zn was more likely to be desorbed from the ferrihydrite surface in the presence HA and DFO-B. In the kaolinite system, Zn adsorption was reduced in presence of citrate and DFO-B, and increased in presence of HA. Zn formed inner sphere complexes at pH 5.5 in the control and in presence of ligands. At pH 7.5, a Zn-Al layered double hydroxide was formed in the control, that was absent in presence of any ligand, suggesting that ligands suppress the formation of Zn-Al LDH in kaolinite. In the mixed ferrihydrite-gibbsite system, Zn adsorption was enhanced in presence of all ligands, excluding DFO-B. Adsorption mechanisms of Zn to ferrihydrite were unaffected by ligand presence. The impact of organic matter (OM) degradation on heavy metal distribution in sewage sludge was investigated. Cu, Pb and As were bond with the OM fraction of sludge, whereas Zn was bond to Fe/Mn oxide fraction. OM degradation increased mobility and bioavailability of Zn and Cu, whereas it had less impact on Pb and As

Fate and Distribution of Heavy Metals in Wastewater Irrigated Calcareous Soils

Accumulation of heavy metals in Jordanian soils irrigated with treated wastewater threatens agricultural sustainability. This study was carried out to investigate the environmental fate of Zn, Ni, and Cd in calcareous soils irrigated with treated wastewater and to elucidate the impact of hydrous ferric oxide (HFO) amendment on metal redistribution among soil fractions. Results showed that sorption capacity for Zarqa River (ZR1) soil was higher than Wadi Dhuleil (WD1) soil for all metals. The order of sorption affinity for WD1 was in the decreasing order of Ni > Zn > Cd, consistent with electrostatic attraction and indication of weak association with soil constituents. Following metal addition, Zn and Ni were distributed among the carbonate and Fe/Mn oxide fractions, while Cd was distributed among the exchangeable and carbonate fractions in both soils. Amending soils with 3% HFO did not increase the concentration of metals associated with the Fe/Mn oxide fraction or impact metal redistribution. The study suggests that carbonates control the mobility and bioavailability of Zn, Ni, and Cd in these calcareous soils, even in presence of a strong adsorbent such as HFO. Thus, it can be inferred that in situ heavy metal remediation of these highly calcareous soils using iron oxide compounds could be ineffective

SARS-CoV-2 in the environment: Modes of transmission, early detection and potential role of pollutions

The coronavirus disease 2019 (COVID-19) is spreading globally having a profound effect on lives of millions of people, causing worldwide economic disruption. Curbing the spread of COVID-19 and future pandemics may be accomplished through understanding the environmental context of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and adoption of effective detection tools and mitigation policies. This article aims to examine the latest investigations on SARS-CoV-2 plausible environmental transmission modes, employment of wastewater surveillance for early detection of COVID-19, and elucidating the role of solid waste, water, and atmospheric quality on viral infectivity. Transmission of SARS-CoV-2 via faecal-oral or bio-aerosols lacks robust evidence and remains debatable. However, improper disinfection and defected plumbing systems in indoor environments such as hospitals and high-rise towers may facilitate the transport of virus-laden droplets of wastewater causing infection. Clinical and epidemiological studies are needed to present robust evidence that SARS-CoV-2 is transmissible via aerosols, though quantification of virus-laden aerosols at low concentrations presents a challenge. Wastewater surveillance of SARS-CoV-2 can be an effective tool in early detection of outbreak and determination of COVID-19 prevalence within a population, complementing clinical testing and providing decision makers guidance on restricting or relaxing movement. While poor air quality increases susceptibility to diseases, evidence for air pollution impact on COVID-19 infectivity is not available as infections are dynamically changing worldwide. Solid waste generated by households with infected individuals during the lockdown period may facilitate the spread of COVID-19 via fomite transmission route but has received little attention from the scientific community. Water bodies receiving raw sewage may pose risk of infection but this has not been investigated to date. Overall, our understanding of the environmental perspective of SARS-CoV-2 is imperative to detecting outbreak and predicting pandemic severity, allowing us to be equipped with the right tools to curb any future pandemic