Groundwater fluoride and nitrate contamination and associated human health risk assessment in South Punjab, Pakistan.

Consumption of high fluoride (F-) and nitrate (NO3-) containing water may pose serious health hazards. One hundred sixty-one groundwater samples were collected from drinking wells in Khushab district, Punjab Province, Pakistan, to determine the causes of elevated F- and NO3- concentrations, and to estimate the human health risks posed by groundwater contamination. The results showed pH of the groundwater samples ranged from slightly neutral to alkaline, and Na+ and HCO3- ions dominated the groundwater. Piper diagram and bivariate plots indicated that the key factors regulating groundwater hydrochemistry were weathering of silicates, dissolution of evaporates, evaporation, cation exchange, and anthropogenic activities. The F- content of groundwater ranged from 0.06 to 7.9 mg/L, and 25.46% of groundwater samples contained high-level fluoride concentration (F- > 1.5 mg/L), which exceeds the (WHO Guidelines for drinking-water quality: incorporating the first and second addenda, WHO, Geneva, 2022) guidelines of drinking-water quality. Inverse geochemical modeling indicates that weathering and dissolution of fluoride-rich minerals were the primary causes of F- in groundwater. High F- can be attributed to low concentration of calcium-containing minerals along the flow path. The concentrations of NO3- in groundwater varied from 0.1 to 70 mg/L; some samples are slightly exceeding the (WHO Guidelines for drinking-water quality: incorporating the first and second addenda, WHO, Geneva, 2022) guidelines for drinking-water quality. Elevated NO3- content was attributed to the anthropogenic activities revealed by PCA analysis. The high levels of nitrates found in the study region are a result of various human-caused factors, including leaks from septic systems, the use of nitrogen-rich fertilizers, and waste from households, farming operations, and livestock. The hazard quotient (HQ) and total hazard index (THI) of F- and NO3- showed high non-carcinogenic risk (> 1) via groundwater consumption, demonstrating a high potential risk to the local population. This study is significant because it is the most comprehensive examination of water quality, groundwater hydrogeochemistry, and health risk assessment in the Khushab district to date, and it will serve as a baseline for future studies. Some sustainable measures are urgent to reduce the F- and NO3- content in the groundwater.

Arsenic in a groundwater environment in Bangladesh: Occurrence and mobilization.

Groundwater with an excessive level of Arsenic (As) is a threat to human health. In Bangladesh, out of 64 districts, the groundwater of 50 and 59 districts contains As exceeding the Bangladesh (50 µg/L) and WHO (10 µg/L) standards for potable water. This review focuses on the occurrence, origin, plausible sources, and mobilization mechanisms of As in the groundwater of Bangladesh to better understand its environmental as well as public health consequences. High As concentrations mainly was mainly occur from the natural origin of the Himalayan orogenic tract. Consequently, sedimentary processes transport the As-loaded sediments from the orogenic tract to the marginal foreland of Bangladesh, and under the favorable biogeochemical circumstances, As is discharged from the sediment to the groundwater. Rock weathering, regular floods, volcanic movement, deposition of hydrochemical ore, and leaching of geological formations in the Himalayan range cause As occurrence in the groundwater of Bangladesh. Redox and desorption processes along with microbe-related reduction are the key geochemical processes for As enrichment. Under reducing conditions, both reductive dissolution of Fe-oxides and desorption of As are the root causes of As mobilization. A medium alkaline and reductive environment, resulting from biochemical reactions, is the major factor mobilizing As in groundwater. An elevated pH value along with decoupling of As and HCO3- plays a vital role in mobilizing As. The As mobilization process is related to the reductive solution of metal oxides as well as hydroxides that exists in sporadic sediments in Bangladesh. Other mechanisms, such as pyrite oxidation, redox cycling, and competitive ion exchange processes, are also postulated as probable mechanisms of As mobilization. The reductive dissolution of MnOOH adds dissolved As and redox-sensitive components such as SO42- and oxidized pyrite, which act as the major mechanisms to mobilize As. The reductive suspension of Mn(IV)-oxyhydroxides has also accelerated the As mobilization process in the groundwater of Bangladesh. Infiltration from the irrigation return flow and surface-wash water are also potential factors to remobilize As. Over-exploitation of groundwater and the competitive ion exchange process are also responsible for releasing As into the aquifers of Bangladesh.

Enhanced visible light photocatalytic degradation of dyes in aqueous solution activated by HKUST-1: performance and mechanism.

HKUST-1 is a copper-based metal-organic framework (MOF) and potential photocatalyst, but minimal research has addressed the performance and mechanism of HKUST-1 in the visible light photocatalytic degradation of dyes. In the present work, HKUST-1 was applied as a photocatalyst to activate peroxomonosulfate (PMS) under visible light (Vis) for dye removal in aqueous solution. The results showed that the removal efficiency of two cationic dyes [rhodamine B (RhB) and methylene blue (MB)] was greater than 95% within 120 min. Free radicals such as SO4 -˙, ·OH were present in the degradation process, with SO4 -˙ playing a dominant role. Zeta potential, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy data were used to investigate the degradation mechanism. In the degradation process, surface charge attraction between HKUST-1 and cationic dyes promotes removal efficiency, with the degradation efficiency of cationic dyes (MB and RhB) more than 50% higher than for anionic dyes [acid orange 7 (AO7) and methyl red (MR)]. On the other hand, HKUST-1 has been proved to activate PMS by conducting photoelectrons, which accelerated the degradation of dyes. Compared with the reaction conditions of PMS/Vis, when the HKUST-1 was present (HKUST-1/PMS/Vis), the degradation rates of MB and RhB increased by 62.7 and 63.2%, respectively.

High arsenic contamination and presence of other trace metals in drinking water of Kushtia district, Bangladesh.

Drinking water with excessive concentration levels of arsenic (As) is a great threat to human health. A hydrochemical approach was employed in 50 drinking water samples (collected from Kushtia district, Bangladesh) to examine the occurrence of geogenic As and the presence of trace metals (TMs), as well as the factors controlling As release in aquifers. The results reveal that the drinking water of shallow aquifers is highly contaminated by As (6.05-590.7 µg/L); 82% of samples were found to exceed the WHO recommended limit (10 µg/L) for potable water, but the concentrations of Si, B, Mn, Sr, Se, Ba, Fe, Cd, Pb, F, U, Ni, Li, and Cr were within safe limits. The Ca-HCO3-type drinking water was identified as having high contents of As, pH and HCO3-, a medium-high content EC, and low concentrations of NO3-, SO42-, K+, and Cl-. The significant correlation between As and NO3- indicates that NO3- might be attributed to the use of phosphate fertilizers and a factor responsible for enhancing As in aquifers. The study also reports that the occurrence of high As and the presence of TMs in drinking water may be a result of local anthropogenic activities, such as irrigation, intensive land use and the application of agrochemicals. The insignificant correlation between As and SO42- demonstrated that As is released from SO42- minerals under reducing conditions. An elevated pH value along with decoupling of As and HCO3- plays a vital role in mobilizing As to aquifer systems. Moreover, the positive relationship between As and Si indicated that As is transported in the biogeochemical environment. The reductive suspension of Mn(IV)-oxyhydroxides also accelerated the As mobilization process. Over exploitation of tube-well water and the competitive ion exchange process are also responsible for the release of As in aquifers.

Distribution and hydrogeochemical behavior of arsenic enriched groundwater in the sedimentary aquifer comparison between Datong Basin (China) and Kushtia District (Bangladesh).

A prompt growth in research on arsenic occurrence and behavior in the environment has occurred over the last decade or so. High arsenic (As) in groundwater has become a major global concern due to its widespread occurrence. A comparative hydrogeochemical study was performed on the occurrence of high As groundwater in Datong Basin, China, and Kushtia District, Bangladesh. A total of 132 groundwater samples (83 from Datong Basin and 49 from Kushtia District) were collected to analyze the major hydrogeochemical components and trace elements in groundwater of both areas. Factor analysis (FA) was applied on the hydrochemical data to identify the major hydrogeochemical processes in sedimentary aquifers. High As groundwater was observed in the low-lying central parts of Datong Basin, which are composed of the Holocene alluvial and lacustrine aquifers. The elevated As concentrations ranged from 0.31 to 452 µg/L and distributed in depths between 20 and 45 m. As-enriched groundwater is mainly Na-HCO3 type water and characterized by higher pH value, high Na+, low Ca2+, SO42-, and NO3- along with moderate TDS. The alkaline and reducing subsurface environment facilitate the leaching of As in sedimentary aquifers. The release and distribution of As in aquifers are resulted from the reduction of As-carrying crystalline iron (Fe) oxide/hydroxides and oxidation of organic matter. The aquifers of Kushtia District, Bangladesh, are unconsolidated, alluvial in nature, and developed from Holocene floodplain and Pleistocene deposits. High As (6.04-590.7 µg/L) groundwater occurs mainly in shallow aquifers. The Ca-HCO3 type groundwater is distinguished by circum-neutral pH, medium-high EC, high HCO3-, and low content of NO3-, SO42-, K+, and Cl-. The reductive suspension of MnOOH increases the dissolved As loads and redox responsive elements such as SO42- and pyrite oxidation act as the main mechanisms for As release in groundwater. As is mobilized by anaerobic leakage from the brown-clay and gray-sand into the sediment. Infiltration from irrigation return and surface wash water are the potential factors that remobilize As. The weak loading of Fe suggests that the release of Fe and As is decoupled in sedimentary aquifers of Kushtia District.