Assessing water quality and human health risk near coal mines and industrial area of Singrauli, India: special emphasis on toxic elements.

Water contamination is a major environmental issue, especially in rapidly growing industrialized areas like Singrauli. This study addresses research gaps regarding the hydrochemical characterization, health risk assessment, and source identification of contaminants. Hydrochemistry shows the concentrations of Na+, Ca2+, F-, Mn, As, Mo, Sr, and Ni were above the permissible limit for drinking usage. Water quality index (WQI), heavy metal pollution (HMPI), and evaluation indices (HMEI) revealed As, Mn, Cd, Mo, Co, and Ni were the key heavy elements contributing towards aqueous media pollution in the Singrauli area. Additionally, F was also considered one of the major contaminants. In health risk assessment, the higher values of hazard quotient (HQ) for non-carcinogens were associated with Mn, As, Mo, and F; and hazard index (HI) values > 1 were found in 70% and 55% of samples for children and adults, respectively. Carcinogenic risk (CR) for human health was associated with As. CR values in 56.7% (for adults) and 61.7% (for children) of the total samples exceeded 1 × 10-4. Monte Carlo simulation was applied and highlighted the significant risk factors responsible for both carcinogenic and non-carcinogenic health impacts. 19.2%, 7.3%, and 6.9% of the simulated HQ values for adults and 30.1%, 16.9%, and 10.6% for children were above the safe limit for F, As, and Mn, respectively. Additionally, only 43.8% and 24.8% of the simulated HI for adults and children were within the safe limit. Irrespective of age groups, all the simulated values of As in CR were above 1 × 10-6; and 60% (for adults) and 77.1% (for children) of the values were above 1 × 10-4. This outcome emphasizes the urgency of pollution control measures, especially for As, F, and Mn, to safeguard public health. Moreover, a multivariate statistical approach revealed that both geogenic and anthropogenic sources were responsible for contamination. Therefore, regular monitoring, filtration, and purification are mandatory to ensure safe drinking water for human consumption.

Influence of interflow carbonate-clay association for groundwater fluoride contamination in eastern Deccan, central India.

In central India, fluoride contamination in deeper basaltic aquifer is geogenic. This study demonstrates the source of fluorine enrichment in aquifer matrix and its release mechanism into groundwater. Magmatic-hydrothermal residual melt, i.e., albitic-calcic-amphibole-apatite-rich intrusive rock is the main source of fluorine enrichment. The association of this rock with interflow carbonate-clay assemblage played a significant role for fluoride contamination. Fluorine-enriched residual melt interacted with interflow carbonate-clay association, and this interaction metasomatized the carbonates and enhanced fluorine concentration in sediments. Bulk fluorine concentration of 988 ppm is measured in the soil developed over the association of intrusive rock and carbonate-clay assemblage. X-ray diffraction and electron-probe micro analysis confirmed the presence of fluorine-bearing and/or containing minerals, i.e., fluorite, fluorapatite, and palygorskite. The presence of bicarbonate and Na+ (from albitic feldspar) in alkaline water enhanced desorption of fluoride from clays, and dissociation from fluorapatite and fluorite from carbonate-clay assemblage, which released fluoride from aquifer matrix to groundwater. Clay horizon acts as an impervious cap on the deeper aquifer and increases the residence time of groundwater. In such favorable physico-chemical condition, fluoride released from aquifer matrix to groundwater and gradually increasing the degree of fluoride contamination.

Rayleigh-Bénard magnetoconvection with temperature modulation.

Floquet analysis of modulated magnetoconvection in Rayleigh-Bénard geometry is performed. A sinusoidally varying temperature is imposed on the lower plate. As Rayleigh number Ra is increased above a critical value Rao, the oscillatory magnetoconvection begins. The flow at the onset of magnetoconvection may oscillate either subhar- monically or harmonically with the external modulation. The critical Rayleigh number Rao varies non-monotonically with the modulation frequency ω for appreciable value of the modulation amplitude a. The temperature modulation may either postpone or prepone the appearance of magnetoconvection. The magnetoconvective flow always oscillates harmonically at larger values of ω. The threshold Rao and the corresponding wavenumber k o approach to their values for the stationary magnetoconvection in the absence of modulation (a = 0), as ω → ∞. Two different zones of harmonic instability merge to form a single instability zone with two local minima for higher values of Chandrasekhar's number Q, which is qualitatively new. We have also observed a new type of bicritical point, which involves two different sets of harmonic oscillations. The effects of variation of Q and Pr on the threshold Rao and critical wavenumber k o are also investigated.