Integrated soil washing and bioreactor systems for the treatment of hexachlorocyclohexane contaminated soil: A review on enhanced degradation mechanisms, and factors affecting soil washing and bioreactor performances.

Investigations about the remediation of Hexachlorocyclohexane (HCH), a persistent organic pollutant of global concern, have been extensively reported to treat the HCH contaminated soil. The difficulty arising due to desorption and long ageing procedures of this hydrophobic organic compound in the soil, make it necessary to exploit techniques like soil washing or addition of surfactants, for enhancing the mass transfer rate of hydrophobic compounds. However, this technique gives rise to the generation of a large quantity of waste solution containing the pollutant and various other toxic substances. Moreover, it is challenging to deal with the complex soil washing solution, and thus a follow-up treatment of such washing solution is essentially required before its discharge. This follow-up treatment could be the bioreactor system to efficiently treat the pollutant in the wash solution, thereby reducing the amount of contaminated soil that has to be treated. Among many suggested remediation methods and treatment technologies, integrated soil washing and post-treatment with the bioreactor system could be an environmentally viable method for the remediation of HCH contaminated sites. This review focuses on the soil washing procedures applied so far for the HCH contaminated soil and various factors affecting the efficiency of separation of the target pollutant. Furthermore, the environmental and reactor design-related factors are also discussed for degradation of HCH in the reactor system. Finally, advantages and environmental feasibility of this proposed combined technology and the challenges that need to be encountered are envisaged.

Prevalence of Refractive Errors Among School-Going Children in Urban Versus Rural Areas.

BACKGROUND: The most common cause of visual impairment globally is refractive error. The prevalence of refractive error has been on the rise since the coronavirus disease 2019 (COVID-19) pandemic, possibly due to increased indoor activities and excessive use of electronic devices. Impaired vision during childhood can affect the overall development of a child adversely, and it often remains unreported due to the inability of children to complain about impaired vision. AIM: The main aim of this study was to assess the prevalence of refractive errors among school-going children in urban and rural areas. METHODS: This was a cross-sectional study that included 2024 children going to schools situated in urban and rural areas. All study subjects were tested for visual acuity for distance using Snellen's chart with and without glasses after taking a brief history regarding visual complaints. All children who had visual acuity less than 6/6 on Snellen's chart underwent refraction check-ups. Retinoscopy was performed in all study subjects. Analysis of the collected data was done using SPSS for Windows, Version 16.0 (Released 2007; SPSS Inc., Chicago, United States). The analysis of numerical data was done by an unpaired t-test, and the analysis of categorical data was done by a chi-square test. A P-value of less than 0.05 was considered statistically significant. RESULTS: The mean age of the children was 10.92 ± 2.73 years, with 10.93 ± 2.73 years in urban and 10.91 ± 2.73 years in rural groups. Females (n=1031; 50.93%) were more in number than males (n=993; 49.06%). The overall prevalence of refractive error was 17.43%. The prevalence was higher in urban areas (22.14%) than in rural areas (12.71%). The age group below 10 years comprised 886 (43.77%) study subjects, and 218 (62.1%) children with refractive error had no ocular complaints. The most common refractive error found in this study was simple myopia in both groups, and the least common was astigmatism. The prevalence of uncorrected refractive error was higher in urban school-going children as compared to rural children. CONCLUSION: The prevalence of refractive error was 17.43% in our study. The prevalence was high in urban areas (22.67%) as compared to rural areas (13.12%). Regular screening of school-going children for refractive errors should be done. Also, awareness regarding the use of electronic gadgets must be raised, especially among urban children.