Different photolysis kinetics at the surface of frozen freshwater vs. frozen salt solutions

Reactions at air-ice interfaces can proceed at very different rates than those in aqueous solution, due to the unique disordered region at the ice surface known as the quasi-liquid layer (QLL) . The physical and chemical nature of the surfacial region of ice is greatly affected by solutes such as sodium halide salts. In this work, we studied the effects of sodium chloride and sodium bromide on the photolysis kinetics of harmine, an aromatic organic compound, in aqueous solution and at the surface of frozen salt solutions above the eutectic temperature. In common with other aromatic organic compounds we have studied, harmine photolysis is much faster on ice surfaces than in aqueous solution, but the presence of NaCl or NaBr – which does not affect photolysis kinetics in solution – reduces the photolysis rate on ice. The rate decreases monotonically with increasing salt concentration; at the concentrations found in seawater, harmine photolysis at the surface of frozen salt solutions proceeds at the same rate as in aqueous solution. These results suggest that the brine excluded to the surfaces of frozen salt solutions is a true aqueous solution, and so it may be possible to use aqueous-phase kinetics to predict photolysis rates at sea ice surfaces. This is in marked contrast to the result at the surface of frozen freshwater samples, where reaction kinetics are often not well-described by aqueous-phase processes

Enabling tourism development through environmental consciousness: towards a theoretical model for Africa

Abstract not available

Different photolysis kinetics at the surface of frozen freshwater vs. frozen salt solutions

Reactions at air-ice interfaces can proceed at very different rates than those in aqueous solution, due to the unique disordered region at the ice surface known as the quasi-liquid layer (QLL). The physical and chemical nature of the surfacial region of ice is greatly affected by solutes such as sodium halide salts. In this work, we studied the effects of sodium chloride and sodium bromide on the photolysis kinetics of harmine, an aromatic organic compound, in aqueous solution and at the surface of frozen salt solutions above the eutectic temperature. In common with other aromatic organic compounds we have studied, harmine photolysis is much faster on ice surfaces than in aqueous solution, but the presence of NaCl or NaBr - which does not affect photolysis kinetics in solution - reduces the photolysis rate on ice. The rate decreases monotonically with increasing salt concentration; at the concentrations found in seawater, harmine photolysis at the surface of frozen salt solutions proceeds at the same rate as in aqueous solution. These results suggest that the brine excluded to the surfaces of frozen salt solutions is a true aqueous solution, and so it may be possible to use aqueous-phase kinetics to predict photolysis rates at sea ice surfaces. This is in marked contrast to the result at the surface of frozen freshwater samples, where reaction kinetics are often not well-described by aqueous-phase processes

Levels of tritium in soils and vegetation near Canadian nuclear facilities releasing tritium to the atmosphere: implications for environmental models

AbstractConcentrations of organically bound tritium (OBT) and tritiated water (HTO) were measured over two growing seasons in vegetation and soil samples obtained in the vicinity of four nuclear facilities and two background locations in Canada. At the background locations, with few exceptions, OBT concentrations were higher than HTO concentrations: OBT/HTO ratios in vegetation varied between 0.3 and 20 and values in soil varied between 2.7 and 15. In the vicinity of the four nuclear facilities OBT/HTO ratios in vegetation and soils deviated from the expected mean value of 0.7, which is used as a default value in environmental transfer models. Ratios of the OBT activity concentration in plants ([OBT]plant) to the OBT activity concentration in soils ([OBT]soil) appear to be a good indicator of the long-term behaviour of tritium in soil and vegetation. In general, OBT activity concentrations in soils were nearly equal to OBT activity concentrations in plants in the vicinity of the two nuclear power plants. [OBT]plant/[OBT]soil ratios considerably below unity observed at one nuclear processing facility represents historically higher levels of tritium in the environment. The results of our study reflect the dynamic nature of HTO retention and OBT formation in vegetation and soil during the growing season. Our data support the mounting evidence suggesting that some parameters used in environmental transfer models approved for regulatory assessments should be revisited to better account for the behavior of HTO and OBT in the environment and to ensure that modelled estimates (e.g., plant OBT) are appropriately conservative

Screening for cervical cancer among women in five countries in sub-saharan Africa: analysis of the role played by distance to health facility and socio-demographic factors

Abstract Background Cervical cancer significantly affects women in Sub-Saharan Africa (SSA). However, limited studies have concentrated on cervical screening behaviour among women in SSA. This study aimed to assess the interplay of distance to health facilities and socio-demographic factors with cervical screening behaviour among women in five SSA countries. Methods The study was based on pooled data of 40,555 women included in Demographic and Health Surveys (DHS) conducted between 2013 to 2021. Proportions and logistic regression models were used in assessing the interplay of distance to health facilities and socio-demographic factors with cervical screening behaviour. Results Approximately, 7.9% of women that saw the distance to a health facility as a big problem, tested for cervical cancer compared to 13.5% who indicated that distance to a health facility is not a big problem. More women in urban areas, with a higher level of education, of richest wealth index, aged 40–44 years and using contraceptives who also indicated that distance to a health facility was a big problem tested for cervical cancer compared to those in rural areas with no education, of poorest wealth index, aged 15–19 years and not using contraceptives. Education, age, contraceptive use, frequent exposure to mass media and Sexual Transmitted Infections (STI) had a significant relationship with testing for cervical cancer. Conclusion The prevalence of cervical cancer screening was low in the five SSA countries largely due to distance barriers and was also significantly influenced by education, age, contraceptive use, frequent exposure to mass media, and STI status. To improve the screening for cervical cancer and its associated benefits in the five SSA countries, there is a need for policymakers, clinicians and public health workers to channel more commitment and efforts to addressing the barriers identified in this study