Introduction: The problem related to water pollution of nitrates and nitrites is both an issue in Iran and also most parts of the world. Studies to evaluate the acute and chronic effects of nitrate and nitrite have demonstrated that different concentrations of these compounds in water and food have been causing multiple diseases. Methods: In this paper, researchers reviewed published articles and research from 1950 to 2016 in English and Farsi, according to key words "nitrate", "nitrite", "water", "food" and "health effects", retrieved from databases, such as Medline, Scopus, Pub Med, and scientific information database (SID). Results: Consumption of drinking water and food containing high concentrations of nitrate and nitrite could cause diseases, such as cancer, methemoglobinemia, and enlargement of the thyroid gland and diabetes mellitus. The positive effects of low concentrations of nitrates and nitrites include a protective effect on the cardiovascular system, regulatory role in blood pressure, and homeostasis (also static) of the vessels Conclusions: As different concentrations of nitrates and nitrites have beneficial and undesirable effects on human health and regarding the high cost of treating water contaminated with nitrite and nitrate, more investigations should be done in setting the standards and levels of parameters used in drinking water.

Background. Regarding the lack of comprehensive systematic review on the efficacy of water fluoridation and prevalence of dental fluorosis, the aim of the current research was to systematically study the prevalence of dental fluorosis at different levels of water fluoride in the world and lay emphasis on the amount of fluoride in drinking water.Methods. Studies were searched in PubMed, Scopus, SID, and IranMedex, with regard to inclusion criteria. Study validity was assessed with some checklists, and analyses were performed to ascertain the prevalence of dental fluorosis among individuals categorized in age groups.Results. Investigation of the heterogeneity and analysis of the subgroups revealed that in the 6-18 year age group, when water fluoride level was less than 0.7 ppm and there was exposure to water fluoride in the first 6-8 years of life, no significant heterogeneity was detected among the studies in this subgroup. Thus, the pooled estimation of dental fluorosis prevalence in this subgroup was 12.9% (95% CI: 7.5-18.3%). Furthermore, meta-regression indicated that the exposure time to fluoride in drinking water, or exposure to fluoride in supplements, diets, air, etc as well as the quality of studies had a significant relation to the difference in the prevalence of dental fluorosis.Conclusion. The results revealed no heterogeneity in just 2 subgroups, and the results of subgroups could be pooled in them. Furthermore, the number of studies included in this review considerably decreased by considering all the detected confounding factors, whereas other similar systematic reviews mentioned at most 2 factors.

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Dam construction is one of the most popular solutions for managing water resources. In recent years, changes in patterns of regional seismicity associated with large impoundment dams have raised concerns among environmentalists. In this study, five large dams located in Iran were studied from this perspective. The Gutenberg-Richter, linear regression and T-test were used to examine the seismic changes in the radius of 100 km of each of the dams during a twenty-five-year period before and after the construction of the dams. The results revealed that the seismicity level and relative density of large and small earthquakes in three of these dams have increased after dam construction. A significant difference between the magnitude of earthquakes, as well as the number of earthquakes before and after the construction of dams in the region, was recognized. However, the results of the T-test statistical analysis indicated that the mean depth of the earthquakes and their distance from the dams before and after construction have not changed significantly. Overall, these results indicated that the construction of large impoundment dams has been associated with some changes in patterns of regional seismicity. The findings would guide researchers to further investigate the type of impacts that dam construction may have on seismicity patterns.