Objective: To understand the pubertal development of primary and secondary school students in urban and rural areas of the Inner Mongolia Autonomous Region in 2021, so as to provide clues for further clarification of the health hazards of early pubertal initiation. Methods: From October to November 2021, primary and secondary school students in 12 provinces and cities of Inner Mongolia were selected by stratified cluster random sampling, including 21 662 girls who had reached menarche and 10 600 boys who had their first seminal emission, as well as 46 183 girls who had not reached menarche and 78 995 boys who had not experienced their first seminal emission. The height and weight of the primary and secondary school students were measured, and the time of first seminal emission or menarche was recorded. The study used the Mann-Whitney U test to analyze the differences between urban and rural students, Spearmans rank correlation to analyze the correlation between overweight and obesity and the age of pubertal initiation, and the Logistic regression model to analyze the correlation between pubertal initiation and age of pubertal initiation. Results: The age of menarche for urban girls [(12.31±1.29) years old] was earlier than that of suburban girls [(12.43±1.24) years old], and the age of first spermatozoa for urban boys [(13.85±1.20) years old] was statistically significant compared with that of suburban boys [(13.79±1.36) years old] (t=12.76, 10.58, P<0.05). There was a negative correlation between the age of menarche and overweight/obesity among girls aged 10-14 years (r=-0.169, P<0.05), and there was no statistically significant correlation between the age of spermarche and overweight/obesity in boys aged 5-9, 10-14, and 15-20 years (r=0.122, -0.022, -0.004, P>0.05). The occurrence of menarche in overweight girls was 1.06(95%CI=1.01-1.11) times higher than that in the normal group, and 1.13(95%CI=1.06-1.20) times higher among obese girls than normalweight girls. Compared to urban areas, primary and secondary school students in suburban counties observed the onset of puberty later [OR=0.88(95%CI=0.85-0.91) for menarche, OR=0.94(95%CI=0.89-0.99) for first spermatozoa] (P<0.05). Conclusions Obesity during childhood and adolescence is associated with earlier onset of puberty among female students in Inner Mongolia, and later onset of puberty among primary and secondary school students in suburban counties compared with those in urban areas.

Background The safety of drinking water is closely related to people's health. In recent years, relevant studies have identified some health related problems with drinking water in Inner Mongolia Autonomous Region. The complex and diverse natural environment embraced by the vast jurisdiction of the region may lead to uneven drinking water quality across the region. Objective To evaluate eight chemicals including arsenic, cadmium, chromium (hexavalent), lead, mercury, fluoride, trichloromethane, and carbon tetrachloride in urban drinking water in Inner Mongolia Autonomous Region in 2021, and to provide reference for optimizing urban water supply system and ideas for further developing strategies to promote population health. Methods A total of 1228 monitoring sites were set up in urban areas of Inner Mongolia, and water samples were collected once in dry season (May) and once in wet season (August−September). Eight chemicals of interest in drinking water were detected according to the Standard examination methods for drinking water, and assessed for health risks using the health risk assessment model recommended by the United States Environmental Protection Agency (USEPA) and following the Technical guide for environmental health risk assessment of chemical exposure. Mann-Whitney U test was used to compare the concentrations of eight chemicals in urban drinking water by water seasons and water sample types. Results In 2021, a total of 2381 samples of urban drinking water were tested in the Inner Mongolia Autonomous Region, including 1195 samples in wet season and 1186 samples in dry season; 389 samples of finished water and 1992 samples of tap water. The positive rates of arsenic and fluoride were 26.25% and 96.77%, respectively. The positive rates of cadmium, chromium (hexavalent), lead, mercury, trichloromethane, and carbon tetrachloride were 6.22%, 16.63%, 6.09%, 16.67%, 18.98%, and 8.36%, respectively. The exceeding standard rate of fluoride was 4.87%. Trichloromethane and carbon tetrachloride were qualified in all samples. There were statistical differences in the concentrations of arsenic, cadmium, chromium (hexavalent), lead, and carbon tetrachloride in urban drinking water between water seasons (Z=−3.847, P<0.05; Z=2.464, P=0.014; Z=−3.129, P=0.002; Z=4.341, P<0.05; Z=4.342, P<0.05). Only fluoride concentration was found statistically different among different water sample types (Z=−2.287, P=0.022). The non-carcinogenic risks of ingestion and dermal exposure to each chemical in drinking water by water seasons and water sample types were all less than 1, but the P₉₅ total non-carcinogenic risks of oral exposure were greater than 1. The P₉₅ carcinogenic risks of oral exposure to some chemicals in drinking water by water seasons and water sample types were>10⁻⁴, which suggested carcinogenic risks, while the carcinogenic risks of dermal explore to chemicals were all less than 10⁻⁶. Conclusion In 2021, urban drinking water in Inner Mongolia Autonomous Region is generally safe, but arsenic, cadmium, chromium (hexavalent), lead, mercury, and fluoride still exceed the national limits, posing certain health risks.