Objective　To explore the characteristics of toxic heavy metal pollution in atmospheric PM2.5 (Particulate matter 2.5) during winter in Nanning City and to evaluate the health risks for the population. Methods　Atmospheric PM2.5 samples were continuously collected in the urban areas of Nanning from January to February 2019. The concentrations of seven toxic heavy metals, including cadmium (Cd), arsenic (As), chromium (Cr), lead (Pb), nickel (Ni), mercury (Hg), and manganese (Mn) in atmospheric PM2.5 were analyzed by X-ray fluorescence spectrometry. The pollution characteristics of toxic heavy metals were studied by geo-accumulation index and enrichment factor methods, and their health risks to children and adults were assessed using the health risk assessment model of the United States Environmental Protection Agency. Results　The mass concentration of atmospheric PM2.5 in Nanning in winter 2019 was (44±29) μg/m3, which was generally at a low level. Different degrees of pollution were found for Hg, Cd, As, Cr, and Pb in PM2.5, with Hg and Cd being more seriously polluted. Hg and Cd were highly enriched in PM2.5, followed by Pb with moderate enrichment. These three elements mainly originated from man-made pollution. As, Cr and Ni were mildly enriched and affected by both natural and anthropogenic sources. The non-carcinogenic risks were in the order of As>Pb>Hg>Cr>Cd>Mn>Ni. The total non-carcinogenic risks for the three populations were all less than 1, which is within acceptable limits. The carcinogenic risks were ranked as Cr>As>Cd>Ni, with Cr, As, and Cd posing carcinogenic risks to children and adults ranging from 1×10-6 to 1×10-4. Moreover, the total carcinogenic risks of heavy metals (Cr, As, Cd, and Ni) were higher than 1×10-4 for children, indicating a potential carcinogenic risk. Conclusions　The mass concentration of PM2.5 and heavy metal elements in Nanning City during the winter of 2019 was relatively low, but the pollution of heavy metals still exists. The non-carcinogenic risk of heavy metals is within an acceptable range, but the carcinogenic risk poses a potential danger to children.

Objective: To analyse the influence path of family economic status on adolescent depressive symptoms, and to explore the chained mediation role of peer relationship and self satisfaction, as well as the moderating effect of the parent-child relationship, so as to provide a theoretical basis for the prevention and control of adolescent depressive symptoms. Methods: Data were obtained from the Database of Youth Health （DYH） in the National Population Health Science Data Center, and a total of 11 277 samples were included. Questionnaires were used to obtain information on family economic status, peer relationship, self satisfaction, parent-child relationship and depressive symptoms. Spearman correlation analysis was used to examine correlations among variables. Hierarchical linear regression analysis was used to analyze effects of family economic status and parent-child relationship on depressive symptom scores. The Process macro program was adopted to test the chained mediating effects of peer relationship and self satisfaction and the moderating effect of parent-child relationship. Results: The prevalence rate of depressive symptoms among adolescents was 24.2%. The prevalence rates of depressive symptoms significantly differed among adolescents with different family economic status and places of residence( χ 2=210.12, 4.18, both P ＜0.05). Adolescents with depressive symptoms had significantly lower scores on peer relationship, self satisfaction, and parent-child relationship compared to those without depressive symptoms ( t = 27.76 , 42.43, 31.12, all P ＜0.05). Family economic status were negatively correlated with adolescent depressive symptom scores ( B =-0.12, P <0.05).Parent-child relationship was negatively correlated with depressive symptom scores ( B = -0.02 , P < 0.05 ). After introducing the parent-child relationship, the negative effect of family economic conditions was reduced ( B = -0.08, P ＜ 0.01). Family economic conditions affected depressive symptoms through the chained mediating pathway involving peer relationship ( B = 2.07 ) and self satisfaction ( B =3.88)(both P <0.05). The parent-child relationship moderated this pathway: under conditions of high quality parent child relationship, the effect of family economic status on peer relationships was weaker ( B = 0.15); under low quality parent-child relationship, the positive effect of family economic status on peer relationships was enhanced ( B = 1.15 ) (both P ＜0.01). Conclusions Family economic status exert both direct and chain mediating effects on adolescent depression, and high quality parent-child relationship can play a protective moderation role. For economically disadvantaged families, it is critical to synergistically enhance parent-child relationship and social support in order to reduce depression risk among adolescents.