Abstract:
Background
Air pollutants PM2.5 and its adsorbed metal elements are important factors affecting public health.
Objective
To explore the distribution characteristics and sources of metal elements in atmospheric PM2.5 in Lanzhou from 2019 to 2020, and to assess the health risks of metal elements to different groups of residents through inhalation.
Methods
From January 2019 to December 2020 in two districts of Lanzhou City (Chengguan District and Xigu District), regular PM2.5 and metal elements antimony (Sb), aluminum (Al), arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), manganese (Mn), nickel (Ni), selenium (Se), and thallium (Tl) were regularly monitored, and their concentrations were described by the median (M) and 25th and 75th percentiles (P25, P75) as not following a normal distribution (because the detection rates of the five elements Be, Cr, Hg, Ni, and Se were less than 70%, the five elements were not included in subsequent analysis), and then compared with the secondary concentration limits in the Ambient Air Quality Standards (GB 3095-2012). The differences between the medians of the two groups were compared by the Mann-Whitney U rank sum test, and the differences among the medians of multiple groups were compared by the Kruskal-Wallis H rank sum test; the enrichment factor (EF) method and principal component analysis were used to evaluate the pollution degree of the metals and their sources; the health risks of five non-carcinogenic metals (Sb, Al, Pb, Mn, and Tl) and two carcinogenic metals (As and Cd) in PM2.5 were evaluated by hazard index (HI) and hazard quotient (HQ) using the incremental lifetime cancer risk (LCR) model and the non-carcinogenic risk assessment model, respectively.
Results
The PM2.5 concentrations M (P25, P75) in Lanzhou City were 38.50 (26.00, 65.00) and 41.00 (29.00, 63.10) μg·m−3 in 2019 and 2020, respectively, and the difference was not statistically significant (Z=−0.989,P > 0.05). The average levels of the metal elements from high to low were: Al > Pb > Mn > As > Cd > Sb > Tl, and the annual average concentration of each metal element in 2019 was higher than that in 2020 ( P<0.05). TheM ( P25, P75) of PM2.5 concentrations in Chengguan and Xigu districts were 52.98 (17.00, 61.00) and 55.40 (17.00, 67.00) μg·m−3, respectively, with no statistically significant differences (P<0.05); the concentrations of Sb and Al in Chengguan District were lower than those in Xigu District (P<0.05), and the concentrations of other metal elements were not different between the two areas (P>0.05). There were seasonal differences in the concentrations of PM2.5 and seven metal elements in Lanzhou City (except PAl=0.007, the other Ps < 0.001). The results of the enrichment factor method showed that the EF values of the six metals (Sb, Al, As, Cd, Pb and Tl) were all greater than 1. Among them, except As, the EF values of other metal elements were all greater than 10, and the EF values of Al and Cd were both greater than 100. The results of principal component analysis showed that the variance contributions of the three principal components were 45.61%, 24.22%, and 14.42%, and the cumulative contribution reached 84.25%. The principal component 1 included Pb, As, Cd, and Sb, the principal component 2 included Al and Mn, and the principal component 3 contained Tl. The non-carcinogenic risks of the five metals were, in descending order, Al > Mn > Pb > Tl > Sb, among which the HQ values of the remaining four metals were less than 1 for adults and children, except the HQ value of Al for adults, which was greater than 1. The ILC values of carcinogenic metal As for adult males, adult females, and children were 2.68×10 −5, 2.51×10−5, and 1.45×10−5, respectively; the ILC values of carcinogenic metal Cd for adult males, adult females, and children were 1.53×10−6, 1.43×10−6, and 8.26×10−7, respectively.
Conclusion
There is pollution of atmospheric PM2.5 and its adsorbed metal elements in Lanzhou. As and Cd elements may pose potential carcinogenic risks to the residents.
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