Background A number of studies have shown that heavy metals in atmospheric PM_2.5 have impacts on human health, while studies on the impact of long-term and low-concentration exposure to lead in PM_2.5 on human health are limited.

Objective To investigate the pollution characteristics of lead in ambient PM_2.5 and assess its chronic health risks.

Methods Daily PM_2.5 concentration data in Jinan from 2014 to 2019 were collected, and the year-by-year trend of PM_2.5 concentration was analyzed. Licheng District (an industrial area) and Shizhong District (a residential area) were elected to install an ambient PM_2.5 monitoring stationrespectively. The sampling instrument was a 100 L·min⁻¹ high-flow PM_2.5 sampler, with a cumulative sampling time of 20-24 h per day, using a quartz fiber filter membrane for lead detection and a glass fiber filter membrane for PM_2.5 determination. The sampling frequency was 7 consecutive days per month from the 10^th to the 16^th (A total of 493 d were sampled and some were missing; 172 d during the heating period and 321 d during the non-heating period). Two PM_2.5 samples were collected in one monitoring site each day. A total of 986 samples were collected in one monitoring site. The lead content in PM_2.5 samples was detected by inductively coupled plasma mass spectrometry. The concentration of PM_2.5 was measured by weighing method. The annual average concentration and enrichment factor of lead in PM_2.5, the change trend of lead content per unit mass of PM_2.5, and the difference between heating period and non-heating period from 2014 to 2019 were estimated. Technical guide for environment health risk assessment of chemical exposure (WS/T 777-2021) was used to assess the health risks of exposure to lead in PM_2.5.

Results The average annual concentration of lead in PM_2.5 ranged from 23.2 ng·m⁻³ to 154.7 ng·m⁻³. The average concentration in heating period from 2015 to 2019 was higher than that in non-heating period, and the differences in 2015, 2017, and 2019 were statistically significant (P < 0.01 or 0.001). The enrichment factors ranged from 200 to 1342 in 2014 to 2019. The average enrichment factors in heating period in 2015, 2017, and 2018 was higher than those in non-heating period, and the difference was statistically significant (P < 0.05 or 0.001). The lead contents per unit mass of PM_2.5 ranged from 493 ng·mg⁻¹ to 1944 ng·mg⁻¹, and the differences between heating period and non-heating period in 2014, 2017, and 2018 were statistically significant (P < 0.05 or 0.001). The average annual concentration and enrichment factor of lead in PM_2.5 showed a downward trend, and thus the lead content per unit mass of PM_2.5 also decreased. From 2014 to 2019, the carcinogenic risk of lead in PM_2.5 in Jinan ranged from 1.69×10⁻⁸ to 2.45×10⁻⁶, showing a significant downward trend year by year, and the 95^th percentile decreased by 3%-46% from the previous year. The carcinogenic risk level of lead was reduced to an acceptable level (<1×10⁻⁶) after 2017.

Conclusion From 2015 to 2019, lead concentration and enrichment factor in PM_2.5 increase during heating period compared with non-heating period, but it is not completely consistent of lead content in PM_2.5 per unit mass. From 2014 to 2016, exposure to lead in PM_2.5 may elevate carcinogenic risk to human. After 2017, the carcinogenic risks of exposure to lead in PM_2.5 are at an acceptable level.