Study Of Fractions And Bioavailability Of Heavy Metals In Particulate Matters In A City Whose Energy Consumption Dominated By Coal

In recent years,haze pollution has been serious in Beijing-Tianjin-Hebei region.Heavy metals(HMs)and arsenic(As)can be easily enriched in atmospheric particulate matters(PMs),they are toxic component in particles,making inhalation an important exposure route to HMs and As.The toxicity of HMs depends not only on total concentration,but also on fraction and bioavailability,which makes it meaningful to research their fraction and bioavailability.The Beijing-Tianjin-Hebei region has suffered serious haze pollution,the Baoding Government has launched a series of pollution control measures such as"coal restriction",and it is urgent to evaluate the actual effects of these measures.The composition of PMs and the fraction of HMs are closely related to their sources.Due to the differences of pollution sources in different seasons and different functional areas,the HMs in PMs may be different.In addition,PMs with different particle sizes have different adsorption capacities for HMs and different health risk to people,which will also cause differences in the fraction distribution of HMs in PMs with different sizes.In this study,PMs collected in different seasons,different functional areas,before and after coal limitation and PMs with different particle size in Baoding city were studied.The total concentrations of PMs,morphological feature,and total contents of As and HMs in PMs samples were investigated.Fractions of As and HMs in the PMs samples were extracted and analyzed using sequential extraction methods.Since Pb,Cd,Cr,Cu and Zn mainly exist as cations in the environment,the BCR sequential extraction method is suitable to extract different fractions of them from solid environmental samples.However,the BCR method is no longer applicable to metalloid such as As,which mostly exist as oxyanions.Therefore,we applied a five-step sequential extraction method for As.The BCR sequential extraction procedure divided HMs in PMs into four fractions:acid-soluble fraction(F1),reducible fraction(F2),oxidative fraction(F3)and residual fraction(F4).Arsenic in PMs was discriminated into five fractions using a five-step sequential extraction method:non-specifically sorbed fraction(F1),specifically-sorbed fraction(F2),amorphous and poorly-crystalline hydrous oxides of Fe and Al fraction(F3),well-crystallized hydrous oxides of Fe and Al fraction(F4)and residual fraction(F5).In the process of sequential extraction step by step,the bioavailability of HMs gradually decreases.Furthermore,in vitro tests(solubility bioavailability research consortium(SBRC)and Gamble's solution extraction)were applied and the bioavailability factor(BF)of each element was calculated.Health risk and cytotoxicity were evaluated and analyzed using the health risk assessment model from U.S.Environmental Protection Agency(US EPA)and real time cell analysis respectively.The results of fraction analysis and bioavailability studies showed that:(1)The distribution of HMs and As in PM2.5 had obvious seasonal differences.The total volume concentrations of As in PM2.5 in winter were significantly higher compared with those in the other seasons.However,the total mass concentration of As in spring was significantly higher,which indicated that PM2.5 could adsorb more arsenic in spring.As in the PM2.5 samples was mainly in F1,especially in summer,with high bioavailability,which indicated that As in PM2.5 was easy to be transformed and caused health risks.The distribution of HMs in PM2.5 were season and element dependent.It was found that Zn was the most abundant element among the five measured metals and followed by Pb,Cu,Cr and Cd.The total contents of each HM in different seasons were in the following order:winter>autumn>spring>summer.The HMs mainly existed in F1 with high bioaccessibility,Zn,Pb and Cu possessed the highest bioaccessibility in summer,while Cd and Cr were the highest in winter.(2)Differences of As and HMs in PM2.5 existed in different functional areas(residential area(RA),industrial area(IA),suburban area(SB),roadside(ST))before and after coal restriction(2016 and 201 7).The proportion of F1-As in PM2.5 increased after coal restriction,while the proportion of F3-As in PM2.5 decreased after coal restriction.The total concentration and bioavailability of As in SB and IA were significantly higher than those in RA,ST and BG.Total contents of HMs in PM2.5 generally decreased after coal restriction.The differences of fraction and bioavailability before and after coal restriction depended on the element and area.(3)The fraction distribution of HMs and As in PMs closely related to the particle size and was influenced by the season.Fine particles took a large percentage in TSP,with the average PM2.5/PM10 and PM10/TSP ratios larger than 0.69.The F1-As with the highest bioavailability and F5-As with the lowest bioavailability had opposite particle size variation.The proportion of Fl-As increased with the decrease of particle size,and the proportion of F5-As increased with the decrease of the particle size.The distribution and bioavailability of HMs in PMs with different particle sizes were elements and seasons dependent.Except for the PMs in autumn,the proportion of F4-Cr in the samples from other seasons increased with the increase of the particle size,and the F1-Cr in the autumn samples decreased with the increase of the particle size.The proportion of Fl-Cu in PM10 was higher than that in PM2.5 and TSP in autumn and winter.The proportion of Pb and Zn in F1 in spring decreased with the increase of the particle size.Health risk assessment indicated that the health risks from inhalation exposure for HMs in PM2.5 declined about 11%to 52%after the coal limiting in this city with the order of SB>IA>RA>ST>BG at different functional areas.The cytotoxicity evaluation results showed that the winter samples had higher cytotoxicity to CHO-K1 cells and produced more reactive oxygen species(ROS),while the spring samples were opposite,with lower cytotoxicity and produced less ROS.Principal component analysis suggested that coal burning was the main source of As in PM2.5 in Baoding,accounting for 41.0%;HMs mainly came from coal burning and motor vehicle emissions,accounting for 69.7%and 13.5%,respectively.This study took Baoding City as an example,innovatively applied fraction analysis to systematically study the fraction,environmental effects and source assessment of HMs in PMs.The results revealed the differences of fraction distribution,bioavailability and health risk of HMs in PMs from different seasons,different functional areas,before and after coal restriction and different particle sizes.The cytotoxicity of PMs was also studied using the real time cell analysis methods.This study enriched and completed the toxicity data of regional air particulate matters,and provided an important reference for regional air pollution control and health effect assessment.