| Owing to their high toxicity,non-degradability and easy inhalation,heavy metals in fine atmospheric particulates can pose a great potential threat to the atmospheric environment.Chengdu,as an economic,cultural and political center of Sichuan and even the whole western region and a new first-tier city,its atmospheric environmental quality is not only affected by the rapid growth of urban population,industry and motor vehicle ownership in recent years,but also adversely affected by the dilution and spread of pollutants due to its special geographical location and climatic conditions limit,resulting in some serious environmental air pollutions from time to time.Chenghua District is located in the old industrial area in the northeast of Chengdu,and adjacent to Longquan and other industrial areas,the air pollution level of this area is more serious than most areas of Chengdu.In the four seasons of spring,summer,autumn and winter,samples of PM10 and PM2.5 in the atmosphere of Chenghua District were collected,respectively.Fernandez method was modified with regard to small sample weight and poor salt tolerance of ICP-MS.Under the optimal conditions,four chemical species of Cu,Pb,Mn,Cd and Cr were extracted and analyzed.The accuracy,precision and detection limits of the method were evaluated.The distribution characteristics of five heavy metals were studied in different seasons and particle sizes.The correlation analyses were conducted between and within total amount and species of each metal.The bioavailability was evaluated and the potential ecological risks of five metals in PM10 and PM2.5 in different seasons were evaluated by Hakanson method,respectively.The main work and conclusions obtained are as follows.1.The optimum conditions for the sequential extraction of five heavy metal species were obtained.The optimal oscillation time for extracting soluble and exchangeable fraction(F1)with pure water is 3 hours,the oscillation temperature is 35°C.The optimum concentration of hydroxylamine hydrochloride is 0.20 mol/L for extracting fraction which is reduciable,oxidizable and bound to carbonate(F2).The volume of 30% hydrogen peroxide is 10 m L when used to extract the fraction bound to organic matter,oxide and sulfide(F3),and it was also found that adding 10 m L first and then 5 m L is better than adding 10 m L directly.The optimum concentration of ammonium chloride as extractant is 0.5 mol/L.Although the optimized hydroxylamine hydrochloride concentration was 20% lower than that given by the Fernandez method,the same extraction effect can be obtained.The concentration of ammonium acetate was 80% lower than that used in Fernandez method,but a better extraction effect was obtained.The salt tolerance of ICP-MS is poor,hence,the reduction of salt concentration is beneficial not only to reduce the blank and detection limit,but also to reduce the dilution required for the sample effectively,which is in turn favorable for the accurate determination of ultra-trace analytes.2.The experimental results showed that the total content of each element and the sum of each species content in three soil reference substances used in the experiment were consistent with the recommended values;that the recoveries of the sum of Cu,Pb,Mn,Cd and Cr species in the samples were higher than 82%;that the RSD of each elememt species is between 0.33% and 6.22%;that the concentrations of each element and its species in determing solutions were more than 3 times of the corresponding detection limits,indicating that the proposed method with lower detection limit is accurate and precise,and the obtained data were reliable and validated.3.In PM2.5 and PM10,both the peaks of total Cu,Pb,Cd and Cr and those of soluble and exchangeable fraction(F1)occurred in December,2017,indicating that the pollutions of the four heavy metals and their behaviours in winter were the most serious and active.The total amount of Mn and the first three forms are not changed greatly all year round,but the highest value of residual fraction(F4)appeared in autumn.This could be due to the windy autumn in Chengdu,and Mn is mainly affected by soil dust.4.In PM2.5 and PM10,the total amount of Cu,Pb,Cd and Cr as well as the maximum value of soluble and exchangeable(F1)heavy metal elements all appeared in December,indicating that heavy metal pollution was the most serious and heavy metal activity was the strongest in winter.The total amount of Mn does not change much in the four seasons,indicating that Mn element is less affected by the seasons.The highest value of Mn residual state(F4)appears in autumn,because chengdu is windy in autumn and affected by the soil background value,which increases the concentration of Mn residual state(F4).5.The optimized Fernandez method was used to extract the samples and the four chemical forms of Cu,Pb,Mn,Cd and Cr in each extract were analyzed by ICP-MS.It was found that there are some differences both in the speciation distributions of different heavy metals in atmospheric particulates with same size and in those of same heavy metals in atmospheric particulates with different size;that the speciation distributions of five heavy metals in atmospheric particles are different from those in soils.In PM2.5,Cu is mainly distributed in soluble and exchangeable fraction(F1),and in the fraction bound to organic matter,oxide and sulfide(F3);Pb,Mn and Cd are mainly distributed in F1 and fraction which is bound to carbonate and is reducible and oxidizable(F2).;Cr is mainly distributed in F2.In PM10,Cu and Mn are mainly distributed in F1 and F3;Pb is mainly distributed in F2;Cd is mainly distributed in F1,F2 and F3;Cr is mainly distributed in F2 and F3.Compared with atmospheric particles,these five heavy metal elements in soils are mainly concentrated in the residual fraction(F4).6.The contents of five heavy metal elements in atmospheric particles with two sizes showed different characteristics.The average contents of Cu,Pb and Cd are higher in PM 2.5,they are 189.4 ?g/g,281.7 ?g/g and 21.53 ?g/g in PM 2.5,but are 176.6 ?g/g,228.1 ?g/g and 18.06 ?g/g in PM10,respectively.The average contents of Mn and Cr are higher in PM10,they are 498.0 ?g/g and 114.6 ?g/g in PM2.5,but are 559.0 ?g/g and 129.8 ?g/g in PM10,respectively.This indicates that not all heavy metals are more likely to concentrate on smaller solid particles.7.Correlation analysis showed following relationships.In PM2.5,there is a significant positive correlation between Cu-? and Cu-T,Cu-? and Cu-T,Cu-? and Cu-?,Pb-? and Pb-T,Pb-? and Pb-T,Pb-? and Pb-T,Pb-I and Pb-?,Mn-? and Mn-T,Mn-? and Mn-T,Cd-? and Cd-T,Cd-? and Cd-T,Cd-? and Cd-T,Cd-? and Cd-?,Cr-? and Cr-T,Cr-? and Cr-T,Cr-? and Cr-?,respectively.In PM10,there is also a significant positive correlation between Cu-? and Cu-T,Cu-? and Cu-T,Cu-? and Cu-T,Cu-? and Cu-?,Pb-? and Pb-T,Pb-? and Pb-T,Pb-? and Pb-T,Pb-? and Pb-?,Mn-? and Mn-T,Mn-? and Mn-T,Mn-? and Mn-T,Mn-? and Mn-?,Cd-? and Cd-T,Cd-? and Cd-T,Cd-? and Cd-T,Cr-? and Cr-T,Cr-? and Cr-T,Cr-? and Cr-T,Cr-? and Cr-?,respectively.8.Bioavailability analysis showed that the bioavailability of five heavy metal elements in PM2.5 followed the order Cd>Cr>Pb>Mn>Cu,and the K value of Cd was 0.814,indicating that Cd was readily bioabsorbed and utilized by living organism;that the K values of Cr,Pb,Mn and Cu were 0.755,0.749,0.712 and 0.522,respectively,suggesting these elements are not easily absorbed by organisms,and Cu has the lowest bioavailability.In PM10,the order of bioavailability was Pb>Cd>Mn>Cr>Cu,and the K values of the five elements are 0.778,0.741,0.611,0.575,and 0.541,respectively,which indicates that these five elements are not easily absorbed by organisms.9.In both PM2.5 and PM10 in northeastern Chengdu Chenghua,the four heavy metal elements of Cu,Pb,Mn and Cr have lower hazard degree,but Cd is extremely harmful.The overall potential ecological risk in the northeast of Chengdu Chenghua is extremely high.The order of ecological hazard of each metal element in PM2.5 is Cd>Pb>Cu>Cr>Mn,and the situation in PM10 is similar to in PM2.5.Because elements with a high degree of danger are more likely to be enriched in small particulates,PM10 is less harmful than PM2.5. |
PDF Full Text Request