| To investigate pollution status of Pb and Cd in surface dust of Hangzhou, urban surface dust samples (78in total) from central areas of Hangzhou were collected every two mouths (October2012to August2013) including three different functional areas(residential areas, recreation areas, and traffic areas) and the botanical garden as a background. The total contents of Pb and Cd and main physicochemical properties were measured; an in vitro test of PBET(Physiologically Based Extraction Test) was employed to assess bioaccessibility in gastric and small intestine phase of Pb and Cd. The research aims to obtain temporal-spatial distribution of Pb and Cd in three different functional areas, relationship between bioaccessibility of Pb and Cd and physicochemical property, and health risk assessment of Pb and Cd in surface dust of Hangzhou. The main results were as follows: (1)The contents of Pb and Cd in surface dusts of Hangzhou exceeded the surface soil background values of Zhejiang province, Pb and Cd pollution of three different functional areas were heavily all year round. The concentration of Pb and Cd ranged in49.63-4041mg/kg and0.20-1.51mg/kg, respectively, and were2.61-212.7and2.33-17.56times the surface soil background values of Zhejiang.(2)The contents of Pb and Cd showed obvious difference in the spatial distribution. Lead contents were1165,124.7, and100.5mg/kg in residential areas, recreation areas, and traffic areas, respectively, with the order of residential areas>recreation areas>traffic areas. The contents of Cd were in order of recreation areas>residential areas>traffic areas, and means of three functional areas were0.93,0.69, and0.49mg/kg, respectively.(3)Temporal variation of Pb showed that residential and recreation areas presented a trend of high level in autumn and winter, and low level in spring and summer. The maximum values (1918and78.89mg/kg) of Pb in residential and recreation areas appeared in December2012, while the minimum values (654.2and99.75mg/kg) appeared in August2013. Contents of Pb in October2012and March2013were higher than April2013and August2013. But Pb of traffic areas and Cd of three different functional areas had no obvious temporal distribution regulation.(4)The bioaccessibility analysis showed that bioaccessibility of Pb and Cd in gastric phase were in range of7.01%-70.91%, and29.27%-99.87%, respectively, while in small instestine phase they ranged in0.29%-19.31%, and7.18%-76.65%, respectively. Bioaccessibility of Pb and Cd in gastric phase significantly higher than those in small instestine phase. Bioaccessibility of Pb and Cd in3functional districts were in order of recreation areas> residential areas, traffic areas.(5)The correlation analysis showed that total contents of Pb and Cd were positively correlation with bioaccessible amount of Pb and Cd in surface dusts(p<0.001), but none with bioaccessibility of Pb and Cd. In addition, contents of P and SOM were positively correlation with bioaccessibility of Cd(P<0.01); positively correlation between total Fe, Mn with bioaccessibility of Pb(P<0.01); bioaccessibility of Pb and Cd were nagative correlated with sand (>50μm)(P<0.01or P<0.05), and positively correlated with silt (2-50μm)(P0.01or P<0.05).(6) Health risk assessment indicated that only total content Pb exposure of residential areas dust has non-cancer risk(HQ>1) for6month-3years old of ordinary children The total content, bioaccessible of gastric and small instestine phase of Pb exposure in recreation and traffic areas had no health risk. Cancer risk of total content Cd, bioaccessible Cd in gastric and small instestine phase exposure for ordinary children were less than10-6, it meant no cancer risk. But for allotriophagia and geophagia, total content Pb exposure of3functional areas had high non-cancer risk, with mean values of3.51-102.6for1-21years old. Bioaccessible Cd in gastric phase exposure showed relatively high non-cancer risk with in range of1.81-53.1for1-21years old, while bioaccessible Cd in small instestine phase exposure just had non-cancer risk for more than6years old people with in range of9.89-22.3. Three Cd exposure pathways had different extent cancer risk for1-21years old people, in the range of3.15x10-6-3.89x10-4,2.19x10-6-3.10x10-4, and1.09x10-6-1.59x10-4, respectively. |
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