| Soil potentially toxic elements（PTEs）enter the human body mainly through ingestion,breathing and skin contact,and then harm human health.Amending soil can reduce the bioavailability of soil PTEs,however most studies focused on the phytoavailability of soil PTEs,and there is limited research on the changes of PTEs to human risk after soil amendment.In this study,a contaminated soil(Pb=261 mg kg-1,Cd=8.05 mg kg-1)from lead smelting area was amended with phosphate and bentonite for one year,and the contaminated soil was then added to mouse feed for Cd/Pb bioavailability assay.Meanwhile,the feed was treated with Pb and Cd reagents.The effects of different amendment treatments on the bioavailability of PTEs in contaminated soil and PTEs concentration in mouse feces were also studied,and the effects of different amendments on the bioavailability of PTEs to plants were studied with a pot experiments.The main results of the study are,（1）Spiking mouse feed with Pb/Cd increased Pb/Cd concentration in mouse kidney,liver and bone.Zinc concentration in kidney and liver of mice was negatively correlated with the dietary Pb/Cd supplemental level.Nickel（Ni）concentration in liver and bone was negatively correlated with dietary Pb/Cd supplementation,respectively.Compared with the control soil without amendment,the concentration of Pb and Cd in kidney of mice fed with phosphate treated soil decreased by 80.2 and 66.0%,respectively（p<0.05）,the concentration of Cd in liver was not significantly affected（p>0.05）,and the concentration of Pb and Cd in bone was not significantly affected,either（p>0.05）.Compared with the control soil,Pb and Cd concentration in organs of mice treated with bentonite was not significantly different（p>0.05）,while Zn concentration in liver decreased by 14.9%（p<0.05）,and Cu and Ni concentration in bone decreased by 62.5 and 34.4%lower than those in control soil,respectively（p<0.05）.The results indicate that phosphate amendment to Pb and Cd contaminated soil can reduce the health risks of Pb and Cd in soil.（2）The feces of mice fed with feed for 2 days and 10 days were collected and analyzed for PTEs concentration.The results showed that the Pb/Cd concentration in mouse feces was significantly and positively correlated with the amount of Pb/Cd added to the feed,respectively.The correlation equations for 2 d were y=2.46x+7.90,r=0.998,p<0.05（Pb）;y=2.21x+5.99,r=0.997,p<0.05（Cd）;for 10 d were y=2.24x+0.934,r=0.965,p<0.05（Pb）;y=2.49x+0.203,r=0.977,p<0.05（Cd）,respectively,and the feces PTEs concentration was 2.71-109 times higher than the feed PTEs concentration.The concentration of feces PTEs in mice showed diversified relationships with the concentration of other PTEs.The addition of phosphate and bentonite to the contaminated soil had no significant effect on the concentration of PTEs in the feces of mice.The uptake of Pb/Cd by mice fed Pb/Cd-added diets for 0-2 days may be faster than on the 9-10 days.（3）Compared with the control,phosphate amendment decreased the bioavailability of Pb and Cd by 37.8 and 50.0%,respectively,indicating that phosphate could reduce the health risk of soil Pb and Cd to human,while bentonite could not reduce the bioavailability of Pb/Cd.The bioaccessibility of Pb in intestinal phase was much lower than that in gastric phase;compared with the control,the bioaccessibility of Cd in soil treated with phosphate in intestinal phase of SBRT method was lower than that of the control（p<0.05）,and bentonite decreased the bioaccessibility of Cd by 77.3%（p<0.05）.Therefore,for the soil of this study,the bioaccessibility of PTEs could not well predict the bioavailability.（4）The effects of contaminated soil amendments on the plant availability of PTEs were investigated by pot experiments.The results showed that the dry weight of lettuce roots with different treatments ranged from 0.017-0.093 g pot-1;the shoot Pb and Cd concentration of lettuce was 3.12-7.31 and 8.69-26.3 mg kg-1,respectively;the root Pb and Cd concentration was 24.6-69.4 and 5.53-35.6 mg kg-1,respectively.Compared with the control,the addition of phosphate,bentonite and lime reduced the soil DTPA extractable PTEs concentration by 19.8-83.4%（p<0.05）,PTEs concentration of lettuce roots treated with amendments was reduced by 11.1-84.4%.Compared to the control,the shoot Zn and Mn contents of lettuce treated with 3 g kg-1 lime were reduced by 57.6and 82.1%,respectively（p<0.05）.The maximum dry weight of above-ground part of lettuce was observed in phosphate treatment.The above results indicate that complex relationships between the effects of phosphate and bentonite on the bioavailability,bioaccessibility and phytoavailability of Pb and Cd in contaminated soil existed,and the results obtained by different assay methods are not consistent. |
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