Assessment Of The Mobility Fraction Pb Of Soil In The Pearl River Delta

The Pearl River Delta is a region with rapid economic development.The Pb element is a typical element of heavy metal pollution.This paper analyzed Pb content characteristics,Pb geochemical fractions and influence factors based on 250 rice-root soil samples from different parent materials in the study area with the method of morphological analysis and principal component analysis,establishing the prediction model finally.The main achievements are as follows:(1)The average values of Pb in the granite,terrigenous clastic and Quatermary soils were 51.87 mg/kg,27.44mg/kg,and 48.25mg/kg respectively.The average values of mobility fraction Pb were 5.3mg/kg,3.8mg/kg and 4.32mg/kg respectively.In the Pearl River Delta,11 samples(4.4%)exceeded the Pb risk screening value.10 samples(12.7%)were located in the granite area,and 1 sample(1.1%)was from the Quaternary region.(2)Pb in soil are mainly composed of residual and Fe-Mn oxidation fraction(total proportion of 69.38%)in the Pearl River Delta.The order of Pb elements in the soil is water-soluble fraction<ion exchange fraction<carbonate fraction<organic fraction<humic acid fraction<Fe-Mn oxidation fraction<residual fraction.With the method of one-step extraction,because the organic fraction content of Pb was higher,the activity of Pb extracted by HNO3 was higher than extracted by CaCl2.(3)The distribution of Pb elements is related to feldspar in the granite soil.Factors influencing the total Pb contents and mobility fraction Pb contents in the granite soil were Al2O3,K2O,S,T1,Mo and total Pb contents,CaO,organic matter contents,cation exchange capacity(CEC).The factors controlling the total Pb contents in the terrigenous clastic soil were Al2O3,K2O,CaO,Na2O,S,Tl and Mo.The factors controlling mobility fraction Pb contents were total Pb contents,P and TFe2O3.Due to the influence of the water system in the Quaternary zone,the relationship between the total Pb contents and diagenetic elements such as Al2O3 and K2O was weakened,and the correlation coefficient with S,Tl and Mo was reduced.Geological provenance is the main factor affecting the heavy metals accumulation in the soils.In the south sea-land interaction sedimentary environment,the control of the geological source factor was weakened.The effect of land-sea interaction became more important.The distribution of Pb element in the Pearl River Delta plain was related to the geochemical properties of Tl.(4)Based on different parent material,the mobility fraction Pb carbonate fraction(water-soluble fraction+ion exchange fraction+carbonate fraction,CaCl2 extraction method,HNO3 extraction method)prediction model was established for the Pb element in the Pearl River Delta.The prediction model fited well.We used the multi-target geochemical survey data to predict the mobility fraction Pb of soil in the Pearl River Delta.And it showed that the average value of mobility fraction Pb of soil in the Pearl River Delta varied greatly with different extraction methods,which were 5.567mg/kg,0.028 mg/kg,22.629 mg/kg.