Effect Of Reclamation On Chemical Species Of Heavy Metals In Tidal Flat Soil From The Pearl River Estuary

Regarding the tidal flat soil in the Pearl River estuary as the research subject, it studied the chemical pecies of heavy metals in the soil reclaimed with different periods and at different stages of desalination in this paper, to estimate the change occured on the chemical species of heavy metals effect of with the different periods and different stages of desalination, to provid effective foundation for utilization of reclaimed tidal flats.1. The chemical pecies of heavy metals in the soil reclaimed with different periods were extracted by Tessier sequential extraction procedure. The evolution of chemical forms of heavy metals in the soil reclaimed with different periods was investigated. The effects of periods on their chemical forms in the soils were studied. the summation of the proportion of exchangeable fractions,carbonate species, oxidiseable forms and the organic combination in the total amount for the five elements(Cu, Pb, Zn, Ni andCr) was compared in different periods, the activity order was as follows:unreclaimed soil> the 1990s> the 1980s> the 1960s> the 1950s. The results showed that:with the increase in the time of reclamation, except Cd, the five other elements (Cu,Pb,Zn,Cr and Ni) have the trend of ageing,and their bioavailability and potential harmfulness has reduced trend.2. The chemical pecies of heavy metals in the soil reclaimed at different stages of desalination were extracted by Tessier sequential extraction procedure. The evolution of chemical forms of heavy metals in the soil reclaimed at different stages of desalination was investigated. The effects of desalination on their chemical forms in the soils were studied. The results showed that:(1)washing and desalination was effective in removing the exchangeable, carbonate and oxide forms of Cd, Pb, Zn,Cu, Cr and Ni. but ineffective for the organic and residual forms of heavy metals. the summation of contribution rate of the exchangeable, carbonate and oxide forms removal on total removal was more than 90% for the elements (Cd,Pb and Zn),but was more than 60% for the elements (Cr and Cu).(2)the summation of the proportion of exchangeable fractions,carbonate species, oxidiseable forms and the organic combination in the total amount for the five elements(Cd and Pb) was compared in different stages of desalination, the order was as follows:T1> T2> T3> T4> T5> T6> T7> T8, this showed that:as salt reduction, the activity decreased for the elements(Cd and Pb). while that not obvious for the telements(Cu, Zn and Cr).