Chemical Mechanism Of Added Rron Salts Influence On The Speciation And Bioavailability Of Arsenic, Antimony And Cadmium In Paddy Soils

A field sample collection were conducted to study the distribution of arsenic and antimony in paddy soil-rice systems at a mine area; and pot experiments with arsenic and antimony polluted soil from Xikuangshan in Hunan province and arsenic and cadmium polluted soil from Lianhuashan in Guangdong Province, respectivelywere conducted to investigate the influence of iron salt to rice growth. The experiment was set in five treatments: CK, AM-Fe(amorphous iron oxides), FeCl2, NaNO3and FeCl2+NaNO3; then the rice was sampledin four stages of tillering stage, elongation stage, heading stage, maturation stage. The results would provide a reference to reduce the As, Sb and Cd accumulation of rice in arsenic, antimony and cadmium polluted soils. The main results were shown as follows:(1) The analysis of sample collected from the mine area showed that there are significant correlations between Fe and As, Fe and Sb in iron plaque, which indicated that iron plaque can immobilize As and Sb and then reduce the toxicities of the two metalloids to rice.(2) The results of pot experiments showed that Fe salts can influence the forms of As, Sb, Cd in soil. Among them, the FeCl2+NaNO3and FeCl2treatments significantly immobilized As, Sb to iron oxide forms (including0.5M HC1extraction form, DCB extraction form, and oxalic acid extraction form), and reduced their mobility in soils. FeCl2+NaNO3and FeCl2failed to reduce the content of dissolved Cd in soil, but the amorphous iron oxide can significantly transform Cd to iron oxide forms (including0.5M HC1extraction form, DCB extraction form, and oxalic acid extraction form). NaNO3can not affect the mobility of As, Sb, Cd in soil. The addition of Fe salts, especially AM-Fe, FeCl2, FeCl2+NaNO3can significantly increase the content of Fe plaque on rice roots and immobilized As, Sb, Cd on the surface of the roots.The forms of As, Sb, Cd in soil changed with the growth period. For example, dissolved As, Sb in maturation stage significantly exceededthat in the first three stages, thus increasing the As, Sb contents inrice.(3)The treatment of FeCl2and FeCl2+NaNO3can significantly reduce the content of As in rice, the content of As, Sb in root and shoot of the four growth period, and then reduce theirbioavailabilityto rice. However, AM-Fe and NaNO3had no significant effect in on the content of As in rice. Fe salts failed to reduce the content of Cd in rice.