Effect Of Two Phosphorus-containing Substances On Migration Of Heavy Metals And Arsenic In Soil To Paddy

Disodium hydrogen phosphate (DSP) and Hydroxyapatite (HAP) as stabilizer were added into compound contaminated soil by heavy metals(Pb, Cd, Zn) and arsenic(As) in round some mine zones in Hunan province, then rice pot experiment was conducted to mainly study the effects of the two substances on distribution of heavy metals and arsenic species in soil, absorbing heavy metals and arsenic by different organs of paddy, competition between phosphorus and arsenic in different organs of rice, rice agronomic traits and so on. And exploring the changing of Pb, Cd, Zn and As exchange state, pH as well as available phosphorus in soil at the different rice growth periods (tillering period, grain filling period and maturity period). The main results are as follows:(1) The rice tillering period, DSP and HAP treatment significantly increased soil pH and the amount of available phosphorus in soil. And at the same dose of phosphorus, the function that increasing soil pH and soil available of DSP was better than HAP. Both DSP and HAP were enable soil Pb, Cd, Zn exchange state to translate into other more difficult insoluble states, and the reducing effect of HAP on heavy metals exchange state in soil was slightly better than the DSP, the curing effect of both of them on soil Pb, Cd, Zn exchange state was:Pb> Cd> Zn. But DSP and HAP treatment activated As in soil, and DSP is greater than HAP for activating As in soil.(2) Soil pH and available phosphorus increased with the increase of adding amount of DSP and HAP in the three periods of rice growth(tillering period, grain filling period and maturity period), and soil pH at grain filling period was significantly lower than others at another two periods. At the same dose of phosphorus treatment, excepting for Pb exchange state with HAP treatment, the contents of soil Pb, Cd, Zn exchange state at rice filling period were basically higher than that at tillering and maturity period with HAP and DSP treatment. The contents of Pb, Cd, Zn exchange state in the rice mature period soil were less than that in the tillering period soil, which indicated that stability of heavy metals in soil by DSP and HAP had not reached equilibrium in a rice growth cycle. Both DSP and HAP increased the content of soil As exchange state in the three periods rice growth, and the contents of As exchange state in tillering and maturity periods soil were significantly lower than that in grain filling period soil at the same dose of phosphorus treatment, which resulted from reducing of soil pH in grain filling period soil. (3) DSP and HAP significantly reduced contents of Pb, Cd in various rice organs (root, stem, husk, rice) and reduced the contents of Zn in rice root, husk and brown rice, but increased the Zn content in stem. And reducing effect of HAP on Pb, Cd, Zn in brown rice was greater than DSP. Both DSP and HAP treatments significantly reduced the contents of total As in root and brown rice, and inorganic As in brown rice, but HAP significantly increased the content of total As in stem. The reducing effect of inorganic As in brown rice was slightly better than the total arsenic under DSP and HAP treatments, and the reducing effect of total As and inorganic As in brown rice under DSP was roughly equal to be with HAP. Compared with control, DSP and HAP made the contents of rice brown Pb, Cd, Zn, total As, inorganic As reduce by48.72%,22.22%,25.35%,21.98%,41.46%and62.82%,66.67%,39.88%,21.98%,40.24%at most. However the contents of Pb, Cd, inorganic As in brown rice still not reached the minimum level of food hygiene standard limits (GB2762-2012). Analysis showed between phosphorus and As was antagonism effect in the transport process from stem to brown rice, and its antagonism effect not obvious in other transport process.(4)Compared with the control, DSP and HAP treatment made the rice tiller number, plant height, stem dry weight, rice dry weight and total paddy rice biomass first increased and then decreased, and decreased rice root dry weight and the amount of iron plaque on rice roots. That indicated appropriate phosphorus can promote the growth of rice, but high dose of phosphorus inhibited the normal growth of rice. Compared with the control, DSP and HAP at0.12g.kg-1increased stem dry weight, rice dry weigh and total paddy rice biomass the most, and made brown rice yield increased by18.69%,25.56%respectively. DSP and HAP made the contents of Pb, Cd, Zn, As in rice above ground first increased, then decreased. Because the high doses of HAP and DSP possibly inhibited the growth of rice, and result in lower brown rice yield, it is not good way to by adding too much phosphorus to control the accumulation of heavy metals and arsenic of rice shoots.