Study On The Transfer And Distribution Of Combined Heavy Metal Pollutants In The Soil-crop System

Study on combined pollution by heavy metals has become one of focuses and problems in modem environmental protection.Research on transfer and distribution of heavy metals in soil- crop systems can provide certain scientific basis for prediction about ecological effects of combined pollution by heavy metals in soil,for assessment of soil environmental capacity and for revision of the Chinese Soil Environment Equality Standard.Pot experiments were conducted to study the transfer and distribution of Cu,Zn,Pb and Cd in soil-crop systems under both mono-pollution and multi-pollution conditions by using swamp cabbage and red amaranth as indicating crops,and chemical forms of Cu,Zn,Pb and Cd in soil under multi-pollution conditions were investigated.The results showed that:(1) Combined pollution by heavy metals restrained the growth of the two crops.Under this experimental condition,Zn was the main factor responsible for the reduction of crop yield, and there was a very significant negative correlation between the content of Zn in soil and the biomass of crop.(2)Compared with that in mono-pollution conditions,bioconcentration factors(BCF)of Cu,Zn,Pb and Cd decreased,transport factors(TF)of Cu increased and TF of Zn,Pb,Cd decreased under multi-pollution conditions.(3)BCF of the four metals in two crops appeared Cd＞Zn＞Cu＞Pb;BCF of the four metals in the root of crops were bigger than that in the stem and leaf of crops.Under multi-pollution conditions,BCF of the four metals in the stem and leaf of red amaranth was bigger than that in swamp cabbage,especially BCF of Zn and Cd.(4)TF of the four metals in swamp cabbage appeared Cd＞Zn＞Pb＞Cu, but appeared Zn＞Cu＞Cd＞Pb in red amaranth.Under multi-pollution conditions,TF of Cu and Zn in red amaranth was 2～7 and 2～4 times of that in swamp cabbage respectively.(5) Chemical forms of heavy metals in soil had important effect on its bioavailability.Under multi-pollution conditions,Cd was mainly associated with water soluble,exchangeable and carbonate fractions;Pb was mainly associated with residual fraction;Zn was mainly associated with residual fraction and water soluble,exchangeable,carbonate fractions;the forms of Cu were related with its content in soil.Bioavailability of the four heavy metals appeared Cd＞Zn＞Pb＞Cu.(6)The best response model of heavy metal in soil-crop systems was mostly non-linear.The transfer and distribution of heavy metal in the soil-crop system not only depended on the contents of heavy metals,but also were influenced deeply by coexistensive elements and interaction of elements.The interaction of heavy metals in soil-crop systems changed greatly with species varions of heavy metals and crops. Pot experiments under simulated acid rain were conducted to study the absorption and Bioconcentration of Cu,Zn,Pb,Cd,Cr,Ni in radish and pakchoi under multi-pollution conditions.The effects of acid rain and coexistensive elements on heavy metals absorption in crops were also discussed.The results showed that:(1)BCF of the six metals in two crops appeared Zn＞Cd＞Ni＞Cu＞Pb＞Cr under acid rain and multi-pollution conditions.(2)The effect of acid rain on heavy metals absorption in crops was related to species of heavy metals and crops.(3)There was a significant positive correlation between the content of heavy metal in two crops and its content in soil under the influence by simulated acid rain.Coexistensive elements have promoting effect on heavy metals(except for Cr)absorption by crops.