Studies On Control Techniques For Reducing Heavy Metal Accumulation In Rice (Oryza Sativa L.) And Pakchoi (Brassica Chinensis L.)

With the investigation,Cd,Pb,Cu and Zn contents in commercial fertilizers and irrigation water were analyzed.The effects of salicylic acid(SA)on pakchoi (Brassica chinensis L.)growth and heavy metal uptake were studied with a sand culture experiment,and the impacts of fertilization and spraying CAI(Cadmium Accumulation Inhibitor)on rice(Oryza sativa L.)and pakchoi growth,heavy metal uptake were also studied with field experiments.The main conclusions were as follows:1.Cd,Pb,Cu and Zn concentrations in 29 commercial fertilizers collected from the periphery of Hangzhou et al.were investigated.The results showed that Cd,Cu and Zn contents in the organic manures were the highest in all fertilizers collected, and so was Pb content in calcium superphosphate.Cd,Pb,Cu and Zn concentrations in urea and potassium chloride were relatively low.According to relevant limits of national standards(GB 8172-1987,GB 18877-2002 and GB 15618-1995),24.1%, 13.8%,17.2%of the fertilizer samples exceeded the limitations for Cd,Cu,Zn.And Pb contents in all fertilizer samples were not excessive.2.Cd,Pb,Cu and gn concentrations in 49 surface-water samples collected from Jiaxing suburbs were investigated.The results showed that the contents of Cd,Pb,Zn and Cu were far below the third and fifth grade limits(mainly agricultural water and the general landscape water applicable)of Surface Water Environment Quality Standard.According to the first grade limitations(mainly the source of water and the State Nature Reserve applicable),14.3%,44.9%of surface-water samples exceeded the limits for Cu and Zn,while Cd and Pb contents in all samples were not over standard.3.Results of the sand culture experiment showed that Cd contents(based on fresh-matter weight)in shoots of pakchoi rose with the increase of Cd treatment level in nutrient solution.Under Cd concentration of 0.05 and 0.10 mg/L conditions,Cd content in shoots of pakchoi reduced with increasing concentration of SA in range of 0～8 mg/L,and in range of 0～10 mg/L under 0.15 mg/L Cd condition.At 0.10 mg/L Cd level,Cd content in shoots of pakchoi was 0.224 mg/kg,being higher than the national limit(0.2 mg/kg)in food standards(GB 2762-2005)for leaf vegetables, which reduced to 0.196 mg/kg by adding 4 mg/L SA.SA didn't affect Cu contents significantly in range of 0～8 mg/L and Zn contents in range of 0～10 mg/L. 4.Compared with relevant control(T1,T5),appropriate application of potassium fertilizer(KCI)and spraying CAI could increase the yields of rice grain and pakchoi. Magnesium(MgSO₄)supply could significantly increase shoot yield of pakchoi.Cd, Pb contents in brown rice raised with increasing of potassium fertilization,from 0.06, 0.36 mg/kg(T1)to 0.15,0.48 mg/kg(T4)respectively.Magnesium fertilization(T5) reduced Cd,Pb contents in brown rice to 0.12,0.39 mg/kg separately.CAI spraying could reduce Cd,Pb contents to 0.10,0.36 mg/kg respectively.Cd contents in brown rice of all treatments were lower than the national limit(0.2 mg/kg)in food standards (GB 2762-2005)for grain,however,Pb contents in brown rice of all treatments were exceeded its limit(0.2 mg/kg).In the condition of potassium fertilization,Cd and Pb contents(based on fresh-matter weight)in shoots of pakchoi increased from 0.10, 0.25 mg/kg(T1)to 0.16,0.42 mg/kg(T4)respectively.When added magnesium fertilizer(T5),the contents reduced to 0.15,0.39 mg/kg.CAI spraying could significantly reduce the contents to 0.10,0.36 mg/kg respectively.The contents of Cd in all shoots of pakchoi were lower than the national limit(0.2 mg/kg)for leaf vegetables,and Pb contents were all higher than the national limit(0.3 mg/kg)except T1 treatment.