The Evaluation And Rapid Detection Of Toxicity Of Heavy Metals In Rice Based On The Luminescent Bacteria

The optimal luminescent conditions were obtained by optimizing culture medium and culture condition of the P.phosphoreum, which provides a good foundation for investigation of toxic substance detection and toxic comprehensive assessment. The luminous intensity of bacteria are inhibited when luminescent bacteria contact with toxic pollutants. The single and joint toxicity of lead, cadmium and mercury in rice were respectively detected using luminescent bacteria test, and joint toxicities of heavy metals mixtures were assessed by toxic unit method (TU) and additive index method (AI). This method is simple, low cost and high accuracy, and can be used to provide simple and economic means for identification of agricultural products safety. The main research contents and conclusions are as follows:1?The luminescent properties of P.phosphoreum were studied, and the components of the culture medium and the culture conditions were optimized. The results showed that the maximum emission wavelength of P.phosphoreum was 475nm. The P.phosphoreum was stably for 16h, which was the most sensitive to heavy metals. The optimal luminescence conditions of P.phosphoreum is 120 r/min,20 ?, culturing 16 h, the initial pH value of mediums is 6.0. The optimum medium components are:tryptone 0.8%. yeast extractO.3%% NaC14%?MgSO40.01% glycerinO.4%?ultra-pure water 1000 mL. Under these conditions, the luminous intensity of P.phosphoreum was increased significantly and the luminescence was more stable.2^ Application of luminescent bacteria test in the safety inspection of agricultural products. The method system of P.phosphoreum for the detection of heavy metals in rice was established based on the luminous inhibition rate as detection indicator and the P. phosphoreum as tested biology. The optimized P.phosphoreum of logarithmic phase were selected, and bacteria number was controlled about 106cfu/mL. The dose effect curve and standard curve are established through investigation of detection time and volume ratio between bacteria and heavy metal standard solution.The results showed that the light inhibition rate was positively correlated with the concentration of heavy metal solution, and the correlation coefficient was higher than 0.96. The list of the toxicity sequence was Hg2+>Pb2+> Cd2+. The linear working range was 0.02-1.6 mg/L,2-20 mg/L,2-64 mg/L for HgCl2, Pb (NO3)2 and CdCl2, respectively. Recovery test were performed by adding Pb (NO3) 2, CdCl2, HgCl2 standard solution of different concentrations. Sample recovery rate range is 60.25%-93.02%, the relative standard deviation of the range is 7.25%-20.12%.3-. The rapid detection method for single and combined heavy metal toxicity were established based on the luminous inhibition rate as detection indicator and the P. phosphoreum as tested biology. The joint toxicities of heavy metals were assessed by toxic unit method and additive index method in order to facilitate the accuracy of the evaluation methods. This method can reveal the combined toxic effects because of coexistence contaminant of various agricultural products, and provide a theoretical basis for the rapid screening of edible safety of agricultural products. The results showed that toxicity of the 3 kinds of heavy metals was Hg2+>Pb2+>Cd2+. For the mixed system, the results of the two evaluation methods are consistent, the joint toxicity of Pb2+ with Cd2+ was synergetic in action while the joint toxicities of Cd2+ with Hg2+, Pb2+ with Hg2+, and Pb2+ with Cd2+, Hg2+ were antagonistic.