Effects Of Surfactants On Growth And Diet Safety Of Vegetables

Vegetables contain vitamins, minerals, cellulose and fiber, which are important part of human being's main food resource. However, vegetables are easily polluted by sewerage, fertilizer and pesticide for its short growth cycle. So more and more people pay close attention to diet safety of vegetables.As one of organic compound, the surfactants can reduce remarkably liquid surface tension under low concentration. And it is widely used in the daily chemical products, textile printing and dyeing industry, lubricants, carriers and food industry. To the best of our knowledge, whether the surfactants promote vegetables to absorb hazardous substances such as pesticides, heavy metal and organic pollutants was seldom reported. For this reason, it is very important to study whether the surfactants is harmful to the edible plant, and whether the surfactants promote the heavy metal accumulation in tested vegetables.In this experiment, the effects of surfactants on growth and diet safety of vegetables were studied with three tested edible plant and three kinds of surfactants.The leaf vegetables and root vegetables were screened for their common edibility. Brassica rapa L(annual leaf vegetable)and Allium tuberosum L. (perennial leaf vegetables)were selected as the leaf vegetables, and Daucus carrot L.(perennial root vegetables)was selected as the root vegetables. Furthermore, Sodium dodecyl-benzene suffonate (SDBS), Cetyltrimethylamm bromide (CTMAB) and Polysorbate 80 (Tween 80, TW80) were selected as tested surfactants.In oder to study the effects of surfactants on the seeds germination and growth of tested vegetables, the proportion change of pectic substance, the number of hydrogen bond in the protein and the proportion change ofα,β-unsaturated group in ester molecule in these seedlings were detected. So the tested vegetables physiological and harmed response mechanisms which caused from the tested surfactants were discussed.The effects of surfactants combined with the heavy metal on the vegetables biomass, the total accumulation and bioconcentration factors of the heavy metal in tested vegetables, and the elemental form of heavy metal in the soil were investigated. The result showed as follows:1. The tested vegetables'physiological response mechanism caused from the tested surfactants was detected by seeds germination experiment.(1) The result showed that the content of soluble sugar, soluble protein and the seedling length of tested vegetables showed an earlier raised and later decreased tendency under the SDBS, CTMAB and TW-80 concentrations ranged from 0.1 to 5.0 mg-L-1. The seed germination rate of tested vegetables remarkably decreased when the concentrations of tested surfactants were 0.5 mg-1(P<0.05), and decreased following with the increase of the tested surfactants concentrations.(2) Considering the germination rate and the inhibition rate of the tested vegetables seedling growth under the tested surfactants effect, the order of the germination inhibition rate influenced by surfactants was:Allium tuberosum L.> Daucus carrot L.> Brassica rapa L., and the order of the surfactants hurt degree was:CTMAB>TW>SDBS.2. The tested vegetables'harmed response mechanism caused from the tested surfactants was detected by analyzing the structural changes of protein, carbohydrates and ester in the tested vegetables seedlings by means of ATR-FTIR (Attenuated Total Reflectance Fourier Transform Infrared Spectrophoto-metre) method. The details were as follows:In the concentration of 0.1 mg-L"1 surfactants-treatment, there were many variations on the molecular structures in radicles of Brassica rapa L. Chinensis Group and Daucus carrot L., the number of hydrogen bonds in protein molecule was enhanced and the protein stability was increased, the proportion of pectin was increased and the histiocytic water-retaining property was increased, the proportion ofα,β-unsaturated group in ester molecule was increased and the fluidity of cell membrane lipids of tested plant improved. At the same conditions, the proportion of pectin in the radicles of Allium tuberosum L. was increased and the histiocytic water-retaining property was increased.Under the surfactant-treatment of 1.0～5.0 mg-L-1, this also brought many variations on the molecular structures in radicles and sprouts of 3 vegetables, the proportion of hydrogen bonds in protein molecule was decreased and the protein structure was loose, the proportion ofα,β-unsaturated group in ester molecule was decreased and the fluidity of cell membrane lipids of tested plant became inferior gradually, the increase of the proportion of cellulose in the tested plant could prevent cell damage caused by the injury from the tested surfactants.3. The vegetables response mechanism caused from the surfactants was researched through a semiquantitative analysis which detects the ratio of the absorption peak intensity of characteristic functional group to that of methylene at 2926 cm-1 in the same infrared spectra as the relative contents of proteins, carbohydrates and ester in the radicles and sprouts of 3 vegetables. The result showed that the contents of proteins and carbohydrates in the radicles of 3 vegetables were higher than the control groups, the content of ester in the radicles of Brassica rapa L. was higher than the control group. The proteins content, carbohydrates content and ester content in tested seedlings were increased under surfactants stress.4. The effects of surfactants combined with the heavy metal on the vegetables biomass were investigated using pot experiment. The results showed that the low concentrations promote the growth of vegetables(0.5 mg·Kg-1Cd+0.5 mg·Kg-1,25.0～50.0 mg·Kg-1 Cu+0.5 mg·Kg-1), and the high concentrations had adverse effect on the growth of vegetables (5.0-10.0mg·Kg-1Cd+0.5mg·Kg-1,100.0～200.0mg·Kg-1 Cu+50.0mg·Kg-1).The effects of the heavy metals content, the heavy metals migration rate and the elemental forms and the heavy metal content in the soil were investigated by atomic absorption spectrometer with the method of principal component analysis (PCA) to handle the above mentioned indices. The results were as follows:(1) The results of Principal Component Analysis (PCA) showed that the PC1,PC2,PC3 and PC4 were four principal component selected from the multi-factor analysis tested in this study. As a result, under the stress of surfactants-Cd, PC1 means the factor of the distribution of Cd, PC2 means the migration factor of Cd, PC3 means the factor of exchangeable form of Cd, PC4 means the factor of surfactants concentration. Another showed that under the stress of surfactant-Cu, PC1 means the factor of the distribution of Cu, PC2 means the migration factor of Cu bioaccumulation on vegetables, PC3 means the migration factor of Cu, PC4 means the factor of surfactants concentration.(2) The principal component had different effects on the diet safety of vegetables respectively according to the different kinds of surfactants combined with the different kinds of heavy metal. As a result, under the stress of surfactants-Cd the sequence of PC1 Variance % was SDBS>CTMAB>TW-80, the sequence of PC2 Variance% was CTMAB>TW-80>SDBS, the sequence of PC3 Variance % was SDBS>CTMAB>TW-80, the sequence of PC4 Variance % was SDBS>CTMAB>TW-80. Another showed that under the stress of surfactant-Cu the sequence of PC1 contributing rate was CTMAB>SDBS>TW-80, the sequence of PC2 Variance % was CTMAB>SDBS>TW-80, the sequence of PC3 Variance % was TW-80> SDBS> CTMAB, the Variance % of PC4 was very close to each other.(3) Principal component score analysis showed that the transport rate of Cu/Cd from root to leaves and the proportion of exchangeable Cd in soil were increased with surfactants existed in soil. Another showed that SDBS and TW-80 also could promote the tested vegetables to absorb Cu.(4) The edible security of vegetables were evaluated through the application of more comprehensive analysis.The results indicated that Brassica rapa L.Chinensis Group was vulnerable to the threat of the heavy metal pollution in soil. Especially SDBS combined with the heavy metal in soil has a profound influence on edible security of Brassica rapa L.Chinensis Group, and CTMAB combined with the heavy metal in soil brought the most serious threat to the edible security of Allium tuberosum L. and Daucus carrot L.