Characteristics Of Heavy Metal Pollution In Vegetable-growing Soils And The Food Safety Assessment Of Vegetables

With the development of industry and agriculture as well as the acceleration ofurbanization, agricultural soils, especially vegetable-growing soils, have been increasinglypolluted by heavy metals (HMs) in China. Heavy metal pollution has been found to be seriouslyharmful to human health because of its long period of residue, invisibility, irreversibility and thecapability of entering human body through food chain. Therefore, the studies on heavy metalcontamination of vegetable-growing soils and vegetables are very important.This dissertation consists of six chapters.In chapter one, the investigating methods of heavy metal pollution in soils and vegetableswere systematically introduced through more than100references. The introduction was mainlyfocused on the pollution assessment of HMs in soils and vegetables, the source identification ofHMs in vegetable-growing soils, and analytical methods of metal species in soils. In addition, themethod of in situ remediation of HMs in contaminated soils was also summarized.In chapter two, the concentrations of HMs (Pb, Cd, Hg, Cr, As, Cu, Zn and Ni) in168soilsamples collected in twenty-seven typical vegetable-growing regions in Fujian Province weremeasured. And the contamination of HMs in soils was assessed with Nemerow comprehensivepollution index, geoaccumulation index (Igeo) and potential ecological risk index (RI),respectively. Results showed that most of the studied soils were contaminated with HMs tosome extent, and the pollution elements mainly included Hg, Cd and Pb. RI of HMs in soilsindicated that only the regions of QZSS and QZJJ were environmental safety. The soils inZZLH, ZZZP, QZNA, FZJA, FZCS, FZTJ and SMYA were heavily contaminated with HMswith the high RI values. Based on the values of ecological risk of single-element (Eir), Cd andHg posed a great ecological risk in soils, followed by Pb. While, the elements of Cu, Zn, Cr, Niand As presented no ecological hazard in the most sampling regions.In chapter three,196vegetables grown in the above sampling regions were collected anddetermined for the concentrations of HMs. And the potential exposure risk of HMs in vegetableswas assessed using the values of hazard quotient (HQ). Results showed that Pb, Cd and Hg werethe major contaminated HMs in vegetables. The amounts of Pb, Cd and Hg in vegetable sampleswere20.9%,14.8%and9.69%higher compared with the limitation of maximum levels invegetables (GB18406.1-2001). In addition, vegetables were found to be able to strongly absorb and concentrate Cd from soils based on the bioconcentration factors (BCF). The high values(1.61and0.851) of HQ for Pb in QZDH and SMYA samples indicated a significantly potentialexposure risk of HMs for the contaminated vegetables. For Cd in ZZSJ samples (HQ=0.517),and Hg in ZZLH and FZCS samples (HQ=0.516and0.524, respectively), the contaminatedvegetables presented potential exposure risk for human body.In chapter four, the regional characteristic and pollution sources of HMs in soils wereinvestigated with the methods of multivariate analysis including correlation matrix (CM), factoranalysis (FA) and cluster analysis (CA). Three factors, which explained77.410%of the datavariation, were extracted based on the method of FA. Metals of Zn, Cd and Pb (and part of Cu)in the initial component matrix were associated in PC1, which explained44.089%of thevariances. The metals in PC1were considered to derive from anthropogenic sources, especiallyfrom the agrochemical materials and atmospheric dust fall. As, Ni and Cu in PC2explaining21.534%of the variances were presumed to be the lithogenic components. Hg and Cr in PC3might be also related to the anthropogenic sources, especially the thermal power plants andsmelting metal industries in the sampling regions. Results of cluster analysis might be helpfulfor the further identification of pollution sources.In chapter five, the chemical forms of HMs in soils were studied with a modified BCRapproach. Results showed that the amounts of Cd and Zn in acid-extractable forms accountedfor36.6%and21.2%of the total HMs in soils, while less than2%for Pb were found in all thesoil samples except for Dehua Xunzhong. However, a significant correlation (r=0.952) of Pbcontents between the acid-extractable fractions and the vegetables was found at p<0.01, whilethe correlation coefficients were0.66and0.61(p<0.01) for Cd and Zn, respectively.In chapter six, the inhibition of uptake of Pb, Cd and Hg in vegetables from thecontaminated soils by the in situ amendments were investigated through pot experiments.Results showed that the application of different modifiers could effectively reduce the contentsof Pb, Cd and Hg in edible parts of vegetables. For example, applying the modifiers of calciumhydroxide, sodium sulfide and activated carbon could reduce30%~40%of Pb contents in edibleparts of vegetables compared with the control group. Zeolite could reduce40%of Cd contentsand humic acid could reduce75%of Hg in edible parts of vegetables.