Study On Evaluation And Health Guideline For Heavy Metals And Fluorine Of Soil Environmental Quality

In this dissertation, contents of heavy metals in vegetable plantation soils and vegetables in Hangzhou suburb and around a lead/zinc mine in Dongguan town, as well as fluorine in soils on Hang-Jia-Hu Plain in China were studied based on geostatistical analysis and GIS. Soil environmental quality was analysed quantitatively on two different scales. Different evaluation methods and evaluation standards for heavy metals were used for comparison. Especially health risk method and critical thresholds of heavy metals in soils under different land uses were discussed, with the results that guideline on soil environmental quality of fluorine in relation to human health, including guideline on total and water soluble fluorine contents of soils, as well as the assessing methods for predicting local fluoride epidemic, were established. The main results obtained are summarized as follows:1. Study on Health Risk Guideline of Heavy Metals in Vegetable Plantation Soil The concentrations of Cd, Zn, Cu, Pb, Cr, Hg and As in soil had different effects on vegetable growth, and the uptake of heavy metals by vegetables followed the order: Cr < Pb < As < Hg < Zn < Cu < Cd. Contents of heavy metals in different kinds and varieties of vegetable differed in uptake and enrichment ability at different soil heavy metal levels. The standards were analyzed, especially standards for environmental quality of heavy metals in vegetable soils were proposed. The environmental capability critical values of Cd, Zn, Cu, Pb, Cr, Hg and As were 0.3, 200, 30, 0.5, 20, 15, and 15 mg kg^-1, respectively.2. Evaluation on Environmental Quality of Pb, Zn, Cu contents in Vegetable Plantation Soils and Vegetables in Hangzhou SuburbThe soils from 4 main vegetable plantations in Hangzhou suburb were polluted with Pb, Zn and Cu compared to natural background values in Hangzhou. The contents of Zn and Cu basically accorded with environmental capability critical values, expect Pb. While using China Environmental Quality Standard for Soils (GB15618-1995 ) as evaluation standard, the soils were not polluted. Contents of heavy metals in Gongshu District were the highest in four investigated districts owing to different locations in city. The concentration distribution of heavy metals had different spatial variability. The order for their enrichment coefficients was as follows: Zn > Pb > Cu. The enrichmentcoefficient for green vegetable was higher than that of Chinese cabbage, indicating green vegetable accumulated heavy metals easily from soils than Chinese cabbage. And the environmental quality of Zn and Cu was suitable for vegetable growth. The permitted concentrations for human health of Zn, Pb, Cu in soil were 1384mg kg'1, 25.3mg kg'1, 411mg kg"1, respectively.3. Risk Assessment of Heavy Metals Contaminated Soil in the Vicinity of a Lead/Zinc MineTotal heavy metal contents ranged from 5271 to 16369mg kg'1 for Pb, 387 to 1221 mg kg'1 for Zn, 3.0-9.3mg kg"1 for Cd and 65-206mg kg"1 for Cu. In general, all heavy metals exceeded China National Standards for Soil Environmental Quality of Heavy Metals by a factor of3⁶5 times. Especially Pb and Cd, exceeded permitted standards by 50 and 22 times, respectively. Solid phase speciation of the soils using Tessier procedure showed that the heavy metals were distributed in the order: Residual ? organically complexed Fe-Mn oxides occluded > carbonate bound > exchangeable > water soluble. Compared to Pb (49.7%), the average residual fraction of Zn (84.5%), Cd (83.8%) and Cu (83.2%) was much higher, indicating that Pb in these soils was more bioAvaillable than other 3 metals. The percentages of the water soluble and the exchangeable fractions of Pb (1.80%) and Cd (2.74%) were markedly greater than those of Zn (0.10%) and Cu (0.15%), suggesting that the former 2 metals were more mobile and toxic to biota. In the organic matter fraction, the ratio of Pb (29.1%) to its total concentration in the soils was higher than those of Zn (4.70%), Cd (3.16%) and Cu (9.50%). Therefore, Pb had a relatively high mobility and toxicity compared to Zn, Cd and Cu in the present studied soils. Strongly positive correlations between H2O-Pb, HbO-Zn, H2O-CU and organic matter in soil were found. That was negatively correlated with pH values at statistically significant levels. The similar negative relationships between pH values and exchangeable heavy metals were also recorded.4. Risk-based Assessment for Safety of Soils and Vegetables around a Lead/Zinc MineThe vegetable plantation soils were polluted with heavy metals Pb, Cd and Zn, except Cu. The content of Pb in vegetables was highest than those of Zn and Cd and all exceeded the China National Food Sanitation Standards. The order for their pollution index was as follows: Pb > Cd > Zn > Cu. Environmental accumulation of heavy metals in the vegetable plantation soils was proportional to heavy metal accumulation in vegetables and both of them were inversely proportional to the distance from the lead/zinc mine. Their enrichment coefficients of these vegetables were different from soil to vegetable root and from root to vegetable leaf.5. Evaluation on Environmental Quality of Heavy Metals in Soils and Vegetables Based on Ggeostatistics and GISThe distribution of soil P^ Zn> Cd> Cu in a large number of soil samples in Dongguan town was asymmetric. The contents of Zn and Cu were lower than those of Cd and Pb. The concentrations distribution of Pb, Zn, Cd and Cu in soils and vegetables were different in spatial variability. There was a close relationship between total and available contents of heavy metals in soil. The contents of Pb and Cd in green vegetables were higher than those of Zn and Cu and exceeded the national sanitation standards for vegetables.6. Assessment of Health Risk based on PIk Z^ Cd^ Cu Critical Thresholds forSoilsThe average contents order of Pb, Zn, Cd, Cu in terms of point, line and area were Pb ? Zn ? Cu ? Cd, and the contents of Pb, Zn, Cd, Cu in terms of point and line were great higher than that of area, especially Pb and Zn contents. The distribution of soil heavy metals was asymmetric. The calculated critical threshold in soil for adult was higher than that for children. The average order of individual risk index for children and adult health was Pb ? Cd > Cu > Zn. Hazard indexes both for children and for adult health were lower than 1 of point angle, higher than 1 of area angle, but that from for children health line angle was higher than 1. Children were more easily affected by soil heavy metals, and risk indexes of Pb. Zn, Cd, Cu for children of in terms of point, line and area were higher than adult's, and hazard indexes for children were 3 times of adult health. The environmental quality of Dongguan town was mainly safe correspondingly. The heavy metal environmental quality in terms of point and line near a lead/zinc mine had higher hazard risk and might bring potential hazard to local residents. The soil was not suitable for vegetable's growth, Other economy crops should be planted.7. Research Progress in Relationship between Soil Environmental Quality Guideline of Fluorine and Human Health in ChinaOwing to the geochemical behaviors of fluorine related to bioavaillability and its influential factors, such as soil parent material, organic matter, pH value, soil texture, topography, climate, rainfall, the concentrations distribution of total fluorine (T-F) was from less to more, but that of water soluble fluorine (Ws-F) was from more to less from northwest to southeast in our country. That is to say, the availlability of fluorine became lower, and Ws-F had less affected on the concentrations of water fluorine. Therefore, in acidic condition, soil fluorine had lower availlability. Thereusually local fluoride epidemic occurred because of food chain containing high fluorine concentration from soil or burning by coal. So to evaluate quality of fluorine using T-F index method and guideline on T-F 800mg kg'1 soil was established. In alkaline condition, local fluoride epidemic was usually caused by drinking water, and soil Ws-F had closed relationship with water fluorine, therefore quality of fluorine was evaluated using Ws-F index method and guideline on Ws-F 2.5mg kg' was established.8. Spatial Distribution Characteristics and Quality Evaluation of Fluorine in Soils on Hang-Jia-Hu PlainThrough semivariograms analysis two forms of fluorine in soils on Hang-Jia-Hu Plain showed spatial relativity in definite range, in which total fluorine (T-F) possessed strange spatial relativity, suggesting it was relatively greatly influenced by natural structural factors of soil parent material, landform and soil type. The water soluble fluorine (Ws-F) possessed medium spatial relativity, suggesting that the spatial variation induced by random factors such as fertilization, management level played a very great role. The spatial distribution map of fluorine content in the surface soils was obtained using Kriging method, finding close relationship of these 2 forms of soil fluorine with soil parent material, pH value, organic matter and soil texture. The spatial distribution of T-F and Ws-F was similar relatively, being all higher in central and eastern parts than that in western part. The main range of T-F and was Ws-F were 200³00mg kg"1 and 0.5¹.0mg kg"1, respectively. The concentrations of T-F in soil were lower, while T-F contents accounting for 23.7% of the area were less than 200mg kg'1 in the studied area. In which T-F contents in soil in Yuhang County were the lowest, less than lOOmg kg"1. It is suggested that local fluoride epidemic such as dental caries due to lack of fluorine should be prevented by using fluoride-containing toothpastes.