| A dam breaking zone of lead-zinc mines along the Huanjiang river including upstream(Zone A),middle stream(Zone B)and down stream(Zone C)of typical sugarcane planting areas located in Huanjiang County Guangxi was chosen as the object of this research.Through field investigations,scientific spot sampling,heavy metal(Cu?Zn?Pb?Cd?As?Ni?Cr)contents and phases,soil physical-chemical properties(pH,organic matter,cation exchange capacities,etc.)were fully analyzed.By adopting GIS technologies and multivariate mathematic statistics,systematically studied the pollution levels,ecological risks,health risks,enrichment characteristics,effect mechanisms,migration mechanisms,migration quantitative models and the distribution patterns of heavy metals in sugar industrial products including sugarcane juice,bagasse and crystal sugar.The major achievements of this research are:1.The research of heavy metals prior controlling screening indicator based on soil environmental risksNemerow comprehensive pollution index method,interval numbers ranking method and human health risk modeling mothods were used to evaluate overall quality of soil in studied zones.According to national soil environment quality standard(GB15618-1995)values of soil grade II,result indicated that zone A was classified as heavily polluted with comprehensively polluted index 4.60,the major pollutants Cd,Pb,Zn anudAs,zone B was classified as non-polluted with the index 0.53,Zone C was slightly polluted with the index 1.05,the major pollutant was Pb,Based on the potential ecological risks(Vi)changing sequence,the risks for zones were A>C>B,for elements it was Cd>Pb>As>Zn>Cu>Ni>Cr.Soil heavy metals induced non-carcinogenic and carcinogenic risks of 3.26,9.93×10-5 and 0.47,5.94×10-5 for children and adults respectively,the risks mainly attributed to As,Pb and Cd,which should be considered as prior controlled heavy metals.2.The enrichment characteristics and mobility pattern of heavy metals in soil-sugarcane(1)Through the monitoring sampling of soil and sugarcane,the accumulation characterizations of heavy metals(Pb,Cd and As)in different sugarcane parts were analyzed.The distribution pattern of Pb and As in sugarcane was root>leaves>stems,for Cd it was root>stems>leaves,and different parts of sugarcane possessed significantly different distribution patterns of Pb,Cd and As,that most of heavy metals were accumulated in sugarcane roots,the contents of Pb,Cd and As in roots,stems and leaves were apparently rise up as the soil comprehensive pollution index increased.The average contents of Pb,Cd and As in sugarcane roots from zone A were 161.08,0.61 and 10.28 mg/kg,values of Pb were 7.73,2.59 times compared to those in zone B,C,for Cd it was 2.51,2.18 times,and for As it was 4.05,1.95 times.(2)The migration pattern in soil-sugar was studied by calculating accumulation coefficients,transferring coefficient and assimilation amount.The results shown that sugarcane possessed different assimilation capabilities for Pb,Cd and As in different polluted zones,the accumulation coefficient in sugarcane roots from Zone C was 1.60.The transferring abilities of heavy metals from sugarcane roots to stems and leaves were different,the transferring coefficients decreased as the pollution level increased,the transferring coefficient of Cd in sugarcane stems in Zone B was as high as 0.60.By the calculations of heavy metal removal rates of whole plants of sugarcane,the theoretical assimilations of Pb,Cd and As in Zone A was the highest,the figures was 936.9 g/hm2?7.22 g/hm2 and 54.2 g/hm2 respectively.3.The establishment of migration quantitatively models of heavy metals in soil-sugar(1)Accumulation coefficients were selected as the indicators of heavy metals migration,the assimilation capacities of heavy metals were Cd>Pb>As.The phases analysis shown that the non-residual phase of Cd and Pb were relatively high,which possessed relatively higher potential bio-availability,while most of As was in residual phase and more stable the ranking of bio-availability was Cd>Pb>As.The higher bioavailability of Cd in soil made its migration ability higher;(2)Through the correlation analysis and principle compound analysis between accumulation coefficients of heavy metals in sugarcane roots and soil physic-chemical indicators including heavy metal phases,pH,OM,cation exchange capacities,EC,by using multi-variant linearity regression method to establish a heavy metal quantitative migration model.The results shown that soil pH,OM,cation exchange capacities,EC,acid-extracted phase of heavy metals,reducible phase of heavy metals played key roles on mobility accumulation and bio-available of Cd,Pb and As in soil-sugarcane system.A log-linear model of heavy metal Cd in the sugarcane root-soil system was established.The coefficient of determination was 0.831;the model was expressed as LnEI =-4.64-0.136Ln ?-0.137Ln?-0.426Ln?-0.125Ln?-0.904L npH + 0.40LnOM-0.72LnTN + 0.36LnTP + 1.03LnTK + 0.12LnCEC-0.10Ln EC,the model was used to predict the motilities of Cd and the correlation between the model predicted value and the measured value was significant:R2 = 0.88.4.The distribution patterns of heavy metals in sugar productsBased on the quantitatively analytical results of heavy metals in sugarcane juice,bassage and crystal sugar,the highest Pb and As levels in sugarcane juice and bagasse were identified in slightly polluted Zone C,the highest value of Cd in sugarcane juice in heavily polluted Zone A,by comprehensively adopting the GB 13078-2001?Hygienical standard for feed?,GB 2762-2012?Maximum levels of contaminants in foods?and GB317-1998?White granulated sugar?to carry out safety assessments,the results indicated that levels of Pb?Cd and As were classified as safety grades.The content of Pb,Cd and As in white granulated sugar were lower than standard control values,that they could be consumed or used as material for other products.The brix,purity,sugar content,and reducing sugar in sugarcane juice were in relatively good condition for high quality.5.Research on difference of heavy metals accumulations by different sugarcane cultivarsThe difference of heavy metal accumulations by seven cultivars including LC 03/1137?LC05/136?GT42?GT29?GF98/296?TT27 and TY were further studied through field trial.The results shown that under the condition of medium comprehensive pollution,GT42 was identified with the best anti-reversion,plant height and yield,which was 240.4 cm and 5412 kg,the theoretical maximum assimilations of Pb,Cd and As were 11.49 kg/hm2.53.97 kg/hm2 and 0.54 kg/hm2.The range of heavy metals in sugarcane juice derived from different cultivars was 0.001-0.002?0.001-0.003?0.042-0.077mg/kg,which conformed to control limits and made the safety production planting of sugarcane on polluted farmland achievable. |
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