枯落物干馏过程中微量元素钴、镍、镉、铬、铅的分异特征及环境健康风险评估

Differentiation Characteristics and Environmental Health Risk Assessment on Co,Ni,Cd,Cr,and Pb in the Process of Litter Distillation

果树枝、秸秆、城市景观绿化所产生的枯落物作为重要的生物质资源,其所含微量元素在干馏过程中含量、赋存状态和结构会发生变化,甚至从枯落物中迁移沉积至生物炭、草木灰中或进入大气气溶胶,造成生态健康风险。试验采集山西省太原市核桃树叶、柳树叶、槐树叶、梧桐叶、高粱秆、大豆蔓等16种常见枯落物样品,以Co、Ni、Cd、Cr、Pb等5种元素为例,在实验室干馏模拟条件下研究环境敏感性元素的迁移变化,并利用电感耦合等离子体原子发射光谱法检测枯落物及干馏产物中5种元素的含量。结果表明,枯落生物质中Cr元素平均含量最高,且经过干馏处理后产物中Cr含量也最高,是需要防护的元素。富集因子结果表明,灰分中5种元素的富集程度为Co 0.38~1.05,Ni 0.38~1.02,Cd 0.41~1.01,Cr 0.12~1.03,Pb 0.44~1.05。挥发率结果表明,枯落物中Cr元素挥发率最高,为88%;其他元素为56%~62%。通过计算慢性非致癌效应的危害系数及致癌效应风险系数进行环境健康风险评估,结果表明,干馏过程中Co、Cd、Cr的释放会产生慢性非致癌效应,16种生物质中超93.75%在干馏过程中存在元素致癌效应危害。从16种常见枯落物生物质干馏过程的环保程度分析可知,大豆蔓是最优质的生物质碳源。

Plant litter produced by fruit tree branches,straw,and urban landscape greening is an important biomass resource.The concentration,occurrence state,and structure of trace elements contained in the litter change in the process of distillation,the trace elements even migrate and deposit from litter to biochar plant ash or enter atmospheric aerosol,leading to ecological health risks.In this paper,samples of 16 common litters such as walnut tree leaves,willow tree leaves,locust tree leaves,parasol leaves,sorghum stalks,and soybean straws were collected in Taiyuan,Shanxi province.The migration and conversion of environmental sensitive elements(Co,Ni,Cd,Cr,and Pb)were studied under simulated distillation conditions in the laboratory.The concentration of these elements in litters and distillation products was detected using inductively coupled plasma atomic emission spectrometry.The results showed that the average content of Cr in litters was the highest,and the content of Cr in products treated by distillation was also the highest,highlighting it was the element needed to be shielded.The enrichment factor results indicated that the enrichment level of the five elements in ash was 0.38 to 1.05 for Co,0.38 to 1.02 for Ni,0.41 to 1.01 for Cd,0.12 to 1.03 for Cr,and 0.44 to 1.05 for Pb.The volatilization rate results indicated that Cr in litter had the highest volatilization rate,reaching up to 88%,while the volatilization rate of other elements ranged from 56%to 62%.Environmental health risk assessment was performed by calculating hazard coefficients for chronic non-carcinogenic effects and risk coefficients for carcinogenic effects.The results showed that the release of Co,Cd,and Cr during distillation could produce chronic non-carcinogenic effects.More than 93.75%of biomass have carcinogenic effects of elements during dry distillation.Based on the analysis of the environmental protection degree in the distillation processes of the biomass of the 16 common litters,soybean straws were the best biomass carbon source.