ASSESSMENT OF BIOAVAILABILITY OF HEAVY METALS AFTER VERMICOMPOSTING IN THE PRESENCE OF ELECTRONIC WASTE

ABSTRACT Heavy metals contained in electronic waste, if discarded improperly, can become bioavailable after vermicomposting, posing a risk to the environment. Small-scale vermicomposting experiments were carried out with printed circuit boards (PCBs) to investigate the migration of heavy metals (Cu, Pb, Zn, Ni, and Sn) to the final compost, as well as the mobility and bioavailability of these metals. High total levels of Pb, Sn and Cu in samples of manure with electronic waste (MEW) and vegetables with electronic waste (VEW) were detected. Based on the initial metal levels in the PCBs and their concentration in the resulting compost, the order of migration of these metals to the MEW and VEW samples was Sn (23.1 %)>Pb (18.4 %)>Ni (4.63 %)>Zn (0.46 %)>Cu (0.14 %) and Sn (24.3 %)>Pb (23.6 %)>Ni (11.33 %)>Zn (1.76 %)>Cu (0.60 %), respectively. Mobility and bioavailability of these metals in the compost were evaluated by three-stage sequential extraction, where F1 was the exchangeable fraction, F2 the organic fraction and F3 the residual fraction. The bioavailability factor (BF) was calculated by the ratio of the sum of fractions F1 and F2 divided by the total sum of the fractions (F1 + F2 + F3). The highest bioavailability factor (BF = 0.92) was found for Pb, the heavy metal considered the greatest environmental concern in this study, indicating the high mobility and the possibility of becoming bioavailable of this metal.

摘要：电子废弃物中蕴含的重金属若处置失当，经蚯蚓堆肥处理后可能具备生物可利用性，进而对环境造成风险。本研究以印刷电路板（PCBs，Printed Circuit Boards）为受试对象开展小型蚯蚓堆肥实验，旨在探究重金属（铜（Cu）、铅（Pb）、锌（Zn）、镍（Ni）及锡（Sn））向最终堆肥产物的迁移规律，以及此类重金属的迁移性与生物可利用性。研究人员在掺加电子废弃物的粪肥样本（MEW）与掺加电子废弃物的蔬菜样本（VEW）中检测到较高的铅、锡及铜总含量。基于印刷电路板中重金属的初始含量与最终堆肥产物中的重金属浓度，上述重金属在MEW与VEW样本中的迁移优先级分别为：锡（Sn，23.1%）>铅（Pb，18.4%）>镍（Ni，4.63%）>锌（Zn，0.46%）>铜（Cu，0.14%），以及锡（Sn，24.3%）>铅（Pb，23.6%）>镍（Ni，11.33%）>锌（Zn，1.76%）>铜（Cu，0.60%）。本研究采用三步连续萃取法对堆肥产物中此类重金属的迁移性与生物可利用性进行评估：其中F1为可交换态组分，F2为有机结合态组分，F3为残渣态组分。生物可利用性因子（BF）通过F1与F2组分的总含量除以所有组分总含量（F1+F2+F3）的比值计算得出。铅（Pb）的生物可利用性因子最高（BF=0.92），也是本研究中被视为最具环境危害性的重金属，这表明该重金属具有较强的迁移性，且存在被生物利用的潜在风险。