修复药剂对碱溶液提取-火焰原子吸收分光光度法测定土壤六价铬的干扰

INTERFERENCE OF REMEDIATION AGENTS TO SOIL Cr(Ⅵ) DETERMINATION BY ALKALINE DIGESTION-FLAME ATOMIC ABSORPTION SPECTROMETRY

生态环境部发布的HJ 1082—2019《土壤和沉积物六价铬的测定碱溶液提取-火焰原子吸收分光光度法》于2020年6月正式实施,是目前国内唯一的法定土壤和沉积物Cr(Ⅵ)测定方法。然而现有研究发现,修复后的Cr(Ⅵ)污染土壤测定结果存在假阳性或负偏差的问题。针对其中与溶解性Cr(Ⅲ)、淋洗剂(柠檬酸盐)和还原剂(FeSO_(4)、Na_(2)S_(2)O_(5)、Na_(2)S和CaS_(x))相关的问题进行研究,结果表明:修复过程中产生的Cr(Ⅲ)在整个修复和检测过程中均处于过饱和状态,导致检测结果出现较小正偏差,存在误判风险。土壤对Cr(Ⅲ)的吸附作用对降低检测正偏差至测定下限以下起着至关重要的作用。柠檬酸盐能显著促进Cr(Ⅲ)溶解,可能导致正偏差。修复后土壤中残留的大量还原剂会在碱消解或pH调节过程中将提取的Cr(Ⅵ)还原为Cr(Ⅲ),导致显著的负偏差。火焰原子吸收分光光度法(FAAS)检测的正偏差程度较小且存在较大不确定性,不能抵消残留还原剂产生的负偏差。

As the only legal method for the determination of hexavalent chromium [Cr(Ⅵ)] in soils and sediments,alkaline digestion/flame atomic absorption spectrometry(specified in China’s national standard,HJ 1082—2019) was implemented in China in June 2020.However,false positive and negative deviation were reported by some researchers and engineering projects for Cr(Ⅵ)-contaminated soils.The positive and negative biases caused by dissolved Cr(Ⅲ),flushing agent(citrate) and reductants(FeSO_(4),Na_(2)S_(2)O_(5),Na_(2)S and CaS_(x)) were investigated in this study.Experimental results showed that Cr(Ⅲ) produced during remediation was supersaturated over the remediation and determination process,resulting in small positive biases which may cause erroneous judgment.The adsorption effect of soil to the Cr(Ⅲ) played a crucial role in mitigating the positive bias to below the determination limit.Citrate could significantly enhance the dissolution of Cr(Ⅲ) to a level resulting in positive bias.When a large number of residual reductants remained in soils after remediation,they could reduce the extracted Cr(Ⅵ) into Cr(Ⅲ) during alkaline digestion or pH adjustment,resulting in significant negative bias.This negative bias couldn’t be offset by the positive bias of FAAS,due to the uncertainty and small amplitude of the positive biases.