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近年来,塑料制品的大规模使用造成了严重的环境污染问题,并引起了社会各界的广泛关注[1]。习近平总书记在2019年9月9日召开的“中央全面深化改革委员会第十次会议”上强调:要有力有序有效治理塑料污染。然而,大块塑料经过长期的机械作用、光降解、生物降解、光氧化降解等过程后,逐渐分解成粒径较小的塑料颗粒,当塑料粒径小于5 mm时,称其为微塑料[2-4]。微塑料因具有粒径小、数量多、分布广等特点,容易被动物所吞食[5],产生的危害性更大。COLLIGNON等[6]在卡尔维湾对浮游动物体的内容物进行了检测,在38个样品中,约占74%的样品均含有不同成分的微塑料颗粒。BESSELING等[7]的研究也证明了水体中聚苯乙烯含量越高,海蚯蚓对微塑料颗粒误食也就越多。近年来,国内学者对我国渤海湾[8]、长江口[9]、珠江流域和部分内陆湖泊[10]水体和沉积物中的微塑料污染特征进行了初步研究,研究结果均表明,微塑料易随食物链进入生物体内,并最终对人类身体健康产生影响。
然而,目前国内外关于微塑料的检测及分析方法还不健全,还未形成统一的标准,特别是微塑料检测中的重要预处理步骤——消解方法尚未统一,对后续的微塑料检测及计数等重要环节产生了不确定性影响。目前,国内外常用的消解方法主要分为4种:酸(HCl、HNO3、HClO4)法[11]、碱(NaOH、KOH)法[11]、氧化剂(H2O2)法[12]和酶法[13]。ROCH等[14]使用1 mg·L−1NaOH和65%浓硝酸进行鱼消化道消解,发现对聚酰胺(PA)产生腐蚀效果。DEHAUT等[15]采用6种不同的消解液进行了研究,发现KOH在24 ℃消解效果最好。DAVIDSON等[16]采用69%~71%HNO3溶液对蛤蜊进行了消解,在90 ℃水浴中加热4 h后发现,组织基本完全消解。MINTENIG等[17]采用酶对样品进行了消解。就常用消解液而言,酸性消解液能较彻底地消解有机物质,但容易破坏微塑料原本的结构[18];碱性消解液与氧化剂均易对微塑料的表面形貌造成影响,但不会对微塑料光学性质、化学特性等产生较大的影响[19-20]。虽然酶对微塑料的影响较小,但因其经济成本较高导致使用率较低。
目前,关于消解方法对微塑料识别的影响研究[21]较少,因此,探求一种合适的微塑料消解方法,对提高微塑料检测的可靠性具有重要意义。本研究采用7种常见的消解液对10种不同类型的微塑料颗粒进行了消解,探究了每种消解液对微塑料颗粒质量和表面形态等的影响,进而筛选出对微塑料影响最小的消解方法,可为后续微塑料的计数、识别等提供重要的数据支撑。
不同消解方法对微塑料质量及其表面特征的影响
Effect of different digestion methods on microplastic quality and surface characteristics
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摘要: 为提高微塑料检测的准确性,以10种不同材质的微塑料作为研究对象,使用7种常用的消解液,通过室内实验的方法对消解前后微塑料的质量、荧光强度、表面形态等进行了研究。结果表明:在7种不同的消解方法中,经H2O2(30%,25 ℃)消解后,微塑料质量减少了2%~5%,消解后微塑料表面荧光强度略有减弱,表面形态和元素组成变化轻微;在FT-IR红外图谱中,微塑料颗粒的特征峰仍存在,对于微塑料识别无显著影响;而其他6种消解方法均在不同程度上降低了微塑料的质量,并对微塑料表面造成了划痕、深裂缝和鳞状裂片等破坏。以上结果可为环境中微塑料的检测和定量分析提供参考。Abstract: In order to improve the detection accuracy for microplastic, 10 kinds of different microplastics were taken as a research object and 7 kinds of commonly used digestion solutions, the weight, fluorescence intensity and surface morphology of microplastics before and after digestion had been investigated through lab scale test. The results showed that among the 7 different digestion methods, H2O2 digestion (30%, 25 ℃) reduced the quality of microplastics by 2%~5%, the fluorescence intensity on the surface of H2O2 digested microplastic decreased slightly, the surface morphology and element composition presented slight variations, but the characteristic peak of microplastic particles in FT-IR infrared spectra still existed, which had no significant influence for the recognition of microplastic. However, the other six digestion methods all reduced the quality of microplastics with varying degrees, and had caused damage to the surface of microplastic such as light scratch, deep crack and scaly lobes. These results can provide data reference for the detection and quantitative analysis of microplastic in the environment.
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Key words:
- microplastic digestion /
- H2O2 /
- fluorescence intensity /
- surface morphology
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