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微塑料(microplastics,MPs)被定义为尺寸小于5 mm的塑料颗粒、碎片或纤维[1],按照来源被分为初级微塑料和次级微塑料[2],初级微塑料主要是以微尺度制造的应用于化妆品等日用品行业[3-4],如个人洗护产品(磨砂膏、牙膏和洗面奶等)、化妆品(眼影、指甲油和粉底液等)、药物和树脂颗粒等[5]。次级微塑料是由大块塑料经过紫外线照射(光降解、脆化、光氧化)、风化和腐蚀等外界因素被分解成较小的塑料碎片[6]。近年来,微塑料对环境的污染越来越受到人们的关注,据报道,在海水[7-8]、淡水[9-10]、土壤[11]、室内灰尘[12]、空气[13]、人和动物粪便[14]以及人体胎盘[15]中都已经检测到微塑料。微塑料作为重要的新型污染物,其对人体、环境以及生态系统造成的潜在威胁应予以高度重视。
目前,提取沉积物中的微塑料通常采用密度分离法——使用饱和盐溶液(如NaCl或NaI溶液)将沉积物中的微塑料悬浮或漂浮于上层溶液,进一步从上清液中将微塑料分离出来[16],但该方法不适合分离粒径更小的塑料颗粒(<10 μm)[17],而且对于高密度微塑料来说,可能沉降于盐溶液底部,导致漏测现象发生。此外,还有研究根据微塑料的物理化学性质进行分离,例如使用油进行疏水性分离或利用尼罗红的吸附能力进行提取[18-19]。目前,多数文献报道中沉积物微塑料以数量浓度计算,主要反映微塑料的数量丰度,而质量浓度参数也是评估微塑料污染状况的重要指标之一。通过质量浓度测量,可反映微塑料在环境介质中的赋存量级,为微塑料环境污染状况进行整体评估及监测提供基础数据[20]。2017年,Connors等[21]指出微塑料暴露浓度以质量浓度(mg·L−1)表示可支持毒理学研究数据的一致性和可比性。Fuller等[22]开发了利用加压流体萃取(PFE)的方法对微塑料的质量浓度进行测量的分析方法,为了减少复杂介质中基质的干扰,在100 ℃下使用甲醇清洗,在180 ℃下用二氯甲烷(dichloromethane,DCM)提取微塑料,吹干后对残留物进行重量分析,并通过傅里叶变换红外光谱(FTIR)进行微塑料成分的鉴定。在实际样品分析中,利用甲醇预清洗可能会损失一部分微塑料,提取物中通常包含色素等其他有机杂质,对于方法的定性定量均可能产生干扰。本研究基于溶解—析出过程的特点,将溶解度参数(δ)作为指示性参数,可为微塑料质量浓度的检测提供新思路。
物质的溶解度参数被定义为:每单位体积物质的气化能的平方根,是一个能够表征简单液体分子间相互作用强度的参数值,用δ表示[23],公式如下:
其中,δ为溶解度参数,(J·cm−3)1/2;
$\Delta \mathop E\nolimits^v /V$ 是每单位体积物质的气化能,又叫内聚能,J·cm−3。通过计算聚合物的溶解度参数,并与溶剂的溶解度参数进行比较,可以对聚合物和溶剂之间的溶解程度进行量化表征。根据计算模型,聚合物和溶剂的溶解度参数越接近,则聚合物的溶解程度越高[24];反之,聚合物和溶剂的溶解度参数差异越大,则聚合物的溶解程度越低,在溶剂中越易析出。
本研究在加压流体萃取法(PFE)的基础上,建立了基于“溶解度参数”计算对沉积物中微塑料进行分析检测的新方法。通过将加压萃取得到的提取物进行浓缩,并根据溶解度参数计算结果,调整溶剂组成比例,选择与微塑料溶解度差异较大的溶剂体系进行微塑料选择性析出,将得到的提取物进行重量分析以及红外光谱检测,实现对沉积物中微塑料的定量定性分析。所建立的方法进一步通过对实际沉积物样品中的微塑料检测进行了验证。该方法可为土壤、沉积物以及室内灰尘等复杂介质中的微塑料测量提取提供新的思路。
基于溶解度参数的计算检测沉积物中微塑料
Determination of microplastics in sediments based on solubility parameter calculation
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摘要: 目前,密度分离法广泛应用于各种环境介质中微塑料的提取。为了进一步准确测量沉积物中微塑料的质量浓度,本研究开发了一种基于溶解度参数(δ)计算的选择性检测方法,建立了加速溶剂萃取(ASE)-微塑料选择性析出-傅里叶变换红外光谱仪(FTIR)检测的技术路线。6种微塑料[聚丙烯(PP)、聚乙烯(PE)、聚苯乙烯(PS)、聚碳酸酯(PC)、聚氯乙烯(PVC)和聚对苯二甲酸乙二醇酯(PET)]被添加到沉积物中,所得到的提取液分别通过3种方式进行预处理:(a)直接抽滤;(b)浓缩;(c)浓缩后调节溶剂体系溶解度参数。结果表明,微塑料的回收率均随着溶剂体系溶解度参数与微塑料的差值│Δδ│的增大有明显提高。此外,增大│Δδ│值对微塑料的选择性析出可明显去除FTIR检测过程中的干扰。将本方法应用于采集自黄河三角洲地区的30个实际沉积物样品的分析检测,共检出4种微塑料,其赋存特征与已有报道一致。本研究所建立的方法可为复杂环境固体基质中微塑料的精确测量提供技术支持。
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关键词:
- 微塑料 /
- 溶解度参数 /
- 加速溶剂萃取(ASE) /
- 沉积物 /
- 傅里叶变换红外光谱(FTIR)
Abstract: Density separation method was widely used as a pretreatment procedure for microplastics analysis in various environmental matrices. To accurately measure the mass concentration of microplastics in sediment, a selective-purification procedure based on solubility parameter (δ) calculation was developed. The technical roadmap of accelerated solvent extraction (ASE)-selective precipitation of microplastics-Fourier Transform infrared spectroscopy(FTIR) analysis was established. Six types of microplastics [polypropylene (PP), polyethylene (PE), polystyrene (PS), polycarbonate (PC), polyvinyl chloride (PVC) and polyethylene terephthalate (PET)] were spiked into sediments for method development. The obtained extract was treated in three different ways: (a) direct filtration; (b) concentration; (c) adjust solubility parameters of the solvent system after concentration. The effect of three kinds of purification treatments was evaluated. The results indicated that the recoveries of microplastics increased obviously with the increase of │Δδ│ value between the solubility parameters of the solvent system and the microplastics. Besides, the interference of FTIR analysis could be removed obviously by increasing the │Δδ│ value for the selective precipitation of microplastics. The established method was successfully applied to the analysis of 30 sediment samples. Four kinds of microplastics were detected, and their occurrence characteristics were consistent with the previous reports. This work provided technical support to meet the need of accurate measurement of microplastics in complex environment solid matrices. -
表 1 6种微塑料的溶解度参数δ值
Table 1. δ values of six microplastics
微塑料 Microplastics 溶解度参数δ/(J·cm−3)1/2 PP 16.98 PE 18.42 PS 19.55 PC 19.43 PVC 19.69 PET 20.53 表 2 单一溶剂的溶解度参数δ值(298.15 K)
Table 2. δ value of single solvent (298.15K)
溶剂 Solvent 溶解度参数δ/(J·cm−3)1/2 二氯甲烷(DCM) 19.84 异辛烷(iso-octane) 14.29 乙腈(ACN) 24.29 甲醇(MeOH) 29.86 表 3 混合溶剂的溶解度参数δ值(298.15 K)
Table 3. δ value of mixed solvent (298.15K)
混合溶剂( V ∶ V )Mixed solvent 溶解度参数δ/(J·cm−3)1/2 DCM∶iso-octane(10∶90) 14.85 DCM∶ACN(10∶90) 23.85 DCM∶MeOH(10∶90) 28.86 表 4 不同析出方法的加标回收率(%)及相对标准偏差RSD(%,n=3)
Table 4. Spiked recoveries (%) and relative satandard deviation (RSD) (%, n=3) of different precipitation methods
直接抽滤 浓缩 浓缩后调节溶剂体系
Solvent system after concentration微塑料
MicroplasticsDirect filtration Direct filtration c1 c2 回收率
Recoveries相对标准偏差
RSD回收率
Recoveries相对标准偏差
RSD回收率
Recoveries相对标准偏差
RSD回收率
Recoveries相对标准偏差
RSDPP 94.67 ± 4.10 4.33 98.54 ± 0.54 0.55 93.16 ± 5.95 6.39 95.55 ± 3.39 3.55 PE 68.98 ± 11.21 16.25 72.16 ± 0.94 1.31 81.82 ± 1.07 1.31 92.75 ± 2.74 2.95 PS 27.32 ± 1.01 3.70 27.14 ± 3.95 14.55 74.61 ± 4.64 6.21 84.88 ± 0.89 1.04 PC 6.56 ± 1.54 23.45 1.96 ± 0.29 15.03 62.17 ± 5.00 8.03 75.67 ± 3.37 4.46 PVC 8.80 ± 1.99 22.65 6.95 ± 1.68 24.16 52.96 ± 2.58 4.87 80.75 ± 0.78 0.97 PET 15.49 ± 4.21 27.15 22.56 ± 2.75 12.20 24.16 ± 4.79 19.82 27.28 ± 2.63 9.63 (c1) PP、PE微塑料用乙腈析出,PS、PC、PVC、PET4种微塑料用异辛烷析出; (c2) 6种微塑料用甲醇析出。
(c1) PP and PE microplastics were precipitated with acetonitrile, PS, PC, PVC and PET microplastics were precipitated with isooctane; (c2) 6 microplastics were precipitated with methanol.表 5 不同处理方式下沉积物中6种微塑料的鉴定结果
Table 5. Identification results of 6 microplastics in sediments under different treatment methods
加标聚合物
Spiked polymers不同处理方式
Different treatment methods聚合物识别
Polymers identifiedOMNIC 匹配度/%
OMNIC MatchPP a PP 83.43 b PP 85.42 c1 PP 84.67 c2 PP 90.53 PE a PE 87.30 b PE 88.83 c1 PE 79.76 c2 PE 89.92 PS a PE 90.11 b PE 85.45 c1 ND - c2 PS 93.19 PC a ND - b ND - c1 PC 94.83 c2 PC 97.22 PVC a PE 81.85 b PVC 68.07 c1 PVC 69.04 c2 PVC 86.29 PET a ND - b ND - c1 PET 69.06 c2 PET 89.98 ND.,未检出。not detected.
表 6 微塑料的红外标准谱图特征峰位置
Table 6. Position of characteristic peak of FTIR standard spectrum of microplastics
塑料类型 红外标准谱图特征峰位置/cm−1 PP 2958、2919、1457、1374、1163、986 PE 2920、2848、1466、721 PS 3082、3060、3026、2920、2850、1601、1452、1375、1181、1028、906、756 PC 2967、2920、2850、1774、1601、1505、1464、1409、1365、1228、1193、1163、1103、1081、1015、831、769 PVC 2920、2850、1431、1330、1247、1093、964、695 PET 2920、2850、1725、1457、1411、1258、1105、1023、729 表 7 黄河三角洲沉积物中微塑料浓度分布及类型
Table 7. concentrations and types of microplastics in sediments of Yellow River Delta
样品
Samples浓度/(mg·g−1)
Concentration微塑料类型
Microplastic types样品
Samples浓度/(mg·g−1)Concentration 微塑料类型
Microplastic types1 0.04 PE 16 0.11 PE 2 0.14 PE 17 0.21 PS 3 0.05 PE 18 0.16 PE 4 0.19 PE 19 0.15 PE 5 0.08 PE 20 0.16 PP 6 0.08 PE 21 0.26 PS 7 0.15 PE 22 0.13 PE 8 0.07 PE 23 0.17 PS 9 0.08 PE 24 0.09 PE 10 0.39 PE 25 0.16 PS 11 0.25 PE 26 0.10 PS 12 0.25 PE 27 0.11 PP 13 0.23 PE 28 0.10 PE 14 0.15 PVC 29 0.27 PE 15 0.17 PE 30 0.25 PE -
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