土壤硒的存在特征及分析测试技术研究进展

伊芹; 程皝; 尚文郁

doi:10.15898/j.cnki.11-2131/td.202006230095

土壤硒的存在特征及分析测试技术研究进展

1.
国家地质实验测试中心, 北京 100037

2.
北京航天威科环保科技有限公司, 北京 100071

基金项目:
中国地质调查局地质调查项目（DD20190323）；中国地质调查局中国地质科学研究院基本科研业务费项目（CJYYWF20182602）

详细信息

作者简介: 伊芹, 博士, 助理研究员, 主要从事土壤岩石矿物分析。E-mail: yiyiustb@163.com

中图分类号: S151.93;O613.52

收稿日期: 2020-06-23

修回日期: 2021-01-04

录用日期: 2021-01-26

刊出日期: 2021-07-28

Review on Characteristics of Selenium in Soil and Related Analytical Techniques

1.
National Research Center for Geoanlysis, Beijing 100037, China

2.
Beijing Aerospace WKS Environmental Technology Co., LTD, Beijing 100071, China

Received Date: 23 June 2020

Revised Date: 04 January 2021

Accepted Date: 26 January 2021

Publish Date: 28 July 2021

摘要

摘要:
硒是重要的生命健康微量元素之一，土壤硒的空间异质性是造成各种病害和环境问题的主要原因。全球土壤硒分布不均匀，大部分属于低硒土壤，土壤硒含量平均值为0.4mg/kg，典型高硒地区土壤硒含量为346~2018mg/kg。准确分析土壤硒含量是开展土壤硒研究的基础，土壤样品来源特征和硒存在形式是土壤硒分析测试方法的选择依据，合理使用标准物质能够有效监控分析质量。本文阐述了土壤硒的主要来源、分布特征和存在形式，总结了近年来土壤硒形态提取方法、硒含量分析技术研究进展和土壤硒标准物质研制现状。指出当前对硒迁移转化机理研究尚不完善，分步提取态的提出为研究土壤硒形态分布和迁移转化提供了新途径，但因未能完全解决提取专一性和提取过程中硒形态转化的问题，该方法仍在进一步发展。光谱技术尤其是原子荧光光谱是中国分析土壤硒含量的主流方法；高精密度、低检出限的质谱技术，以及具备原位形态分析能力的同步辐射X射线技术，在超痕量分析和形态分析领域具有显著优势。针对当前具有硒含量定值的土壤标准物质能覆盖的土壤基体和硒含量的范围有限，本文提出有待加强研制具备硒梯度含量变化和硒形态含量定值的系列标准物质，以满足分析质量监控需求。
- 土壤 /
- 硒 /
- 形态 /
- 定量分析 /
- 标准物质
Abstract: BACKGROUND
Selenium is an essential micronutrient for humans. The spatial heterogeneity of selenium in soil is the main cause of various diseases and environmental problems. Selenium in soil is unevenly distributed across the globe, with most soils being low in selenium. Globally, the average selenium content in soil is 0.4mg/kg, while it is 346-2018mg/kg in typical high-selenium areas. Thus, accurate analysis of selenium in soil is of great significance in research on seleniferous soil. The reasonable use of reference materials can aid in the effective monitoring of the quality of analysis.
OBJECTIVES
To summarize the status of research on selenium in soil, and the development of the corresponding analytical methods and reference materials.
METHODS
This article describes the distribution characteristics, speciation, and migration and transformation characteristics of selenium in soil. Furthermore, the methods for extracting selenium speciation in soil, the progress of research on selenium content analysis technology, and the status of the development of soil selenium reference materials in recent years are summarized.
RESULTS
Because of limited advancements in the development of analytical techniques, research on the mechanism of migration and transformation is still incomplete. The emergence of sequential extraction techniques provides a new way to study the distribution, migration, and transformation of soil selenium speciation. However, this method is still under development and has many shortcomings, such as inadequate selectivity and inevitable speciation transformation. Atomic fluorescence spectroscopy is the mainstream approach for the analysis of selenium content in soil, especially in China. Mass spectrometry, with high precision and a low detection limit, and synchrotron radiation X-ray technology, with in-situ speciation analysis capabilities, offer significant advantages in the analysis of trace and ultra-trace elements and speciation analysis. There is a significant gap in the research on reference materials with gradient content and certified speciation content.
CONCLUSIONS
Methods with a low detection limit, high sensitivity, and matrix interference resistance are urgently needed. The combined application of sequential extraction, mass spectrometry, and X-ray fluorescence can promote research on selenium in soil. Moreover, related certified reference materials with gradient content and certified speciation content are in short supply.
- soil /
- selenium /
- speciation /
- quantitative analysis /
- reference material

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图 1 自然界硒循环

Figure 1.

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表 1 土壤中部分含硒化合物及其存在环境

Table 1. Part of selenium forms in soil and their existing environment

土壤中部分硒物种		各形态硒的主要性质及其存在环境特征
无机硒	元素态硒(Se⁰)	不可溶，元素态硒在土壤中含量甚微，一般不参与化学反应，不能为植物所吸收，但在适宜条件下，可通过水解、氧化剂以及微生物直接氧化为亚硒酸盐和硒酸盐^[5]
	负二价硒化合物(Se^2-，HSe^-，H₂Se)	除碱金属的硒化物外，大部分硒化物不可溶，不能被植物吸收利用。多为半干旱地区含未经强烈风化的富硫化合物和含黄铁矿土壤中硒的主要存在形式。排水不良的土壤更容易积累不溶性硒化物^[35]
	四价硒化合物(SeO₂，SeO₃^2-，HSeO₃^-，H₂SeO₃)	四价硒主要是以二氧化硒和亚硒酸盐两种形式存在。其中，二氧化硒是一种较稳定的氧化物，主要来自于化石燃料的燃烧，其在大气中流动性很强^[35]，可以固体颗粒形式存在，也可溶于水，并能够与水发生反应生成亚硒酸。亚硒酸盐既是土壤中硒的主要存在形式，也是可被植物吸收的主要无机硒形态，广泛存在于温带湿润地区土壤中；在酸性或中性且排水良好的土壤中，可通过配体交换反应在土壤表面形成内界表面配合物，很容易被氧化物和黏土矿物等吸附^[34]
	六价硒化合物(SeO₄^2-，HSeO₄^-，H₂SeO₄)	六价是硒的最高价态，相应化合物易被植物吸收，可溶性高。六价硒在土壤中主要以硒酸和硒酸盐的形式稳定存在，很难被土壤吸附，是土壤可溶性硒的主要组成部分，是植物可利用硒的主要来源^[36]。在碱性和氧化良好的土壤中，六价硒占主导地位^[37]
有机硒	富里酸硒、胡敏酸硒、多肽硒、二甲基硒醚、二甲基二硒醚、硫代硒醚、二硫代硒醚、硒代胱氨酸、硒代半胱氨酸、甲基硒代半胱氨酸、γ-谷氨酸硒甲基硒代半胱氨酸、硒代乙硫氨酸、硒代蛋氨酸	土壤中有机硒化合物主要来源于动植物残体腐解和微生物作用。通常以负二价形式存在，是植物可利用硒的另一种存在形式，其成分复杂，种类繁多^{[15, 35, 38]}

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表 2 适用于土壤硒形态分析的分步提取方案

Table 2. Sequential extraction schemes suitable for soil selenium speciation analysis

硒元素形态	浸提剂
硒元素形态	Shaheen等^[44]	Tessier等^[42]	王亚平等^[45]	Fan等^[46]	Qin等^[47]	唐沫岚等^[48]	Wang等^[49]	Favorito等^[50]
水溶态	-	-	水	水	水	水	水	水
弱酸提取态(可交换态)	-	1mol/L氯化镁(pH=7)	0.11mol/L乙酸	0.1mol/L磷酸二氢钾-磷酸氢二钾(pH=7)	0.1mol/L磷酸二氢钾-磷酸氢二钾	0.1mol/L磷酸二氢钾-磷酸氢二钾	0.1mol/L磷酸二氢钾-磷酸氢二钾(pH=7)	磷酸提取态0.01mol/L磷酸二氢钾-磷酸氢二钾
弱酸提取态(碳酸盐结合态)	0.1mol/L乙酸	1mol/L乙酸钠(pH=5)	0.11mol/L乙酸	0.1mol/L磷酸二氢钾-磷酸氢二钾(pH=7)	-	-	0.1mol/L磷酸二氢钾-磷酸氢二钾(pH=7)	1mol/L乙酸胺(pH=5)
有机结合态(可还原态)	0.50mol/L盐酸羟铵	0.04mol/L盐酸羟铵+25%乙酸	0.50mol/L盐酸羟铵	0.1mol/L氢氧化钠	0.1mol/L氢氧化钠	0.1mol/L氢氧化钠	富里酸结合态：0.1mol/L氢氧化钠90℃水浴，盐酸酸化至pH=1。腐植酸结合态：0.1mol/L氢氧化钠	0.1mol/L过硫酸钾(先提取晶形铁铝氧化物结合态，再提取有机结合态)
铁锰氧化物结合态(可氧化态)	双氧水(pH 2~3)-1.0mol/L乙酸铵	0.02mol/L硝酸+30%双氧水	双氧水(pH 2~3)-1.0mol/L乙酸铵	-	-	-	-	无定形铁铝氧化物结合态：0.2 mol/L草酸铵+ 草酸。晶形铁铝氧化物结合态：0.04mol/L盐酸羟铵+25%乙酸
酸溶态	-	-	-	-	-	3mol/L盐酸	-	-
乙酸提取态	-	-	-	15%乙酸	15%乙酸	-	-	-
元素态	-	-	-	1mol/L亚硫酸钠(pH=7)	1mol/L亚硫酸钠(pH=7，先提取元素态，再提取乙酸提取态)	-	-	-
硫化物/硒化物结合态	-	-	-	-	0.5mol/L氯化铬+6mol/L盐酸	-	-	-
残渣态	王水	盐酸-氢氟酸-高氯酸	盐酸-硝酸-氢氟酸-高氯酸	硝酸-高氯酸	硝酸-氢氟酸	硝酸-氢氟酸-高氯酸	硝酸-高氯酸	硝酸
注：“-”表示该方法未涉及此形态。

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表 3 原子光谱技术分析土壤硒含量应用实例

Table 3. Application examples of soil selenium content analyzed by atomic spectroscopy

样品处理方法和硒含量分析测试技术	检出限	硒含量线性范围	RSD (%)	回收率(%)
硝酸-盐酸微波消解，ET-AAS测定^[54]	-	-	1.2~9.6	约100.2
王水加热消解，HG-AAS测定^[55]	0.10~0.62 mg/g	-	1.4~6.6	-
超声辅助碱性提取，HG-AAS测定^[56] (仅分析四价硒)	6μg/L	20~100 μg/L	-	-
硝酸提取，HG-AAS测定^[57]	-	-	-	65.0
硝酸-氢氟酸微波消解，HG-AAS测定^[58]	0.02 μg/L	0.08~16 μg/L	<3	94.9~99.5
直接进样，高分辨连续光源HG-AAS测定^[59]	30 ng/g	-	3~10	-
GF-AAS测定^[60]	-	-	-	-
王水-氢氟酸-硼酸- 程序控制石墨消解，HG-AFS测定^[61]	-	-	2.1~9.3	79.9~108.5
微波消解，HG-AFS测定^[62]	0.0097 mg/kg	0~20 μg/L	2.6~4.2	93.6~95.0
悬浮液进样，HG-AFS测定^[63]	0.06 μg/L	0~50 μg/L	3.08~5.54	94.6~107.2
硝酸-盐酸-高氯酸消解，HG-AFS测定^[11]	-	-	-	-
硝酸-盐酸消解，HG-AFS测定^[4]	0.002 μg/g	-	1.8~4.4	-

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表 4 质谱分析土壤硒常见同质异位素干扰

Table 4. Isobaric interference in the determination of selenium in soil by ICP-MS

质荷比	丰度(%)	同质异位素	氩基干扰离子	多原子离子	双电荷
⁷⁴Se⁺	0.89	⁷⁴Ge⁺	³⁶Ar³⁸Ar⁺，⁴⁰Ar³⁴S⁺	³⁷Cl₂⁺，⁵⁸Fe¹⁶O⁺，⁵⁸Ni¹⁶O⁺，³⁹K³⁵Cl⁺，⁴²Ca¹⁶O₂⁺	-
⁷⁶Se⁺	9.36	⁷⁶Ge⁺	⁴⁰Ar³⁶Ar⁺，⁴⁰Ar³⁶S⁺，⁴⁰Ar³⁵Cl¹H⁺，³⁸Ar₂⁺	⁶⁰Ni¹⁶O⁺，⁴²Ca¹⁶O¹⁸O⁺，⁷⁵As¹H⁺	-
⁷⁷Se⁺	7.63	-	³⁸Ar₂¹H⁺，⁴⁰Ar³⁷Cl⁺，³⁹K³⁸Ar⁺，³⁶Ar⁴⁰Ar¹H⁺	⁶⁰Ni¹⁶O¹H⁺，⁶⁰Ni¹⁷O⁺，⁷⁶Ge¹H⁺，⁷⁶Se¹H⁺，⁶⁰Ni¹⁶O¹H⁺，⁴²Ca³⁵Cl⁺	¹⁵⁴Sm⁺⁺
⁷⁸Se⁺	23.78	⁷⁸Kr⁺	⁴⁰Ar³⁸Ar⁺，⁴⁰Ar³⁷Cl¹H⁺，⁴⁰Ar³⁶Ar¹H₂⁺，³⁸Ar⁴⁰Ca⁺	⁴⁴Ca¹⁶O¹⁸O⁺，⁷⁷Se¹H⁺，⁶²Ni¹⁶O⁺，⁴¹K³⁷Cl⁺	¹⁵⁶Gd⁺⁺
⁸⁰Se⁺	49.61	⁸⁰Kr⁺	⁴⁰Ar⁴⁰Ca⁺，⁴⁰Ar³⁸Ar¹H₂⁺ ，⁴⁰Ar⁴⁰Ar⁺，⁴⁰Ar⁴⁰K⁺	⁴⁴Ca¹⁸O₂⁺，⁶⁴Ni¹⁶O⁺，⁶⁴Zn¹⁶O⁺，⁴⁸Ca¹⁶O₂，³²S¹⁶O₃⁺，⁷⁹Br¹H⁺	¹⁶⁰Gd⁺⁺¹⁶⁰Dy⁺⁺
⁸²Se⁺	8.73	⁸²Kr⁺	⁴⁰Ar₂¹H₂⁺，⁴⁰Ar⁴²Ca⁺，³⁴S¹⁶O₃⁺	⁸¹Br¹H⁺，⁶⁶Zn¹⁶O⁺，⁶⁸Zn¹⁴N⁺，³⁴S¹⁶O₃⁺，⁶⁵Cu¹⁶O¹H⁺，⁸¹Br¹H⁺	¹⁶⁴Dy⁺⁺
⁸⁰Se¹⁶O⁺	-	⁹⁶Ru⁺，⁹⁶Zr⁺，⁹⁶Mo⁺，⁵⁶Fe⁴⁰Ar⁺	-	⁹⁵Mo¹H⁺	¹⁹²Os⁺⁺

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表 5 具备硒含量定值的国际土壤标准物质

Table 5. Standard reference materials of soil with certified value of seleniumin developed by foreign nations

标准物质编号	研制机构	样品类型	硒含量(mg/kg)	硒含量分析方法
BCR-320R	IRMM	河道沉积物	0.96±0.18	-
BCR-667	IRMM	河口湾沉积物	1.59±0.08	-
ERM-CC135a	LGC	被污染砖厂土壤	0.9±0.3
LGC6145	LGC	被污染黏土	可提取硒含量1.81±0.13	CRC-ICP-MS
LGC6187	LGC	河底沉积物	可提取硒含量1.2±0.2	-
NIST-SRM-2706	NIST	新泽西土壤	0.3	INAA
NIST-SRM-2709a	NIST	圣华金土壤	1.5	CCT-ICP-MS
NIST-SRM-2710a	NIST	蒙大拿土壤Ⅰ	1	CCT-ICP-MS
NIST-SRM-2711a	NIST	蒙大拿土壤Ⅱ	2	CCT-ICP-MS
NIST-SRM-1646a	NIST	河口湾沉积物	0.193±0.028	RNAA，HYDR，ICP-MS
NIST-SRM-2586	NIST	铅污染地区土壤	0.6	HF-AAS
JSAC0461	JSAC	褐色森林土	0.44	AFS，HG-AAS，HG-ICP-MS，ICP-MS
JSAC0462	JSAC	褐色森林土	71.6±2.1	AFS，HG-AAS，HG-ICP-MS，ICP-MS
JSAC0463	JSAC	褐色森林土	141.5±3.6	AFS，HG-AAS，HG-ICP-MS，ICP-MS
JSAC0464	JSAC	褐色森林土	291.9±5.8	AFS，HG-AAS，HG-ICP-MS，ICP-MS
JSAC0465	JSAC	褐色森林土	587±13	AFS，HG-AAS，HG-ICP-MS，ICP-MS
JSAC0466	JSAC	褐色森林土	1175±26	AFS，HG-AAS，HG-ICP-MS，ICP-MS
注：IRMM—标准物质和测量协会；LGC—英国政府化学实验室；NIST—美国国家标准与技术研究所；JSAC—日本分析化学会。INAA—仪器中子活化分析；RNAA—放射中子活化分析；HYDR—氢化物发生-原子吸收光谱法。“-”表示标准物质证书中未明确说明硒分析方法。

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