Analysis method for organic fluorine compound in soil, and diagnostic method for soil

Abstract

Provided is a novel analysis method with which it is possible to perform a highly reliable quantitative evaluation of a fluorine compound contained in soil, and it is possible to predict penetration and migration of the fluorine compound contained in the soil into an aqueous phase. This analysis method includes: an extraction step 1 for performing water extraction of the soil; an extraction step 2 for using an organic solvent to perform extraction of the soil after the extraction step 1; and an analysis step for respectively analyzing the water extract obtained in the extraction step 1 and the organic solvent extract obtained in the extraction step 2.

Description

Method for analyzing organofluorine compounds in soil and method for diagnosing soil

[0001] The present invention relates to a method for analyzing organofluorine compounds in soil and a method for diagnosing soil.

[0002] Patent Document 1 describes an analytical method using a liquid chromatography tandem mass spectrometer (LC-MS / MS) in which a contaminated object contaminated with multiple organic pollutants is extracted, purified, and concentrated using an aqueous solution such as pure water, and the contaminated substances are then sequentially extracted, purified, and concentrated using a polar solvent such as methanol.

[0003] Patent Document 2 describes a method for analyzing organic fluorine compounds, which comprises: an extraction step capable of selectively extracting an organic fluorine compound selected from perfluoroalkylsulfonic acid, perfluoroalkylcarboxylic acid, and salts thereof when the organic fluorine compound is contained in an analysis sample; a decomposition step in which the extract obtained in the extraction step is subjected to steam decomposition at 600 to 1300°C for 10 to 60 minutes; and an analysis step in which the presence or content of fluoride ions in the decomposition product obtained in the decomposition step is analyzed.

[0004] Japanese Patent Publication No. 2014-81242 Japanese Patent Publication No. 2009-294010

[0005] Patent Document 1 describes the identification and quantification of organofluorine compounds when the contaminated substance is water, but does not disclose any analytical method for identifying and quantifying PFAS contained in soil.

[0006] Furthermore, Patent Documents 1 and 2 do not disclose any method for sequentially extracting and analyzing PFSA with an aqueous solution and an organic solvent.

[0007] There is a demand for an analytical method that can quantitatively and accurately diagnose soil containing fluorine compounds more than the methods described in Patent Documents 1 and 2. Furthermore, being able to quantify the amount of fluorine compounds contained in soil that permeate and migrate into groundwater and the amount of fluorine compounds that do not permeate into groundwater and remain in the soil is extremely useful not only for predicting soil contamination but also for predicting the impact on groundwater contamination.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a novel analytical method that can quantitatively evaluate fluorine compounds contained in soil with high reliability and can predict the penetration and migration of fluorine compounds contained in soil into the aqueous phase.

[0009] In order to solve the above-mentioned problems, an analytical method according to one embodiment of the present invention is a method for analyzing organofluorine compounds in soil, and includes an extraction step 1 in which the soil is extracted with water, an extraction step 2 in which the soil after extraction step 1 is extracted with an organic solvent, and an analysis step in which the water extract obtained in extraction step 1 and the organic solvent extract obtained in extraction step 2 are analyzed, respectively.

[0010] A soil diagnostic method according to an aspect of the present invention performs the analysis method according to an aspect of the present invention.

[0011] According to one aspect of the present invention, a novel analytical method can be provided that can quantitatively evaluate fluorine compounds contained in soil with high reliability and predict the penetration and migration of fluorine compounds contained in soil into the aqueous phase.

[0012] <Method for Analyzing Organofluorine Compounds in Soil> The method for analyzing organofluorine compounds in soil includes an extraction step 1 in which the soil is extracted with water, an extraction step 2 in which the soil after extraction step 1 is extracted with an organic solvent, and an analysis step in which the water extract obtained in extraction step 1 and the organic solvent extract obtained in extraction step 2 are each analyzed.

[0013] According to the above configuration, it is possible to quantitatively evaluate the fluorine compounds contained in the soil with high reliability, and also to predict the penetration and migration of the fluorine compounds contained in the soil into the water phase.

[0014] The soil to be analyzed is not limited as long as it contains or is expected to contain fluorine compounds, but for reference, soil for which investigation of soil contamination is mandatory under the Soil Contamination Countermeasures Act, which will be described later, can be mentioned.

[0015] Fluorine compounds have excellent water- and oil-repellent properties, as well as excellent chemical and thermal stability, and have therefore been widely used in water repellents, coating agents, fire foams, etc. Because of their excellent chemical and thermal stability, fluorine compounds do not decompose when released into the environment, and remain in soil and groundwater for long periods of time.

[0016] Fluorine compounds contained in contaminated soil include polyfluoroalkyl compounds, and these polyfluoroalkyl compounds may include all of the related substances designated as perfluoroalkyl compounds or polyfluoroalkyl compounds (sometimes referred to as PFAS) as defined in the Stockholm Convention (POPs Convention), the European REACH Regulation, the Chemical Substances Control Law, etc.

[0017] For example, the POPs Convention regulates perfluorooctanoic acid (PFOA) and its salts, perfluorooctanoic acid-related substances, perfluorohexane sulfonic acid (PFHxS) and its salts, perfluorohexane sulfonic acid-related substances, perfluorooctane sulfonic acid (PFOS) and its salts, and perfluorooctanesulfonylfluoride (PFOSF), but exempts PFOS from the prohibition of manufacture and use in semiconductor applications, photographic film applications, etc. Furthermore, for example, the designation of Type 1 Specified Chemical Substances under the Chemical Substances Control Law (July 2019) stipulates the designation of an isomer of perfluorooctanoic acid (PFOA) as a Type 1 Specified Chemical Substance, and the provision by government ordinance of two substances as PFOA-related substances for which exceptional uses must be established. The Chemical Substances Control Law stipulates that other substance groups are included in the exemplary list of POPRC19 and will be specified by Cabinet Order as a general definition of PFOA-related substances, with specific substance groups to be specified separately by Ministerial Ordinance. It also stipulates that specific substance groups for other PFOA-related substances will be designated in new Ministry of Health, Labour and Welfare, Ministry of Economy, Trade and Industry, and Ministry of the Environment ordinances to be established after hearing opinions at a joint meeting to be held in the future. The fluorine compounds analyzed in this invention include PFOA and its isomers, PFOA-related substances, and other substance groups that may become subject to regulation in the future. For example, EPA Method 1633, an analytical method developed by the U.S. Environmental Protection Agency (EPA), also targets more than 40 types of PFAS.

[0018] PFAS include perfluoroalkylsulfonic acids (PFSAs), perfluoroalkylcarboxylic acids (PFCAs), and other fluorine compounds, and the perfluoroalkyl groups in these compounds may be linear or branched. The perfluoroalkylsulfonic acids (PFSAs) and perfluoroalkylcarboxylic acids (PFCAs) may be salts of these acids or amide compounds of these acids.

[0019] More specifically, PFAS includes perfluorobutane sulfonic acid (PFBS), perfluorohexane sulfonic acid (PFHxS), perfluoroheptane sulfonic acid (FHpS), perfluorooctane sulfonic acid (PFOS), perfluorodecane sulfonic acid (PFDS), perfluorooctane sulfonamide (FOSA), N-methylperfluorooctanoic acid amide (N-MeFOSA), N-ethylperfluorooctanoic acid amide (N-EtFOSA), N-methylperfluorooctanoic acid amide acetic acid (N-MeFOSAA), N-ethylperfluorooctanoic acid amide acetic acid (N-EtFOSAA), 6:2 polyfluorooctanesulfonic acid (6:2FTSA), 8:2 polyfluorodecanesulfonic acid (8:2FTSA), 6:2 chloropolyfluoroether sulfonic acid (6:2Cl-PFESA), perfluorobutanoic acid Examples of perfluorooctanoic acid include perfluoropentanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), perfluorotridecanoic acid (PFTrDA), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDA), perfluorooctadecanoic acid (PFOcDA), 8:2 fluorotelomer unsaturated carboxylic acid (8:2FTUCA), 8:2 polyfluoroalkyl phosphate diester (8:2diPAP), hexafluoropropylene oxide dimer acid (HFPO-DA), and 4,8-dioxa-3H-perfluorononanoic acid (DONA).

[0020] In addition to the PFAS exemplified above, for example, 8:2 fluorotermer alcohol (8:2FTOH), 6:2 fluorotermer alcohol (6:2FTOH), 4:2 fluorotermer alcohol (4:2FTOH), 8:2 fluorotermer acrylate (8:2FTAC), 6:2 fluorotermer acrylate (6:2FTAC), perfluorosulfonamidoethanols (FOSEs), N-methylfluorooctanesulfonamidoethanol (N-MeFOSE), N-ethylfluorooctanesulfonamidoethanol (N-EtFOSE), perfluoroheptanoic acid (PFHpA), perfluoroundecanoic acid (PFUnA), and perfluorododecanoic acid, which are applied in EPA Method 1633, may be used. Examples of substitutes for PFAS include (PFDoA), perfluorotridecanoic acid (PFTrA), perfluorotetradecanoic acid (PFTeA), 6:2 fluorotermersulfonic acid (6:2FTS), 8:2 fluorotermersulfonic acid (8:2FTS), perfluorooctanesulfonamide (PFOSA), perfluoromethoxypropanoic acid (PFMPA), perfluoromethoxybenzoic acid (PFMBA), N-fluorodecanoic acid (NFDHA), perfluorooctanoyl fluoride (POPF), perfluoromethylcyclohexane (PFMeCyH), perfluorodecanesulfonamide (PFDSA), perfluorononanesulfonamide (PFNSA), and amidooctanoic acid (ADONA).

[0021] Other fluorine compounds that may be included in PFAS include aromatic acids having perfluoroalkyl groups, fluorides of aromatic acids, and nonionic surfactants having perfluoroalkyl groups. When a fluorine compound such as a perfluoroalkyl compound is used as a surfactant, some of the fluorine compound remains in the soil and then permeates and migrates into groundwater.

[0022] [Extraction Step 1] In extraction step 1, before extracting the contaminated soil containing fluorine compounds with water, a specified amount of a target internal standard (surrogate) may be added to and mixed with a known amount of contaminated soil, and then the contaminated soil containing the target internal standard may be extracted with water.

[0023] The target internal standard substance includes a stable isotope-labeled compound of the above-mentioned PFAS. The stable isotope-labeled compound is a compound in which some or all of the atoms in the above-mentioned PFAS are substituted with D (deuterium), １８ O. １５ N, and １３ It is a compound substituted with a stable isotope such as C. From the viewpoint of improving the accuracy of qualitative and quantitative analysis of the PFAS to be analyzed, it is more preferable to use a stable isotope-labeled compound having a structure closest to that of the PFAS to be analyzed.

[0024] The amount of target internal standard to be added to soil is determined based on the estimated amount of PFAS contained in the soil, and the target internal standard is added to a predetermined amount of collected soil so as to achieve a predetermined concentration. Two or more target internal standards, i.e., multiple target internal standards, may be added to a single soil sample so that the PFAS to be analyzed can be qualitatively and quantitatively analyzed. Mixing of the target internal standard with the soil can be performed using, but is not limited to, a known stirring device such as a vortex mixer.

[0025] In extraction step 1, the water used to extract the soil to which the target internal standard has been added may typically be pure water suitable for PFAS testing.

[0026] Water extraction of soil should be performed at least once for each soil sample, but multiple times are preferred, and at least three times is even more preferred. By performing water extraction at least three times for each soil sample, the target internal standard and PFAS contained in the soil can be sufficiently extracted into the aqueous phase. The amount of water used for each water extraction should be determined in advance for quantitative analysis, and this amount of water should be a predetermined amount. The predetermined amount of water used for water extraction in extraction step 1 is not limited, but for example, for a soil sample of approximately 5 to 50 g, it is recommended to adjust the amount of water to approximately 50 to 500 mL in total, i.e., 10 times the amount of water relative to the soil sample. Thus, one of the advantages of the present invention is that it allows for accurate analysis using a small amount of water.

[0027] The extraction time for PFAS in one water extraction is preferably 0.5 hours or more, or may be 24 hours or more, but is not limited thereto, and is preferably 24 hours or less. For example, by extracting three times for 0.5 hours, substantially all of the PFAS remaining in the soil can be extracted with an organic solvent.

[0028] The supernatant aqueous phase obtained by water extraction of a soil sample can be first centrifuged to separate sediment and suspended matter, and then purified using a known solid-phase extraction column. The solid-phase extraction column can be selected from reverse-phase solid-phase extraction columns, normal-phase solid-phase extraction columns, cation-exchange solid-phase extraction columns, and anion-exchange solid-phase extraction columns depending on the PFAS and target internal standard. The solid-phase extraction column is not limited, but is preferably a weak anion-exchange solid-phase extraction column, for example. The support of the solid-phase extraction column can be any of polymer, silica gel, and activated carbon, and is preferably a water-wettable polymer in a reverse-phase / weak anion-exchange mixed mode.

[0029] Collection of PFAS from the aqueous phase using a solid-phase extraction column can be performed using an organic solvent as the column extraction solvent. Examples of the organic solvent include alcohols such as methanol and ethanol, and ammonia-mixed methanol. The ammonia-mixed methanol can be, for example, methanol containing 0.1 to 1.0% aqueous ammonia as an alkaline compound, with 0.1% ammonia-mixed methanol being more preferred. Extraction of PFAS using a solid-phase extraction column can be performed by varying the solvent supplied to the column. For example, methanol can be used as the extraction solvent for fraction 1, and ammonia-mixed methanol can be used as the extraction solvent for fraction 2. This allows neutral PFAS to be collected as fraction 1 and ionic PFAS to be collected as fraction 2 from the PFAS immobilized on the solid-phase extraction column.

[0030] Fraction 1 and Fraction 2 obtained in extraction step 2 may be concentrated and adjusted to a predetermined volume with an organic solvent to obtain an organic solvent extract sample. Alternatively, Fraction 1 and Fraction 2 may be combined, concentrated, and adjusted to a predetermined volume with an organic solvent to obtain an organic solvent extract sample. This organic solvent extract sample is subjected to the analysis step described below. Furthermore, by analyzing Fraction 1 and Fraction 2 separately, the neutral fraction and the ionic fraction can be analyzed separately, and the behavior of each PFAS occurring due to soil texture, etc. can be examined in more detail.

[0031] [Extraction Step 2] In extraction step 2, the soil after the water extraction is extracted with an organic solvent, which allows substantially all of the PFAS remaining in the soil to be extracted without transferring to the aqueous phase.

[0032] Examples of organic solvents used in extraction step 2 include alcohols, acetonitrile, and ammonia-methanol, and may also be mixed solvents of these organic solvents, with the alcohols being selected from, for example, methyl alcohol, ethyl alcohol, etc. By using a water-soluble organic solvent as the extraction solvent in extraction step 2, PFAS, which are difficult to penetrate and transfer into the aqueous phase, can be extracted from the soil by the organic solvent. Here, the organic solvent may be, for example, an organic solvent containing an alkaline compound such as ammonia water, such as ammonia-methanol. By using an organic solvent containing an alkaline compound such as ammonia-methanol as the organic solvent used in extraction step 2, PFAS remaining in the soil can be extracted more thoroughly.

[0033] When the organic solvent is ammonia methanol, the ammonia concentration is preferably 0.1 to 1.0 wt%, and more preferably 0.5 wt%. This allows for efficient extraction of fluorine compounds from the soil being analyzed, with an extraction recovery rate of approximately 100%. Furthermore, since the weak anion solid-phase extraction column operates under acidic conditions, acetic acid or formic acid is used to adjust the pH of the basic extraction solution to an acidic level. However, this use can be kept to a minimum to reduce worker exposure to chemicals.

[0034] Organic solvent extraction of soil should be performed at least once for each soil sample, but is preferably performed multiple times, more preferably at least three times. By performing organic solvent extraction at least three times for each soil sample, the target internal standard and PFAS remaining in the soil without dissolving in water can be sufficiently extracted into the organic solvent phase. The amount of organic solvent used for each organic solvent extraction should be determined in advance for quantitative analysis, and it is recommended to use a predetermined amount of organic solvent.

[0035] The extraction time for PFAS in one organic solvent extraction is not limited, but may be 0.5 hours or more and 24 hours or less, as long as it is an extraction time conforming to the extraction step 1. Here, the extraction time may be 0.5 hours.

[0036] The supernatant organic solvent phase obtained by organic solvent extraction of a soil sample can be first centrifuged to separate sediment and suspended matter, and then purified using a known solid-phase extraction column. The solid-phase extraction column can be selected from reverse-phase, normal-phase, cation-exchange, and anion-exchange columns depending on the PFAS and target internal standard. The solid-phase extraction column is preferably, but not limited to, a reverse-phase / weak anion-exchange mixed-mode water-wettable polymer column. The support of the solid-phase extraction column can be a polymer, silica gel, or activated carbon, preferably a weak anion-exchange mixed-mode water-wettable polymer.

[0037] Collection of PFAS from the organic solvent phase using a solid-phase extraction column is preferably carried out using an organic solvent as the extraction solvent, and examples of such organic solvents include methanol and ammonia-mixed methanol. Examples of ammonia-mixed methanol include ammonia-methanol containing 0.1 to 1.0% aqueous ammonia as an alkaline compound. In extracting PFAS using a solid-phase extraction column, the solvent supplied to the column can be changed to collect neutral PFAS as fraction 1 and ionic PFAS as fraction 2 among the PFAS immobilized on the solid-phase extraction column. By analyzing fractions 1 and 2 separately, the neutral and ionic fractions can be analyzed separately, allowing for more detailed analysis of the behavior of each PFAS, particularly neutral PFAS, occurring in soil conditions. However, this is not limiting, and fractions 1 and 2 may also be collected together.

[0038] Fraction 1 and Fraction 2 obtained in extraction step 2 may be concentrated and adjusted to a predetermined volume with an organic solvent to obtain an organic solvent extract sample. Fraction 1 and Fraction 2 may be combined and concentrated, and adjusted to a predetermined volume with an organic solvent to obtain an organic solvent extract sample. The organic solvent extract sample is subjected to the analysis step described below.

[0039] [Analysis Step] In the analysis step, the aqueous extract sample obtained in extraction step 1 and the organic solvent extract sample obtained in extraction step 2 may be analyzed separately. Then, the total amount of PFAS contained in the soil before extraction step 1 may be determined from the amount of PFAS contained in the aqueous extract sample and the amount of PFAS contained in the organic solvent extract sample. As described above, the aqueous extract sample and the organic solvent extract sample may be analyzed separately as fractions 1 and 2, or may be analyzed mixed together.

[0040] The analytical method employed in the analysis step may be chromatography, and from the viewpoint of being able to perform detailed analysis according to the type of PFAS contained in the soil, it is preferable to use a chromatography method equipped with a quadrupole mass spectrometer.Specific examples include LC-MS, LC-MS / MS, and GC-MS / MS, and the analytical method can be selected depending on the type of PFAS.

[0041] By separately analyzing the aqueous extract sample obtained in extraction step 1 and the organic solvent extract sample obtained in extraction step 2, the amount of PFAS contained in the aqueous extract sample can be quantified, and the amount of PFAS, target internal standards, and organic solvent extracts migrating from contaminated soil to groundwater can be predicted. Here, when collecting the aqueous extract sample obtained in extraction step 1 using a solid-phase extraction column, fraction 1 extracted with an organic solvent and fraction 2 extracted with an organic solvent containing an alkaline compound may be collected separately, and each of fractions 1 and 2 may be subjected to the analysis step. Alternatively, when collecting the organic solvent extract sample obtained in extraction step 2 using a solid-phase extraction column, fraction 1 extracted with an organic solvent and fraction 2 extracted with an organic solvent containing an alkaline compound may be collected separately, and each of fractions 1 and 2 may be subjected to the analysis step. This allows for more detailed analysis of neutral PFAS and ionic PFAS contained in the aqueous extract sample and the organic solvent extract sample, respectively.

[0042] The present invention has the advantage of being able to predict and diagnose soil characteristics, such as how much of the PFAS contained in the soil will migrate from the soil (soil phase) to groundwater (aqueous phase) in the future, and how much PFAS will remain in the soil, and further being able to predict and diagnose soil characteristics depending on the type of PFAS. Thus, a diagnostic method for diagnosing soil characteristics by performing an analytical method according to one embodiment of the present invention is also within the scope of the present invention.

[0043] For example, the total amount of the organofluorine compounds contained in the aqueous extract sample determined in the analysis step and the total amount of the organofluorine compounds contained in the organic solvent extract sample can be calculated, and the ratio of the amount of the organofluorine compounds contained in the aqueous extract to the total amount can be used to calculate the groundwater migration ratio as the ratio of the organofluorine compounds in the soil that are predicted to migrate to groundwater in the future.Furthermore, the soil remaining ratio can be calculated as the ratio of the organofluorine compounds that are predicted to migrate to groundwater and remain in the soil without migrating to groundwater from the ratio of the amount of the organofluorine compounds contained in the organic solvent extract to the total amount.

[0044] For reference, the soil to be analyzed may be soil for which the Soil Contamination Countermeasures Act requires reporting of the results of soil contamination surveys to prefectural governors, etc.

[0045] The Soil Contamination Countermeasures Act requires reporting in the following three cases: (1) When the use of a specified facility using hazardous substances is discontinued (Article 3 of the Soil Contamination Countermeasures Act); (2) When the facility is of a certain size (3,000 m2); ２ ) When a prefectural governor or other relevant person recognizes that there is a risk of soil contamination when notifying a change in the characteristics of the land as described above (Article 4 of the same Act). (3) When a prefectural governor or other relevant person recognizes that there is a risk of health damage due to soil contamination (Article 5 of the same Act). If any of the above three cases apply, it is advisable to conduct a geological survey and select a survey area.

[0046] Land that is deemed to be "free" from the risk of soil contamination is land that continues to be completely isolated from the use or storage of solid or liquid substances containing specific hazardous substances, and examples of such land include employee residential facilities, parking lots, sports grounds, gymnasiums, and unused land, and there is no need to collect soil samples.

[0047] Land that is deemed to be "low" risk of soil contamination is land that is used for business purposes and cannot be said to be completely isolated from the use or storage of solid or liquid substances containing specified hazardous substances. Examples of such land include offices, workshops, material storage areas, warehouses, employee and work vehicle access roads, and business parking lots.２ It is advisable to conduct the survey using the five-point equal mix method of soil in the unit plot.

[0048] Land that is deemed to be at a "relatively high risk" of soil contamination is the site of a facility that has used or stored designated hazardous substances or solid or liquid substances containing designated hazardous substances, including designated facilities, wastewater treatment facilities, and hazardous substance storage areas. ２ It is advisable to conduct a soil survey in each plot.

[0049] Soil samples should be collected from land that is deemed to have a "low" or "relatively high" risk of soil contamination under conditions similar to those for Type 3 specified hazardous substances (pesticides, etc.) among specified hazardous substances, and analyzed using the analytical method of the present invention.

[0050] [Summary] The analytical method according to Aspect 1 of the present invention is a method for analyzing organofluorine compounds in soil, and includes an extraction step 1 in which the soil is extracted with water, an extraction step 2 in which the soil after extraction step 1 is extracted with an organic solvent, and an analysis step in which the water extract obtained in extraction step 1 and the organic solvent extract obtained in extraction step 2 are analyzed, respectively.

[0051] Furthermore, in the analytical method according to Aspect 2 of the present invention, in the above-mentioned Aspect 1, the organic solvent is a water-soluble organic solvent, and the water-soluble organic solvent is selected from alcohols, acetonitrile, ammonia-methanol, and mixed solvents thereof, and the alcohols are more preferably selected from methyl alcohol and ethyl alcohol.

[0052] Furthermore, in the analytical method according to Aspect 3 of the present invention, in the above-mentioned Aspect 1 or Aspect 2, it is more preferable that the water-soluble organic solvent contains an alkaline compound, and the alkaline compound is selected from ammonia water.

[0053] Furthermore, in the analytical method according to Aspect 4 of the present invention, in any one of Aspects 1 to 3, a target internal standard may be added to the soil before the extraction step 1 is carried out.

[0054] Furthermore, in the analytical method according to Aspect 5 of the present invention, in any one of Aspects 1 to 4, it is preferable to determine a migration rate of the organofluorine compound into groundwater from the ratio of the amount of the organofluorine compound contained in the aqueous extract to the total amount of the organofluorine compound contained in the aqueous extract and the organic solvent extract, and to determine a residual rate in soil from the ratio of the amount of the organofluorine compound contained in the organic solvent extract to the total amount.

[0055] A soil diagnostic method according to a sixth aspect of the present invention performs the analysis method according to any one of the first to fifth aspects.

[0056] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0057] An embodiment of the present invention will now be described.

[0058] <Analysis of Soil Samples> A soil sample containing PFAS was prepared, and qualitative and quantitative analyses of the PFAS contained in the soil sample were performed. The soil sample was analyzed three times, and the standard deviation and coefficient of variation were calculated from the analysis results. The soil sample used for analysis was obtained from agricultural land at the National Agriculture and Food Research Organization (Tsukuba City, Ibaraki Prefecture).

[0059] Extraction of fluorine-containing compounds (PFAS) contained in soil was performed according to the following steps (1) to (9) (Extraction Step 1). In Extraction Step 1, PFAS was extracted using pure water. (1) A known concentration (10 μg / kg) of a target internal standard (surrogate) was added to 5 g of soil. (2) The mixture was stirred and mixed using a vortex mixer for 10 seconds. (3) 10 to 20 mL of pure water was added and the mixture was shaken on a shaker for 30 minutes. (4) The mixture was centrifuged for 10 minutes, and the supernatant was collected. (5) Steps (3) and (4) were repeated three times, and the supernatants were collected. (6) The supernatants from the three aqueous extractions were centrifuged for 10 minutes, and the supernatants were collected. (7) The mixture was purified using a solid-phase column. (8) Fraction 1 (neutral PFAS) and Fraction 2 (ionic PFAS) were collected, and each fraction was concentrated. (9) The molecular species and concentrations contained in fractions 1 and 2 were identified by LC-MS / MS.

[0060] The solid-phase column and LC-MS / MS conditions used in extraction step 1 are as follows: Solid-phase column: Oasis WAX (a water-wettable polymer-based solid-phase extraction column with a reversed phase and weak anion exchange mixed mode, manufactured by Waters) Column extraction solvent for fraction 1: 100% methyl alcohol Column extraction solvent for fraction 2: 0.1% ammonia in methanol LC-MS / MS device: LCMS-8060NX (manufactured by Shimadzu Corporation) Column: Shim-pack (a C18-based solid-phase extraction column, manufactured by Shimadzu Corporation) Mobile phase: A: 2 mmol / L ammonium acetate in H ２ O / acetonitrile = 95 / 5 B: acetonitrile Note that for each of the target internal standard substances M3-PFBS to M3-HFPO-DA shown in Table 1 below, calibration curves were prepared using standard products of 0.002 μg / L, 0.01 μg / L, 0.05 μg / L, 0.05 μg / L, 0.2 μg / L, 1 μg / L, 5 μg / L, and 10 μg / L.

[0061] The following Table 1 shows the target internal standard in extraction step 1. １３ C ３ -PFHxS, １３ C ８ -PFOS, １３ C８ -PFOA, and １３ C ９ The analytical results of PFSAs and PFCAs when using PFNA are shown in Table 1. In Table 1, the quantitative results for each of the PFSAs and PFCAs are shown, and the percentage of each target internal standard detected in the water extract sample is shown, with a predetermined concentration taken as 100%.

[0062]

[0063] Next, PFAS contained in the soil after aqueous extraction was extracted with an organic solvent (extraction step 2) according to the following steps (1) to (7). In extraction step 2, PFAS was extracted using 0.5% ammonia methanol. (1) 10 mL of 0.5% ammonia methanol was added to the soil after aqueous extraction in extraction step 1, and the mixture was shaken on a shaker for 30 minutes. (2) The mixture was centrifuged for 10 minutes, and the supernatant was collected. (3) Steps (1) and (2) were repeated, and the supernatants from three centrifugations were collected. (4) The supernatants from the three aqueous extractions were centrifuged for 10 minutes, and the supernatants were collected. (5) The mixture was purified using a solid-phase column. (6) Fraction 1 (neutral PFAS) and Fraction 2 (ionic PFAS) were collected, and each fraction was concentrated. (7) The molecular species and concentrations contained in Fractions 1 and 2 were identified using LC-MS / MS. The solid phase column and LC-MS / MS device used are the same as those used in extraction step 1, and therefore their explanation will be omitted.

[0064] Table 2 below shows the analytical results of the PFSAs and PFCAs extracted in extraction step 2. In Table 2, the quantitative results are shown for each of the PFSAs and PFCAs, and the percentage of each target internal standard detected in the 0.5% ammonia methanol extract sample is shown, with a predetermined concentration taken as 100%.

[0065]

[0066] Table 3 below shows the total amounts of PFSAs and PFCAs extracted in extraction steps 1 and 2, and the total amount of target internal standards extracted in extraction steps 1 and 2.

[0067]

[0068] From the analytical results shown in Tables 1, 2, and 3, PFHxS was extracted at an average of 237 ng / kg in extraction step 1, and at an average of 24 ng / kg in extraction step 2, for a total average of 261 ng / kg. From this, it is predicted that about 90.8% of the PFOA released into the soil migrates into the aqueous phase, i.e., groundwater, and about 9.2% may remain in the soil. In addition, the amount of PFOA extracted in extraction step 1 is １３ C ３ - PFHxS is 89% and was extracted in extraction step 2 １３ C ３ -Since PFHxS is 7%, the amount of PFHxS detected in extraction step 1 and extraction step 2, １３ C ３ -It is judged that the ratio is roughly close to the detected amount of PFHxS.

[0069] In addition, an average of 159 ng / kg of PFOS was extracted in extraction step 1, and an average of 251 ng / kg was extracted in extraction step 2, for a total average of 410 ng / kg. From this, it is estimated that about 38.8% of the PFOS released into the soil in this soil migrates into the aqueous phase, i.e., groundwater, and about 61.2% may remain in the soil. In addition, 44% of the PFOS was extracted in extraction step 1 as M8-PFOS, and 44% was extracted in extraction step 2 as M8-PFOS. １３ C ８ -Since PFOS is 46%, the amount of PFOS detected in extraction step 1 and extraction step 2, １３ C ８ -It is judged that the ratio is close to the detected amount of PFOS.

[0070] In addition, PFOA was extracted at an average of 881 ng / kg in extraction step 1, and at an average of 197 ng / kg in extraction step 2, for a total average of 1078 ng / kg. From this, it is estimated that about 81.7% of the PFOA released into the soil migrates into the aqueous phase, i.e., groundwater, and about 18.3% may remain in the soil. In addition, the amount of PFOA extracted in extraction step 1 １３ C ８ - PFOA is 90% and extracted in extraction step 2 １３ C ８ -Since PFOA is 9%, the amount of PFOA detected in extraction step 1 and extraction step 2, １３ C ８ -It is judged that the ratio is roughly close to the amount of PFOA detected.

[0071] In addition, PFNA was extracted at an average of 498 ng / kg in extraction step 1, and at an average of 233 ng / kg in extraction step 2, for a total average of 731 ng / kg. From this, it is predicted that about 68.1% of the PFNA released into the soil in this soil sample migrates into the aqueous phase, i.e., groundwater, and about 31.9% may remain in the soil. In addition, the PFNA extracted in extraction step 1 １３ C ９ - PFNA is 70% and extracted in extraction step 2 １３ C ９ -Since PFNA is 27%, the amount of PFNA detected in extraction step 1 and extraction step 2, １３ C ９ -It is considered that the ratio is close to the amount detected by PFNA.

[0072] As described above, the target internal standard substance added to the soil sample and the PFAS already contained in the soil sample behave similarly in the aqueous phase and the soil phase, and it is considered that the present invention can diagnose the retention of PFAS in soil.

[0073] Furthermore, as shown in Tables 1, 2, and 3, the detected amount of the target internal standard substance is within the range of a standard deviation of 1 to 5%. １３ C ３ -PFHxS, １３ C８ -PFOS, １３ C ８ -PFOA, １３ C ９ It was confirmed that the reproducibility of all PFNAs was within a standard deviation range of 2-3%. In addition, the total of the target internal standard substances in extraction step 1 and extraction step 2 was 27-159%, respectively. １３ C ３ -PFHxS, １３ C ８ -PFOS, １３ C ８ -PFOA, １３ C ９ -PFNA showed a detection rate of 90 to 99%, confirming that it was possible to recover approximately 100% of the target internal standard substance added to the soil sample.

[0074] For example, from the evaluation results in Tables 1 to 3 above, compared to perfluorooctanesulfonic acid amide (FOSA), in N-MeFOSA and N-EtFOSA, the hydrogen bonded to the nitrogen is replaced with a methyl group or an ethyl group, and intramolecular hydrogen bonding between the oxygen of the sulfonic acid amide and the amide group is not possible, and as a result, the unshared electron of the oxygen of the sulfonic acid amide bonds strongly with the transition metal in the soil. For this reason, it is considered that the poor extraction efficiency of N-MeFOSA and N-EtFOSA is the reason for the low detection accuracy. In addition, １３ C ４ The large extraction amount of -8:2diPAP is considered to be due to the influence of impurities.

[0075] Table 4 below shows the groundwater migration ratio and soil residual ratio for each PFAS determined from the evaluation results in Tables 1 to 3. The soils used for soil samples 1 to 3 are black soils, a type of soil that is typical of Japan and is extremely difficult to analyze for PFAS due to the large number of analytical impurities. However, as described above, various PFASs were detected with high reliability. Furthermore, as shown in Table 4, the groundwater migration ratio and soil residual ratio for each PFAS show different trends, and it is thought that the groundwater migration ratio and soil residual ratio will also show different trends depending on the soil, i.e., differences in soil texture.

[0076]

[0077] Tables 5 and 6 below show the mean values, standard deviations, and coefficients of variation for PFSAs and PFCAs extracted from the Andosol samples. Each of the analytical results shown in Tables 5 and 6 was evaluated using the same Andosol sample. Table 5 shows the analytical results from this extraction process 1, and Table 6 shows the analytical results from the Ministry of the Environment's leaching test (provisional measurement method for PFOS, PFOA, and PFHxS in soil (Ministry of the Environment, Water and Air Environment Bureau, Environmental Management Division, July 31, 2023)). The analysis using extraction process 1 shown in Table 5 was performed by extracting 5 g of soil sample three times with water, shaking for 30 minutes each, for a total of 1 hour and 30 minutes, and using a total of 50 mL of water for the three extractions. The results of the Ministry of the Environment's leaching test shown in Table 6 were obtained by soaking 60 g of soil sample in 600 mL of water for 6 hours.

[0078]

[0079]

[0080] The analytical results of this method shown in Table 5 are judged to show roughly similar concentrations compared to the Ministry of the Environment's leaching test method shown in Table 6, even though the test volume was reduced from 60 g to 5 g, the water volume from 600 mL to 50 mL, and the extraction time from 6 hours to 1 hour and 30 minutes. Comparing this method shown in Table 5 with the Ministry of the Environment's leaching test method shown in Table 6, the average PFHxS concentrations for both methods were 3 ng / kg, PFOS were 7 ng / kg and 4 ng / kg, PFOA were 65 ng / kg and 62 ng / kg, and PFNA were 35 ng / kg and 11 ng / kg, indicating roughly similar concentrations. This method is simpler and requires less time than the Ministry of the Environment's leaching test method, but the results are generally closer, indicating it is a useful method for assessing PFAS leaching from soil to water.

[0081] The present invention can be used to analyze PFAS contained in contaminated soil and to diagnose the contaminated soil. Furthermore, the absorption and migration of PFAS from soil to crops and other sources via water can be used to assess the risk of PFAS to humans. Because the present invention can be used to analyze PFAS in solids such as soil and to diagnose contamination, it can also be applied to bottom sediments and waste.

Claims

1. A method for analyzing organic fluorine compounds in soil, comprising: an extraction step 1 in which the soil is extracted with water; an extraction step 2 in which the soil after extraction step 1 is extracted with an organic solvent; and an analysis step in which the water extract obtained in extraction step 1 and the organic solvent extract obtained in extraction step 2 are analyzed, respectively.

2. The analytical method according to claim 1, wherein the organic solvent is a water-soluble organic solvent selected from alcohols, acetonitrile, ammonia-methanol, and mixed solvents thereof, and the alcohols are selected from methyl alcohol and ethyl alcohol.

3. The analytical method according to claim 1 or 2, wherein the organic solvent contains an alkaline compound, and the alkaline compound is selected from aqueous ammonia.

4. The analytical method according to claim 1, wherein a target internal standard substance is added to the soil before carrying out the extraction step 1.

5. The analytical method according to claim 1, wherein the migration rate of the organofluorine compound into groundwater is determined from the ratio of the amount of the organofluorine compound contained in the aqueous extract to the total amount of the amount of the organofluorine compound contained in the aqueous extract and the amount of the organofluorine compound contained in the organic solvent extract, and the remaining rate in soil is determined from the ratio of the amount of the organofluorine compound contained in the organic solvent extract to said total amount.

6. A method for diagnosing soil, which comprises carrying out the analytical method according to any one of claims 1 to 5.

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