토양오염공정시험기준 6가크롬 분석의 이해와 결과 해석 Understanding of a Korean Standard for the Analysis of Hexavalent Chromium in Soils and Interpretation of their Results원문보기
A new Korean standard for the determination of Cr(VI) in soils has been officially published as ES 07408.1 in 2009. This analytical method is based on the hot alkaline digestion and colorimetric detection prescribed by U.S. EPA method 3060A and 7196A. The hot alkaline digestion accomplished using 0....
A new Korean standard for the determination of Cr(VI) in soils has been officially published as ES 07408.1 in 2009. This analytical method is based on the hot alkaline digestion and colorimetric detection prescribed by U.S. EPA method 3060A and 7196A. The hot alkaline digestion accomplished using 0.28 M $Na_2CO_3$ and 0.5 M NaOH solution (pH 13.4) at $90{\sim}95^{\circ}C$ determines total Cr(VI) in soils extracting all forms of Cr(VI), including water-soluble, adsorbed, precipitated, and mineral-bound chromates. This aggressive alkaline digestion, however, proved to be problematic for certain soils which contain large amounts of soluble humic substances or active manganese oxides. Cr(III) could be oxidized to Cr(VI) by manganese oxides during the strong alkaline extraction, resulting in overestimation (positive error) of Cr(VI). In contrast, Cr(VI) reduction by dissolved humic matter or Fe(II) could occur during the neutralization and acidic colorimetric detection procedure, resulting in underestimation (negative error) of Cr(VI). Futhermore, dissolved humic matter hampered the colorimetric detection of Cr(VI) using UV/Vis spectrophotometer due to the strong coloration of the filtrate, resulting in overestimation (positive error) of Cr(VI). Without understanding the mechanisms of Cr(VI) and Cr(III) transformation during the analysis it could be difficult to operate the experiment in laboratory and to evaluate the Cr(VI) results. For this reason, in this paper we described the theoretical principles and limitations of Cr(VI) analysis and provided useful guidelines for laboratory work and Cr(VI) data analysis.
A new Korean standard for the determination of Cr(VI) in soils has been officially published as ES 07408.1 in 2009. This analytical method is based on the hot alkaline digestion and colorimetric detection prescribed by U.S. EPA method 3060A and 7196A. The hot alkaline digestion accomplished using 0.28 M $Na_2CO_3$ and 0.5 M NaOH solution (pH 13.4) at $90{\sim}95^{\circ}C$ determines total Cr(VI) in soils extracting all forms of Cr(VI), including water-soluble, adsorbed, precipitated, and mineral-bound chromates. This aggressive alkaline digestion, however, proved to be problematic for certain soils which contain large amounts of soluble humic substances or active manganese oxides. Cr(III) could be oxidized to Cr(VI) by manganese oxides during the strong alkaline extraction, resulting in overestimation (positive error) of Cr(VI). In contrast, Cr(VI) reduction by dissolved humic matter or Fe(II) could occur during the neutralization and acidic colorimetric detection procedure, resulting in underestimation (negative error) of Cr(VI). Futhermore, dissolved humic matter hampered the colorimetric detection of Cr(VI) using UV/Vis spectrophotometer due to the strong coloration of the filtrate, resulting in overestimation (positive error) of Cr(VI). Without understanding the mechanisms of Cr(VI) and Cr(III) transformation during the analysis it could be difficult to operate the experiment in laboratory and to evaluate the Cr(VI) results. For this reason, in this paper we described the theoretical principles and limitations of Cr(VI) analysis and provided useful guidelines for laboratory work and Cr(VI) data analysis.
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문제 정의
분석과정 중에 발생할 수 있는 오류를 최대한 줄이기 위해서는 pH와 산화환원전위 (Eh)에 따른 Cr(VI) 과 Cr(III) 사이의 열역학적이고 동역학적인 관계에 대한 이해가 필수적이다. 그래서 본 논문에서는 개정된 토양오염공정시험기준 Cr(VI) 분석법 (ES 07408.1, 2009)의 이론적 원리와 실험적 제한점을 고찰하여, 토양시료의 6가크롬 추출과 정량 분석결과를 해석하는데 도움이 되고자 한다.
가설 설정
Cr(VI)이 자연적으로 토양에 존재하는 경우는 극히 드물고, 토양에 존재한다면 대부분은 인위적인 토양투입에 의한 것이다. 유기물 함량이 비교적 높고, pH가 중성 이하인 농경지 표토층에서는 투입된 Cr(VI)이, 토양 매트릭스와 Cr(VI) 농도에 따라 반응속도는 다르겠지만, Cr(III)으로 환원될 것이다. 인위적인 투입이 없고, 유기물 함량이 높은 농경지 표토층에서는, 망간산화물에 의한 Cr(III)의 산화가 거의 일어나지 않기 때문에, Cr(VI)이 존재하지 않는다고 볼 수 있다.
이론/모형
2. Change of Eh-pH condition (three dark circles) during the extraction (1), neutralization (2), and colorimetric detection procedure (3) using Korean Standard ES 07408.1.
Relation of mobile Cr(VI) contents of 116 agricultural and industrial soils to their background colours of extracts. Mobile Cr(VI) was determined using German DIN 19734 (1999) with colorimetric measurement (see Fig. 1).
Relation of total Cr(VI) contents of 40 agricultural soils to their organic matter contents. Total Cr(VI) was determined using Korean Standard ES 07408.1 (2009) with colorimetric measurement.
, 2000). 이 분석법은 U.S. EPA 3060A (1996)와 7196A (1992)를 수용한 것이다 (Fig. 1). 미국에서는 자외선-가시광선 분광광도계를 이용하는 것 외에도 U.
후속연구
중성의 pH 조건에서 Cr(VI)의 환원 속도가 비록 느리긴 하지만, 가능한 오래 보관하지 않고 바로 정량하는 것이 바람직하다. 앞으로 세부적인 연구가 더 필요하겠지만, 중성화 단계 없이 곧바로 Cr(VI)을 정량하는 것도 고려해 봐야 한다고 사료된다.
질의응답
핵심어
질문
논문에서 추출한 답변
자연환경에서 크롬은 어떠한 형태로 존재하는가?
크롬의 이동성, 생물학적 이용가능성 및 이와 연관된 생태독성은 크롬의 화학적 형태와 밀접한 관계가 있다. 자연환경에서 크롬은 주로 6가크롬 (Cr(VI))과 3가크롬 (Cr(III))의 산화상태로 존재하며, 대부분의 Cr(VI)은 Cr(III)에 비해 용해도, 이동성, 생물학적 이용가능성 및 생태독성이 10~100배 더 높다 (Ruedel et al., 2000; Welp, 1999; Welp et al.
우리나라와 외국의 크롬 토양 오염기준은?
, 2010). 토양 오염기준은 외국의 경우 토지이용과 보호대상에 따라 0.29~5 mg Cr(VI) kg-1이고, 우리나라 농경지의 경우 우려기준과 대책 기준은 각각 5와 15 mg Cr(VI) kg-1이다 (Table 1). 독일과 일본에서는 지하수 보호를 위한 토양 침출수 농도를 각각 0.
환경부 토양오염공정 시험기준에 따라 크롬 산분해를 할 경우의 단점은?
1). 그러나 산 분해를 할 경우, 추출과정에서 함께 용출된 전자공여체인 유기물, Fe2+ 등이 Cr(VI)을 Cr(III)으로 환원시킬 위험이 있기 때문에, 실제 토양에 존재하는 것보다 적은 양의 Cr(VI)이 검출될 수 있다 (Jung et al., 2011; 아래 본문 내용 참고).
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