Analysis of Metals Contained in Soil

Significance of the Topic

Soil contamination by heavy metals is a growing environmental and public health concern, especially in regions undergoing redevelopment of former industrial sites. Accurate analysis of metal levels in soils is essential to assess contamination, enforce regulations, and protect human health.

Objectives and Overview of the Study

This application note presents analytical procedures for determining harmful metal concentrations in soils, in compliance with Japan’s Soil Contamination Countermeasures Law. The focus is on evaluating soil elution standards and total content levels for target elements using atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), and ICP mass spectrometry (ICP-MS).

Methodology and Sample Preparation

Two preparation methods are described:

• Elution Standard Method: Soil is dried, sieved (2 mm), mixed with 1 M HCl (or pH-adjusted buffer for Cr6+), at a 10:1 liquid-to-solid ratio, shaken for six hours, centrifuged, and filtered (0.45 μm).
• Total Content Method: Dried and sieved soil (2 mm) is mixed with 1 M HCl (or alkaline buffer for Cr6+) at a 100:3 ratio, shaken for two hours, then filtered (0.45 μm).

Used Instrumentation

Flame and flameless AAS (FAA, FLAA), hydride generation AAS, vapor‐reduction AAS for mercury, ICP-OES, and ICP-MS were employed to cover detection of Cd, Cr6+, Hg, Se, Pb, As, and B.

Key Results and Discussion

Analysis of certified standard soils (JSAC0411, SRM2711, NIES No. 2) demonstrates:

• Cd measurements by AAS, ICP-OES, and ICP-MS agree closely (e.g., 0.2 mg/kg in JSAC0411).
• Pb determinations range from 10.5 mg/kg (FAA) to 12.0 mg/kg (ICP-MS) in JSAC0411, showing high consistency across techniques.
• Elution values tend to be lower than total content due to incomplete dissolution in mild acid conditions.

Benefits and Practical Applications

The described methods enable laboratories to:

• Monitor compliance with soil contamination regulations.
• Support site redevelopment by providing reliable data on metal levels.
• Implement quality control through cross‐validation among AAS, ICP-OES, and ICP-MS.

Future Trends and Opportunities

Advances may include integration of high-resolution ICP-MS for ultra-trace detection, portable field analyzers for on-site screening, and coupling with chromatographic speciation to distinguish toxic metal forms.

Conclusion

The combination of standardized sample preparation and complementary spectrometric techniques provides robust, reproducible analysis of heavy metals in soil. Elution and total content methods serve different regulatory needs, and instrument choice should balance sensitivity requirements and sample throughput.