🌿 Heavy metals in soil (ICP-OES)
In short
Multi-element determination of heavy metals (Pb, Cd, Cr, Cu, Zn, Ni, As, Hg) in soil after acid digestion, by ICP-OES method. The test is performed according to PN-EN ISO 11885:2009; Linear range: 3–5 orders of magnitude. The procedure comprises 6 steps (about 1 days 1 h 43 min–1 days 1 h 45 min in total); it is used for: Assessment of soil contamination with heavy metals (2016 Polish regulation), Testing soils on post-industrial sites (brownfields), Environmental monitoring around industrial plants.
At a glance
- Standard: PN-EN ISO 11885:2009
- Category: Environmental
- Procedure steps: 6
- Total time of stages: 1 days 1 h 43 min–1 days 1 h 45 min
- Determined elements: Pb, Cd, Cr, Cu, Zn, Ni, As, Hg, Co, Mn, Fe, V, Ba + others
- Detection limit: 0.01–1 mg/kg d.m. (element-dependent)
- Linear range: 3–5 orders of magnitude
Overview
Determination of heavy metals in soil is a key element of soil environment assessment. Metals such as lead, cadmium, chromium, copper, zinc, nickel, arsenic, and mercury accumulate in soil and do not biodegrade, posing a long-term threat to ecosystems, groundwater, and human health.
The 2016 Polish regulation on soil quality standards specifies permissible metal concentrations depending on soil group (I — residential areas, IV — industrial). E.g., lead: 100 mg/kg (gr. I) to 600 mg/kg (gr. IV), cadmium: 1 mg/kg (gr. I) to 15 mg/kg (gr. IV).
The method involves soil sample digestion with acid mixture (HNO₃ + HCl, i.e., aqua regia, or HNO₃ + HF + HClO₄) in microwave digester, followed by multi-element analysis of the solution by ICP-OES. In one analytical cycle, 20–30 elements are determined simultaneously.
Method principle
The soil sample is digested in closed PTFE vessels in a microwave digester with acid mixture (aqua regia: 3 vol. HCl + 1 vol. HNO₃ according to ISO 11466, or mixture with HF for complete dissolution of silicates). The digest is diluted with ultrapure water and analyzed on ICP-OES spectrometer. Argon plasma (6000–10000 K) atomizes and excites elements, which emit radiation at characteristic wavelengths. Detection on a CCD polychromator enables simultaneous measurement of many elements.
Applications
- Assessment of soil contamination with heavy metals (2016 Polish regulation)
- Testing soils on post-industrial sites (brownfields)
- Environmental monitoring around industrial plants
- Agricultural soil quality assessment
- Control of sewage sludge used in agriculture
- Soil remediation — effectiveness verification
Key parameters
| Parameter | Value |
|---|---|
| Determined elements | Pb, Cd, Cr, Cu, Zn, Ni, As, Hg, Co, Mn, Fe, V, Ba + others |
| Detection limit | 0.01–1 mg/kg d.m. (element-dependent) |
| Linear range | 3–5 orders of magnitude |
| Precision (CV) | 3–10% |
| Digestion | Aqua regia, 180°C, 30 min (microwave) |
Standard
- Standard number
- PN-EN ISO 11885:2009
- Title (PL)
- Jakość wody — Oznaczanie wybranych pierwiastków metodą optycznej spektrometrii emisyjnej z plazmą indukcyjnie sprzężoną (ICP-OES)
- Title (EN)
- Water quality — Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES)
Step-by-step procedure
-
Sample preparation
Dry soil at 40°C. Sieve through 2 mm sieve, then grind <2 mm fraction to <0.25 mm. Weigh 0.5 g.
-
Microwave digestion
Add 9 mL HCl + 3 mL HNO₃ (aqua regia). Program: ramp to 180°C/15 min, hold 20 min.
-
Filtration and dilution
After cooling, transfer quantitatively to 50 mL flask. Fill to mark with ultrapure water. Filter (0.45 µm).
-
ICP-OES calibration
Prepare standards: 0, 0.1, 0.5, 1, 5, 10, 50 mg/L in 5% HNO₃. Calibrate instrument.
-
Sample measurement
Measure samples with blank and CRM every 10 samples. Check spike recovery (90–110%).
-
Calculations
Convert concentrations to mg/kg dry mass of soil. Account for dilution and moisture.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| ICP-OES spectrometer | Thermo iCAP 7400, Agilent 5800, PerkinElmer Avio 220 | 350,000–700,000 PLN |
| Microwave digester | Anton Paar Multiwave 5000, CEM Mars 6, Milestone Ethos UP | 150,000–300,000 PLN |
| Autosampler | Thermo ASX-560, Agilent SPS 4 | 25,000–60,000 PLN |
| Analytical balance | Mettler Toledo ME204, 0.1 mg accuracy | 5,000–15,000 PLN |
| PTFE digestion vessels | 100 mL vessels, set of 6–12 pcs. | 500–2,000 PLN/pc. |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Nitric acid 65% suprapur | 7697-37-2 | Trace analysis grade |
| Hydrochloric acid 30% suprapur | 7647-01-0 | Aqua regia component |
| Multi-element standard solutions | — | ICP Multi-Element Standard IV, 1000 mg/L, certified CRM |
| Argon 5.0 | 7440-37-1 | Plasma gas, 99.999% purity |
| Ultrapure water | — | Resistivity >18.2 MΩ·cm |
Health and safety (OHS)
- Aqua regia — highly corrosive, releases chlorine. Work in fume hood.
- HF (if used) — extremely dangerous, causes deep burns and hypocalcemia
- Microwave digester — pressure up to 40 bar, follow safety procedures
- Acid-resistant gloves, apron, safety goggles mandatory
- Acid waste with metals — collect separately
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 11885:2009 — “Water quality — Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES)”.
How does this method work?
The soil sample is digested in closed PTFE vessels in a microwave digester with acid mixture (aqua regia: 3 vol. HCl + 1 vol.
What is the measuring range and accuracy?
Determined elements: Pb, Cd, Cr, Cu, Zn, Ni, As, Hg, Co, Mn, Fe, V, Ba + others; Detection limit: 0.01–1 mg/kg d.m. (element-dependent); Linear range: 3–5 orders of magnitude; Precision (CV): 3–10%.
How long does the test take?
The times given for the individual stages add up to approximately 1 days 1 h 43 min–1 days 1 h 45 min. The procedure comprises 6 steps.
What equipment is required?
ICP-OES spectrometer, Microwave digester, Autosampler, Analytical balance, PTFE digestion vessels. Indicative cost of the core instrument (ICP-OES spectrometer): 350,000–700,000 PLN.
Where is this test used?
Assessment of soil contamination with heavy metals (2016 Polish regulation); Testing soils on post-industrial sites (brownfields); Environmental monitoring around industrial plants; Agricultural soil quality assessment; Control of sewage sludge used in agriculture; Soil remediation — effectiveness verification.
What safety precautions apply?
Aqua regia — highly corrosive, releases chlorine. Work in fume hood.; HF (if used) — extremely dangerous, causes deep burns and hypocalcemia; Microwave digester — pressure up to 40 bar, follow safety procedures; Acid-resistant gloves, apron, safety goggles mandatory; Acid waste with metals — collect separately.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 11885.