🌿 Heavy metals in soil (ICP-OES)

Environmental PN-EN ISO 11885

Overview

STATUS (as of 02.11.2026). PN-EN ISO 11885:2009 — English version (Polish title in the PKN catalogue: “Jakość wody — Oznaczanie wybranych pierwiastków metodą optycznej spektrometrii emisyjnej z plazmą wzbudzoną indukcyjnie (ICP-OES)”), published 23.07.2009, implements EN ISO 11885:2009 and ISO 11885:2007 [IDT]; it replaced PN-EN ISO 11885:2001 (Polish version). The card has no withdrawal note — the standard is current. It is a standard for measurement in solution; soil digestion is covered by a separate standard: in the regulation — PN-ISO 11466:2002 “Jakość gleby — Ekstrakcja pierwiastków śladowych rozpuszczalnych w wodzie królewskiej” (implements ISO 11466:1995 “Soil quality — Extraction of trace elements soluble in aqua regia” [IDT]; withdrawn on 21.11.2023, the card names no successor; ISO 11466:1995 itself was withdrawn on 2.08.2022). Aqua regia digestion of soil, sludge and waste is described today by ISO 54321:2020 “Soil, treated biowaste, sludge and waste — Digestion of aqua regia soluble fractions of elements”, adopted by CEN as EN ISO 54321:2021 (which replaced EN 13657:2002) and by PKN as PN-EN ISO 54321:2021-07 — English version, Polish title “Gleba, uzdatnione bioodpady, osady ściekowe oraz odpady — Roztwarzanie frakcji pierwiastków rozpuszczalnych w wodzie królewskiej”, published on 2.07.2021.

MEASUREMENT SCOPE (PN-EN ISO 11885, clause 1). Dissolved elements, elements bound to particles and total content in different types of water for 35 elements: aluminium, antimony, arsenic, barium, beryllium, bismuth, boron, cadmium, calcium, chromium, cobalt, copper, gallium, indium, iron, lead, lithium, magnesium, manganese, molybdenum, nickel, phosphorus, potassium, selenium, silicon, silver, sodium, strontium, sulfur, tin, titanium, tungsten, vanadium, zinc and zirconium — mercury is not on the list. Taking the interferences into account, the same elements can be determined in digests of water, sewage sludge and sediments. The scope may be extended to other matrices if it is shown that the additional interferences have been carefully considered and corrected for — the user demonstrates fitness for purpose. A soil digest is such another matrix.

AQUA REGIA DIGESTION (ISO 54321:2020). The standard describes digestion of soil, treated biowaste, sludge and waste with aqua regia in three ways: A1 — heating under reflux for (120 ± 10) min, A2 — heating block at (105 ± 5) °C for (120 + 10) min, B — microwave digestion in a closed vessel at (175 ± 5) °C for (10 ± 1) min; each is followed by filtration or centrifugation (clause 4). Aqua regia does not necessarily decompose the sample completely: the extracted concentrations represent the aqua regia soluble fraction under the test conditions, not necessarily the total content — for environmental protection purposes they are considered fit for purpose (clause 1). Compared with ISO 11466, which required 16 h of standing after the acids were added, heating starts once the first strong reaction has ceased — in validation the difference between 2 h and 16 h of waiting was negligible (introduction).

REGULATIONS. Assessment of land surface contamination — Regulation of the Minister of the Environment of 1.09.2016 (Dz.U. 2016 item 1395; in force, amended by the Regulation of the Minister of Climate and Environment of 31.10.2024, Dz.U. 2024 item 1657). Annex 3 point 4 gives, for arsenic, barium, chromium, tin, zinc, cadmium, cobalt, copper, molybdenum, nickel and lead, the ICP-OES reference methodology: a test procedure based on PN-ISO 11466 and PN-EN ISO 11885 (PN-ISO 11466 has been withdrawn since 21.11.2023); mercury is determined there by another technique — cold vapour (PN-ISO 16772) or amalgamation. Permissible contents in soil (0–0.25 m, mg/kg dry mass of the earthy fraction ≤ 2 mm dried at 105 °C) are given in Annex 1 as applicable from 15.05.2025, e.g. lead: group I 200, group IV 600; cadmium: group I 2, group IV 15. Group I includes residential areas among others, group IV — industrial areas, mining land and transport areas (§ 3).

WHAT WE DO NOT GIVE HERE. Of PN-EN ISO 11885, clauses 1–4 and the beginning of clause 5 (Table 1 up to cobalt) are available; interferences, reagents, apparatus, procedure and expression of results (clauses 6–11) and precision data are outside this text — we give no standard concentrations, calibration points or control frequencies. Of ISO 54321 the text up to the beginning of clause 9 is available — we give no precision data from Annexes A–B, which are outside it; we have not read the text of PN-ISO 11466.

Method principle

The soil sample — the earthy fraction ≤ 2 mm — is digested with aqua regia, i.e. hydrochloric and nitric acid in a volume ratio of 3 : 1, under reflux, in a heating block or in a closed vessel in a laboratory microwave system; after filtration or centrifugation and making up to volume, the solution is analysed by ICP-OES (ISO 54321, clauses 4 and 8).

In the measurement the solution is nebulized, the aerosol is transported to the plasma torch and the elements are excited in a plasma generated by inductively coupled radio-frequency power; the spectra are dispersed by a grating spectrometer, the line intensities are measured by a detector and the background is corrected by an appropriate technique (PN-EN ISO 11885, clause 4).

Applications

• Assessment of land surface contamination — metals and the metalloid in soil and ground (Regulation of the Minister of the Environment of 1.09.2016, Dz.U. 2016 item 1395, Annex 3 point 4)
• Comparison of results with permissible contents for land groups and subgroups (Annex 1 as worded by Dz.U. 2024 item 1657)
• Aqua regia digests of soil, treated biowaste, sludge and waste (ISO 54321, clause 1) — for matrices outside the scope of PN-EN ISO 11885 after demonstrating that interferences have been taken into account

Key parameters

Standard

Standard number

PN-EN ISO 11885:2009

Title (PL)

Jakość wody — Oznaczanie wybranych pierwiastków metodą optycznej spektrometrii emisyjnej z plazmą wzbudzoną indukcyjnie (ICP-OES)

Title (EN)

Water quality — Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES)

Step-by-step procedure

1. Sample preparation

   Pretreatment of the soil e.g. according to ISO 11464 and determination of dry matter (ISO 54321, 8.1); the earthy fraction ≤ 2 mm is analysed and the result refers to dry mass dried at 105 °C (regulation, Annex 1, explanatory note 1).

2. Blank

   Digestion in parallel without sample, with the same quantities of reagents; acceptable limits are set by the laboratory (ISO 54321, 8.2).

3. Digestion — method A1

   About 3 g of sample weighed to 0.001 g, moistened with 0.5–1.0 ml of water, (21.0 ± 0.1) ml of HCl and (7.0 ± 0.1) ml of HNO₃; absorption vessel with about 15 ml of HNO₃ 0.5 mol/l; stand until effervescence almost ceases, heat under reflux for 2 h, rinse with 10 ml of HNO₃ 0.5 mol/l and make up to the mark; 30 ml of aqua regia suffice to oxidize about 0.5 g of organic carbon (ISO 54321, 8.3.1).

4. Digestion — methods A2 and B

   A2: at most 2 g of sample (typically 0.5–1 g) with at most 0.15 g of organic carbon, (6.0 + 0.1) ml of HCl and (2.0 + 0.1) ml of HNO₃, heating block at (105 ± 5) °C for (120 + 10) min; B: the same sample amount, (6 ± 0.1) ml of HCl and (2 ± 0.1) ml of HNO₃ in a closed vessel, heating at about 10–15 °C/min to (175 ± 5) °C and (10 ± 1) min at that temperature; in both methods 1 ml of additional concentrated HNO₃ for each additional 0.1 g of organic carbon; then filtration or centrifugation (ISO 54321, clause 4, 8.3.2, 8.4).

5. ICP-OES measurement

   Selection of lines according to Table 1 of PN-EN ISO 11885, taking spectral interferences into account; calibration with a calibration blank, check with an independent solution and drift control; background correction (clauses 4–5, 3.4–3.8).

6. Result

   Content of the aqua regia soluble element in mg/kg dry mass; in contamination assessment — comparison with the value in Annex 1 of the regulation for the land group.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The digestion standard warns: some reagents are highly corrosive and very toxic, and the work involves high temperature and high pressure — only a laboratory-grade microwave system (not a domestic oven), work in a fume hood, pressurized vessels are not opened before they have cooled down (ISO 54321, warning)
• Strong oxidising reagents with samples rich in organic matter can form explosive intermediates (ISO 54321, warning)

Frequently asked questions