🌿 Microwave digestion of sewage sludge, treated biowaste and soil with concentrated nitric acid before determination of elements — portion up to 2 g (usually 0.5–1 g) with at most 0.5 g organic carbon, 10 ml HNO3 15 mol/l, heating at 10–15 °C/min to (175 ± 5) °C and 10 min at that temperature in a closed vessel of PFA, PTFE or quartz (at least 45 ml, at least 3000 kPa); the result is the nitric acid soluble fraction, not the total content, PN-EN 16173

Environment PN-EN 16173

Overview

WHAT THE STANDARD COVERS. The scope on the PKN catalogue card of PN-EN 16173:2012 (English version) begins (our translation): “This European Standard specifies a method for microwave digestion of sewage sludge, treated biowaste and soil using nitric acid. The method is suitable for microwave-assisted nitric acid extraction from sewage sludge, treated biowaste and soil of the following elements: cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), nickel (Ni) and zinc (Zn). This European Standard may also be applied to the extraction of other elements. Digestion with nitric acid does not always ensure total decomposition of the sample”; the card then contains a note on dependence on the measurement method. The list of elements on the card (seven) is shorter than in Clause 1 of the text of EN 16173:2012 we read (over 60 — below); the sources read do not say why. We read the text of the standard in the iTeh sample of SIST EN 16173:2013 (text of EN 16173:2012, English): from the title page through the contents, foreword, introduction and Clauses 1–6 up to and including the description of the heating programme in Clause 7. Outside the sample remain the rest of Clause 7 (after cooling — filtration, centrifugation or settling, transfer to a flask), Clause 8 (test report) and Annex A (repeatability and reproducibility data).

ACCORDING TO THE TEXT OF EN 16173:2012 (introduction, Clauses 1–6, part of Clause 7). The standard was prepared by CEN/TC 400 “Horizontal standards in the fields of sludge, biowaste and soil” (secretariat DIN) under European Commission mandate M/330. Introduction: multi-element digestion before analysis; nitric acid need not decompose the sample completely, and the extract need not reflect total concentrations — for most environmental applications, however, the result is fit for purpose. Validation (Table 1): municipal sludge, compost, sludge-amended soils. Warnings: strongly corrosive and partly very toxic reagents, high temperature and pressure; a laboratory microwave system with isolated, corrosion-resistant safety devices is required — domestic ovens must not be used, because corrosion from acid fumes may disable the safety devices and fail to switch off the magnetron with the door open; work in a fume hood; with samples rich in organic matter explosive intermediates are possible; pressurised vessels must not be opened before cooling. Scope (1): microwave digestion with nitric acid before determination of Al, As, Ba, Be, Bi, B, Cd, Ca, Ce, Cs, Cr, Co, Cu, Dy, Er, Eu, Gd, Ga, Ge, Au, Hf, Ho, In, Ir, Fe, La, Pb, Li, Lu, Mg, Mn, Hg, Mo, Nd, Ni, Pd, P, Pt, K, Pr, Rb, Re, Rh, Ru, Sm, Sc, Se, Si, Na, Sr, S, Te, Tb, Tl, Th, Tm, Ti, W, U, V, Yb, Y, Zn, Zr — and other elements. References (2): EN 16179 (sample pre-treatment), EN ISO 3696. Principle (3): the portion with acid in a sealed vessel of fluorocarbon polymer or quartz is heated by microwaves; after cooling the contents are filtered, centrifuged or allowed to settle, transferred to a flask, made up and measured by an appropriate method. Sources of error (4): the sample must not be heated before digestion and volatile products must not escape; the container can be a source of error (elemental mercury quickly penetrates polyethylene in both directions, glass contributes B, Na, K, Al); quartz, silicates, titanium dioxide, alumina and other oxides may not dissolve — elements bound in them are considered immobile in the environment; high acid and solute concentrations in the solution must be addressed in the measurement; the whole portion must be in contact with the acid; with samples containing volatile or easily oxidisable substances one starts with at most 0.1 g, and with a vigorous reaction the sample is left in the open vessel until it ceases (e.g. rapid release of CO2 from carbonates); filtration must not introduce contamination. Reagents (5): analytical grade, a blank with the same amounts of acids; water at least of grade 2 according to EN ISO 3696; nitric acid 15 mol/l (ρ = 1.4 kg/l) and 0.5 mol/l. Apparatus (6): microwave system resistant to corrosion, with temperature feedback control — control to ± 5 °C, power adjustment within 2 s, sensors accurate to ± 2 °C, including at the final temperature of (175 ± 5) °C; temperature feedback is the primary performance mechanism of the method, because vessels and instruments differ; with a deviation of more than 2 °C from an external calibrated thermometer the temperature measurement system is calibrated; turntable at least 3 rpm; vessels of microwave-transparent materials (PFA, modified PTFE, quartz), with an internal volume of at least 45 ml, withstanding at least 3000 kPa, with controlled pressure relief and an inert inner wall; energy regulation according to the temperature of the solution (measured indirectly in each vessel, optically from outside or in only one vessel); vessels cleaned e.g. in 10 % nitric acid; hardened ashless cellulose filter papers, 50 ml or 100 ml flasks, balance to 0.1 mg or better. Procedure (7): reagent blank in parallel; portion up to 2 g (usually 0.5–1 g of dry sample) with at most 0.5 g organic carbon, weighed to 0.001 g; (10 ± 0.1) ml nitric acid 15 mol/l in a fume hood, standing until visible reaction has stopped; liquid sludge — according to EN ISO 15587-2 or after suitable drying; weigh the vessel before digestion; fill all positions of the carousel (usually 6, 12, 16 or 40) — the missing ones with vessels containing acid only, so that energy absorption is the same; the method is operationally defined: heating at 10–15 °C/min to (175 ± 5) °C and (10 ± 1) min at that temperature, cooling to room temperature; too high a temperature increase risks a vigorous reaction, opening of the valve and loss of analytes.

STATUS (card as of 03.10.2026). The card of PN-EN 16173:2012 (English version, published 22-10-2012, 11 pages, price group F) has no “Withdrawn” header: Health, Environment and Medicine Sector, KT 216 Waste, ICS 13.030.01 and 13.080.10, “Introduces: EN 16173:2012 [IDT]”; the card has no “Replaces” or “Replaced by” fields. There is no Polish language version in the PKN search engine (term “PN-EN 16173”, 03.10.2026). In the iTeh catalogue (read on 03.10.2026) EN 16173:2012 has the status “Published”, stage 90.93 “Decision to confirm” (review completed 30.09.2026) and a link to Directive 86/278/EEC (protection of the environment, in particular of the soil, when sewage sludge is used in agriculture). PKN withdrew the sister aqua regia digestion standard PN-EN 16174:2012 on 30.03.2022 (card, as of 03.10.2026); ICP-MS measurement in such solutions is described in a separate entry on PN-EN 16171 (a standard withdrawn on 05.03.2026).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read on 03.10.2026). The number 16173 appears in 10 records at 4 laboratories: AB 085, AB 199, AB 680, AB 700. In the current PCA documents (read on 03.10.2026, issues from 21.10.2025 to 21.08.2026) the number appears in 10 items of the same 4 laboratories (AB 700 — 5, AB 199 — 3, AB 085 and AB 680 1 each). Notation everywhere “PN-EN 16173:2012”; only at AB 085 is it in first place, in the other items — after the measurement standard. The “Laboratories” tab (“PN-EN 16173”) shows the same 4 laboratories — checked with the tab query on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). The standard always stands next to a measurement standard. AB 085 — soil, elements by ICP-MS with PN-EN 16171 (e.g. arsenic, chromium, cadmium, cobalt (0.2–400) mg/kg). AB 199 — soil, sewage sludge and waste with code 19 08 05: mercury by CVAAS (0.10–33) mg/kg with PN-ISO 16772 (excluding clauses 7.1 and 7.2), metals by ICP-OES with PN-EN ISO 11885 (Cr, Cd, Cu (1.0–1600) mg/kg, Ni, Pb (4.0–1600) mg/kg, Zn (4.0–8000) mg/kg) and arsenic (4.0–1600) mg/kg in soil. AB 680 — sewage sludge, calcium (0.40–30) % and magnesium (0.10–1.00) % by FAAS with PN-EN ISO 7980. AB 700 — in five items (sewage sludge, process and bottom sediments, soil; organic fertilisers, soil improvers, growing media, digestate; waste by DAB-11 groups) elements by ICP-OES or ICP-MS — always with PN-EN 16173:2012 and PN-EN 16174:2012 together, i.e. with the nitric acid digestion standard and the withdrawn aqua regia digestion standard. Waste, bottom sediments and digestate lie outside the scope of the standard (sewage sludge, treated biowaste, soil).

WHERE A SEEMINGLY CORRECT RESULT IS EASY. In comparison: the result after nitric acid and the result after aqua regia are two different fractions — at AB 700 both standards stand in one item, so the report must show which digestion was used. In decomposition: quartz, silicates, titanium and aluminium oxides remain undissolved (4) — the result is not the total content. In conditions: the method is operationally defined — a different final temperature, time, heating rate or empty carousel positions (different energy absorption) give a different result without a trace in the solution (6.1, 7); that is why temperature sensors deviating by more than 2 °C from a calibrated thermometer must be calibrated. With the sample: heating before digestion and escape of volatile products lower the result for elements forming volatile compounds; a polyethylene container changes elemental mercury in both directions (4). For safety and mass: more than 0.5 g organic carbon or too fast heating risks opening of the valve and loss of analytes (7).

WHAT WE DO NOT GIVE. We have not read the rest of Clause 7, Clause 8 or Annex A, so we do not give the way of separating the solid part, the final volume, dilution or precision data. We do not give requirements of regulations on sewage sludge and soil — we have not read the texts of the acts for this entry.

Method principle

A portion of sludge, biowaste or soil (up to 2 g, usually 0.5–1 g dry matter, at most 0.5 g organic carbon) is covered with 10 ml of concentrated nitric acid, after the reaction ceases it is closed in a vessel of PFA, PTFE or quartz and heated in a laboratory microwave system with temperature feedback: 10–15 °C/min to (175 ± 5) °C and 10 min at that temperature. After cooling the undissolved part is separated, the solution made up in a flask and measured by an appropriate technique (ICP-OES, ICP-MS, AAS); the result is the nitric acid soluble fraction of the elements.

Applications

• Sewage sludge, treated biowaste and soil — digestion before determination of over 60 elements (among others Cd, Cr, Cu, Fe, Hg, Pb, Ni, Zn) and others (1)
• Nitric acid soluble fraction — not the total content (introduction, 1, 4)
• Soil, sludges, organic fertilisers, soil improvers and waste — always with a measurement standard (ICP-OES, ICP-MS, CVAAS, FAAS) in the accreditation scopes of 4 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN 16173:2012

Title (PL)

Osady ściekowe, uzdatnione bioodpady oraz gleba — Roztwarzanie frakcji pierwiastków rozpuszczalnych w kwasie azotowym

Title (EN)

Sludge, treated biowaste and soil — Digestion of nitric acid soluble fractions of elements

Step-by-step procedure

1. Portion

   Up to 2 g (usually 0.5–1 g dry sample), at most 0.5 g organic carbon, to 0.001 g; reagent blank in parallel. PN-EN 16173:2012 current (PKN card as of 03.10.2026).

2. Acid

   (10 ± 0.1) ml HNO3 15 mol/l in a fume hood; leave until visible reaction has stopped (with a vigorous one — in an open vessel).

3. Carousel

   Close and weigh the vessels; fill all positions — missing ones with vessels containing acid only.

4. Heating

   10–15 °C/min to (175 ± 5) °C, (10 ± 1) min at that temperature; cool to room temperature.

5. Solution

   Filtration, centrifugation or settling, transfer to a flask and making up — we do not give the details; measurement by an appropriate technique.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Strongly corrosive and partly very toxic reagents, high temperature and pressure; work in a fume hood (warning in the introduction)
• Domestic ovens are not allowed — corrosion from acid fumes may disable the safety devices and fail to switch off the magnetron with the door open (warning)
• Too fast a temperature increase risks a vigorous exothermic reaction and opening of the valve; do not open pressurised vessels before cooling (7, warning)

Frequently asked questions