🌿 Digestion of sewage sludge, treated biowaste and soil with aqua regia (1 volume of HNO3 and 3 volumes of HCl) before determination of over 60 elements — method A: boiling under reflux for 2 h, with an absorption vessel trapping volatile species; method B: microwave digestion in a closed vessel at (175 ± 5) °C for (10 ± 1) min; then filtration and making up in a volumetric flask; the result is the aqua regia soluble fraction, not the total content; PN-EN 16174 withdrawn on 30.03.2022

Environment PN-EN 16174

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of SIST EN 16174:2013 (text of EN 16174:2012, English): from the title page through the contents, foreword, introduction and Clauses 1–6 up to and including 7.1.4 (heating device of method A). Outside the sample remain the rest of Clause 7 (apparatus of method B), Clause 8 (blank test and procedure of both methods), Clause 9 (test report) and Annex A (repeatability and reproducibility data). The “Scope” field of the PKN card of PN-EN 16174:2012 speaks of “three methods” and lists 18 elements (As, Ba, Cd, Cr, Co, Cu, Fe, Pb, Hg, Mo, Ni, Se, Sr, Tl, V, Zn, P, S), whereas the text of EN 16174:2012 we read speaks in Clause 1 of two methods and over 60 elements (below); the sources read do not say why.

ACCORDING TO THE TEXT OF EN 16174:2012 (introduction, Clauses 1–6, beginning 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; CEN approved it on 24.05.2012. Introduction: multi-element digestion before analysis; aqua regia need not decompose the sample completely, and the extract need not reflect the total concentrations — for most environmental applications the result is nevertheless fit for purpose. Validation (Table 1): sludges — municipal, industrial, from the electronics industry, ink waste sludge, sewage sludge; biowaste — compost and composted sludge (method A only); soils — agricultural and sludge-amended. Warnings: strongly corrosive and partly very toxic reagents, high temperature and pressure; laboratory-grade microwave equipment with isolated, corrosion-resistant safety devices is required — domestic ovens shall not be used; work in a fume hood or in closed force-ventilated equipment; with samples high in organic matter explosive intermediates are possible; pressurised vessels shall not be opened before cooling. Scope (1): two methods for digesting sewage sludge, treated biowaste and soil with aqua regia, for Al, Sb, 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, Ag, Na, Sr, S, Te, Tb, Tl, Th, Tm, Sn, Ti, W, U, V, Yb, Y, Zn and Zr — and, where applicable, other elements; digestion need not be complete, and the extracted concentrations need not reflect the total content. Normative references (2): EN 15936 (total organic carbon), EN 16179 (sample pretreatment), EN ISO 3696. Definition (3.1): aqua regia — a solution of one volume of concentrated nitric acid and three volumes of concentrated hydrochloric acid. Principle (4): method A — boiling under reflux for 2 h, filtration and making up in a volumetric flask; method B — microwave digestion at (175 ± 5) °C for (10 ± 1) min in a closed vessel, filtration and making up in a volumetric flask. Sources of error (5): the sample shall not be heated before digestion, and volatile reaction products shall not escape; high acid and solute concentrations may interfere with the determination; glass containing e.g. B, Na, K, Al may contaminate the sample; the whole portion must be in contact with the acids; some elements may be lost by precipitation of sparingly soluble chlorides, fluorides and sulfates. Reagents (6): analytical grade, so as not to raise blanks; a blank through the whole procedure with the same amounts of acids; water of at least grade 2 according to EN ISO 3696; hydrochloric acid 12 mol/l (ρ = 1.18 kg/l); nitric acid 15 mol/l (ρ = 1.4 kg/l) and 0.5 mol/l (35 ml of concentrated acid to 1 l); antifoaming agent, e.g. n-dodecane or octanol. Apparatus for method A (7.1): digestion vessel resistant to temperature and pressure, e.g. a 250 ml glass flask (quartz possible), with an inert inner wall; reflux condenser; absorption vessel trapping volatile species, fitted on the condenser (Figure 1); heating device, e.g. a thermostatically controlled heating mantle or an aluminium block.

STATUS (cards as of 03.10.2026). The PKN card of PN-EN 16174:2012 (English version, published 22-10-2012, 12 pages, price group F) has the header “Withdrawn”: withdrawal date 30-03-2022; Health, Environment and Medicine Sector, KT 216 Waste, ICS 13.030.01 and 13.080.10, “Introduces: EN 16174:2012 [IDT]”; the card has no “Replaced by” field, and the PKN search (term “PN-EN 16174”, 03.10.2026) shows no other editions. In the iTeh catalogue (read on 03.10.2026) the Slovenian counterpart SIST EN 16174:2013 was withdrawn on 14.12.2021 with the note “Replaced By SIST EN ISO 54321:2021” (Soil, treated biowaste, sludge and waste — Digestion of aqua regia soluble fractions of elements), and EN 16174:2012 itself has the status “Withdrawn” (stage 99.60, withdrawal from 15.09.2021, completed on 30.09.2026). The PKN catalogue contains the current PN-EN ISO 54321:2021-07 (English version, KT 191 Soil Chemistry) — its “Scope” field speaks of two methods for digesting soil, treated biowaste, sewage sludge and waste with aqua regia; the 54321 card has no “Replaces” field, so PKN does not formally link the two standards. We do not state what EN ISO 54321 changed in the digestion conditions for the result — we did not compare the texts; the standard is described in a separate entry on PN-EN ISO 54321. Digestion with nitric acid is described in a separate entry on PN-EN 16173.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 03.10.2026). The number 16174 appears in 20 records at 8 laboratories: AB 005, AB 085, AB 213, AB 322, AB 700, AB 869, AB 965, AB 1539. In the current PCA documents (read on 03.10.2026, issues from 21.10.2025 to 11.09.2026) the number appears in 20 rows of the same 8 laboratories (AB 213 and AB 700 5 each, AB 869 — 4, AB 1539 — 2, the others 1 each) — all issued after PKN withdrew the standard. The form is “PN-EN 16174:2012”, at AB 965 and AB 869 with the addition “Metoda B” (method B); at AB 213 once “PN-EN 16174 :2012” (with a space). None of these items is suspended. The “Laboratories” tab (“PN-EN 16174”) shows the same 8 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. Soil: AB 005 — elements by ICP-OES with PN-EN ISO 11885 (e.g. As (1.0–2000), Ba (2.0–6000) mg/kg); AB 085 — tin (2.0–400) mg/kg by ICP-MS with PN-EN 16171; AB 965 — among others lead, cadmium, nickel and zinc with PN-ISO 11047 (method A), with digestion by method B; AB 1539 — metals with PN-EN ISO 22036. Soil, sewage sludge and waste with code 19 08 05: AB 869 — elements with PN-EN ISO 11885 and mercury with PN-EN ISO 12846, always by method B. Sewage sludge: AB 322 — total phosphorus (0.3–6.0) % spectrophotometrically with PN-EN ISO 6878; AB 1539 — metals (sludges and waste with codes 19 08 05, 19 09 03, 19 08 02). Compost, biomass, stabilisate, sewage sludge and plant cultivation aids: AB 213 — elements with PN-EN ISO 22036 (written “PN-EN 22036:2024-07”) and mercury with PN-EN 16175-1 (CVAAS, (0.05–25.0) mg/kg). AB 700 — in five items (sludges, soil, fertilisers, waste by DAB-11 groups) elements by ICP-OES or ICP-MS — always with PN-EN 16173 and PN-EN 16174 together. Fertilisers, plant cultivation aids, biomass, stabilisate and wastes other than sludges lie outside the scope of the standard (sewage sludge, treated biowaste, soil).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With the edition: the standard has been withdrawn by PKN since 30.03.2022 and replaced in CEN by EN ISO 54321 — for each of the 20 items the PCA document was issued after the withdrawal; the report must show according to which standard the digestion was carried out. With the method: methods A (boiling 2 h) and B (microwave, 175 °C, 10 min) are different conditions, and a reference without “method A/B” does not say which was used — at 6 of the 8 laboratories the scope does not specify it. When comparing: a result after aqua regia and one after nitric acid (PN-EN 16173) are two different fractions — at AB 700 both standards stand in one item. With decomposition: the result is not the total content (1). With losses: heating the sample before digestion and escape of volatile products lower the result, and sparingly soluble chlorides, fluorides and sulfates may precipitate part of the elements (5); this is why method A has an absorption vessel (7.1.3).

WHAT WE DO NOT GIVE. We did not read the rest of Clause 7, Clause 8 or Annex A, so we do not give the test portion mass, the volume of aqua regia, the heating programme of method B, the microwave apparatus, the final volume or precision data. Nor do we compare EN 16174 with EN ISO 54321 — we did not read the text of the successor for this entry.

Method principle

A portion of sludge, biowaste or soil is covered with aqua regia (1 volume of concentrated HNO3 and 3 volumes of concentrated HCl) and digested by one of two methods: A — boiling under reflux for 2 hours, with an absorption vessel for volatile species on the condenser; B — microwave heating in a closed vessel at (175 ± 5) °C for (10 ± 1) min. The solution is filtered, made up in a volumetric flask and measured by an appropriate technique (ICP-OES, ICP-MS, CVAAS, spectrophotometry); the result is the aqua regia soluble fraction of the elements.

Applications

• Sewage sludge, treated biowaste and soil — digestion before determination of over 60 elements (1)
• Aqua regia soluble fraction — not the total content (introduction, 1)
• Soil, sewage sludge, compost, fertilisers, plant cultivation aids and waste — always with a measurement standard in the accreditation scopes of 8 laboratories in PCA, despite the withdrawal of the standard by PKN

Key parameters

Standard

Standard number

PN-EN 16174:2012

Title (PL)

Osady ściekowe, uzdatnione bioodpady oraz gleba — Roztwarzanie frakcji pierwiastków rozpuszczalnych w wodzie królewskiej

Title (EN)

Sludge, treated biowaste and soil — Digestion of aqua regia soluble fractions of elements

Step-by-step procedure

1. Sample

   Pretreatment according to EN 16179; do not heat the sample before digestion (5). PN-EN 16174:2012 withdrawn 30-03-2022 (PKN card as of 03.10.2026).

2. Aqua regia

   Portion covered with aqua regia (HNO3:HCl = 1:3), the whole portion in contact with the acids; a blank in parallel. We do not give masses and volumes.

3. Method A

   Boiling under reflux for 2 h, with an absorption vessel for volatile species.

4. Method B

   Microwave in a closed vessel: (175 ± 5) °C for (10 ± 1) min; open vessels after cooling.

5. Solution

   Filtration and making up in a volumetric flask; measurement by an appropriate technique; method A or B in the report.

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 or in closed force-ventilated equipment (warning)
• 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)
• With samples high in organic matter explosive intermediates are possible; do not open pressurised vessels before cooling (warning)

Frequently asked questions