🌿 Mercury in soil — aqua regia extract according to ISO 11466, reduction with tin(II) chloride, measurement of the absorbance of mercury vapour at 253.7 nm (CV-AAS) or of fluorescence (CV-AFS), calibration from 0 to 16 µg/l, standard addition method for each type of soil, PN-ISO 16772

Environment PN-ISO 16772

Overview

WHAT THE STANDARD COVERS. Scope from the PKN card, in full (our translation): "A method is given for the determination of mercury using cold-vapour atomic absorption spectrometry or cold-vapour atomic fluorescence spectrometry, in an aqua regia extract of soil obtained in accordance with PN-ISO 11464 and PN-ISO 11466. The limit of quantification of the method is at least 0.1 mg/kg" (on the card without a full stop at the end). We have a sample of ISO 16772:2004 (first edition) from the cover to subclause 7.5 and the beginning of Clause 8 (page 5).

ACCORDING TO THE 2004 EDITION (foreword, Clauses 1–7.5). The standard was prepared by ISO/TC 190 "Soil quality", subcommittee SC 3 "Chemical methods and soil characteristics". WARNING of the standard: mercury is highly toxic — safety measures must be taken when working with mercury and its solutions, and national and international regulations must be known. Principle (Clause 3): mercury is reduced with a tin(II) chloride solution to its elemental form and released from the solution in a closed system; the vapour passes through a cell in the light beam of an AAS spectrometer and the absorbance is measured at 253.7 nm — the signal is a function of the concentration; alternatively the vapour is introduced into the cell of an atomic fluorescence spectrometer and the fluorescence intensity is measured; NOTE — tin(II) chloride was chosen because sodium borohydride reduces many elements present in soil extracts, which may cause matrix problems. Reagents (Clause 4): analytical grade, water of grade 2 according to ISO 3696 with a mercury concentration negligible compared with the lowest standard; hydrochloric acid 37 % and nitric acid 65 % from one batch (with different batches — a blank for each), nitric acid (1+4), diluted aqua regia (1+9: 21 ml HCl and 7 ml HNO3 per 1000 ml), tin(II) chloride 100 g/l in hydrochloric acid, prepared on the day of use (the blank can be lowered by purging with nitrogen for 30 min); mercury stock solution 1000 mg/l — preferably a certified commercial one (checked regularly) or from metallic mercury 100 mg ± 0.4 mg in 17 ml of nitric acid (stable for at least six months); standard solutions of 20 mg/l and 0.2 mg/l (the latter prepared on the day of use; low concentrations are stored in quartz, PFA or FEP bottles, because mercury vapour diffuses through low-density polyethylene); carrier gas — argon or nitrogen 99.99 % (for AFS argon is clearly preferable — higher sensitivity). Apparatus (Clause 5): glassware and PFA/FEP bottles soaked for at least 6 h in 5 % nitric acid (the acid changed weekly), class B volumetric glassware; AAS spectrometer with a hollow-cathode or electrodeless discharge lamp and automatic background correction; AFS spectrometer with a mercury lamp, a 254 nm filter and a photomultiplier (see EN 13506); cold-vapour generator — batch system or flow-injection system (FIAS); quartz cell with a path of 10 cm or longer heated to 50–100 °C (AAS), permeation dryer (AFS). Quality control (Clause 6): certified reference materials to assign values to in-house materials, control charts, rejection of results outside the agreed limits. Procedure (Clause 7): 10 ml of the extract according to ISO 11466 is diluted with water to 100 ml; the blank is carried along with the extraction, using cleaned quartz sand instead of soil; before each batch at least five calibration solutions and a blank — e.g. 0, 2, 4, 6, 10 and 16 µg/l (in a manual system 10 ml corresponds to 0–160 ng of mercury), prepared on the day of use (unstable diluted standards can be stabilised e.g. with 1 ml of K2Cr2O7 solution 5 g/l); each standard is measured at least twice; samples above the calibration range are diluted with diluted aqua regia; for each type of soil the concentration in the extract must be determined at least once by the standard addition method — if the results of the standard addition method and of the calibration curve are equal, the curve may be used.

STATUS (state of the card on 30 September 2026). The card of PN-ISO 16772:2009 (Polish version) has no "Withdrawn" header — the standard is CURRENT: published 04-06-2009, 12 pages, price group F, Health, Environment and Medicine Sector, KT 191 for Soil Chemistry, ICS 13.080.10, "Introduces: ISO 16772:2004 [IDT]". PKN search for "PN-ISO 16772" (30 September 2026): this standard and PN-EN 16772:2016-07 from another field (sampling of invertebrates in the hyporheic zone of rivers).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation-scope database, data loaded up to 17 September 2026, read on 30 September 2026). 10 records at 10 laboratories — the same number of cells in the current PCA documents. All write "PN-ISO 16772:2009"; AB 199 — "z wyłączeniem pkt. 7.1, 7.2" (excluding clauses 7.1, 7.2) and alongside PN-EN 16173:2012, AB 1436 — "z wyłączeniem p. 7.1" (excluding clause 7.1), AB 300 — alongside PN-ISO 11466:2002. The "Laboratories" tab looks for notations that BEGIN with "PN-ISO 16772" and will show all 10 laboratories — checked with the tab's query on the production server labcoda.pl on 30 September 2026: 10. Current scopes on the PCA website (read on 30 September 2026, issues from 05.02.2026 to 22.09.2026): all entries are in the issues in force and none is suspended.

QUANTITY, ITEMS AND RANGE. Mercury content (AB 1302 — concentration and content; AB 213 without a name of the quantity), technique: cold-vapour atomic absorption spectrometry (CVAAS) — all 10; no one has the fluorescence technique (CV-AFS) in the scope. Items: soil — 6 laboratories, soil and ground — AB 550, AB 719, AB 1302, at AB 199 also sewage sludge and wastes with code 19 08 05. Ranges in mg/kg: from 0.0012 to 300 (AB 550), from 0.030 to 100 (AB 300), from 0.05 to 10 (AB 894), from 0.05 to 20 (AB 1183), from 0.05 to 25.0 (AB 213), from 0.050 to 2.5 (AB 1436), from 0.050 to 2.50 (AB 1539), from 0.10 to 33 (AB 199), from 0.100 to 60.0 (AB 719), from 0.20 to 100 (AB 1302).

ALONGSIDE THIS STANDARD. In the copy 64 laboratories have entries for mercury in soil or ground, including 9 of these 10 (AB 213 describes the entry without a name of the quantity); 55 of them — only without this standard, most often according to in-house procedures. Of the standards: PN-EN ISO 12846 (AB 213, AB 300, AB 418, AB 550, AB 1436), PN-EN 16175-1 (AB 213, AB 680), EPA 7473 (AB 085, AB 550; at AB 550 — atomic absorption spectrometry with the amalgamation technique). Extraction with aqua regia according to PN-ISO 11466 and mercury in water according to PN-EN ISO 12846 (CV-AAS) and PN-EN ISO 17852 (CV-AFS) have separate entries in the Knowledge Base.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — extract: the standard concerns mercury in an aqua regia extract according to ISO 11466 — AB 199 has PN-EN 16173 in the same entry and excludes clauses 7.1 and 7.2, and AB 1436 excludes clause 7.1 — a result from another digestion or another preparation of the solution is another route to the result, which the report must state. Second — matrix: for each type of soil the calibration curve must be compared with the standard addition method at least once — without this it is not known whether the matrix suppresses the signal. Third — reductant: tin(II) chloride, not sodium borohydride — borohydride reduces many elements of the extract and causes matrix problems. Fourth — blank: it is carried along with the extraction, on quartz sand; acids from different batches require a separate blank. Fifth — losses and contamination: diluted standards are unstable (prepared on the day of use), mercury vapour diffuses through low-density polyethylene, and water condenses in the AAS cell if the cell is not heated. Sixth — lower limit: the standard gives a limit of quantification of "at least 0.1 mg/kg"; seven laboratories have a lower limit in the scope (from 0.0012 to 0.05 mg/kg) — this is a result of their validation, not of the standard.

WHAT WE DO NOT GIVE. The sample ends at the beginning of Clause 8: we do not give the complete formula for calculating the result (we know only part of the explanations, including the dilution factor f = 10 of the test solution from 7.1), the expression of results, precision data or the requirements for the report.

Method principle

Mercury in an aqua regia extract of soil is reduced with a tin(II) chloride solution to its elemental form and released in a closed system; the mercury vapour flows through the cell of an atomic absorption spectrometer, where the absorbance is measured at 253.7 nm, or enters the cell of an atomic fluorescence spectrometer, where the fluorescence intensity is measured. The signal is a function of the mercury concentration; calibration with at least five standards and a blank, and for each type of soil — a check by the standard addition method.

Applications

• Soils and ground — mercury content in the scopes of 10 laboratories (at AB 199 also sewage sludge and wastes 19 08 05), always by the CVAAS technique
• Aqua regia extracts prepared according to ISO 11466 — according to the scope of the standard

Key parameters

Standard

Standard number

PN-ISO 16772:2009 (wersja polska; ISO 16772:2004 IDT)

Title (PL)

Jakość gleby — Oznaczanie zawartości rtęci metodą spektrometrii atomowej techniką zimnych par lub metodą fluorescencyjnej spektrometrii atomowej techniką zimnych par w ekstraktach uzyskanych z gleby z zastosowaniem wody królewskiej

Title (EN)

Soil quality — Determination of mercury in aqua regia soil extracts with cold-vapour atomic spectrometry or cold-vapour atomic fluorescence spectrometry

Step-by-step procedure

1. Test solution and blank

   Dilute 10 ml of the extract according to ISO 11466 with water to 100 ml; blank — extraction of quartz sand. PN-ISO 16772:2009 current (state of the card on 30 September 2026).

2. Calibration

   At least five standards and a blank (e.g. 0–16 µg/l) from the 0.2 mg/l solution, on the day of use; measure each at least twice.

3. Measurement

   Reduction with tin(II) chloride in the cold-vapour generator, measurement of the absorbance at 253.7 nm (or of fluorescence); dilute samples outside the range with aqua regia (1+9).

4. Matrix check

   For each type of soil the standard addition method at least once; if the results agree — the calibration curve.

5. Result

   Mercury content in mg/kg taking the dilution into account; the complete formula and precision are NOT GIVEN.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Mercury is highly toxic — safety measures when working with mercury and its solutions; mercury compounds must not be released into the environment (warning of the standard)
• SUBSTANTIVE NOTE: the result refers to an aqua regia extract according to ISO 11466 — another digestion and excluded clauses must be stated in the report; for each type of soil a check by the standard addition method is required

Frequently asked questions