☠️ Mercury in water
In short
Determination of mercury in water by atomic absorption spectrometry (AAS) — after oxidation with potassium bromate and bromide, mercury is reduced with tin(II) chloride, stripped from the solution and measured, with enrichment by amalgamation or without enrichment. The test is performed according to PN-EN ISO 12846:2012; Working range — with enrichment: usually 0.01–1 µg/l; mean limit of quantification in the validation trial 0.008 µg/l (clause 1). The procedure comprises 7 steps; it is used for: Water intended for human consumption — mercury 1.0 µg/l (Journal of Laws 2026, item 748, Annex 1 Part B), Surface waters — maximum allowable concentration 0.07 µg/l (Journal of Laws 2021, item 1475, Annex 14), Waste water — reference method (Journal of Laws 2019, item 1311, Annex 12 item 50); industrial and municipal waste water after additional digestion and validation (7.4).
At a glance
- Standard: PN-EN ISO 12846:2012
- Category: Physicochemistry
- Procedure steps: 7
- Working range — with enrichment: usually 0.01–1 µg/l; mean limit of quantification in the validation trial 0.008 µg/l (clause 1)
- Working range — without enrichment: usually from 0.05 µg/l; limit of quantification in the validation trial 0.024 µg/l (clause 1)
- Wavelength: 253.7 nm (clause 3)
Overview
STATUS (as of 29.10.2026). PN-EN ISO 12846:2012 — English version (with a Polish title in the PKN catalogue), published 15.06.2012, implements EN ISO 12846:2012 and ISO 12846:2012 [IDT]; it replaced PN-EN 12338:2001 and PN-EN 1483:2007. The national amendment PN-EN ISO 12846:2012/Ap1:2016-07 (approved 14.07.2016) only adds these two standards to the "Replaces" field on the national title page — no technical changes. The standard is current — no withdrawal note. ISO 12846:2012 (first edition; it replaced ISO 5666:1999 and ISO 16590:2000) is published in the ISO catalogue, with no newer edition.
SCOPE (clause 1). Two methods for determining mercury in drinking, surface, ground and rain water and in waste water — after appropriate pre-digestion. Clause 6: with enrichment by amalgamation of the mercury, e.g. on a gold/platinum adsorber — practical working range usually 0.01–1 µg/l, mean limit of quantification reported by the participants of the validation trial 0.008 µg/l. Clause 7: without enrichment — practical working range usually from 0.05 µg/l, limit of quantification from the validation 0.024 µg/l. These figures are an orientation and do not replace laboratory data; the choice of method depends on the equipment, matrix and concentration range. For extremely low concentrations, down to 0.002 µg/l without pre-concentration, the standard points to atomic fluorescence spectrometry (ISO 17852), and specific AAS mercury analysers allow determinations down to 0.010 µg/l. Industrial and municipal waste water — after an additional digestion step and method validation (7.4); possible mercury losses must be considered for anaerobic reducing industrial effluents.
MERCURY IN WATER (introduction to the standard). In natural waters mercury compounds generally occur at concentrations below 0.1 µg/l; higher ones may be found e.g. in industrial waste water; both inorganic and organic compounds may be present, and mercury accumulates in sediments. When the sample contains particles, an additional digestion is needed to decompose all mercury compounds — it may be omitted only if a large amount of previous comparison data demonstrates this. In the low-concentration range the highest-purity reagents, clean vessels, mercury-free laboratory air and a very stable measuring system are essential.
INTERFERENCES (clause 4). Mercury is adsorbed and desorbed on the walls of vessels; mercury vapour diffuses through many plastics — tubing of glass or special plastics (e.g. FEP) is used, silicone tubing is unsuitable. Gold, silver and platinum form amalgams and suppress the signal, iodide suppresses it severely; volatile organic substances absorb in the UV range, which, despite background correction, degrades the signal-to-noise ratio. Before reduction all solutions are brought to the same temperature (below 25 °C), and the cell is protected against water condensation, e.g. by heating it with an infrared lamp. Table 1 gives the concentrations in the measurement solution (0.5 mol/l HCl, SnCl₂ reduction) above which the signal falls by more than 10 %: Cu(II) and Ni(II) 500 mg/l, Ag(I) 1 mg/l, As(V), Bi(III) and Sb(III) 0.5 mg/l, iodide 0.1 mg/l, Se(IV) 0.05 mg/l.
LEGAL REQUIREMENTS. Water intended for human consumption: mercury 1.0 µg/l (Regulation of the Minister of Health of 22 May 2026, Journal of Laws 2026, item 748, Annex 1 Part B item 27); limit of quantification not greater than 30 % of the parametric value and measurement uncertainty up to 30 % (Annex 4 Part B). Surface waters: for mercury and its compounds the maximum allowable concentration in water is 0.07 µg/l (river and lake water bodies as well as transitional and coastal waters; no annual average concentration in water is set), in biota 20 µg/kg wet weight (Journal of Laws 2021, item 1475, Annex 14, indicators 4.1.21 and 4.1.21.B). Waste water: PN-EN ISO 12846 is the reference method for mercury, alongside PN-EN ISO 17852 (fluorescence spectroscopy), with a detection requirement of 0.1 of the permissible concentration at the sampling point and accuracy and precision of ± 30 % at a concentration equal to the detection limit (Journal of Laws 2019, item 1311, Annex 12 item 50).
WHAT WE DO NOT GIVE HERE. The publicly available text of the standard ends at 6.1.10.3 (mercury standard solutions). Apparatus (6.2, including the sampling vessels of 6.2.5.2), the course of the determination with amalgamation (from 6.3), the method without enrichment (clause 7), digestion of waste water (7.4) and validation data (Annex A) lie outside it — so we do not give test portion volumes, flow rates, the desorption programme or the number of calibration points.
Method principle
Monovalent and divalent mercury and organomercury compounds are converted to mercury(II) by oxidation with potassium bromate and bromide (KBrO₃–KBr) and then reduced with tin(II) chloride in an acid medium to elemental mercury. The mercury is stripped from the solution with a stream of inert gas or mercury-free air (clause 3).
With enrichment, the mercury vapour is carried by inert gas with negligible mercury content to a quartz tube with heating and an adsorbent (e.g. gold-platinum gauze), on which the mercury is retained; other adsorbents based on amalgamation are allowed if fitness for purpose is demonstrated. After rapid heating of the adsorbent (desorption at a minimum of 600 °C) the carrier gas transports the mercury to the absorption cell, where the absorbance is measured at 253.7 nm. Without enrichment the mercury goes directly into the cell, also measured at 253.7 nm. The concentration is calculated from a calibration curve or by the standard addition method.
Preservation of samples with dichromate and nitric acid and digestion e.g. with potassium permanganate and peroxodisulfate are not part of the standard — the user has to validate such a route.
Applications
- Water intended for human consumption — mercury 1.0 µg/l (Journal of Laws 2026, item 748, Annex 1 Part B)
- Surface waters — maximum allowable concentration 0.07 µg/l (Journal of Laws 2021, item 1475, Annex 14)
- Waste water — reference method (Journal of Laws 2019, item 1311, Annex 12 item 50); industrial and municipal waste water after additional digestion and validation (7.4)
- Ground water and rain water (clause 1)
Key parameters
| Parameter | Value |
|---|---|
| Working range — with enrichment | usually 0.01–1 µg/l; mean limit of quantification in the validation trial 0.008 µg/l (clause 1) |
| Working range — without enrichment | usually from 0.05 µg/l; limit of quantification in the validation trial 0.024 µg/l (clause 1) |
| Wavelength | 253.7 nm (clause 3) |
| Oxidation and reduction | potassium bromide/bromate reagent (2 ml per 100 ml of sample), reduction with tin(II) chloride in an acid medium |
| Desorption from the adsorbent | at a minimum of 600 °C (clause 3) |
| Sample storage | preservation within 48 h of collection (bromide/bromate at the latest 6 days after collection); analysis within 2 weeks, at most 4 weeks (clause 5) |
Standard
- Standard number
- PN-EN ISO 12846:2012
- Title (PL)
- Jakość wody — Oznaczanie rtęci — Metoda absorpcyjnej spektrometrii atomowej (AAS) ze wzbogacaniem lub bez wzbogacania
- Title (EN)
- Water quality — Determination of mercury — Method using atomic absorption spectrometry (AAS) with and without enrichment
Step-by-step procedure
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Sampling
According to ISO 5667-1 and ISO 5667-3, only in the vessels specified in 6.2.5.2; the vessel must contain no mercury and cause no loss of mercury by adsorption or diffusion (clause 5).
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Stabilization
Add 1.0 ml of hydrochloric acid per 100 ml of sample, preferably already in the field — it is recommended to put the acid in the bottle in the laboratory before sampling; such a bottle is not rinsed with the sample (clause 5).
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Oxidation in the laboratory
On arrival add 2 ml of bromide/bromate reagent per 100 ml of sample — preservation within 48 h of collection, at the latest 6 days after collection. Allow to stand for at least 30 min; if the yellow colour of free bromine does not persist, add a further 1 ml and wait another 30 min. Take into account the dilution of the sample by the reagent, e.g. by weighing the full and the empty dry bottle (clause 5).
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Blanks
A reagent blank with the same amounts of reagents is analysed together with the corresponding sample; for all aqueous samples a field blank is also prepared in the same type of container and with the same reagents (clause 5).
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Storage
Preserved samples are analysed within 2 weeks of collection, at most after 4 weeks; decolorization of the sample (consumption of free bromine) indicates insufficient stability (clause 5).
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Standards
Solutions B and C from solution A, diluted with reagent blank; if more bromide/bromate reagent was added to the samples, the same amount is added to the standards (clause 5, 6.1.10).
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Reduction and measurement
Solutions at the same temperature (below 25 °C); reduction with tin(II) chloride, stripping of the mercury, with enrichment — retention on the adsorbent and desorption at a minimum of 600 °C; absorbance measured at 253.7 nm; calculation from a calibration curve or by the standard addition method (clauses 3–4). Details of the procedure are in the part of the standard outside the available text.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Atomic absorption spectrometer with a mercury system | measurement at 253.7 nm with automatic background correction; the cell is protected against water condensation, e.g. by heating with an infrared lamp (clauses 3–4) | — |
| Enrichment unit (method of clause 6) | quartz tube with heating and an amalgamating adsorbent, e.g. gold-platinum gauze; desorption at a minimum of 600 °C (clause 3) | — |
| Tubing | of glass or special plastics, e.g. FEP; silicone tubing is unsuitable (clause 4) | — |
| Sampling vessels | containing no mercury and causing no loss of mercury by adsorption or diffusion; the type of vessel is specified in 6.2.5.2 (outside the available text of the standard) | — |
| Borosilicate glass volumetric flasks | for mercury stock solutions B and C (6.1.10.2–6.1.10.3) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Water | — | grade 1 according to ISO 3696 — for all sample preparations and dilutions (6.1.1) |
| Potassium bromate, 0.0333 mol/l | 7758-01-2 | dissolve 1.39 g of KBrO₃ in 250 ml of water; if necessary purify by heating overnight in a muffle furnace at 250 °C ± 20 °C; the solution is stable for about 1 month (6.1.2) |
| Potassium bromide, 0.2 mol/l | 7758-02-3 | dissolve 5.95 g of KBr in 250 ml of water; the solution is stable for about 1 month (6.1.3) |
| Potassium bromide/bromate reagent | — | equal volumes of the bromate and bromide solutions; 200 ml is enough to digest 100 samples; colourless solution, stable from several days to several weeks — stability has to be checked (6.1.4) |
| Hydroxylammonium chloride, 120 g/l | 5470-11-1 | dissolve 6.0 g in water in a 50 ml flask; may be purified by adding 1.0 ml of SnCl₂ solution and purging overnight with mercury-free nitrogen (500 ml/min); stable for about 1 month; L-ascorbic acid 100 g/l is also permissible after demonstrating fitness for purpose. Its use is described in the part of the standard outside the available text (6.1.5) |
| Nitric acid, ρ = 1.4 g/ml | 7697-37-2 | with negligible mercury content (6.1.6) |
| Hydrochloric acid, w = 360 g/kg (ρ = 1.19 g/ml) | 7647-01-0 | for stabilizing samples and standards; if necessary purified: 1 ml of SnCl₂ solution per 1 l of acid and purging with argon, nitrogen or air, e.g. 2 l/min for 15 min (6.1.7) |
| Tin(II) chloride, 20 g/l (as SnCl₂·2H₂O) | 10025-69-1 | dissolve 10.0 g of the dihydrate in 50 ml of hydrochloric acid with heating and dilute with water to 500 ml; traces of mercury are removed by purging with argon or nitrogen, e.g. 2 l/min for 15 min (6.1.8) |
| Reagent blank | — | per 100 ml: 1.0 ml of hydrochloric acid and 2 ml of bromide/bromate reagent; if the mercury content exceeds twice the limit of quantification — reject and prepare again from purer reagents (6.1.9) |
| Mercury solutions A, B, C | — | A — 1000 mg/l, commercial quantitative standard solution (stable for at least 6 months) or 0.1354 g of HgCl₂ in 20 ml of water with 5 ml of nitric acid, diluted to 100 ml; B — 10 mg/l (1 ml of A to 100 ml of reagent blank), prepared weekly; C — 100 µg/l (1 ml of B to 100 ml), on the day of use. All standards contain as much bromide/bromate reagent as the samples — excess bromide suppresses the signal (6.1.10) |
Health and safety (OHS)
- Potassium bromate, used in significant quantities for preservation, is carcinogenic — take suitable precautions; residual bromate is reduced to bromide before disposal (warning of the standard)
- The bromide/bromate reagent is added in the laboratory, not during field sampling (warning in clause 5)
- Mercury and its compounds are very toxic — extreme caution with samples and solutions that may contain mercury; the tests are carried out by suitably qualified staff
- Mercury(II) chloride is not dried — it is highly toxic and volatile (6.1.10.1)
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 12846:2012 — “Water quality — Determination of mercury — Method using atomic absorption spectrometry (AAS) with and without enrichment”.
How does this method work?
Monovalent and divalent mercury and organomercury compounds are converted to mercury(II) by oxidation with potassium bromate and bromide (KBrO₃–KBr) and then reduced with tin(II) chloride in an acid medium to elemental mercury. The mercury is stripped from the solution with a stream of inert gas or mercury-free air (clause 3).
What is the measuring range and accuracy?
Working range — with enrichment: usually 0.01–1 µg/l; mean limit of quantification in the validation trial 0.008 µg/l (clause 1); Working range — without enrichment: usually from 0.05 µg/l; limit of quantification in the validation trial 0.024 µg/l (clause 1); Wavelength: 253.7 nm (clause 3); Oxidation and reduction: potassium bromide/bromate reagent (2 ml per 100 ml of sample), reduction with tin(II) chloride in an acid medium.
How long does the test take?
The procedure comprises 7 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Atomic absorption spectrometer with a mercury system, Enrichment unit (method of clause 6), Tubing, Sampling vessels, Borosilicate glass volumetric flasks.
Where is this test used?
Water intended for human consumption — mercury 1.0 µg/l (Journal of Laws 2026, item 748, Annex 1 Part B); Surface waters — maximum allowable concentration 0.07 µg/l (Journal of Laws 2021, item 1475, Annex 14); Waste water — reference method (Journal of Laws 2019, item 1311, Annex 12 item 50); industrial and municipal waste water after additional digestion and validation (7.4); Ground water and rain water (clause 1).
What safety precautions apply?
Potassium bromate, used in significant quantities for preservation, is carcinogenic — take suitable precautions; residual bromate is reduced to bromide before disposal (warning of the standard); The bromide/bromate reagent is added in the laboratory, not during field sampling (warning in clause 5); Mercury and its compounds are very toxic — extreme caution with samples and solutions that may contain mercury; the tests are carried out by suitably qualified staff; Mercury(II) chloride is not dried — it is highly toxic and volatile (6.1.10.1).
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 12846.