Mercury in water: origin, risks, regulation and filtration
Mercury is an element naturally present in the Earth's crust, but human activities have significantly contributed to its dispersion in the environment. It can exist in metallic form, as inorganic compounds, or as organic forms, most notably methylmercury. These different forms do not behave the same way nor do they have the same health effects. In drinking water, regulations primarily target total or inorganic mercury, while human exposure to methylmercury mainly stems from certain fish and seafood.
- Chemical symbol
- Hg
- Atomic number
- 80
- Family
- Toxic metal
- EU value
- 1 µg/L
What is mercury?
Mercury is a chemical element with the symbol Hg and atomic number 80. It is a metal naturally found in certain rocks, ores, and coal deposits.
Metallic mercury is liquid at room temperature. This unusual characteristic has historically encouraged its use in thermometers, barometers, certain measuring devices, and various industrial processes.
Mercury is persistent: it does not disappear from the environment. It can be transported through the atmosphere, deposited in soil and water, and then change its chemical form through natural and biological processes.
Key takeaway: speaking about "mercury" without specifying its chemical form can be misleading. Metallic mercury, inorganic mercury, and methylmercury present different exposure pathways, behaviors, and effects.
What are the different forms of mercury?
| Form | Examples | Main exposure pathways | Main concerns |
|---|---|---|---|
| Elemental mercury | Liquid metallic mercury | Primarily inhalation of vapors in the event of a spill or occupational use. | Possible effects on the nervous system, kidneys, and lungs. |
| Inorganic mercury | Mercurous or mercuric salts | Ingestion of contaminated water or products, occupational exposure, or contact with certain old products. | Kidney damage and corrosive effects for certain compounds. |
| Organic mercury | Methylmercury, ethylmercury | Mainly consumption of contaminated fish or aquatic organisms for methylmercury. | Neurotoxicity and specific risk to the development of the nervous system in the fetus and young child. |
Measuring total mercury in water does not always reveal the exact distribution between its different forms. Speciation analysis may be necessary when the origin or form of the contaminant must be accurately determined.
What is mercury used for?
Mercury has been used in many sectors due to its electrical conductivity, its regular expansion with temperature, and its ability to form amalgams with other metals.
- older thermometers, barometers, and measuring devices;
- certain switches, relays, and electrical equipment;
- fluorescent lamps and certain discharge lamps;
- older industrial processes for manufacturing chlorine and caustic soda;
- amalgams used in certain dental restorations;
- artisanal or industrial gold extraction via amalgamation;
- certain older medicinal products, cosmetics, or antiseptics;
- specialized scientific and technical applications.
Many uses are now prohibited, limited, or gradually being phased out in the European Union. Nevertheless, mercury remains present in some old devices, waste, lamps, industrial equipment, and contaminated sites.
How does mercury enter the water?
Natural geological origin
Mercury can be released naturally through the weathering of rocks or ores that contain it. Certain geological or volcanic areas may have naturally higher concentrations.
Coal combustion and industrial activities
The burning of coal and certain industrial processes can release mercury into the atmosphere. It can be transported over long distances before depositing into soils, lakes, rivers, and oceans.
Mining activities
Ore extraction and the use of mercury to recover gold can directly contaminate soils and waterways. This source remains significant in certain parts of the world.
Waste and mercury-containing equipment
Lamps, measuring devices, switches, and other mercury-containing waste can release this metal when broken, burned, or disposed of under unsuitable conditions.
Former industrial sites
Some soils, sediments, or groundwater may remain contaminated long after the cessation of an industrial activity that used mercury.
What are the health risks of mercury?
Health effects strongly depend on the form of mercury, the dose, the exposure pathway, and its duration. The main organs affected can include the nervous system, kidneys, digestive system, lungs, skin, and eyes.
Inorganic mercury
Ingestion of certain inorganic mercury compounds can affect the kidneys. Some inorganic salts are also corrosive to the skin, eyes, and digestive tract.
Metallic mercury
The main risk associated with metallic mercury is the inhalation of its vapors. Significant or repeated exposure can cause neurological, respiratory, and renal effects.
Methylmercury
Methylmercury can cross the placenta and affect the development of the brain and nervous system in the fetus. Consumption of certain predatory fish is generally the primary source of human exposure to this form.
Effects associated with significant exposure may include:
- coordination and balance disorders;
- tremors;
- sensory or visual disturbances;
- memory and attention deficits;
- muscle weakness;
- kidney damage;
- effects on the neurological development of the fetus and child.
A regulatory value for drinking water should not be used to directly assess the risks associated with methylmercury in fish. The exposure pathways and the chemical forms involved are different.
Which populations are most sensitive?
- pregnant women;
- fetuses;
- infants and young children;
- people who frequently consume certain fish species that strongly accumulate methylmercury;
- workers exposed to mercury vapors or compounds;
- populations living near mining or industrial sites or in areas that are permanently contaminated.
Recommendations regarding fish consumption depend on the species, its size, its origin, and the person's profile. They should be consulted with the competent health authorities.
What are the effects of mercury on the environment?
Mercury is persistent and can cycle between the air, soil, sediments, and water. In some aquatic environments, microorganisms can transform a portion of inorganic mercury into methylmercury.
Methylmercury can then accumulate in living organisms. Its concentration generally increases along the food chain, a phenomenon called biomagnification. Predatory fish at the top of this chain can thus exhibit concentrations higher than those of the surrounding water.
Mercury can affect the reproduction, behavior, growth, and survival of fish, birds, and other organisms.
A very low concentration in water does not necessarily mean an absence of risk to ecosystems, because certain forms of mercury can accumulate in aquatic organisms.
What is the limit for mercury in drinking water?
The European Union sets a parametric value of 1 microgram per liter for mercury in water intended for human consumption.
| Reference | Value | Notes |
|---|---|---|
| European Union | 1 µg/L | Parametric value set by the European directive on the quality of water intended for human consumption. |
| World Health Organization | 6 µg/L | Guideline value regarding inorganic mercury in drinking water. |
| United States – EPA | 2 µg/L | Maximum regulatory concentration of 0.002 mg/L for inorganic mercury. |
European, WHO, and EPA values differ notably due to their regulatory frameworks, exposure assumptions, and the form of mercury considered. The legally applicable value depends on the country in which the water is distributed.
How can you tell if water contains mercury?
Mercury present at trace levels generally cannot be identified by the taste, odor, or color of the water. Laboratory analysis is required.
Depending on the goal, the analysis may look for:
- total mercury;
- dissolved mercury;
- inorganic mercury;
- methylmercury or other organic forms;
- mercury associated with suspended matter or sediments.
Mercury can be present at very low concentrations. Sampling, bottle conditioning, and sample preservation must therefore be carried out with care to avoid contamination or loss of the compound before analysis.
Which technologies can reduce mercury in water?
The choice of treatment depends on the form of mercury, its concentration, pH, the presence of organic matter, and other constituents of the water.
Processes that may be used include:
- certain specialized adsorbent media;
- certain activated carbons formulated or impregnated for mercury;
- certain ion exchangers;
- properly sized and maintained reverse osmosis;
- coagulation, precipitation, and filtration in certain collective systems;
- treatment or removal of the source when the contamination originates from an industrial site, waste, or equipment.
Not all activated carbon filters necessarily reduce all forms of mercury. Performance must be verified for the specific filter in question, under defined test conditions.
A control analysis of filtered water is recommended when a known contamination exists. Periodic checks make it possible to verify that the media retains its reduction capacity before it is replaced.
Imperial test results for mercury
Mercury is included in the performance analysis table published for Monderma Imperial GF and Imperial AMB filters. The tests were conducted by Envirotek Laboratories in the United States.
Mercury: result shown in the Envirotek table
Verification of the result: the change from 6.0 µg/L to 0.04 µg/L corresponds mathematically to a reduction of approximately 99.33%, rounded to 99.4% in the table.
Interpretation limit: the line dedicated to mercury does not specify on its own whether the compound tested was elemental mercury, inorganic mercury, methylmercury, or another defined form. The result should therefore not be automatically extended to all chemical forms of mercury.
Laboratory performance corresponds to the conditions of the test protocol. Actual results may vary depending on water composition, pH, initial concentration, flow rate, contact time, maintenance, and the service life of the cartridges.
A test conducted according to an NSF/ANSI protocol does not necessarily mean that the complete filter is NSF certified for the reduction of mercury. Official certifications and performance tests must be presented separately.
View Monderma certifications and analysesFrequently asked questions about mercury in water
Can you see or smell mercury in water?
No. In trace amounts, mercury generally does not produce any taste, odor, or color that allows its presence to be detected. A laboratory analysis is required.
Is the mercury present in water always methylmercury?
No. Drinking water may mainly contain inorganic forms, whereas methylmercury is primarily a concern related to its accumulation in fish and other aquatic organisms.
What is the European limit for mercury in drinking water?
The European Union sets a parametric value of 1 µg/L for mercury in water intended for human consumption.
Does boiling water remove mercury?
Domestic boiling is not a reliable method for removing dissolved mercury. Water loss through evaporation may even increase the concentration of certain contaminants in the remaining volume.
Can mercury accumulate in fish?
Yes. Some of the mercury present in aquatic environments can be transformed into methylmercury, then accumulate and concentrate in the food chain.
Does an activated carbon filter always remove mercury?
No. Performance depends on the type of carbon, other media that may be associated, the form of the mercury, water composition, and conditions of use. A filter-specific test must be consulted.
How can you verify that a filter remains effective?
When contamination is known, the most reliable method is to analyze the water before filtration and then the filtered water. Periodic checks allow you to monitor performance until the media is replaced.
Related contaminants
Mercury belongs to the category of toxic metals. You can also consult the other fact sheets dedicated to metals and trace elements that may be present in water.
Scientific and administrative sources
This fact sheet is primarily based on public bodies, international institutions, and government scientific databases. No commercial blog, comparison site, or affiliate site is used as a health source.
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World Health Organization – Mercury and health
Information regarding the different forms of mercury, their
health effects, and sensitive populations.
Consult the official WHO fact sheet -
World Health Organization – Mercury in drinking water
Chemical fact sheet presenting the presence of inorganic mercury
in water, its effects, and the 6 µg/L guideline value.
Consult the WHO chemical fact sheet -
European Union – Directive (EU) 2020/2184
Official text relating to the quality of water intended for human
consumption and the parametric value for mercury.
Consult the directive on EUR-Lex -
European Commission – Mercury and the environment
Information on European restrictions, uses, and pollution linked to
mercury.
Consult the European Commission page -
Environmental Protection Agency – Mercury in drinking water
US regulation setting a maximum concentration of 0.002 mg/L for
inorganic mercury.
Consult EPA regulations -
Environmental Protection Agency – General information on mercury
Presentation of elemental, inorganic, and organic forms of mercury
and their main origins.
Consult the official EPA page -
PubChem – National Institutes of Health
Official data on the element mercury, its symbol Hg, and its atomic
number 80.
Consult the PubChem sheet -
Monderma – Certifications and laboratory analyses
Certifications, reports, and analysis table for the filters in
question.
Consult Monderma certifications and analyses
