Figure 3 -4 below gives examples of anthropogenic mercury releases to the different environmental media (here termed as pathways, but often also called compartments or routes).
Examples of anthropogenic mercury releases to the environmental media
Destinations of releases to the environment and types of releases to each receiving environmental medium:
Air - the atmosphere: Point sources and diffuse sources from which release may be spread locally, regionally and hemispherically/globally with air masses.
- Emissions from major point sources such as coal fired power plants, metal extraction, waste incineration, chlor-alkali facilities, secondary scrap recycling/smelting, cement production, industrial inorganic chemicals production and diffuse sources such as housing (fossil fuel combustion);
- Emissions from artisanal gold mining;
- Emissions from cremation, primarily due to dental fillings containing mercury;
- Emissions from mercury-containing paints;
- Diffuse releases from uncollected waste products (fluorescent lamps, batteries, thermometers, mercury switches, lost teeth with amalgam fillings etc.);
- Evaporation of previous discharges to soil and water;
- Evaporation of mercury disposed of on landfills.
Water – aquatic environment: Point sources and diffuse sources from which mercury will be spread to marine environments (oceans), and freshwaters (rivers, lakes etc.).
- Direct discharges from industry and households to aquatic environments;
- Emissions from artisanal gold mining;
- Indirect discharges via waste water treatment systems;
In addition to the release pathways (air, water, land) mentioned above, this Toolkit works with the output pathways "products", "general waste" and "sectors specific waste treatment". This is done for practical reasons in the inventory work, yet the final receiving media may in the long term ultimately be land, air and water. Some examples of mercury flows/releases to "products", "general waste" and "sectors specific waste" are given in Figure 3 -5 below.
Examples of mercury flows/releases to the intermediate pathways
"products", "general waste" and "sector specific waste treatment"
Products (as output pathway): By-products that contain mercury, which are sent back into the market and cannot directly be allocated to environmental releases;
By-products with mercury content, either in trace concentrations where mercury is an impurity in recovered materials, or as by-product mercury or raw by-product mercury compounds from primary metal extraction (mining)
- Gypsum wallboard produced from solid residues from flue gas cleaning on coal fired power plants (with mercury trace concentrations);
- Sulphuric acid produced from desulphurization of flue gas (flue gas cleaning) in non-ferrous metal plants (with mercury trace concentrations);
- Chlorine and sodium hydroxide produced with mercury-based chlor-alkali technology (with mercury trace concentrations).
- Metal mercury or calomel as by-product from non-ferrous metal mining (high mercury concentrations
General waste: Also called municipal waste in some countries. Typically household and institution waste - the large bulk of general waste from the population - where the waste undergoes a general treatment, such as incineration or deposition under controlled circumstances.
- Consumer products with intentional mercury content, such as batteries, thermometers, human teeth with mercury amalgam fillings, electronic devises with mercury switches, fluorescent tubes, etc. that is not collected/treated in separate systems;
- Normal high volume product waste like paper, plastic, etc., with very small trace concentrations of mercury.
Sector specific waste treatment: Waste from industry and consumers that is collected and treated in separate systems, and in some cases recycled.
- Hazardous industrial waste with high mercury content, usually from intentional mercury use – that may be stored in sealed containers on specially protected deposits, or in some cases incinerated (due to content of other substances which are combustible);
- Hazardous waste from secondary smelting/scrap recycling operations;
- Hazardous consumer waste with mercury content, mainly separately collected batteries, thermometers, mercury switches, lost teeth with amalgam fillings etc.;
- High volume rock/waste from extraction of metals or minerals;
- Solid residues from waste incineration (slag/bottom ash and fly ash).
Figure 3 5 Examples of mercury flows/releases to the intermediate pathways "products", "general waste" and "sector specific waste treatment" of anthropogenic mercury releases to the different environmental media.
As illustrated in Figure 3 -3, waste disposal is a major output/release route in the life-cycle of mercury-containing products and materials. Waste treatment and wastewater treatment are examples of mercury release sources, for which the origin of the mercury has to be assessed, in order to consider properly possibilities for cost effective release reductions. While these systems are implemented for the reduction of environmental impacts from various pollutants, they do not generally provide terminal elimination of all the mercury present in the wastes. This is due to mercury's special characteristics in combination with the applied technologies and procedures (as described in sections 5.8 - 5.10 on the different waste treatment systems). For mercury, reduction or elimination of mercury before it becomes a waste (in products and processes) is considered widely as a cost effective release reduction option.
For more information on output pathways, see the description of the Toolkit inventory approach in section 4.4.4. For examples of the relative importance of mercury releases from different sources from a number of countries, and also between impurity mobilization and intentional mercury use, see chapter 6 of the Global Mercury Assessment report (UNEP, 2002).