The releases of mercury to the biosphere can be grouped in four categories (UNEP, 2002):
Natural sources - releases due to natural mobilization of naturally occurring mercury from the Earth's crust, such as volcanic activity and weathering of rocks;
Current anthropogenic (associated with human activity) releases from the mobilization of mercury impurities in raw materials such as fossil fuels – particularly coal, and to a lesser extent gas and oil – and other extracted, treated and recycled minerals;
Current anthropogenic releases resulting from mercury used intentionally in products and processes, due to releases during manufacturing, leaks, disposal or incineration of spent products or other releases;
Re-mobilization of historic anthropogenic mercury releases previously deposited in soils, sediments, water bodies, landfills and waste/tailings piles.
Figure 3.1 shows these release categories with main types of possible control mechanisms.
Releases
mostly beyond
human control
- Reduce consumption
- Use alternative raw materials
- “End-of-pipe” techniques
This Toolkit aims at guiding users in the identification and quantification of human-generated mercury releases that can potentially be reduced through various regulatory actions or other approaches. Therefore, the Toolkit concentrates on current anthropogenic releases from mobilization of mercury impurities, from intentional use of mercury in products and processes and from human-generated deposits such as landfills, contaminated sites and mine tailing piles. These overall modes of anthropogenic releases form the backbone of the categorization of release sources in the Toolkit.
Natural mercury sources and remobilization of previous atmospheric deposition are not covered in this Toolkit, as release reduction initiatives are not relevant for these sources. These sources do, however, contribute to the adverse impacts of mercury on human health and the environment, and may in some areas warrant particular attention for these reasons. For more reading on natural mercury sources and remobilization, see the Global Mercury Assessment (UNEP, 2002).
A fact that is basic to the understanding of mercury’s pathways in society and the environment is that mercury is an element and, although it may change between different forms in its cycle, it cannot be broken down or degraded into harmless substances. This means that once mercury has been brought into circulation in the society/biosphere by human activity it does not “disappear” again in time spans comparable to human lifetime and will need to be managed (stored or disposed of) for the longer term.
Releases throughout the "life-cycle" of a product or process
To illustrate the nature of mercury flows in society and mercury releases to the environment, the life-cycle concept can be of use. The life-cycle concept is a "cradle to grave" approach that recognizes that all stages in the “life” of a product or process (extracting and processing raw materials, manufacturing, transportation and distribution, use/reuse, recycling and waste disposal) may have potential environmental impacts. The life-cycle approach can be used during data gathering and development of an inventory and for ranking the environmental burdens of products, processes and services.
The diagram below breaks down a product or process life-cycle inventory into inputs containing mercury and outputs of mercury in material and environmental releases.
Mercury in
products
Figure 3 2 Illustration of a life-cycle inventory broken down into inputs and outputs for material as well as environmental releases
Mercury releases may occur at all stages of the life-cycle of a mercury-added product or process. As mercury is an element and therefore neither formed nor degraded during this life-cycle (though it may change form), the total inputs of mercury will equal the total outputs. This means that the mercury releases from a particular human activity can be viewed as the consecutive distribution of the original mercury input to various media or release pathways during various stages of the life cycle of the product or process in question.
Examples of the life-cycle of mercury in a process and a product, and the mercury releases occurring throughout the life-cycle are given in Figure 3 -3. Only those phases in the life-cycle that are relevant to releases of mercury are shown in the figure.
a) The life-cycle of mercury in production of electricity from coal combustion.
Extraction
(of coal)
Production
(of electricity)
Disposal
(of wastes/residues)
Post-deposition
25
Releases to land, water and air from solid residues not deposited under controlled, safe conditions
100
Releases to air and mercury in residues from combustion and flue gas cleaning
50
25
Deposition of mercury in
solid residues under
controlled, safe conditions
?
Long-term releases of mercury to air and water from deposited solid residues
b) The life-cycle of mercury in mercury oxide batteries.
Extraction (of mercury)
Production
(of batteries)
Use
Disposal
Post-deposition
100
Releases and waste from extraction of mercury from ore
20
80
Releases from manufacturing of batteries
10
70
10
Releases to land, water
and air from waste
batteries not collected
to controlled waste
treatment
25
Releases to air and
deposition of mercury in residues from incineration of batteries collected with household waste
?
Long-term releases
of mercury to air and water from deposited incineration residues
25
Deposition of mercury
in batteries collected
with household waste
?
Long-term releases
of mercury to air
and water from
deposited waste
10
Deposition of mercury
in separately collected
batteries
Notes: Numbers indicate relative percent of the original mercury input (content in coal and ore, respectively) following the different release pathways, in a fictive, but realistic example.
A red arrow indicates where direct releases occur and a blue arrow indicates other flows.
Figure 3 3 Illustration of the life-cycle of mercury in a) a process (production of electricity from coal combustion) and b) a product (mercury oxide battery) (hypothetical - for illustration purposes)
For the sake of convenience, releases from primary extraction of mercury, as well as releases from treatment of general (household) waste and waste water, are described and assessed separately in this Toolkit, but the important links between these phases and the production and use phases in between, are noted in the description of the mercury release sources.
he diagram below breaks down a product or process life-cycle inventory into inputs containing mercury and outputs of mercury in material and environmental releases.
25
