As mentioned above, the mercury input factor is simply defined as the mercury content (for example in gram Hg) per unit of feed material processed or product produced (for example metric ton or piece) as relevant for the individual source type. However, as described in sections 4.4.1 and 4.4.2 above, the input factors for sub-categories with more than one life cycle phase are a bit more complicated. Nonetheless, examples of mercury inputs to each release source type are - to the extent data has been available - presented in the source description sections in chapter 5. The examples are derived from easily available literature, and reflect conditions prevailing at the place and the time they were observed. In chapter 5, time and origin of the data is generally described along with the data given.
It is important to note that, for certain source sub-categories, the mercury input factors change over time. Significant examples of this are consumer products that over recent years have been subject to a regulatory pressure towards reduction - or elimination - of mercury content, such as batteries and light sources.
Similarly, the mercury input factors vary with geography. Changes in mercury content in products have not happened at the same speed in all regions of the world. Also, for natural raw materials - including fuels - mercury concentrations vary considerably with geographical location due to differences in geology and, for some sources, also due to previous anthropogenic mercury deposition loads.
Thus, the choice of mercury input factors may have significant effects on the release estimates calculated. Some recommendations with regards to choosing mercury input factors include:
For quick, rough first estimates of mercury releases for a sub-category, the default input factors as presented in chapter 5 may be used; unless the default input factors clearly do not reflect the prevailing conditions. It should be noted that, as described in section 4.1.1, the default factors defined in this draft Toolkit are preliminary and subject to future revisions.
In cases where a mercury input example factor is given that is judged to reflect the prevailing conditions better than the default input factor(s), this can be used for the release calculations. The same is the case for sub-categories for which no default distribution factors are presented in this Toolkit.
Where your own well-documented, valid mercury input data are available, or can be obtained given available resources, their use in the inventory calculations is highly recommended instead of the default, or example, factors.
In all cases, an input factor should be chosen that seems to best represent the sub-category under investigation. Also, the input factors used and their background should be explicitly noted in the inventory report. This will facilitate later updating of the inventory, enable external evaluation of the inventory and enhance comparability between inventories.
Whatever input factors (as well as other data) are chosen, it may be appropriate to review and/or confirm these factors/data for local/national conditions before major decisions are taken on implementation of mitigation initiatives.
In order to assist users of the Toolkit to estimate the releases from individual source sub-categories, advice on main source specific data is given under a separate sub-heading for each sub-category described in chapter 5.
4.4.4Choice of output distribution factors
As mentioned above, output distribution factors are the relative shares of the inputs that follow the output pathways relevant in the individual case. Examples of output distribution factors for each of the mercury release source types are - to the extent data has been available - described in chapter 5. Like for input factors, these examples are derived from easily available literature, and reflect conditions prevailing at the place and the time they were observed. In chapter 5, time and origin of data are generally described along with the data given.
Recalling from section 4.1.1 above, the output pathways include:
Direct releases to the atmosphere (air);
Direct releases to aquatic environments (water);
Direct releases to land (terrestrial environment, including ground water);
Flows of mercury as an impurity in marketed products (for example gypsum wallboard produced from solid residues from flue gas cleaning on coal fired power plants);
Flows of mercury to the public waste water treatment system;
Flows of mercury to the general waste treatment system;
Flows of mercury to sectors specific waste treatment or disposal systems.
The principles applied in this "output pathway" vary between the sectors; it may for example involve separate collection and recycling, special safe deposition for high concentration mercury waste, or use of low concentration residues in road construction or other similar activities. To distinguish such disposal activities from uncontrolled "direct releases to land", the first mentioned should be characterized by an element of evaluation by risk assessments or informed acceptance from the authorities. Knowledge of the actual treatment or disposal taking place should always be noted in the developed inventory reports.
It should be noted that uncontrolled, informal or illegal deposition or incineration of waste on manufacturing sites or other places, with no evaluated mercury retention, is considered as direct releases to land, atmosphere and water, as relevant.
Note also that in the source description sections, a distinction between direct release to water and releases to the waste water system is not made. This is because the distribution between these two pathways is so variable among countries and local conditions that it is difficult to state anything general about it in a global perspective. When performing the inventory, it must therefore be noted for each source quantified, if the water releases are discharged directly, or to the waste water system. For some countries it may not be relevant, or it may be complicated to make the distinction between direct releases to water, and releases to waste water treatment. In such cases they can be treated as one output pathway.
Marketing products and materials with intentional mercury contents is not considered a release pathway in the Toolkit context. Marketed mercury amounts with such products and materials are how-ever dealt with extensively in the source description sections (Chapter 5), and must also be quantified in the inventory in order to estimate mercury releases to the environment. Examples of such products and materials are mercury thermometers, batteries and metallic mercury.
General key factors for the distribution of mercury outputs
For point sources like coal combustion, waste incineration and non-ferrous metal production, key aspects in the distribution of outputs are often the emission reduction systems applied on the point source. The mercury retention efficiency and other factors vary extensively depending upon the emission reduction devices used and how well they are functioning.
For manufacturing facilities such as mercury-cell chlor-alkali plants, mercury thermometer factories and battery production facilities, the magnitude of the mercury releases are very dependent on how well a facility incorporates prevention measures, advanced clean-up measures, proper operations, and various other work practices to minimize leaks, spills, and other non-specific mercury releases, or fugitive releases. For this Toolkit this concept will be called the “workplace procedures” for mercury.
Good workplace procedures could include, among others, the following: production takes place in closed units (rather than open units); equipment is well maintained to prevent mercury losses; the processes are monitored closely and often for mercury leaks so that leaks are detected early; detected leaks are fixed immediately using proper techniques; mercury spills are carefully collected; careful recycling of mercury wastes and losses is applied; and procedures for safe handling and storage of mercury feedstock and wastes exist, are well-described and followed in practice.
These source types may also employ release reduction systems that are somewhat similar to systems used on “point sources”, such as filters for the production room exhaust ventilation system (rather than being vented directly to air without being filtered); and mercury content in process water are carefully precipitated and retained in filters (rather than being directly released to sewer system). These source types also may have process vents that can be controlled with more classic end-of-pipe controls such as scrubbers, carbon filters, and retorts.
For consumer products with intentional use of mercury, the disposal phase is often important for the distribution of outputs to receiving media. Disposal habits and waste management systems vary greatly between countries and sometimes even localities. Important parameters include: The extent to which waste collecting systems exist, are well functioning, and controlled by environmental authorities; and the extent to which mercury-bearing wastes are collected and treated separately, and which waste treatments techniques are applied for the different waste streams.
Thus, output distribution factors may vary extensively between countries and even between localities and individual point sources. Therefore, selection of the most appropriate output distribution factors is crucial for the accurate quantification of mercury releases.
For the choice of output distribution factors, the recommendations given in section 4.4.3 for mercury input factors also apply.
