Paradigm for Substance Flow Analyses 3 Level of Detail and ReliabilityThe SFAs may be conducted at different levels of detail and reliability. As regards the analyses carried out and published in Denmark so far, it is relevant to distinguish between:
In addition the analysis can be extended with one or more of the extensions. A number of possible extensions are specified in Appendix 1. The definition of level is a part of the initial 'Goal definition' and it is recommended to define the level of detail and reliability to be achieved/aimed at, before a substance flow analysis is initiated. Accordingly, all reports on SFAs should specify the degree of uncertainty that applies to the results. This way, it will be possible for the client to assess, for instance by spot checks, whether the analysis has been completed satisfactorily. In principle, the uncertainty of consumption data in relation to detailed analyses and overview analyses, respectively, cannot be documented, as that would require the existence of knowledge about the 'true' values. As regards detailed analyses, the method of analysis in itself including the use of cross-checks (cf. Box 1) is assumed to support the correctness of the stated degree of uncertainty. Detailed analyses Examples of detailed analysis are the SFAs for mercury /Hansen 1985; Maag et al. 1996/, lead /Hansen & Busch 1989;Lassen and Hansen 1996/, copper /Lassen et al. 1996/ and tin /Lassen & Hansen 1997/. These analyses have typically required an effort of 3-5 man months per substance and are estimated by the authors to have fulfilled what is designated the 80/20 rule, i.e. a minimum of 80% of the consumption has been identified according to fields of application and determined within an interval of + 20% around the mean value. The remaining part of the consumption has been determined with a considerably higher degree of uncertainty. In the previous analyses it has often not been stated explicitly how the intervals should be interpreted, but it is recommended that the interval itself according to section 2.3.1 in subsequent detailed analyses represent a 90% certainty level. As regards the assessment of losses to the environment, it also applies that a precise level of uncertainty cannot be stated. In the case of substances that are predominantly imported into Denmark as additives contained in finished products, the uncertainty of the outcome of a detailed analysis may be significantly higher. One important factor in this context is that cross-checks for consumption data cannot be carried out. Obviously, this leaves little possibility to check the distribution of the consumption on different fields of application. In such cases, it will be difficult, even with an extensive effort, to achieve a result with a lower degree of uncertainty than that of an overview analysis. In reality, the result may be verified only by comparison to investigations from other countries or by obtaining information about the size of the production in Europe or world-wide, and on this basis, make an estimate of the likely consumption per inhabitant in Denmark. For substances predominantly imported into Denmark with finished products it is recommended to extend the SFA with a detailed analysis of the application of the substance in an international perspective. Overview analyses Among the examples of overview analysis are those for arsenic, chromium, cobalt and nickel /8/. The typical time requirement of these analyses has been about 1 man month per substance (only possible because of the greater efficiency achieved by carrying out more analyses in parallel) and, in terms of accuracy (as assessed by the authors), it is estimated that 80 per cent of the consumption has been determined with an accuracy of +50% and the remaining 20% with significantly greater uncertainty. The estimates of losses to the environment will also be subject to greater uncertainty than what is the case in detailed analyses. Another characteristic difference worth mentioning is the fact that, in connection with detailed analyses, a considerably greater effort is put into verification of data on consumption by means of cross-checks, whereas such cross-checking has been practically impossible in the case of overview analyses. This is due to the fact that, in some of the overview analyses carried out until now, a significant part of the consumption was estimated on the basis of information about the consumption in the USA. For comparison, at least one enterprise (often 2-4 usually but not all industries) within all significant fields of application were contacted as part of the detailed analyses. Other levels of detail In principle, SFAs can be made both more or less detailed and reliable than what is described above. If the analyses are to be more accurate than level (1), it will, in practice, be necessary to collect information from virtually all relevant enterprises, including importers of manufactured products, and to verify discharge data etc. In addition, detailed information will need to be obtained about all links in the chain of treatment and final disposal of waste and residual products. In principle, it should thereby be possible to reduce the uncertainty of consumption data to a marginal level. At the same time, it should be possible to minimise the uncertainty of data on discharge to the environment to a level corresponding to that implied in sampling and chemical analysis. Up until now, no analyses at this level of detail have been carried out in Denmark and the time consumption involved would probably also be unreasonably high (1 year or more per analysis?). In order to minimise the time consumption, it may be necessary to use foreign analyses/data as a basis and presume that these data (proportionally according to population) also apply to Danish conditions. Provided that foreign data are available, it is thus possible to make estimates of the consumption distributed on fields of application, which may provide an initial overview of the situation but usually not in any significant degree of detail. As the Danish systems for treatment and disposal of waste and residual products differ significantly from the practice in other countries (for instance, incineration of solid waste is more widely used in Denmark than in the rest of Europe), it will normally not be possible to use foreign data to estimate the environmental exposure in this part of the process. Furthermore, the differences in the industrial structure and discharges from manufacturing processes may also be significant. As it appears, there is a close connection between the level of detail and reliability of SFAs and the effort invested. The information given above about inputs required builds on experience with heavy metals and organic compounds with rather complex but still known patterns of application and flow in the society. In the case of substances with a simple pattern of application and dispersion, the analysis will be less time-consuming than what is stated above. Other substances may, on the contrary, require more input.
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