Metal Stocks in Society – Scientific Synthesis - UNEP

Metal Stocks in Society – Scientific Synthesis25There are what seem to be obvious gaps inthe information available for materials usedin large quantities. For example, there appearsto exist no global estimate for zincstocks in society. Neither are there globalstock estimates for the major alloying metalschromium, manganese, nickel, and tin, andonly a few at country level for these metals.The stocks of magnesium, a light metal seeingincreasing use in reduced-weight vehicles,have been evaluated only in Japan. Foruranium and zirconium, necessary elementsfor nuclear power, there are no extant stockestimates at all.Anthropogenic stock estimates of the specialtymetals are almost nonexistent. Thissituation is partly due to lack of data, partly tolack of interest in such studies in the past fewdecades. One might target for attention thelanthanides (separately or as a group), whichsee extensive use in electronics and medicalequipment, and indium, an element essentialat present for flat-panel displays, and oneperceived to be under supply pressure as itis only available as a byproduct of zinc oreprocessing (Fraunhofer Institute for Systemsand Innovation Research, 2009).Another obvious area of need is anthropogenicstock studies focused on less-developedcountries. The gaps between the stocksof those countries and those of more-developedcountries have much to tell us aboutpotential future demands for resources, butlittle effort is underway to fill those knowledgegaps.Quantification of metal stocks in society islimited by the availability of data in most cases.Information on flows into use is generallybetter than on flows out of use. Were governmentsto routinely collect discard, recycling,and waste data, in-use stock estimates couldbe significantly improved.It is notable that very few studies of in-usestocks make any attempt to discuss or estimateuncertainty. Unlike laboratory systemswhere uncertainty can be rather preciselydetermined, in-use stock uncertainty is relatedto such factors as the average lifetimesof different products groups and the elementalcompositions of buildings and equipment,which have significant but poorly determinedvariability. Some researchers (e. g., Rostkowskiet al., 2007) have discussed potentialsources of error in these studies. It is thoughtthat recent stock estimates are accurate toperhaps +/- 25 %, and such accuracies areperfectly adequate bases on which to basepublic policy.An avenue of research yet to be extensivelyexplored is that of spatially-explicit in-usestock estimation. van Beers and Graedel(2007) have shown in a bottom-up study thatrelatively fine spatial resolution can be obtainedthrough the utilization of GIS and spatially-explicitstock and population data. A recentstudy by Terakado et al. (2009) attemptedto estimate the spatial distribution of thein-use stock of copper in Japan by utilizationof nocturnal light images from satellite.This appears to be the first effort to exploitthe combination of GIS and remote sensingfor inferring in-use metal stock. Such workcould be advantageous, as the results couldbe linked with other spatial attributes usefulto decision makers.It is worth noting that a variety of spatialboundaries have been the subject of anthropogenicstock studies, and one could askwhat makes the choice of a city or any othergeopolitical border appropriate for a stockstudy? The answer depends on the problemfor which the in-use stock estimate is to beused. If one seeks to create a map of in-usestock for the purpose of providing insight intofuture scrap flows, then a geopolitical or anyother sort of spatial boundary seems appropriate.Similarly, city boundaries are usefulin employing in-use stock studies to estimatedissipative outflows (e. g., Sörme and Lagerkvist,2002; McKenzie et al., 2009) However,if one seeks to infer conclusions aboutpopulation affluence via in-use stock, a systemthat (such as city borders) is too smallmight be inappropriate for some metals. Forexample, a small spatial boundary might beappropriate for a metal which is mostly con-