The zinc paradox – a problem for USEtox-based indicators of national chemical footprints?
Paper in proceedings, 2016
Considering the immense problem of chemical pollution worldwide, there is a great need for methods that can be used to calculate indicators of chemical footprints. Such indicators can be calculated for products and services using life cycle assessment (LCA), but also for whole nations. Indicators of national chemical footprints may include emissions within the nation’s borders only, or also emissions related to consumption (thus having a life cycle perspective). A limited number of studies (<5) have attempted to calculate indicators of national chemical footprints using the USEtox consensus model for toxicity impact assessment in LCA. One of these is our calculation of indicators of a national chemical footprint for Sweden. Two other studies have made similar assessments for Europe. Using the national perspective of these studies enables a rough validation of USEtox results, since the indicators of national chemical footprint based on USEtox can be compared to non-LCA toxicity assessments done on national levels. Such validations are not possible for LCA studies of single products. Notably, the results of existing assessments of indicators of national chemical footprints, including our Swedish study, all pinpoint zinc as the dominating substance. Zinc typically accounts for >50% of the toxicity impacts for both ecotoxicity and human toxicity. For ecotoxicity, this is not unreasonable considering the notable toxicity of zinc to aquatic organisms. For human toxicity, this result is more surprising. Zinc is an essential trace element for humans that many take as a dietary supplement to prevent zinc deficiency. Non-LCA sources describe zinc as “relatively harmless” to human health. The World Health Organisation (WHO) does not list zinc among the top ten chemicals of major public health concern, although there are other metals on the list (mercury, lead, cadmium and arsenic). These contradictory claims about zinc’s health impact seem to constitute a paradox. We present a review of existing studies assessing indicators of national chemical footprints, and of toxicological research related to zinc. We further discuss potential causes of this zinc paradox, as well as implications for assessments of indicators of national chemical footprints with USEtox.