This book sets out to improve the reliability of cost-benefit analyses particularly of hazardous substances present in air, water, soil and food. It suggests that the human health risk assessment of chemicals is performed in a bottom-up analysis, i.e., following a spatially resolved multimedia modelling approach. In order to support cost-benefit analyses, the approach is accompanied by monetary valuation of human health impacts, yielding so-called external costs. Results for selected priority metals show that these external costs are small compared to those by the classical air pollutants and involve rather long time horizons touching on the aspect of intergenerational equity within sustainable development. When including further hazardous substances, the total external costs attributable to contaminants are expected to be more substantial.