Similarities, Differences and Synergisms Between HERA and LCA—An Analysis at Three Levels

ABSTRACT

Linkages between Human and Environmental Risk Assessment (HERA) and Life-Cycle Assessment (LCA) can be analyzed at three levels: the basic equations to describe environmental behavior and dose-response relationships of chemicals; the overall model structure of these tools; and the applications of the tools. At level 1 few differences exist: both tools use essentially the same fate and effect models, including their coefficients and data. At level 2 distinctive differences emerge: regional or life-cycle perspective, emission pulses or fluxes, scope of chemicals and types of impacts, use of characterization factors, spatial and temporal detail, aggregation of effects, and the functional unit as basis of the assessment. Although the two tools typically differ in all these aspects, only the functional unit issue renders the tools fundamentally different, expressing itself also in some main characteristics of the modeling structure. This impedes full integration, which is underpinned in mathematical terms. At level 3 the aims of the tools are complementary: quantified risk estimates of chemicals for HERA versus quantified product assessment for LCA. Here, beneficial synergism is possible between the two tools, as illustrated by some cases. These also illustrate that where full integration is suggested, in practice this is not achieved, thus in fact supporting the conclusions.

Key Words:

• HERA
• LCA
• functional unit
• toolbox
• combined approach.

Notes

¹The dichotomy introduced here between including a process in its full extent and including it only for a part has been described at various places under various names. Udo de Haes et al. (2000) approach it from the technical side and use the terms full-mode and attribution-mode. Heijungs (2001) speaks of commodity-flow accounting and activity-level analysis. Barnthouse et al. (1997) approach this dichotomy from the consequence side and uses the terms absolute and relative to indicate these two modes. Likewise, Olsen et al. (2001) employ the terms absolute and comparative. Below, we will further use the terms of Barnthouse et al., absolute and relative, relative meaning in relation to a functional unit. (Udo de Haes et al. 2000): HERA takes all activities in this region fully into account, LCA takes activities into account as far as they are needed for the functional unit