Complementary to this, we define environmental lifetime as the time it takes for an item's mass to reduce to zero because of degradative processes. Accordingly, we propose that persistence can be included in material selection by considering the design objective to minimize environmental lifetime at end-of-use. Much like other MIs (Table , Section S1), we developed an approach to derive MIs for environmental lifetime by i) defining the appropriate objective equation and ii) substituting relationships for the initial geometry of the item specified by the design constraints.