Figure 6.

The joint toxicity of metal mixtures tended to be approximately additive on a response‐addition basis for Cu and Zn mixtures and less than additive for all other combinations. The solid line is the 1:1 line representing perfect agreement between predicted and observed abundance. Dashed lines indicate a 2 times difference from the 1:1 line. Where observed mayfly abundance in the mixture exposures is greater than that predicted from response addition (plotted below the 1:1 line), we interpret the mixture toxicity to be less than additive and vice versa.