Appendix 2
Aquatic Toxicity Assessment of Clipper Herbicide Formulation
In order to assess the toxicity of combined exposure of active and other formulation ingredients,
the toxic unit approach was used to estimate combined toxicity. The toxic unit approach is based
on concentration addition. The combined effect of multiple compounds or substances is
calculated by summation of the concentration divided by an effect concentration.
The concentration addition is commonly applied by the use of toxic units (TU). The TU is
defined as the quotient ci/ECxi which rescales the absolute concentrations of substances to
individual potencies. The combined effect is estimated by the summation of TUs.
The TU values were calculated for fish, aquatic invertebrates and algae. The results are shown in
Fig. A2-1, A2-2, and A2-3 below. These results indicate that for fish and algae the combined
effect is dominated by the effect of flumioxazin, with very small contributions from effects of the
other ingredients. For invertebrates the contribution of other ingredient #4 (a surfactant) exceeds
the contribution of flumioxazin.