Based on the results from the algal toxicity tests (EC₅₀ < 100 mg/L), TMP is already classified as ‘harmful to aquatic organisms’ and ‘possibly able to cause long-term adverse effects in the aquatic environment’ (Phrases R42 and R43). However, as frequently happens, an acute lethality test on Brachydanio rerio (Halling-Sørensen et al. 2000) yielded negative results, pointing to a no observed effect concentration (NOEC) for fish of 100 mg/L (Chemwatch 2009). For P. reticulata, these data would have been confirmed by our test, but referring to the sublethal endpoint (swimming activity inhibition), exposure to 100 mg/L is not devoid of effects. In fact, the protocol for the acute lethality test (OECD 203 1992) recommends the importance of recording any sublethal effect. Thus, it will be important, in the future, to evaluate the same endpoint with scaled concentrations of TMP to determine both the NOEC and the EC₅₀ with confidence limits.

Swimming activity inhibition was also recorded with the other five compounds; more detailed study is therefore recommended, although with less urgency than with TMP. It is worth noting that in this study, the evaluation of more refined components of swimming that could increase the sensitivity of the tests has not been considered. These actions include acceleration, freezing, angles of turns, horizontal and vertical distribution, predator avoidance, etc. In Fig. 18.2, for example, one notes that the control group swims more peripherally (P. reticulata) or has a higher tendency to move in the water column (D. magna) compared to the TMP-exposed groups.