Risk of triclosan based on avoidance by the shrimp Palaemon varians in a heterogeneous contamination scenario: How sensitive is this approach?

As the exposure of organisms to contaminants can provoke harmful effects, some organisms try to avoid a continuous exposure by using different strategies. The aim of the current study was to assess the ability of the shrimp Palaemon varians to detect a triclosan gradient and escape to less contaminated areas. Two multi-compartmented exposure systems (the linear system and the HeMHAS-Heterogeneous Multi-Habitat Assay System) were used and then results were compared. Finally, it was aimed how sensitive the avoidance response is by comparing it with other endpoints through a sensitivity profile by biological groups and the species sensitive distribution. The distribution of the shrimps along the triclosan gradient was dependent on the concentrations, not exceeding 3% for 54 μg/L in the linear system and 7% for 81 μg/L in the HeMHAS; 25% of organisms preferred the compartment with the lowest concentrations in both systems. Half of the population seems to avoid concentrations around 40-50 μg/L. The triclosan concentration that might start (threshold) to trigger an important avoidance (around 20%) was estimated to be of 18 μg/L. The profile of sensitivity to triclosan showed that avoidance by shrimps was less sensitive than microalgae growth and avoidance by guppy; however, it might occur even at concentrations considered safe for more than 95% of the species. In summary, (i) the HeMHAS proved to be a suitable system to simulate heterogeneous contamination scenarios, (ii) triclosan triggered the avoidance response in P. varians, and (iii) the avoidance was very sensitive compared to other ecotoxicological responses.