Life-stage-dependent sensitivity of the cyclopoid copepod Mesocyclops leuckarti to triphenyltin

The effects of triphenyltin (TPT) on non-target aquatic groups like copepods have not yet been studied in detail. Recently, Mesocyclops leuckarti was suggested as a representative species for freshwater cyclopoid copepods to study the effects of plant protection products. We conducted 96h acute toxicity tests in the laboratory to study the effects of TPT on the different life stages of M. leuckarti. We used the recently proposed General Unified Threshold model of Survival (GUTS) to mechanistically describe the underlying toxicokinetic and toxicodynamic process for the nauplii, copepodites and adults (males and females) of M. leuckarti. Experimental results showed that nauplii were significantly more sensitive to TPT compared to the other stages. Also, the 96h LC50 values were much lower than the 48h LC50 values, suggesting that standard acute toxicity test durations for aquatic invertebrates may underestimate toxic effects with respect to compounds like TPT which have a slow mechanism of action. The GUTS analysis, which mechanistically described the toxicity of TPT to the different life stages of M. leuckarti, suggested that the differences in sensitivity were a consequence of a lower threshold of effects in the nauplii compared to a higher threshold in the later stages. This study shows the potential of using the GUTS to understand how toxic compounds interact with different life-stages. Further experiments to provide a more detailed understanding of toxicokinetics of TPT in copepods could be useful.