Multi-generational exposure to fipronil, 2,4-D, and their mixtures in Chironomus sancticaroli: Biochemical, individual, and population endpoints*

Conventional farming delivers a range of pesticides to aquatic ecosystems leading to implications for the indigenous species. Due to the multiple applications and persistence of molecules, organisms may be exposed for a prolonged period over multiple generations. The present study outlines a full life-cycle design over three generations of Chironomus sancticaroli exposed to the insecticide fipronil, the herbicide 2,4-D, and their mixtures. The experiment started with newly hatched larvae from the parental generation and lasted with the emerged adults from the second generation. Five nominal concentrations of fipronil and 2,4-D were tested, as well as six combinations of both pesticides. As additional responses, the total carbohydrates and the lipid classes were evaluated in the parental generation. The first and second generations were more susceptible to the tested compounds compared with the parental ones. Survival of larvae and pupae was decreased by both pesticides and their mixtures along with the generations. Only fipronil impaired the survival of emerged adults. Both pesticides (isolated and in the mixture) altered the emergence and the fraction of males and females. Moreover, the number of eggs produced, and their hatchability decreased. Only one combination of the pesticides increased the content of carbohydrates. Fipronil, 2,4-D, and its mixture altered the profile of the lipid classes. All mixture treatments and the three highest concentrations of fipronil extinguished the population of C. sancticaroli at the end of the first generation. In the remaining treatments with the insecticide, the population did not survive the second generation. Only three concentrations of 2,4-D and the control persisted until the end of the experiment. The results indicate that a prolonged exposition to these pesticides may disrupt the natural populations of exposed organisms with consequences to ecosystems' functioning, considering the importance of chironomids to aquatic and terrestrial environments.