Zooplankton are adversely affected by chronic exposure to Raphidiopsis raciborskii (Cyanobacteria) and acetamiprid: A study of single and combined toxicity

Abstract

Agriculture has expanded worldwide in recent years, with large amounts of inorganic fertilizers used, which can reach aquatic ecosystems and potentially worsen eutrophication and harmful cyanobacterial algal blooms (CyanoHABs). Additionally, the excessive use of neonicotinoid pesticides poses a significant environmental problem, impacting non-target organisms and the health of ecosystems. This study examined the chronic single and combined effects of the neonicotinoid acetamiprid and a saxitoxin-producing cyanobacterial strain (Raphidiopsis raciborskii LETC-CY-05) on survivorship and reproduction of two species of cladocerans (Daphnia similis and Daphnia laevis). In single exposures, D. similis was more affected by the cyanobacterium than by acetamiprid. In contrast, although D. laevis exhibited greater overall tolerance to both toxic agents than D. similis, this species was more sensitive to acetamiprid than to cyanobacterium. The overall toxicity was influenced by a 10-fold variation in toxin content per biomass across the different cyanobacterial cultures used in the experiments, even in treatments with lower biomass concentrations. Combined zooplankton exposure to the pesticide and toxic cyanobacterium yielded different interaction effects, ranging from antagonism to synergism on the proportion of toxicants. For D. similis, the most harmful effects were observed when the cyanobacteria:acetamiprid proportion was 1:1, while for D. laevis, this occurred at 1:1 and 2:1 proportions. These results demonstrate that the interaction between acetamiprid and cyanobacteria can lead to enhanced toxicity in zooplankton, underscoring the importance of assessing multiple stressors and their interactive effects in aquatic ecosystems, as single-exposure assessments may fail to capture the full scope of ecological risks.