Decoupling bioaccumulation and trophic transfer: nanoatrazine accumulates in microalgae but shows limited transfer to zooplankton.

Nanoformulations of pesticides have been proposed as a strategy to improve agricultural efficiency while potentially reducing environmental contamination. However, little is known about the bioaccumulation and trophic transfer of nanopesticides in aquatic food webs. In this study, the bioaccumulation of poly(ε-caprolactone)-encapsulated nanoatrazine (nATZ-PCL) was evaluated in the microalga Raphidocelis subcapitata, as well as its potential transfer to the zooplanktonic consumer Daphnia magna through dietary and direct exposure pathways. Physicochemical characterization demonstrated that the nATZ-PCL presented relative stability under most tested conditions, although aggregation behavior was observed in the algal culture medium over time. Atrazine accumulation was detected in R. subcapitata, particularly under EC25 exposure conditions in the absence of natural organic matter (NOM). In contrast, atrazine was not detected above the analytical detection limit in D. magna following either dietary exposure with pre-exposed algae or direct exposure in reconstituted medium. The results suggest that nanoparticle aggregation, reduced bioavailability, limited assimilation efficiency, and depuration processes may have restricted the trophic transfer of nATZ-PCL to the primary consumer. These findings demonstrate that bioaccumulation in primary producers does not necessarily imply efficient transfer across aquatic trophic levels and contribute to a better understanding of the environmental behavior of nATZ-PCL in aquatic systems.