Fig. 3: The number of Au-NMs at each trophic level.

a Schematic representation of the trophic transfer of NMs based on particle number. Despite being exposed to the same number of Au-NMs, algae accumulate (associated with the cell or internalized in the cells) different numbers of Au-NMs as a function of NM size and shape. Smaller numbers of the Au-NMs accumulate in the daphnids compared to the algae. The NMs undergo dissolution and aggregation in the daphnids gut as a function of the NM properties, which changes the size distribution of the NMs accumulated in the daphnids. A high percentage of the NMs are excreted from the daphnids and only a small fraction is transferred to the fish. No particle number-based biomagnification occurs in fish. However, the number of accumulated NMs in fish is a function of the initial NM size and shape. The biodistribution of the Au-NMs in fish was also NM size- and shape-dependent, where a higher number of particles were detected in the brain compared to other tissues. b Particle number (per mg wet weight tissue) of Au-NMs accumulated at each trophic level (algae, daphnids, and fish tissues) as a function of NM size and shape. c Schematic representation of the trophic transfers (Algae–Daphnia, Daphnia–Fish, and Algae–Fish) considered to calculate the number-based biomagnification factors (NBMF). d The calculated NBMFs of the Au-NM in the different trophic levels of the assembled food chain used in this study. Note that the trophic transfer of Algae–Fish was calculated by dividing the total number of the particles in fish by the total number of the particles in algae, although the fish was not fed with algae directly (**P < 0.001, ***P < 0.0001). S: spherical, R-s: rod-shaped. Error bars = SD, biologically independent samples (n = 5). Data were analysed using one-way ANOVA followed by Duncan’s post hoc test (b, d) (***p < 0.0001; **p < 0.001; *p < 0.05).