In Vivo Gold Nanoparticles Distribution in a Ciliate Simulated by an EM Algorithm-Based Mixture Size Distribution Model

Analyzing and modelling the relationship between particle size and size distribution of engineered nanoparticles (NPs) in vivo represents an important challenge to properly assess the environmental fate and effects of NPs. This study used single-particle ICP-MS to investigate how three sizes of spherical gold (Au) NPs and their mixtures influenced the particle size and size distribution within a ciliate Tetrahymena thermophila under the same particle number concentration exposure. Smaller particles tended to aggregate and bioaccumulate in vivo and the calculated concentration factor was negatively related to the NPs size. The in vivo size distributions of NPs with mixed sizes were approximated well by the Expectation-Maximization (EM) algorithm-based mixture size distribution model (MAE<0.001, RMSE<0.005, ρ>0.96), which were verified by our mixture size experiment results. The model reliably predicted the size distributions of different mixed sizes Au NPs in vivo. The modeling results suggested that the smaller particle size accounted for a large proportion in the mixed distribution when the difference of particle size among the mixtures was small. Our results demonstrated the importance of particle size and size distribution of NPs in their environmental fate. Modeling can provide guidance for future evaluation of the environmental risks of mixtures of NPs