The physicochemical properties of NPs provide an additional level of interpretation. Particle size, morphology, surface characteristics, aggregation status, and dissolution behavior can influence the interactions of ZnO-NPs with biological barriers and tissues, thereby contributing to differences in their biological effects. Such physicochemical attributes may also affect the extent to which ZnO-NPs interact with circulating hemocytes and alter cellular functions; however, these factors were not characterized in the present study and therefore cannot be directly linked to the hemocytic responses observed here.