For the 7 d sublethal tests (Bioassay 2), the test medium was prepared from stock suspensions to produce a concentration of 200 mg L1 for only two particle types (NP and NPn), considering the preliminary test results which demonstrated that the neonates would live no longer than one week in the other three types of particle suspension. During the sublethal experiments, in addition to daily renewals of the medium, the animals were sucked up and the body size (top of the eye to the base of the spine) of each organism was measured daily using an ocular micrometer on an optical microscope to characterize the growth.