Twyla Michelle Blickley, Christopher Szakal, R David Holbrook



The literature suggests that nano-sized titanium dioxide is acutely toxic to Daphnia magna at concentrations greater than 100 mg/L, which is well above what is considered environmentally-relevant (0.7 g/L -16 g/L). We are chronically exposing this freshwater invertebrate to low levels of TiO2 (1 g/L -1000 g/L) to determine sub-lethal toxicological effects. Nano-sized TiO2 (NIST SRM-1898) suspensions were prepared by sonication, coated in bovine serum albumin (BSA), and dispersed in PBS, thus yielding particles that were ~75 nm in diameter. To determine particle behavior in the water column, the material was mixed into OECD Daphnia media, transferred to graduated cylinders, and measured for concentration via UV/VIS spectroscopy at 1, 24, 48, and 168 hours. Negligible settling occurred during the first 48 hours; however, 65 % of the total suspended material had precipitated to the bottom layer by day 7. Ongoing studies involve aqueously exposing Daphnia neonates to these BSA-TiO2 suspensions for 14 or 21 days. At the conclusion of the exposures, daphnids are rinsed with clean OECD media before excising their eggs. The eggs are currently being evaluated for TiO2 deposition with Secondary Ion Mass Spectrometry (SIMS). Additionally, adult Daphnia are being aqueously exposed to 1 mg/L BSA-TiO2 for 7 days and the gut tract contents are examined for transformation of the particles with SIMS. The goal of these studies is to determine where the nanoparticles reside in the aquatic environment as well as where and in what form the particles exist within the organism.