Near shore freshwater algal blooms are aesthetically displeasing and potentially unhealthy. We have used TiO₂-photocatalytic oxidation to kill the green alga Cladophora glomerata collected from southern Lake Michigan shorelines. The toxic potential of nanoparticles such as TiO₂ has rarely been addressed despite their increased use. This study will assess the potential of TiO₂ to kill animal cells using Chinese hamster ovary (CHO) and mouse fibroblast (3T3) cell lines. In addition, we will determine if cell death is apoptotic. Cell lines will be cultured in 75 cm² flasks in Dulbecco's Modified Eagle's Medium supplemented with 10% fetal calf serum at 37°C in an atmosphere containing 5% CO₂. For each experiment, cells will be seeded in 24-well culture plates at an approximate density of 10⁵ cells/well. Dose-response curves for UV-activated TiO₂ will be generated using Trypan Blue exclusion to determine the best time to study cell death mechanisms in each cell line. To determine if the cells die apoptotically, total DNA will be extracted, stained with ethidium bromide and subjected to agarose gel electrophoresis for detection of DNA fragmentation.