The use of any material for practical applications engenders risk. What is important is an understanding what constitutes acceptable risk. For nanomaterials, the key point is in determining whether a nanoscale substance is inherently toxic and under what specific circumstances, it can be particularly harmful. Hence, in both cellular and marine studies, our group has found that the toxicity of a nanomaterial is often a function not only of its actual chemical composition but also of its particular morphology including structure, size, and shape.