Dr. Andrew Maynard, Science Advisor to the Project on Emerging Nanotechnologies, and his co-authors outline a series of five grand challenges to nanotech risk assessment in a commentary in this week's Nature:

• Develop instruments to assess exposure to engineered nanomaterials in air and water, within the next 3-10 years.

• Develop and validate methods to evaluate the toxicity of engineered nanomaterials, within the next 5-15 years.

• Develop models for predicting the potential impact of engineered nanomaterials on the environment and human health, within the next 10 years.

• Develop robust systems for evaluating the health and environmental impact of engineered nanomaterials over their entire life, within the next 5 years.

• Develop strategic programs that enable relevant risk-focused research, within the next 12 months.

As you can see, it's not easy trying to regulate a technology when we don't even have adequate instruments to measure it and policies to govern it. (hat tip to softmachines.org)