Using an advanced form of genetic engineering, scientists are manipulating the structure of cells to create new life forms designed to perform specific functions, such as detecting arsenic in drinking water or producing biofuels from algae. More than 500 companies, universities and other organizations worldwide are conducting research in the new field, known as synthetic biology, and developing products with the technology. Proponents say it will safely revolutionize everything from food and fuel production to medicine and manufacturing. But the field is largely self-regulated, leading critics to warn that synthetic biology — especially when used on an industrial scale — poses potential environmental and health risks that as yet are unexplored. Additionally, some ethicists question whether scientists should be creating new life forms. And others fear that the proliferation of do-it-yourself labs, where the public is free to experiment with synthetic biology, could enable terrorists to use the technology to create bioweapons.