Regulatory agencies spend years analyzing the relevant science and listening to the public’s input. The laws governing pesticide registration require original Good Laboratory Practices (GLP) research, conducted under rigorous conditions, each time a chemical is re-registered. Samples from these studies are kept for decades. As new technology becomes available, additional analysis can be conducted to ensure the original results are supported.
There is not one regulatory agency mandated with protecting public health in the world that identifies 2,4-D as a human carcinogen.