One of several measures used to advise on the hazards of environmental exposure to toxic substances in the soil. The NEDEL is calculated by making studies of appropriate populations of humans exposed to the toxic agent in the soil, and determining whether the persons show significantly elevated levels of the toxic agent, symptoms of toxicity, or both. The measure was developed by the Centers for Disease Control and Prevention (CDC) and the Montana Department of Health and Environmental Sciences. Other measures have been developed from studies of laboratory animals: the no observable defect level (NOEL); the no adverse response level (NARL); and the acceptable daily intake (ADI).