In the case of nuclear accidents, for example, individual governments decide, in the light of their interpretation of a range of evidence, at what level of radioactive contamination pasture land, drinking water, milk, eggs, vegetables and fish are to be banned as unfit for consumption, firstly by humans and secondly by livestock. Different countries, and even different local authorities within countries, have different criteria. Some have none at all. Sometimes the criteria changes and what was once acceptable may become dangerous in the future. Some may apply rigorous criteria to ban suspect foodstuffs, but may then apply very relaxed criteria to assess the risk from foodstuffs imported from neighbouring countries where very permissive criteria, if any, are applied.
For 71 percent of the 3,000 highest-volume chemicals in the U.S. economy no human health-effect screening has ever been conducted. A 1984 report released by the National Academy of Sciences' National Research Council documented a lack of "even minimal" health screening tests for 78 percent of high-production-volume chemicals in the U.S. In July of 1997, the Environmental Defense Fund released a study entitled "Toxic Ignorance" that pointed to the lack of improvement in screening over the last 13 years. In conjunction with the report's release, the EDF called for commitments from the chief executive officers of the 100 top chemical manufacturers in the U.S. to complete preliminary health screening tests on each company's top-selling chemicals before the year 2000, and disclose the results to the public. According to the EDF study, the testing requested would cost between 1/10 of a cent to 2/3 of a cent per dollar of profit for the top 100 US companies, which made profits of $29.4 billion last year on $230.5 billion of chemical sales. In the meantime, the effects of these chemicals on wildlife, and on humans, remain unknown.
According to the British Toxicological Society, there is "no reliable method" to extrapolate data from laboratory animals to human beings.