In addition to the acute harm caused by large quantities of poisonous chemicals, in the late 1980s people discovered that despite the increasing level of controls over the use of chemicals, even low levels of some compounds could still lead to chronic effects such as tumors, birth defects and genetic mutations.
除了造成急性傷害的化學毒物，一九八○年代後，人類進一步發現，化合物雖陸續受到管制，但在低劑量下，仍會導致人體腫瘤、畸胎、遺傳基因突變等慢性傷害。