Answer:
Standards should aim to prevent health impairment. Zeilhuis (1991) argues that the no observed (adverse) effect level (NOAEL/NOEL) should be the basis for standards. An adverse effect is the "causation, promotion, facilitation and/or exacerbation of a structural and/or functional abnormality. The abnormality has the potential of lowering the quality of life, causing a disabling illness or leading to a premature death" (WHO, 1978).