1. Standards may be classified into effect and quality standards. Effect (quality) standards specify a threshold below (above) which any situation is accepted. In what follows, only effect standards will be discussed. The extension to quality standards is straightforward.
2. Environmental standards often refer to admissible pollution levels in environmental compartments, such as air, water, soil, and so on. Emission standards are another type of threshold level which relate to the pollution source. For instance, they limit the amount of toxic substances contained in each cubic meter of water for industrial plants. Standards can be set at different stages of hazard evolution, from the source to the final target. This also determines different management measures and options (see Fischhoff, 1984). In the remainder of the text, the term environmental standard is used in a general sense unless otherwise specified.
3. From the economic point of view, it is interesting to analyse under what conditions it is economically convenient to observe a standard. Reckhow (1994), for instance, analysed the costs of obeying a water standard considering violating costs, such as fines, and the costs of treating waste products. Under an uncertainty distribution of the concentration of industrial discharges, the study highlights a series of cases in which it is convenient to aim at expected pollution levels higher than the standard.
4. Toxicology, or environmental toxicology, is the study of the adverse effects of substances on humans; ecotoxicology is the study of the adverse effects of substances on non-human species (Rand, 1991).
5. In a similar fashion. Fischhoff (1984) describes advantages and disadvantages of the application of standards at various phases of the risk development process.