Medical substances (pharmaceuticals) are a group of substances that until recently have been exposed to the environment with very little attention. The reason why they may be interesting as environmental micropollutants, is that medical substances arc developed with the intention of performing a biological effect. Especially antibiotics used as growth promoters, as feed additives in fish farms are anticipated to end up in the environment. Very little is known about the exposure routes of the medical substances to the environment. Only few investigations have reported findings of medical substances in other field samples than sediment or treated waste water samples. Several substances seem to be persistent in the environment. This paper outlines the different anticipated exposure routes to the environment, summarises the legislation on the subject and gives an outline of present knowledge of occurrence, fate and effect on both the aquatic and terrestrial environments of medical substances. Present knowledge does not reveal if regular therapeutic use may be the source of a substance carried by sewage effluent into the aquatic system, even though clofibrate, a lipid lowering agent, has been identified in ground and tap water samples from Berlin. Further research would be necessary to assess the environmental risk involved in exposing medical substances and metabolites to the environment.
Steroid isolation , depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more  or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram.  [ page needed ] The methods of isolation to achieve the two scales of product are distinct, but include extraction , precipitation, adsorption , chromatography , and crystallization . In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS , are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample. Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography .  : 10–19 Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity.