Amalgam (dentistry) and other metals may be present in some alloys. This combination of solid particles is known as amalgam alloy. The composition of the alloy particles are controlled by the ISO Standard (ISO 1559) for dental amalgam alloy in order to control properties of set amalgam such as corrosion and setting expansion. It is important to differentiate between dental amalgam and the amalgam alloy that is commercially produced and marketed as small filings, spheroid particles, or a combination of these, suitable for mixing with liquid mercury to produce the dental amalgam. Amalgam is used most commonly for direct, permanent, posterior restorations
Environmental chemistry chemicals in what concentrations are present naturally, and with what effects. Without this it would be impossible to accurately study the effects humans have on the environment through the release of chemicals. Environmental chemists draw on a range of concepts from chemistry and various environmental sciences to assist in their study of what is happening to a chemical species in the environment. Important general concepts from chemistry include understanding chemical reactions and equations, solutions, units, sampling, and analytical techniques. A contaminant is a substance present in nature at a level higher than fixed levels or that would not otherwise be