Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity and biological activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science. Environmental chemistry involves first understanding how the uncontaminated environment works, which 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.

Contamination. A contaminant is a substance present in nature at a level higher than typical levels or that would not otherwise be there. This may be due to human activity. The term contaminant is often used interchangeably with pollutant, which is a substance that has a detrimental impact on the surrounding environment. Whilst a contaminant is sometimes defined as a substance present in the environment as a result of human activity, but without harmful effects, it is sometimes the case that toxic or harmful effects from contamination only become apparent at a later date. The "medium" (e.g. soil) or organism (e.g. fish) affected by the pollutant or contaminant is called a receptor, whilst a sink is a chemical medium or species that retains and interacts with the pollutant.

Environmental indicators. Chemical measures of water quality include dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total dissolved solids (TDS), pH, nutrients (nitrates and phosphorus), heavy metals (including copper, zinc, cadmium, lead and mercury), and pesticides.

Applications. The major application areas of environmental chemistry are as below.

Risk or hazard assessments of environmental impact. The risk factor of the chemicals is determined for safety of environment. This is detected by various techniques.

Management of environment. Environmental chemistry studies the development of new chemical products and their behavior in the atmosphere. The complete life cycle of chemical is used for proper handling and storage methods of chemicals that are helpful for detecting the adverse effect on environment.

Groundwater protection. The ground water is polluted by polluted soil and waste site leachate. So the pollutant identification is done in environmental chemistry by knowing the concentration, distribution and fate of hazardous chemicals.

Protection of surface water. The effect of contaminants in the water and sediments phase is measured for checking the quality of surface water. This is done by sedimentation processes, bacteriological processes, radiation processes, etc.

Soil protection.The soil quality is checked by measuring the impact of soil contaminants on the soil. This is analyzed by various chemical and eco-toxicological indicators.

Cleaner production and waste management. This includes the management and re-use of waste and site remediation. The re-use and site remediation are done by analyzing the pollutants in environmental samples and knowing about their nature. The re-use of waste involves the innovative uses of waste products.

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