TAILIEUCHUNG - Chemicals: Health relevance, transport and attenuation

Reactions and transformations of chemicals. Many chemicals undergo reaction or transformation in the subsurface environment. In contrast to retardation contaminants may be removed, rather than simply slowed down. Reactions of harmful chemicals to yield benign products prior to arrival at a receptor are the ideal, . many toxic hydrocarbons have potential to biodegrade to simple organic acids (of low health concern and themselves potentially degradable), carbon dioxide (bicarbonate) and water. Transformation often causes a deactivation (lowering) of toxicity. Reactions and/or transformations incorporate processes such as chemical precipitation, complexation, hydrolysis, biodegradation (biotic reactions) and chemical reactions (abiotic reactions). . | M. Rivett J. Drewes M. Barrett J. Chilton S. Appleyard H. Dieter D. Wauchope and J. Fastner Chapter 4 - p. 1 4 Chemicals Health relevance transport and attenuation The presence of substances in groundwater may be affected by naturally occurring processes as well as by actions directly associated with human activities. Naturally occurring processes such as decomposition of organic material in soils or leaching of mineral deposits can result in increased concentrations of several substances. Those of health concern include arsenic fluoride selenium uranium nitrate metals and radionuclides such as radon. Problems of aesthetic quality and acceptance may be caused by iron manganese sulphate chloride and organic matter. Sources of groundwater contamination associated with human activities are widespread and include diffuse as well as point source pollution like land application of animal wastes and agrochemicals in agriculture disposal practices of human excreta and wastes such as leaking sewers or sanitation systems leakage of waste disposal sites landfills underground storage tanks pipelines and pollution due to both poor practices and accidental spills in mining industry traffic health care facilities and military sites. The ready availability of carbon through the exploitation of hydrocarbon oil reserves over the past century has lead to a vast amount of organic compounds being introduced into the environment either through the use of oil in fuels or the development and production of other chemical products by industry. Literally tens of thousands of synthetic organic chemicals have been and continue to be developed. Many organic chemicals are known to have potential human health impacts and drinking-water quality standard listings developed. These listings have been continually added to and revised as new toxicological data and chemical products are developed. Organic chemicals commonly used by industry with known or suspected human health impacts that are often .

• Hoá dầu
• Sterilizing Value
• Heat Distribution
• Canning Process
• Ice Temperature
• Storage Technology
• Maillard Reaction