PFOA and PFOS are fluorinated organic chemicals that are part of a larger group of chemicals referred to as perfluoroalky substances(PFASs). PFOA and PFOS have been most extensively produced and studied of these chemicals. They have been used to make carpets, clothing, fabrics for furniture, paper packaging for foods and other materials (cookware) that are resistance to water, grease or stains. They are also used for firefighting at air fields and in a number of industries processes. Because these chemicals have been used in a array of consumer products, most people have been exposed to them. Between 2000 and 2002, PFOS was voluntarily phased out of production in the U.S. by its primary manufacture. In 2006, eight major companies voluntarily agreed to phase out their global production of POFA and PFOA-related chemicals, although there are limited number of ongoing uses. Scientists have found PFOA and PFOS in the blood of ...
Aqueous chlorine reacts with certain organic materials present in water sources to form trihalomethanes (THMs). Long-term exposure to these harmful byproducts of disinfection has been linked to an increased risk of cancer and infant birth delivery problems. It is estimated that THMs in drinking water are responsible for as many as 2-17 percent of the bladder cancers diagnosed each year in the United States. To protect the public, the U.S. Environmental Protection Agency has established a maximum contaminant level of 0.08 milligrams per liter (mg/L) for THMs. To conform to these regulations, many municipal water supplies have switched to an alternative method of disinfection using chloramination; more than 1 in 5 Americans uses drinking water treated with chloramines. Chloramination involves the addition of anhydrous or aqueous ammonia (NH 3 ) before or after the addition of chlorine (HOCl) to produce monochloramine (NH 2 Cl). This reaction is as follows: N...
The presence of arsenic (As) in nature is due mainly to natural deposits of metalloids in the earth’s crust and usually in ancient rock formations. Arsenic enters ground water through erosion or from manmade sources such as wood preservative, petroleum production, semi-conductor manufacture or due to misuse of animal feed additives and arsenic-containing pesticides (e.g. Paris green). Since soluble arsenic is tasteless and colorless, a chemical water analysis is necessary to detect its presence. Higher levels of arsenic tend to be found more in ground water sources than in surface water sources (lakes and rivers) of drinking water. Compared to the rest of the United States, the western states have more water systems with arsenic levels greater than 10 micrograms per liter (µg/L, ppb). Parts of Midwest, New England, and Texas have some systems whose current arsenic levels are greater than 10 µg/L (or ppb). In ground water, arsenic can combine with other elements to form inorganic ...
Comments
Post a Comment