What is Barium – Barium Element Definition
Barium occurs naturally in trace amounts in most surface and ground water from their exposure to barium-containing minerals. Industrial release of barium occurs from oil and gas drilling muds, coal burning, and auto paints. It is also widely used in brick, tile, and ceramics manufacture. The insoluble and un-absorbed salt, barium sulfate, is used clinically as a radiopaque dye for X-ray diagnosis of the gastrointestinal tract.
Chronic exposure may contribute to hypertension. Rats ingesting 0.5 mg/kg/day−1 barium in drinking water (10 mg/L) for 16 months or 6 mg/kg/day−1 (100 mg/L) for 4 months demonstrated hypertensive effects; however, another 4-month study of rats exposed to 15 mg/kg/day−1 in drinking water found no effect. Human epidemiological studies with community drinking water containing from 2 to 10 mg/L barium did not provide definitive results (U.S. Environmental Protection Agency, 1989b; Agency for Toxic Substances and Disease Registry, 1992b). The MCLG and MCL for barium are 5 mg/L, based on hypertension among humans.
What is Asbestos – Asbestos Element Definition
Asbestos is the name for a group of naturally occurring, hydrated silicate minerals with fibrous appearance. Included in this group are the mineral chrysotile, crocidolite, anthophyllite, and some of the tremolite-actinolite and cummingtonite-grunerite series. All except chrysotile fibers are known as amphibole. Most commercially mined asbestos is chrysotile. Asbestos element occurs in water exposed to natural deposits of these minerals, asbestos mining discharges, and asbestos-cement pipe.
The physical dimensions of asbestos fibers rather than the type are more important in health effects, with the shorter, thinner fibers more highly associated with cancer by inhalation. Human occupational and laboratory animal inhalation exposures are associated with the cancer, mesothelioma, found in lung, pleura, and peritoneum. An NTP study also observed gastrointestinal cancers in rats dietarily exposed to intermediate range fiber (65 percent of the fiber larger than 10 um, 14 percent larger than 100 μm) for their lifetime. Epidemiologic studies of asbestos element in drinking water have had inconsistent results, but there are suggestions of elevated risk for gastric, kidney, and pancreatic cancers (Cantor, 1997). The USEPA based its 1/1,000,000 cancer risk estimate and the MCLG and MCL on 7 × 106 fibers/L > 10 micron observed in the NTP rat study (USEPA).
What is Arsenic – Arsenic Element Definition
Arsenic concentrations in U.S. drinking waters are typically low. However, an estimated 5,000 community systems (out of 70,000) using groundwater and 370 systems (out of 6,000) using surface water were above 5 ug/L. These were primarily in the western states. Dissolution of arsenic-containing rocks and the smelting of nonferrous metal ores, especially copper, account for most of the arsenic in water supplies. Until the 1950s, arsenic element was also a major agricultural insecticide.
Arsenic element may be a trace dietary requirement and is present in many foods such as meat, fish, poultry, grain, and cereals. Market-basket surveys suggest that the daily adult intake of arsenic is about 50 ug, with about half coming from fish and shellfish. In fish, fruit, and vegetables, it is present in organic arsenical forms, which are less toxic than inorganic arsenic. However, arsenic is not currently considered essential (National Research Council, 1989). Extrapolating from animal studies, Uthus (1994) calculated a safe daily intake of between 12 and 40 ug.
In excessive amounts, arsenic element causes acute gastrointestinal damage and cardiac damage. Chronic doses can cause Blackfoot disease, a peripheral vascular disorder affecting the skin, resulting in the discoloration, cracking, and ulceration. Changes in peripheral nerve conduction have also been observed. Epidemiological studies in Chile, Argentina, Japan, and Taiwan have linked arsenic in drinking water with skin, bladder, and lung cancer (reviewed by Smith et al., 1992; Cantor, 1997). Some studies have also found increased kidney and liver cancer.
Ingestion of arsenical medicines and other arsenic exposures have also been associated with several internal cancers, but several small studies of communities in the United States with high arsenic levels have failed to demonstrate any health effects. Micronuclei in bladder cells are increased among those chronically ingesting arsenic in drinking water. Inorganic arsenate and arsenite forms have been shown to be mutagenic or genotoxic in several bacterial and mammalian cell test systems and have shown teratogenic potential in several mammalian species, but cancers have not been induced in laboratory animals.
USEPA has classified arsenic as a human carcinogen, based primarily on skin cancer (U.S. Environmental Protection Agency, 1985).The ability of arsenic to cause internal cancers is still controversial. Under the NIPDWR regulations, an MCL of 50 ug/L had been set, but it is under review. Currently, USEPA’s Risk Assessment Council estimates that an RfD (for non-carcinogenic skin problems) ranges from 0.1 to 0.8 ug/kg/day−1, which translates into an MCLG of 0 to 23 ug/L. Based on a 1-in-10,000 risk of skin cancer, USEPA estimated that 2 ug/L might be an acceptable limit for arsenic in drinking water.
What is Aluminum – Definition
Aluminum element occurs naturally in nearly all foods, the average dietary intake being about 20 mg/day. Aluminum salts are widely used in antiperspirants, soaps, cosmetics, and food additives. Aluminum is common in both raw and treated drinking waters, especially those treated with alum. It is estimated that drinking water typically represents only a small fraction of total aluminum intake. Aluminum element shows low acute toxicity, but administered to certain laboratory animals is a neurotoxicant. Chronic high-level exposure data are limited, but indicate that aluminum affects phosphorus absorption, resulting in weakness, bone pain, and anorexia.
Carcinogenicity, mutagenicity, and teratogenicity tests have all been negative. Associations between aluminum and two neurological disorders, Alzheimer’s disease and dementia associated with kidney dialysis, have been studied. Current evidence suggests that Alzheimer disease is not related to aluminum intake from drinking water, but other sources of aluminum appeared to be associated with Alzheimer. Dialysis dementia has been reasonably documented to be caused by aluminum. Most kidney dialysis machines now use specially prepared water.
Aluminum element was included on the original list of 83 contaminants to be regulated under the 1986 SDWA amendments. USEPA removed aluminum from the list because it was concluded that no evidence existed at that time that aluminum ingested in drinking water poses a health threat (U.S. Environmental Protection Agency, 1988b). USEPA has a secondary maximum contaminant level (SMCL) of 50 to 200 μg/L to ensure removal of coagulated material before treated water enters the distribution system.
