Many of us are increasingly unsettled about the potential harm of a growing number of contaminants in tap water, especially those which adversely impact human health. Since the 1970s, sampling for water pollutants has markedly increased. Now hundreds of manufactured chemicals have been found in the groundwater and various other drinking water sources. Chemical contamination of drinking water can be traced to several different causes, including wrongful disposal of household cleaners, leaking underground storage tanks, seepage from landfills, discharge from factories and increased pesticide & fertilizer use over the past fifty years.
As troubling as the discovery of contaminated drinking water is, it’s a more hopeful sign that in recent decades, laboratories have become much more finely skilled in detecting a long list of chemicals. More importantly, our scientific knowledge of the health risks linked to drinking water contaminants has also improved. As a result, various home water treatment options are now widely available for reducing exposure to chemicals in tap water.
Some contaminants are known to cause cancer in the human population. Others are suspected culprits. These contaminants are commonly referred to as carcinogens. When the Environmental Protection Agency (EPA) establishes primary drinking water standards for carcinogens, the EPA acknowledges that no concentration in drinking water is safe, but it also must decide what level of risk is tolerable for the purpose of regulation. For many carcinogens, the concentration in drinking water causing no more than one cancer per million is typically in the range of a few parts per billion. Although more research continues to be done on an ongoing basis, here are our current “top ten” contaminants of possible concern:
Synthetic Organic Chemicals: Pesticides, Fertilizers, THMs, VOCs, Solvents
1. Pesticides are manufactured by humans from carbon, chlorine, hydrogen, nitrogen and other elements for a variety of purposes. The health effects of pesticides depend on their chemical characteristics. The use of pesticides, which include insecticides, herbicides and fungicides, is widespread in commercial farming and residential landscaping. Pesticides enter the groundwater during accidental spills, improper application, illegal dumping, manufacturing discharge or excessive rainfall after normal application. These agricultural chemicals can contain substances that disrupt the endocrine system. Some of these chemicals break down very slowly, so they persist in the environment—even in non-agricultural areas.
2. Fertilizers are another group of chemicals commonly used in agriculture to increase crop yield. Fertilizer by-products, formed as a result of natural chemical processes, however, can be potentially carcinogenic. These agricultural chemicals are one of the major sources of water pollution. For instance, the nitrogen in fertilizers gets converted into nitrate that seeps into groundwater. When ingested, nitrates form nitrosamines which have been found to cause tumor growths in animal studies.
3. Water Disinfection By-Products (THMs) are another issue. Although disinfection of the drinking water supply with chemicals like chlorine has dramatically reduced outbreaks of waterborne illnesses and deaths, research has suggested that long-term exposure to disinfection by-products may elevate cancer risk. Hundreds of disinfection by-products have been identified, but only a few are monitored. Even fewer have been tested for carcinogenicity. One common category of by-products are trihalomethanes, which form when chlorine and/or bromine combine with organic material in the water, such as decomposing leaves or animal waste. Some examples of THMs that may exist in drinking water are chloroform and bromoform.
4. Volatile Organic Compounds (VOCs) are chemicals that tend to evaporate quickly at normal room temperature. When dissolved in water that is stirred or heated, VOCs readily move into the surrounding air. VOCs are commonly found in agricultural and industrial areas where runoff, leaks, spills and dumping may contaminate groundwater. Some VOCs, such as benzene and carbon tetrachloride, are known to cause certain forms of cancer, including leukemia.
5. Dry Cleaning Solvents, such as trichloroethylene and perchloroethylene, are solvents commonly used in the professional laundry cleaning industry. Ever since the invention of modern dry cleaning techniques, cleaners have nearly always used some form of petroleum solvent or synthetic petroleum distillate. Many cleaners today have put a marketing spin on this calling it “organic”–which is essentially factual since petroleum is an organic substance. It implies, however, that these solvents are “green” or environmentally friendly, which they are certainly not. They are toxic. As known carcinogens, they must be handled with extreme caution. According to the April 2010 report of the President’s Cancer Panel, people living in the area of Camp Lejeune, North Carolina, had been consuming water for thirty years contaminated by these two chemicals at levels more than 40 times higher than the current permitted limit. High rates of cancers, birth defects and illnesses have been attributed to this massive water pollution.
Inorganic Chemicals: Heavy Metals, Arsenic and Asbestos, Perchlorate
Unlike organic chemicals which contain carbon, inorganic chemicals may or may not contain carbon. Inorganic chemicals can get into the drinking water supply when groundwater passes through contaminated earth. They can also contaminate water as a direct result of human activities: mining, agricultural practices, industrial dumping, oil or gas drilling, improper disposal of household batteries, corrosion of municipal water systems, and other sources. Long-term consumption of water containing high levels of certain inorganic chemicals is known to cause chronic health effects, including some forms of cancer.
6. Heavy metals such as chromium comprise one category of inorganic chemicals. Iron, copper, and zinc are common heavy metals found in drinking water, but they are not considered carcinogens. Heavy metals which are known or suspected to cause cancer include nickel, lead, chromium, cadmium and beryllium. The EPA has established drinking water standards for each of these inorganic contaminants. Hexavalent chromium is an essential element in steel production, wood preserving, leather tanning, dye manufacturing and more. Long-term exposure to chromium compounds has also been known to cause nasal, nasopharyngeal and lung cancers. Improper disposal of the chemical by industrial plants has exposed the general public to chromium through drinking water. In fact, according to a 2010 study commissioned by the Environmental Working Group, water supplies in 31 out of 35 American cities were polluted with hexavalent chromium. Here are the “top ten” cities at risk for exposure.
7. Arsenic, a highly toxic substance, naturally occurs in drinking water. Inorganic arsenic typically exists in a soluble state (easily dissolved in water) so it will often enter groundwater from the use of certain insecticides and defoliants. Activities such as mining, ore processing and fossil fuel burning also increase arsenic levels in water. The current drinking water standard for arsenic is 50 mcg/L. The EPA is considering tightening this drinking water standard further, however, based on studies that suggest arsenic may cause cancer at even lower levels. Inorganic arsenic in drinking water has been linked to many types of cancer, including: bladder, kidney, prostate, lung and skin cancer.
8. Asbestos, under natural conditions, is a mineral found in certain rock formations. When asbestos is detected in the drinking water supply, it can be traced to various manufactured sources such as building and fireproofing materials. Asbestos poses a greater risk to humans who breathe it in the air. The current drinking water standard for asbestos is 7 million fibers per liter.
9. Perchlorate, a rocket fuel component and by-product of missile testing, has permeated into drinking water systems from numerous industrial sites. This pollutant is now so widespread that it has been detected in the urine of people throughout all parts of the US. Long-term exposure to perchlorate has been shown to induce thyroid cancer in rodents in the laboratory, but its carcinogenic effects on the human population is still unclear.
Radioactive Chemicals: Radon and Radium
10. Radon is a colorless, odorless and tasteless gas, known to cause cancer when inhaled or consumed over an extended period of time. Radon is produced by the natural radioactive decay of radium in the ground. Some rocks, such as sandstone, limestone and granite, contain high concentrations of radium–which in turn produce increased levels of radon. Groundwater found in these rock formations may contain elevated amounts of radon. Radon moves easily from water to air, which means that waterborne radon contributes to airborne radon. In general, airborne radon poses a greater health risk than waterborne radon. The EPA, however, reports that the general cancer risk associated with waterborne radon is higher than any other drinking water contaminant. Scientists estimate that the lifetime risk of developing cancer from water containing high levels of radon is approximately one in ten thousand.
If you suspect that your drinking water is unsafe, one of the first steps to consider is to seek additional information about your local water supply. Contact your municipal water supplier for a copy of the most recent test results for your area, or have your private water supply tested for the specific contaminants of concern. If a water quality problem is detected, you may choose from a range of treatment options. We will discuss different water filters for reducing the risk of potential carcinogens in our next article.