Nonvolatile organic chemicals are also known as Synthetic Organic Chemicals or SOCs. Nearly all SOCs are pesticides, with a few notable exceptions (PCBs and dioxin). They differ from VOCs because they do not escape readily into the air form water.

Dozens of pesticides, including herbicides, insecticides, and fungicides, are used throughout Pennsylvania on crops, golf courses, and lawns. The risk to private water supplies from pesticide applications depends on many factors including the amount, mobility, and toxicity of the pesticide, the proximity of the application to the water supply, and the depth and construction of the water source.

Pesticides are not common in private water supplies, but they are often detected in agricultural areas of the state. A 1993 study by Penn State scientists found detectable residues of at least one pesticide in 27% of the rural wells surveyed in corn-producing regions of Pennsylvania. (Although the pesticides were commonly detected, none of these wells contained a concentration above the drinking water standard.) Pesticide concentrations are generally higher in wells located in limestone, which includes most of the prime agricultural regions of Pennsylvania.

Detailed descriptions are given below for some of the pesticides most often found in Pennsylvania groundwater.

Atrazine is the most commonly used herbicide in Pennsylvania. It is applied to nearly 90% of the corn crop in the state. It is water-soluble, moves easily into groundwater and surface water after application, and is by far the most common pesticide reported in private water supplies in Pennsylvania. In a 1993 study, Atrazine was detected in 22% of private water supplies in corn-producing regions of Pennsylvania. Because it is classified as a possible human carcinogen that also damages the liver, kidneys, and heart, Atrazine has a primary drinking water standard of 0.003 mg/l (3 m g/L).

2,4-D is widely used to kill broadleaf weeds in farm fields and pastures and on lawns and golf courses. It also is used to kill algae and aquatic plants in ponds and lakes. 2,4-D damages the liver, circulatory, and nervous systems. Like atrazine, it is one of the most commonly used pesticides in Pennsylvania and also one of the most commonly found in groundwater in agricultural areas of the state. 2,4-D has a primary drinking water standard of 0.07 mg/L (70 m g/L).

Chlorpyrifos, also known as Dursban, is one of the most commonly used insecticides on corn crops in Pennsylvania. It is also used to control pests on cattle, and it is widely used around the home for control of cockroaches, fleas, and termites. Chlorpyrifos does not mix well with water and sticks tightly to soil particles. It was detected in trace amounts in a small percentage of private water systems in a 1993 study. Chlorpyrifos is presently considered a possible human carcinogen. No drinking water standard exists for chlorpyrifos, but the U.S. Environmental Protection Agency recommends that children not drink water containing levels greater than 0.03 mg/L. The U.S. EPA recently announced a ban on the production of chlorpyrifos, starting in June 2000.

Glyphosate is one of the most widely used pesticides in the United States. It is a herbicide used mostly for control of broadleaf weeds and grasses in pastures, corn, soybeans, and lawns. It is a component of the often-used herbicide Roundup. Glyphosate has a primary drinking water standard of 0.7 mg/L (700 m g/L) because it causes kidney damage and reproductive effects after long-term exposure. Glyphosate is strongly absorbed to soil and does not readily move to or in groundwater.

Metolachlor is the second most commonly used herbicide on corn in Pennsylvania. It is slightly less mobile than atrazine but still moves easily through soil to groundwater. A 1993 survey of private water systems in Pennsylvania found metolachlor to be the third most commonly detected pesticide in the state.

There are no reported short-term effects from exposure to metolachlor in water, but it is listed as a possible carcinogen with prolonged exposure. No drinking water standard exists, but further testing is being done by the U.S. Environmental Protection Agency. In the interim, the EPA has issued a health advisory for metolachlor of 0.07 mg/L (70 m g/L).

Simazine is commonly used for control of broad-leaved and grassy weeds on crops, orchards, and Christmas tree farms. It is also used to control plants and algae in ponds and lakes. Simazine has a primary drinking water standard of 0.004 mg/L (4 m g/L) because it is a probable carcinogen that also can cause damage to the testes, kidneys, liver, and thyroid after long exposure. Simazine travels easily through soils to groundwater and persists in groundwater for long periods of time.

Dioxin (also known as 2,3,7,8-TCDD) is a contaminant formed in the production of some chlorinated organic compounds, including a few herbicides. It may also be formed when some chlorinated organic chemicals are burned. Dioxin has been linked to a variety of health effects including liver damage, reproductive effects, birth defects, and cancer. Most dioxin in water comes from improper disposal of industrial wastes. It is not very water-soluble, and most dioxin is found adhering to sediment or organic particles. It does not move easily into groundwater because it is usually trapped in soil. It has the lowest drinking water standard of any regulated substance (0.00000005 mg/L or 0.00005 m g/L).

PCBs are a group of manufactured organic chemicals that are odorless and tasteless in water. They have been used widely as insulating materials, coolants, and lubricants in electrical equipment. The manufacture of PCBs stopped in the United States in 1977 because of health effects, but products containing PCBs are still prevalent. Most PCBs in groundwater originate from improper waste disposal. In water, a small amount of PCBs may remain dissolved, but a larger amount sticks to organic particles and sediments. PCBs have been shown to cause numerous health effects including liver, kidney, and nervous system damage. They are also considered probable carcinogens. As a result, a primary drinking water standard of 0.005 mg/L (0.5 m g/L) exists for PCBs.

Organic chemicals are a large group of over 100 mostly man-made chemicals. They can occur in drinking water sources from industrial activity, landfills, gas stations, pesticide use, or air deposition. Organic chemicals vary in their ability to pollute groundwater and their toxicity. Many organic chemicals are carcinogenic (cancer causing), so they often have very low drinking water standards, usually measured in m g/L. Remember that m g/L are the same as ppb (parts per billion).

Generally speaking, organic chemicals can be grouped into two major categories: volatile organic chemicals (VOCs) and nonvolatile or synthetic organic chemicals (SOC’s). The discussion below introduces these general groups of organic chemicals and describes in detail the most common examples in each group.

VOCs are man-made compounds that volatilize from water into air. They present a health risk not only from drinking contaminated water, but also from inhaling VOCs that escape from the water as it is used during showering or other home uses. VOCs also are absorbed directly through the skin during bathing and showering. They are commonly used as solvents, fuels, paints, or degreasers. Virtually all VOCs produce an odor in water, although it may not be obvious before the drinking water standard is exceeded. Nearly all VOCs have primary drinking water standards, because they are carcinogenic (cancer-causing) or cause damage to the liver, kidneys, nervous system, or circulatory

system.

VOCs are not common in private water systems in Pennsylvania, but they are becoming a more important concern as industrial activities, landfills, gas stations, and other sources of these pollutants encroach on rural areas. The U.S. Geological Survey conducted a recent survey of 118 wells in southern and eastern Pennsylvania. The survey analyzed well water for 69 different VOCs and detected at least one VOC in 27% of the samples. (Although the VOCs were commonly detected, none of the samples exceeded drinking water standards.) VOC contamination of wells was much more common in urban areas than agricultural areas.

Dozens of VOCs are regulated in public, but the most common are described below.

Benzene is a clear, colorless liquid that is used primarily as an industrial solvent and chemical intermediate. It is lighter than water, migrates easily in groundwater, and is slow to decay. It is also present as a gasoline additive. Because it is a known human carcinogen, benzene has a primary drinking water standard of 0.005 mg/L (5 m g/L).

Carbon tetrachloride is a colorless liquid that is heavier than water but migrates easily in groundwater. It has been used mostly for the production of chlorofluorocarbons and in the dry-cleaning industry. Carbon tetrachloride has a primary drinking water standard of 0.005 mg/L (5 m g/L) because it is a probable human carcinogen with other acute effects on the gastrointestinal and nervous system.

Chloroform is a colorless liquid that is used primarily to make other chemicals. It also can be found in small amounts when chlorine is added to water. Chloroform travels easily in groundwater and does not easily degrade. Chloroform is believed to be a carcinogen. It has been one of the most commonly reported organic chemicals in Pennsylvania groundwater.

Chloroform is one of a group of organics known as trihalomethanes or TTHMs. No specific drinking water standard exists for chloroform, but the primary standard for TTHMs is 0.08 mg/L (80 m g/L).

MTBE is the most common organic chemical found in Pennsylvania groundwater. It has been used extensively as a gasoline additive in some parts of the United States to reduce air pollution emissions from automobiles. It smells like turpentine and can often be detected in water at low concentrations. Most MTBE originates from gasoline spills or leaking underground storage tanks. It is more water-soluble than other components of gasoline, so it contaminates groundwater more easily. Once in groundwater, MTBE is slow to decay. MTBE is a possible human carcinogen, but little information is available on other health effects. Pennsylvania presently has no drinking water standard, but numerous other states have set standards in the 0.02 to 0.2 mg/L range (20 to 200 m g/L). More information on MTBE is available online at the U.S. Environmental Protection Agency and U.S. Geological Survey Web sites.

Tetrachloroethylene (commonly known as PCE) and Trichloroethylene (commonly known as TCE) are similar chemicals that have been found in Pennsylvania around industrial sites and landfills. Most of the groundwater contamination from these chemicals has occurred due to improper disposal of industrial wastes. Both chemicals are used as industrial solvents for metal degreasing, but PCE is used primarily in the dry-cleaning industry. Both are heavier than water and move freely through soil and groundwater, but TCE is much more water-soluble than PCE. PCE is a possible carcinogen that causes liver, kidney, and nervous system damage. TCE is a probable carcinogen that also causes acute effects to the liver, kidneys, and central nervous system. Both PCE and TCE have primary drinking water standards of 0.005 mg/L (5 m g/L).

Xylenes are a component of gasoline. They also are used in the manufacturing of some chemicals, and therefore appear commonly in industrial wastes. Xylenes cause liver, kidney, and nervous system damage. Xylenes biodegrade and move slowly in groundwater. Xylene has been reported in much higher concentrations than most other VOCs in Pennsylvania, but the drinking water standard for xylenes is also much higher (10 mg/L or 10,000 m g/L).