Lab Science News

A recent United States Geological Survey (USGS) study of public drinking water wells in California, Connecticut, Nebraska and Florida found that some were contaminated, but in amounts so minimal, human health was unlikely to be affected. The USGS tracked the movement of contaminants in groundwater and public-supply wells in four different aquifers.

According to the USGS, wells are not equally vulnerable to contamination because of differences in three factors: the general chemistry of the aquifer, groundwater age, and direct paths within aquifer systems that allow water and contaminants to reach a well. The importance of each factor differs among the various aquifer settings, depending upon natural geology and local aquifer conditions, as well as human activities related to land use and well construction and operation. However, the USGS feels that the study of the four different aquifer systems can be applied to similar aquifers and wells throughout the nation.

Examples of specific chemical findings from the USGS study:

• In the Central Valley Aquifer near Modesto, Calif., the USGS found that agricultural and urban development have enabled uranium to move from sediments to water in the upper part of the aquifer. This water can drain down the well when it is not pumping and enter the lower aquifer. When pumping resumes, contaminant concentrations can be temporarily elevated in water pumped from the well.
• In the Glacial Aquifer in Woodbury, Conn., it was found that the young age of the water throughout the aquifer makes it vulnerable to contamination from man-made compounds. The USGS also found that dry wells used in Woodbury to capture stormwater runoff reroute the potentially contaminated water directly into the aquifer used as a drinking water source. This direct transfer prevents soil and unsaturated sediments near the land surface from filtering out some of the contaminants.
• In the High Plains Aquifer near York, Neb., the USGS found some contaminants in a public-supply well that seems protected by overlying clay. Nearby irrigation wells have allowed water containing nitrate and volatile organic compounds to leak down from an overlying shallow aquifer into the aquifer that serves as the drinking water source for the public-supply well.
• In the Floridan Aquifer near Tampa, Fla., it was found that a large percentage of young water and contaminants from a shallow sand aquifer travels quickly along natural conduits until it reaches a supply well in a lower rock aquifer that serves as a drinking water source. Because of these natural conduits, the supply well is vulnerable to the man-made contaminants in the upper aquifer, and the mixing of waters from the two aquifers has caused arsenic concentrations to increase in water reaching the supply well.

The study of public-supply well vulnerability to contamination is one of five national priority topics being addressed by the USGS with their National Water-Quality Assessment (NAWQA) Program. The study began in 2001 with the following general objectives:

1. Identify the dominant contaminants and sources of those contaminants in public-supply wells in representative water-supply aquifers across the Nation;
2. Assess the effects of natural processes (such as degradation) and human activities (such as irrigation) on the occurrence of contaminants in public-supply wells in representative aquifers;
3. Identify the factors that are most important to incorporate into public-supply well vulnerability assessments in different settings and at different spatial scales;
4. Develop simple methods and models for screening public-supply wells for vulnerability to contamination in unstudied areas and from newly emerging contaminants; and
5. Increase understanding of the potential effects of water-resource development and management decisions on the quality of water from public-supply wells.

Approximately 35% of the U.S. population receives their drinking water from public groundwater systems. Public drinking water systems are considered public when 25 or more people are connected to the well or there are at least 15 service connections for a minimum 60 days per year.

 
Reference:
http://oh.water.usgs.gov/tanc/NAWQATANC.htm

Chlorine has been used to disinfect water for almost a century due to its ability to kill bacteria and viruses in water. The use of chlorine as a disinfectant has been an effective contribution to public health eliminating plagues such as cholera and typhoid, and reducing the incidence of intestinal illness and other health problems caused by waterborne pathogens such as cryptosporidium. The benefits of disinfection, however, do not come without an effect.

Depending on the disinfection procedure used (chlorination, chloramines, bromine, ozone etc.) and the chemical composition of the water prior to disinfection, many different organic chemical disinfection byproducts can form in drinking water. Trihalomethanes (THMs) are a byproduct of chlorine disinfection and to a lesser degree, disinfection using chloroamines. The THMs (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) are formed when free chlorine combines with organic matter, like decaying vegetation commonly found in lakes and reservoirs. Total Trihalomethanes (TTHM) are regulated by the EPA at a maximum allowable annual average of 80 parts per billion. Some of the THMs are very volatile and will vaporize into air easily, so they may be inhaled while showering, however, the EPA has determined that this exposure is minimal compared to that from consumption. The Levels of THMs formed can vary widely on a number of factors including temperature, amount of chlorine used, season, and amount of plant material in the water, among others.

Some drinking water systems use chloroamines as a residual disinfection agent in place of chlorine. Chloroamine is not as reactive as chlorine and less THMs are formed. However, there are also drawbacks to chloroamine use. Chloroamine may cause nitrification and corrosion and may also increase exposure to other disinfection byproducts, such as N-nitrosodimethylamine (NDMA).

EPA Method 524.2 is used to analyze samples for TTHMs. This method involves concentrating the THMs from a water sample using a technique known as purge and trap. This technique isolates the volatile organic compounds (VOCs) from the water. The VOCs are then desorbed into a gas chromatograph/mass spectrometer (GC/MS) where they are separated, their identity is confirmed, and their concentrations are determined. Standard reporting limits for individual TTH with this method are 0.5 µ/L

Every day millions of gallons of treated and untreated wastewater are discharged into the waterways of the world. This wastewater may contain varying concentrations of pharmaceuticals and personal care products (PPCPs) including prescription and over the counter medications, nutraceuticals, illicit drugs, detergents, perfumes, insect repellent, sunscreens, and steroids, some of which have been identified in a recent article by The Associated Press¹.

Recent studies have shown that many of these PPCP compounds at low concentrations can have negative effects on the endocrine systems of aquatic organisms. These compounds are collectively known as Endocrine Disrupting Compounds (EDCs). Other concerns regarding PPCPs include contamination of drinking water, estrogenic effects on humans and wildlife, and development of antibiotic resistant bacteria.

In 1999 and 2000, a study was performed by the USGS (Koplin, et al, 2000²) in which the concentrations of 95 of these compounds were measured in 139 streams in 30 states (mostly downstream from intense urbanization and livestock production). Eighty-two of the 95 compounds of interest were found and 80% of the streams tested contained one or more of these compounds. Multiple compounds were found in many samples. The average number was seven and the greatest number was 38. Concentrations were low, rarely exceeding health advisories or aquatic-life criteria. However, advisory limits are not available for many of these compounds. Little is known about the effects of long-term low exposure to these compounds, potential interactions with other compounds in the environment (synergistic or antagonistic), possible cumulative effects over time, or what effect any degradation products of these compounds may have.

These compounds enter the environment from a wide variety of sources including agriculture use of pesticides and antibiotics, industrial discharges, and household use of chemicals and pharmaceuticals. Most wastewater treatment and domestic septic systems are not designed to remove these compounds. In another USGS study (Stackelberg et al., 2004³), between 11 and 17 of these compounds were found in all finished drinking water samples at a conventional water treatment plant.

Analytical testing for these compounds requires the use of sophisticated instrumentation and experienced chemists. Due to their chemical nature, many of these compounds are not amenable to standard environmental gas chromatographic (GC) techniques. They are generally larger, less volatile, and more polar than other organic compounds that can be analyzed via GC and GC/MS techniques. Some of these compounds are also thermally labile, breaking down at elevated GC temperatures. Since PPCPs include many different classes of compounds with varying physical and chemical properties, Liquid Chromatography/Mass Spectroscopy/Mass Spectroscopy (LC/MS/MS) provides a convenient approach for determining a relatively wide range of chemicals of interest.⁴

On Tuesday, January 11th, 2005 the Committee to Access the Health Implications of Perchlorate Ingestion, convened by the National Research Council at the request of the EPA, DOD, NASA, and the DOE, released their report on the adverse health effects of perchlorate ingestion from clinical, toxicological and public health perspectives. The report also evaluated relevant scientific literature and key fi ndings of the EPA’s 2002 draft risk assessment document on perchlorate. The full report can be found on-line at http:// www.nap.edu/catalog/11202.html.

The committee noted that a noobserved- effect level (NOEL) or lowestobserved- adverse-effect level (LOAEL) identifi ed from a critical study, is used as the basis for establishing a reference dose for daily oral exposures. The committee decided to use a NOEL rather than a LOAEL as the basis for perchlorate risk assessment. They based their reference daily dose on the identified critical study done by Greer, et al (2002)1 in which healthy men and women were given doses of perchlorate of 0.007 to 0.5 mg/Kg body weight per day for 14 days. In this study, the NOEL was found to be 0.007 mg/Kg/day. Using this amount and applying an uncertainty factor of 10 to protect the most sensitive population (identifi ed as pregnant women who may have hypothyroidism or iodide defi ciency), the committee recommended a reference daily dose of perchlorate of 0.0007 mg/Kg of body weight per day from all sources. The EPA’s draft reference daily dose from the 2002 risk assessment was 0.00003 mg/Kg per day. The committee also noted that additional studies are needed, especially long-term, chronic exposure as well as clinical, mechanistic and epidemiological studies.

The release of the report generated a flurry of media reports with widely different safe drinking water levels touted – everything from maximum levels of 3 ppb to 200 ppb. However, as of February 18, 2005, the EPA has set an offi cial reference dose (RfD) of 0.0007mg/kg/day of perchlorate consistant with the National Research Council’s reference dose. The EPA translates the new RfD to a Drinking Water Equivalent Level (DWEL) of 24.5 ppb. As new information becomes available, CAS will post updates at www.caslab.com.

Learn more about Perchlorate Testing…

1 Greer, M/A., G, Goodman, R.C. Pleus, and S.E. Greer. 2002. Health effects assessment for environmental perchlorate contamination: The dose response for inhibition of thyroidal radioiodide uptake in humans. Environ. Health Perspect. 110:927