Americans whose drinking water is supplied by private wells may be at risk of exposure to bacteria, nitrates, pharmaceuticals and other drinking water contaminants that are known to pose health risks to humans. If a home's drinking water is not supplied by a public drinking water utility, the responsibility for ensuring the drinking water supply is safe rests solely on the homeowner.

It is not only public water treatment plants that face concerns related to contamination by pharmaceuticals and personal care products, groundwater that supplies private drinking water wells can also become contaminated by products that are used in our everyday lives.

"This causes trace-levels of these chemicals to be found in the environment," explains Heather Gall, an assistant professor at Pennsylvania State University who's research focuses on contaminants of emerging concern in groundwater and surface waters. "Recently developed analytical technologies are now advanced enough for us to detect these compounds in water at increasingly low levels."

A well-functioning domestic septic system discharges effluent slowly into the drain field, where it is broken down further by soil microbes as it filters through the soil, biodegrading pollutants that are present before the discharged water reaches the groundwater. The problem, however, is that in the US, as much as one fifth of septic tank systems do not function effectively. This increases the possibility of these pollutants reaching the groundwater, particularly contaminants that do not readily break down in the environment. From there, they can enter well water supplying a domestic household further downhill.

Drinking water containing pharmaceutical medications poses a potential health risk as it may cause harmful effects if consumed. But are the concentrations found in private wells high enough to pose a health threat?

To answer this question, Gall teamed up with the Pennsylvania Master Well Owner Network. Twenty-six homeowners collected water samples from the wells supplying their household with drinking water.

"Since our project engaged private well owners, we wanted to focus on compounds they may be familiar with," says Gall.

For this study, which was recently published in the Journal of Environmental Quality, Gall and her team tested the water samples for two anti-inflammatory drugs that can be purchased over-the-counter, four commonly used antibiotics and a common stimulant. Each of these chemicals reacts differently as it passes through soil particles in the drain field.

Gall found that two factors — sorption potential (likelihood of a medicine adhering to other particles such as water or soil) and biodegradability — played the biggest role in determining whether a medicine was able to reach the groundwater.

Sorption Potential

Chemicals with low sorption are less likely to adhere to soil particles in the drain field, allowing them to pass through soils to reach the groundwater more readily. The study revealed that the medicine that was most likely to reach the groundwater was ofloxacin — an antibiotic that was the most prolific drug found in the samples tested. By contrast, the anti-inflammatory naproxen exhibited the highest sorption and was most likely to be trapped by soils in the drain field, which could explain why it wasn't detected in any of the water samples tested in this study.

Biodegradability

Medicines that readily break down as they pass through the soil are less likely to enter groundwater. However, some pass through the soil and only start breaking down once they reach the groundwater. Biodegradability is measured using 'half-life' — the period it takes for half of the chemical to break down in the environment. For example, the half-life of ofloxacin (the most commonly detected drug) is four years. Other chemicals such as caffeine (a stimulant) and acetaminophen (a common anti-inflammatory medication) have a half-life of less than a day, and were found in less than 50% of the water samples tested.

The study found that biodegradability and sorption potential of a drug ultimately plays a key role in whether it's able to reach and contaminate groundwater. The results indicate that septic systems can impact water quality in private wells. But the levels of the drugs detected in the water samples tested suggest the health risk is minimal.

While we have very little control over the active ingredients in medications that we excrete, which can persist in the environment even after being treated, we can take steps to reduce out impact.

"We can do our best to be good environmental stewards by bringing expired and unused medicines to take-back locations, and of course, by maintaining septic tanks for many water quality reasons," says Gall.

For homeowners supplied by private wells who have concerns regarding the quality of their drinking water, Gall recommends having well water tested to ensure it meets primary drinking water standards, as well as using available treatment technologies to remove unwanted emerging contaminants that could potentially pose a health risk. A good quality drinking water filter can ensure your family always has a supply of safe drinking water.

Journal Reference

Faith A. Kibuye, Heather E. Gall, Kyle R. Elkin, Bryan Swistock, Tamie L. Veith, John E. Watson and Herschel A. Elliott. Occurrence, Concentrations, and Risks of Pharmaceutical Compounds in Private Wells in Central Pennsylvania. Journal of Environmental Quality, Vol. 48 No. 4, p. 1057-1066. doi:10.2134/jeq2018.08.0301