Can soil help remove antibiotics from wastewater effluent?

Reference: Franklin, A.; Williams, C.; Watson J. (2018). Assessment of soil to mitigate antibiotics in the environment due to release of wastewater treatment plant effluent. Journal of Environmental Quality. doi:10.2134/jeq2018.02.0076

Antibiotics in the Environment

Over the last two decades scientists have found low, but measurable levels of antibiotics in the environment.  How do they end up there? There are two ways this happens: first, when you take medicine, your body only uses a portion of the drug; the remainder is excreted through urine or feces. The second way is disposal: people get rid of unused or expired prescriptions by flushing them down the toilet.  Both cases introduce antibiotics into our wastewater.

Unfortunately, most wastewater treatment plants are not designed to remove antibiotics, as they are a relatively new contaminant.  Treated wastewater, called effluent, is released directly to surface waters such as rivers, lakes, and oceans. This means any antibiotics present in effluent are also released to surface waters.  While the levels of antibiotics in wastewater are typically low, there may be long-term health concerns for humans, animals, and the environment.  In addition, continued exposure to antibiotics can lead to antibiotic resistance bacteria.  We’ve covered antibiotic resistance before here at envirobites (in nanotechnology, non-crop plants, remote regions, and manure), but generally speaking, antibiotic resistance is dangerous because it means our drugs to cure infections stop working.

Pills. Source: Wikimedia Commons.
How can soil help?

One potential solution to the antibiotic problem is to direct wastewater effluent to soil rather than surface waters.  The hope is that soil can act as a natural filter and remove antibiotics from the wastewater effluent before it reaches groundwater and eventually surface water.  Antibiotics can be absorbed by soil particles, degraded by soil microorganism, or taken up by plants.

Testing, testing…

Alison Franklin and colleagues measured the concentrations of three human antibiotics at the Living Filter at Pennsylvania State University.  At the Living Filter, effluent from the University Park wastewater treatment plant is spray irrigated onto croplands.  The scientists collected effluent, soil samples, and groundwater samples to test for three common antibiotics: sulfamethoxazole, trimethoprim, and ofloxacin.  These drugs are commonly used to treat infections such as urinary tract infections, ear infections, or bronchitis, and all three are commonly found in wastewater effluent and natural waterways.

The researchers did indeed find all three antibiotics in the University Park wastewater effluent that was spray irrigated onto the agricultural soil.  They also found all three antibiotics in the soil at Living Filter after 10 weeks of effluent irrigation.  In the groundwater samples, sulfamethoxazole was present most frequently and at the highest concentration.  Ofloxacin was also consistently present but at lower concentrations than sulfamethoxazole.  Trimethoprim was below the detection limit for most groundwater samples.

Combining the soil and groundwater results, the scientists were able to conclude that sulfamethoxazole does not interact with the soil, resulting in a larger portion reaching groundwater.  Some ofloxacin accumulates in soil, meaning it is less mobile, but still reaches the groundwater.  Finally, trimethoprim degrades quickly, does not accumulate in the soil, and does not reach the groundwater.

However, all three antibiotics had lower concentrations in the groundwater than in US surface waters that directly receive wastewater effluent, indicating that soil may be a viable option for reducing the amount of antibiotics reaching natural waterways.

Summary

Antibiotics are being released to surface waters through wastewater effluent, which may pose a threat to the environment and organisms, including humans.  Using wastewater treatment effluent for spray irrigation may reduce the amount of antibiotics that reach surface water systems. However, this study showed that this is not true for all antibiotics: some were still found in groundwater, even after spray application to soil.  Since many humans rely on groundwater wells for drinking water, it is important to understand how antibiotics travel through the environment, and if they can end up in drinking water.  While the antibiotic concentrations in the groundwater in this study would not cause toxicity from a single dose, future studies should look at the cumulative effect from constant exposure to low concentrations of antibiotics.

So next time, think twice before you flush those old antibiotics down the toilet. (In fact, check out medicine take-back programs and other options from the FDA.)

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Elizabeth Brannon

I recently graduated with a Ph.D. in Biology and Environmental Science from the University of Rhode Island where I studied greenhouse gas emissions from wastewater treatment. I am committed to developing a better understanding of the impacts we have as humans on the planet. I'm a hard core New England sports fan and when I'm not cheering on the Patriots you can find me outside on an adventure!

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