The Problem With Medications and Septic Systems

The Problem With Medications and Septic Systems

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Medications are a part of daily life for many people connected to a wastewater treatment plant or a septic system. The human body does not completely metabolize medications, so they enter septic systems unavoidably through our body wastes. According to the Centers for Disease Control and Prevention:

  • 48.9 percent of people used at least one prescription drug in the past 30 days.
  • Approximately 23 percent of people used three or more prescription drugs in the past 30 days.
  • Approximately 12 percent of people used five or more prescription drugs in the past 30 days.

Chemotherapy drugs are potent, lifesaving treatments for patients with many types of cancer. Chemo interrupts the cellular functions of fast-growing cells and, when possible, triggers cell death. In a cancer patient, fast-growing cells tend to be cancer cells, so these are the cell types most affected by these drugs. However, other fast-growing cells (e.g., hair) are also affected. The biologic pathways targeted by a major subgroup of cytotoxic chemotherapies include DNA replication and repair functions. In a cancer patient, many genotoxic drugs are given at near-lethal doses both singly and in combinations with other cytotoxic drugs to trigger overwhelming DNA mutations and thus trigger cell death. At lower levels, genotoxic drugs tend to trigger DNA mutations without death. OSHA states that the drugs (after injection into patients) are concentrated in the urine.

Many of these chemo drugs are completely broken down by the patient's body and are not a problem; however, some are excreted from the patient unchanged or as active metabolites. These drugs are fully functional even if they are in the patient’s sweat, vomit, urine and feces. As the patient and their family dispose of the patient’s biological waste, all are exposed to dangerous amounts of these DNA-mutating drugs. Most of the biological waste enters wastewater treatment plants or septic systems, where it is partially degraded and may harm the beneficial bacteria in systems. One example, cyclophosphamide, is known to survive standard wastewater treatment and may maintain its drug function for months or years.

Cytotoxic drugs are not cancer-specific. They can act against any growing cell with the amounts of damage increasing with increased rate of cell growth and the concentration of drug. This means that these drugs do not distinguish between the patient and anyone else and possibly the beneficial bacteria in our septic systems.

With wastewater treatment plants, the use of medication is less of an issue as they have the benefit of dilution due to the larger number of people using a system and additions from commercial sources of wastewater. Normal use of many medications, including over-the-counter drugs, will not harm your septic system. However, antibiotics and certain strong medications such as those used in chemotherapy can affect the operation of your system. The problem is that we do not know which chemotherapy drugs will be problematic, as they are not tested for their impacts to wastewater treatment.

High concentrations of antibiotics along with other pharmaceuticals and chemicals can kill or retard the growth of the anaerobic bacteria in the septic tank, pretreatment system and soil treatment area. These anaerobic bacteria are necessary for proper operation of the system because they digest some of the organic matter entering the septic tank. They reduce the amount of solids in the tank and reduce the biochemical oxygen demand of the effluent. If the septic tank bacteria are reduced, solids accumulate in the tank faster and can create problems in the soil treatment area. In pretreatment and soil treatment systems, aerobic bacteria are needed to continue the treatment process, and they can be negatively impacted as well.

Steps to take

If a member of the household is expected to be taking medications on a short-term basis (less than three months), the septic tank should recover after the treatment. If the tank is cleaned after the treatment, it will recover more quickly. If the medications, including chemo drugs, will be used long-term, here are some recommended steps for homeowners to consider to protect their septic systems.

1. Unused medications should never be flushed. High concentrations of antibiotics will destroy the beneficial bacteria. Many more takeback programs have developed across the U.S., often associated with law enforcement, pharmacies, or hospitals that will dispose of the medication.

2. Minimize the use of other products that kill bacterial such as antibacterial soap, drain cleaners, quaternary ammonia, cleaners and bleach, as these products further stress the bacteria in the system.

3. After a new treatment program begins, the septic tank should be evaluated to determine if it is operating normally. It should have a septic odor from methane and hydrogen sulfide production along with the three distinct layers: sludge, scum and a clear zone. If there is no clear zone or if there are visible solids in the clear zone, this is an indication that the bacteria in the tank may be upset. If the septic tank has a chemical odor or is yellow in color, this can indicate a toxic tank as well.  

Septic tank showing the three layers and an effluent screen with an alarm
Septic tank showing the three layers and an effluent screen with an alarm

4. Increased maintenance of your system may be required with certain strong medications, such as chemotherapy drugs. The septic tank may have to be pumped more often to remove solids that are accumulating rapidly due to the loss of beneficial bacteria. A septic professional can monitor the system, take samples of BOD or TSS, and recommend a management plan, which may include the following steps.

  • If the septic tank gets too toxic, it may be necessary to use the tank as a holding tank during a prescribed treatment.
  • Fill the septic tank with clean water after pumping to dilute the concentrations of the medicines at the restart of the system.
  • Certain design changes may be necessary to protect the pretreatment or soil treatment area. These changes could include adding an effluent screen, which is placed on the outlet of the septic tank to limit solids exiting the tank. The effluent screen will need to be cleaned frequently if the septic tank is upset. An alarm is a critical part of an effluent filter installation, as it will indicate when the filter needs to be cleaned.
  • If hair loss is expected, an effluent screen is particularly helpful in preventing hair from being washed into the septic system. Hair can remain suspended in the wastewater and is carried to the drainfield, where it could plug the soil and cause drainfield failure.
  • Adding additional septic tanks or a pretreatment device are other possible design changes to try to break down the contaminants with either more detention time or aeration.

About the author: Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation, and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association and the National Onsite Wastewater Recycling Association, and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system maintenance and operation by sending an email to


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