Septic Tanks Can Hold Dangerous Levels of Chemo Drugs

Septic professionals servicing onsite systems should inquire if anyone is undergoing chemotherapy when troubleshooting or cleaning systems

Septic Tanks Can Hold Dangerous Levels of Chemo Drugs

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Editor’s note: This article is a direct follow-up to "Could Your Septic Job Make You Sick?" It is also related to "The Problem With Medications and Septic Systems."

We have all heard of the risk of secondhand smoke — but what about secondhand chemo? The drugs used in some forms of chemotherapy are called cytotoxins. Cytotoxic drugs can be used to destroy tumors, boost the outcomes of surgery or radiotherapy, reduce metastases and alleviate cancer symptoms. Cytotoxins can cause serious illness and even cancer in anyone who comes in contact with the bodily fluids of someone undergoing chemotherapy.

To date 27 chemotherapy drugs, of the over 200 commonly prescribed to treat many forms of cancer, have been identified with a high risk of impacting human health, even at low doses. The International Society of Oncology Pharmacy Practitioners has a list of 34, and the World Health Organization suggests human waste collection for 48 hours following chemotherapy treatment.

In a hospital setting, the EPA strictly regulates the disposal of unused cytotoxic substances and any container or instrument contaminated by them. But what happens when people go home after having chemotherapy? Approximately 85 percent of those undergoing treatment receive their infusions at a hospital or health care facility and are immediately sent home. Courses of treatment are generally given at three to four week intervals. In this way, the cancer cells do not have time to recover but normal tissue usually does. In the two to three days after treatment, the patient is excreting relatively high amounts of the cytotoxin in their urine, feces, vomit and sweat.

Little to no information is given about the risk to family members and caregivers. This waste can still have enough of the dangerous drug to kill developing cells and/or cause mutations in all exposed people.

Cytotoxins are known to cause birth defects, immune dysfunction such as myelodysplastic syndrome (pre-leukemia), and miscarriages. Patients can even develop other cancers that don’t appear for several years. For example, cyclophosphamide, which is used to treat breast cancer, can cause bladder cancer. In a recent study of two patients undergoing chemotherapy, the urine was collected from the family members over the first 48 hours after treatment. One hundred percent of the family member’s urine contained the cytotoxins although at much lower concentrations.

There is also a risk of these cytotoxins getting into our water supply. Typical wastewater treatment plants are not designed to remove cytotoxins, and they have been found in surface water at very low concentrations. 

There is also a risk for septic systems; due to the lack of dilution, the cytotoxins could be at high enough concentrations to damage the beneficial bacteria needed for the system to function properly. To date there is no published research on the treatment of cytotoxins in soil treatment systems, but there is concern that they may pass to groundwater beneath systems.

In December 2019, a new federal rule on hazardous drug handling, USP 800, will take effect. These regulations will force the control of hazardous drugs, including some of the drugs that are excreted by chemo patients in their urine, feces, vomit, sweat and saliva. This will require that the bodily fluids from those undergoing some forms of chemo will be required to be collected and properly disposed of instead of going down the drains of homes across the U.S.

Until this is fully implemented, septic professionals servicing onsite systems should inquire if anyone is undergoing chemotherapy when troubleshooting or inspecting systems. When working directly with sewage, for instance while sampling or cleaning septic tanks, it is best to err on the side of safety and assume the tank could be contaminated.   

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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