How Pharmaceuticals Affect the Biology of Your Septic System


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How prescription drugs affect a septic system

Our bodies contain a multitude of bacteria – some good, some bad and many that have little effect on us at all.

But despite the fact that our world is dominated and shaped by these microscopic organisms, we rarely think about them. Until something goes wrong.

This is as true for the bacteria in our bodies as for the microorganisms in our septic systems. And many people forget that: what passes through your body unavoidably enters your septic system and can have an enormous impact on how effectively your system operates.

prescriptions and septic systems

When we take medications like prescription drugs, for instance, at the top of our minds is the hope of feeling better. Rarely do we think about or even realise that the human body does not completely break down prescription drugs, so these can ultimately end up in your septic system.

What happens when prescription drugs enter my septic system?

To understand what happens when prescription drugs enter a septic system, it helps to understand how prescription drugs work in the first place.

Almost one million Canadians opted for emptier grocery bags and colder homes in order to pay for prescription drugs in 2016. This is according to a late-2017 study conducted by researchers at the University of British Columbia and the University of Toronto, in collaboration with several other institutions.

It’s hardly a surprise: prescription drugs are an incredibly common and, in many cases, a life-saving treatment for an enormous number of ailments – from skin infections to cancer. Importantly, many of these prescription medications work by attacking foreign bacteria and viruses. And it’s this factor that can ultimately affect your septic system.

prescription drugs and septic systems

Let’s take a closer look at one of the strongest treatments: chemotherapy:

Chemotherapy and your Septic System

Chemotherapy is the use of drugs to treat cancer in humans and animals. Most chemotherapy treatments use a subgroup of medicines called cytotoxic drugs. These contain chemicals which are toxic to cells, preventing their replication or growth.

As cytotoxic drugs circulate in the blood, they either interrupt the development of rapidly growing cells or, when possible, eliminate these cells altogether. This can be a really great thing because, in cancer patients, rapidly growing cells are usually cancer cells.

Chemotherapy and septic systems

Unfortunately, these drugs also attack other fast-growing cells, like: those in the roots of body hair; bone marrow, which is constantly producing blood cells, and; your skin and the lining of your digestive system, which are constantly renewing themselves.

As chemotherapy drugs move through the blood, much of these drugs are broken down by the patient’s body. Some, however, don’t get broken down and are instead expelled in urine and faeces.

The problem (aside from the incredible damage drugs like the cytotoxic subgroup can inflict on a patient’s body), is that these prescription drugs are not cancer-specific. They do not differentiate between cancer cells and other fast-growing cells with which they might come into contact.

This is bad news for your septic system, which relies on the help of bacteria to break down the household sewage and other types of organic matter that finds its way into the tank. High concentrations of antibiotics, as well as other medicines, poisons and chemicals, can kill or restrict the growth of the anaerobic bacteria inside your septic system.

But these anaerobic bacteria are crucial to the smooth operation of a septic system. Without this bacteria, solid effluent would accumulate inside your septic system faster than it could be broken down, creating problems further along the treatment process.

In more complex systems like aerobic septic systems, the aerobic bacteria that are needed to continue the treatment process can also be negatively affected.

Can all prescription drugs affect my septic system?

We all get sick from time to time and, let’s face it: when you get very sick, there is little that you want or care about apart from feeling better again. The health of your septic system is definitely not the first thing on your mind.

Luckily, the occasional use of antibiotics by one or two people in a family residence will not do any harm to your septic system or drain field. So if you’ve caught the flu or have an infection and are prescribed drugs for a few days, there’s no need to start worrying.

In fact, a little bit of any type of chemical won’t have a dramatic effect on your septic system. The key here is potency. The more concentrated the chemical, the stronger the effect. And this is true, whether we’re talking about bleach, detergents or prescription drugs.

It’s when high levels of a chemical or poison enter your septic system that problems will start to arise.

We’ve focused on chemotherapy drugs in this article – in particular, the subgroup of medicines called cytotoxic drugs – because these types of drugs actively seek out and harm fast-growing cells. So these types of medications are naturally geared up to attack microorganisms like the bacteria in your septic system.

Also, it is very common to be prescribed an extremely high dosage of chemotherapy drugs or antibiotics, while other prescription drugs are only ever used in limited amounts (for example contraception or medication to ease anxiety or depression).  

But the thing to bear in mind is that your septic system is home to a multitude of tiny, living organisms in the form of anaerobic or aerobic bacteria. Sometimes both. So in very high concentrations, just about all types of prescription drugs, medications, chemicals and poisons will have some effect on these organisms and, in turn, your septic system.

What steps can I take to reduce the effect?

A dose of strong medication for a few days every now and then will not be an incredible burden on your septic system. But if someone in your household needs to take highly potent drugs for several weeks or months, it’s important to start considering alternative methods of care for your septic system.

  1. Call your septic system expert

The best and easiest thing to do from the outset is to call your septic system expert and alert them to the situation. They will usually be able to add extra bacteria into your system to keep it functioning properly.

  1. Increase how frequently the tank is pumped

Your septic system expert might also suggest a shorter amount of time between the regular pumping of your septic tank. In usual circumstances, septic systems need to be pumped once every three years. In situations where the bacteria are not able to break down solid waste as fast as they normally would, the system will need to be pumped more frequently: every two years, for instance.

  1. Be careful how you dispose of leftover medications                                                                                                                                                                                                                                                                                                                      If you don’t need your medications anymore – firstly, that’s awesome! Secondly, make sure you don’t dispose of your leftover medications by flushing them down the toilet or pouring them down the sink. Instead, get in touch with your local pharmacy – they should be able to take these off your hands and dispose of the drugs for you.
  1. Remember: your septic system is home to living organisms

If you are already dealing with limited bacteria due to prescription drugs making their way into your septic system, the last thing you want to do is eliminate more of these helpful microorganisms. So be aware of what you’re flushing down the toilet or sink. As mentioned, chemicals and poisons like bleach and disinfectants can dramatically reduce the health and number of bacteria in your septic system.

Some Great Household Tips To Keep Your Septic System Running Efficiently:


Sewage effluent is recognized as a major source of multiple pharmaceuticals, including their metabolites, entering aquatic environments. Removal rates for pharmaceuticals in wastewater treatment plants (WWTPs) range from less than 10 to almost 100% and depend on the physicochemical characteristics of the pharmaceutical and type of treatment technology

[Antibiotics in the aquatic environment–a review–part I. Kümmerer K Chemosphere. 2009 Apr; 75(4):417-34.]

Sources of human pharmaceuticals in sewage include patient use in the community, discharges from hospitals and, in some cases, wastewater from pharmaceutical manufacturing [ Pharmaceuticals and personal care products in the environment: agents of subtle change? Daughton CG, Ternes TAEnviron Health Perspect. 1999 Dec; 107 Suppl 6():907-38.].

Sewage can be discharged into marine environments through coastal and ocean outfalls for WWTPs combined sewer overflows and via rivers receiving WWTP effluents [Occurrence, distribution and partitioning of nonionic surfactants and pharmaceuticals in the urbanized Long Island Sound Estuary (NY).  Lara-Martín PA, González-Mazo E, Petrovic M, Barceló D, Brownawell BJ Mar Pollut Bull. 2014 Aug 30; 85(2):710-9.].

For example, the Yangtze River in China transports sewage from 400 million people out to sea and releases an estimated 152 tonnes of pharmaceuticals annually [Organic micropollutants in the Yangtze River: seasonal occurrence and annual loads. Qi W, Müller B, Pernet-Coudrier B, Singer H, Liu H, Qu J, Berg M Sci Total Environ. 2014 Feb 15; 472():789-99.].

Sewage may also be discharged into the marine environment from boats. Ships, including cruise liners, may discharge (under Annex IV of MARPOL 73/78 ships) treated sewage into the sea 4 nautical miles from the nearest land and 12 nautical miles for untreated sewage. [Organisation IM. 2003. International Convention for the Prevention of Pollution from Ships (MARPOL), Annex IV Prevention of Pollution by Sewage from Ships (entered into force 27 September 2003). ].

The volumes of sewage discharged can be significant as cruise liners can have passenger numbers equivalent to populations found in small towns. Sewage effluents from small boats, on the other hand, may not receive any treatment prior to being discharged. Typhoon shelters for small boats were a point source of antibiotics in Victoria Harbour, Hong Kong [Antibiotics in the Hong Kong metropolitan area: Ubiquitous distribution and fate in Victoria Harbour.  Minh TB, Leung HW, Loi IH, Chan WH, So MK, Mao JQ, Choi D, Lam JC, Zheng G, Martin M, Lee JH, Lam PK, Richardson BJMar Pollut Bull. 2009 Jul; 58(7):1052-62.].

As discussed by Kookana et al. [ Potential ecological footprints of active pharmaceutical ingredients: an examination of risk factors in low-, middle- and high-income countries.  Kookana RS, Williams M, Boxall AB, Larsson DG, Gaw S, Choi K, Yamamoto H, Thatikonda S, Zhu YG, Carriquiriborde P Philos Trans R Soc Lond B Biol Sci. 2014 Nov 19; 369(1656):.]  in this issue, many large cities in Asia still rely on septic tanks with poorly managed septage which can contaminate surface and groundwaters with pharmaceuticals and ultimately be discharged into coastal areas.

Sewage impacted groundwater can also be a source of pharmaceuticals entering coastal waters. Pharmaceuticals have been detected in a coastal aquifer on the Yucatan Peninsula, Mexico injected with municipal sewage discharges [Contaminants in the coastal karst aquifer system along the Caribbean coast of the Yucatan Peninsula, Mexico. Metcalfe CD, Beddows PA, Bouchot GG, Metcalfe TL, Li H, Van Lavieren H Environ Pollut. 2011 Apr; 159(4):991-7.].

Reuse of treated domestic wastewater for irrigation contributed to pharmaceutical contamination in groundwater on Mallorca [Pollution pathways of pharmaceutical residues in the aquatic environment on the island of Mallorca, Spain.  Rodríguez-Navas C, Björklund E, Bak SA, Hansen M, Krogh KA, Maya F, Forteza R, Cerdà Arch Environ Contam Toxicol. 2013 Jul; 65(1):56-66.].

Throughout the world, rural and peri-urban areas including popular coastal holiday areas are reliant on septic tanks or small decentralized systems for sewage treatment disposal Withers PJ, Jordan P, May L, Jarvie HP, Deal NE. 2013. Do septic tank systems pose a hidden threat to water quality? Front. Ecol. Environ. 12, 123–130. ].

Depending on their treatment efficiency and the capacity of the local soils, these systems are a potential source of pharmaceuticals in coastal waters via leakage to ground and surface waters [Occurrence of herbicides and pharmaceutical and personal care products in surface water and groundwater around Liberty Bay, Puget Sound, Washington. Dougherty JA, Swarzenski PW, Dinicola RS, Reinhard M J Environ Qual. 2010 Jul-Aug; 39(4):1173-80.].

Luis Goncalves, ROWP, IN, PL

I fell into this amazing trade quite by accident, I have always loved being around heavy machinery and moving earth and in contrast love working with designing things.  This trade in the septic field has led me down a wonderful path of exploring all of my skills and passions while working hard at achieving success.

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