“Scoping” sustainability: rethinking sterile water use in colonoscopies

Health care has a significant environmental impact, leading to 7% of all Australian carbon emissions; 44% from hospital treatment alone.¹ The total number of colonoscopies each year total over 900 000 in Australia, and will continue to increase, in particular due to colorectal cancer screening and with increasing number of younger patients presenting with this disease.²

Endoscopy and day procedure units are among the key contributors to emissions due to its significant reliance on disposable consumables and energy-intensive practices.^3-5 Among these is the large quantities of sterile water for irrigation during colonoscopies, a standard approach globally.

Sterile water has been used in colonoscopy for decades to minimize infection risk, even though there is a significant lack of quality data to support this.^{6, 7} Recommendations on sterile water use appear to be derived from endoscope reprocessing protocols rather than evidence.⁸ Two studies from the 1990s have reported no increased incidence of infections when tap or filtered water was used instead of sterile water.^{9, 10}

There is also very little information on the precise environmental impact of sterile water bottle use during colonoscopies. We therefore carried out a life cycle analysis on sterile water use in Victoria, where ~230 000 colonoscopies are conducted annually.^{11, 12} We collected data from multiple Victorian hospitals regarding water usage and waste disposal practices. Using clinician-reported and colonoscopy usage data, and by measuring the dry mass of these Baxter 1000 mL polypropylene (PP) bottles typically used to supply sterile water, we estimated the annual statewide consumption of sterile water and its associated PP mass. Three stages of the PP lifecycle were considered: manufacturing, transport, and disposal (Fig. 1). Environmental impact factors were applied to the total annual polypropylene (PP) mass to estimate manufacturing emissions. Transportation emissions were calculated based on a 1000 km road journey from a supplier manufacturing facility in Sydney to Melbourne, assuming standard trucking and packing efficiencies. Disposal emissions were estimated based on landfill, recycling, and incineration emission factors, as detailed in Table 1.

Our analysis excluded transport of waste to disposal endpoints within Victoria, as this varied by health service. We also omitted the environmental impact of the oil used in PP production as well as the sterilization process of the water itself. We assumed all bottles are used in Melbourne, with none transported regionally. These assumptions therefore lead to conservative estimates to our calculations.

Figure 2 illustrates that the estimated 77 342 sterile water bottles used annually in Victoria generate between 15 247 and 31 330 kgCO₂-eq of emissions from PP, depending on disposal method. If all bottles were recycled, emissions would total 23 035 kgCO₂-eq, equivalent to ~300 gCO₂-eq per bottle. Understandably, direct landfill emissions are low due to the slow degradation of PP, but do not represent the long-term impacts on the surrounding environment as it breaks down.

A large day procedure unit in a Victoria healthcare centre reported a cost of around $1.50 AUD per bottle, similar to costs reported by a large UK health service.¹⁵ This translates to an annual expenditure of ~$116 000 for the state, excluding waste disposal costs.

Apart from the environmental and financial costs, there are other challenges experienced. Water bottles are often discarded before they are completely empty, and water usage patterns are dependent upon both patient bowel preparation quality and individual clinician technique. Healthcare facilities also face barriers to recycling, with many plastic bottles ending up in general or clinical waste despite PP being widely recyclable.¹⁶

Considering these findings, we believe several actionable steps can be taken within each healthcare provider. First, standardizing correct sterile water use and appropriate disposal practices through updated policies and staff training would address gaps in training and established systems which contribute significantly to ineffective healthcare waste practices.¹⁷

Further research is also necessary to evaluate the evidence that sterile water is necessary for routine colonoscopies. Recommendations published by the American Society for Gastrointestinal Endoscopy have taken on the position that while sterile water should be used in procedures involving mucosal penetration, endoscopic units may independently assess the risks of using clean tap water and sterile water as viable options for non-invasive procedures.¹⁸ Operations on the colon are regarded as occurring in a contaminated area, and the use of sterile water does not mitigate infection risk. As soon as sterile water enters the colon, it is no longer sterile.

New technology development should also be considered. The routine use of AI to help detect pathology may reduce the amount of water used for irrigation.¹⁹ Point-of-use filtration systems (with or without ultraviolet light disinfection) could also be a viable option.²⁰ Poor bowel preparation due to patient compliance may be enhanced using smartphone applications, which have showed great promise.²¹

Reducing single-use plastics should also be a priority. While evidence suggests that bottles should be replaced daily to prevent microbial growth,²² a more efficient approach could involve employing a single sterile bottle at the start of the procedural list, refilling it with filtered tap water as needed, and ensuring appropriate recycling at day's end. Using larger bottles could also help reduce waste by decreasing the frequency of bottle replacements.

To conclude, the routine use of sterile water in colonoscopies presents an opportunity for sustainable change in healthcare. In Victoria alone, it generates significant CO₂ emissions and waste management challenges worsen the environmental impact. Robust new studies are needed to guide evidence-based changes in clinical practices and to inform the development of novel technologies which will help reduce our impact on the environment.