Effect of distributing urine-collection bags on contrast-material load in wastewater.

Objectives: Contrast materials (CM) are ubiquitous in modern clinical practice. Metabolically inert and excreted in urine, treatment plants (WWTP) have difficulty removing CM from wastewater and CM increasingly emerge as environmental contaminants. This study evaluates the effect of urine-collection bag (UCB) distribution on corresponding CM load in WWTP influent.

Materials and methods: This prospective observational multicenter study includes patients scheduled for contrast-material-enhanced computed tomography (iodine-CM) or magnetic resonance imaging (gadolinium-CM) at an academic and a regional hospital. At each centre, data were collected over a 3-week control-period and a 3-week intervention-period with standard-clinical-care UCB distribution (4pp). Control and intervention were compared for cumulative iodine- and gadolinium-CM-loads in WWTP influent using linear regression analysis, corrected for administered CM. Compliance was evaluated in interviews with consenting patients; results were used to estimate achievable UCB-distribution effects.

Results: UCB were distributed to 69.1% (1188/1719) eligible patients, and had a statistically significant effect on WWTP influent CM-loads: intervention versus control -17.4% iopromide [F(1,37) = 54.7, p < 0.001, η² = 0.60; R² = 0.966]; -14.8% ioversol [F(1,37) = 154.5, p < 0.001, η² = 0.82; R² = 0.989]; -7.2% gadolinium at the academic hospital [F(1,37) = 43.3, p < 0.001, η² = 0.54, R² = 0.967]; -33.2% gadolinium at the regional hospital [F(1,37) = 1.13, p = 0.296, η² = 0.03]. Interviews were conducted with 47.0% (558/1188) patients: 92.1% (514/558) reported using UCB, and they used 89.2% (1834/2056) of the UCB they were provided with. Compliance-based estimates were: achievable compliance 29.9% to 43.6%, interceptable CM 26.7% to 38.9%.

Conclusion: UCB distribution had a significant but small impact on reducing wastewater CM-loads. Compliance data overestimate UCB-distribution effect, which underscores the importance of wastewater measurements when evaluating mitigation strategies.

Key points: Question Contrast materials (CM) increasingly emerge as environmental contaminants; because treatment plants are currently unable to remove CM from wastewater, the effects of urine-collection-bag distribution are evaluated. Findings Standard-care urine-collection-bag distribution after CT and MRI led to small but significant CM-load reductions in wastewater; compliance data, however, led to sizeable overestimation of (achievable) effects. Clinical relevance Urine-collection bag distribution had a significant but small impact on reducing contrast materials in wastewater. Most studies only include compliance data, but results show these overestimate impact, underscoring the importance of contrast-load measurements when evaluating mitigation strategies.