Excess Greenhouse Gas Emissions From Medical Imaging Related to Environmental Exposures

Introduction

Climate change adversely affects human health, resulting in higher demand for health care. Short-term environmental exposures to heat and fine particulate air pollution are associated with increased utilization of radiography and CT in the emergency department. ¹ The delivery of health care—including medical imaging—also generates substantial waste and greenhouse gas (GHG) emissions, thus contributing to the climate crisis.^2-4 The impact of climate-related exposures on the generation of GHG emissions from increased medical imaging is currently unknown. The purpose of this study was to determine the impact of environmental exposures on generation of downstream GHG emissions due to excess medical imaging utilization.

Methods

This retrospective study does not involve human subjects or patient level data and institutional research ethics board approval was not required. Daily imaging utilization counts from 4 emergency departments in Toronto were linked to local daily environmental data—including fine particulate matter (PM_2.5) and ambient temperature—over a 10-year period (January 2013-December 2022). The current study builds on a prior publication quantifying excess medical imaging related to climate-related environmental exposures. ¹

Downstream GHG emissions generated in the delivery of excess medical imaging related to environmental exposures were modelled locally (across the four included emergency departments) and extrapolated nationally across Canada. We assumed similar effect sizes across Canada and estimated that 4% of the total Canadian population is served by the 4 emergency departments included in the study (current total Canadian population is approximately 41 million). Excess GHG emissions were modelled based on excess imaging utilization associated with each environmental exposure, the proportion of heat exposure and air pollution exposure days, and mean GHG emissions generated by each imaging study (0.65 kg CO₂e for radiographs and 7.9 kg CO₂e for CT).^5,6 Heat exposure days were defined as days where the mean temperature exceeded 20°C, the mean local daily ambient temperature in summer months (June to September). Air pollution exposure days were defined as days with mean daily PM_2.5 >12 μg/m³, based on previously demonstrated adverse health effects at higher levels. ¹ GHG emission equivalencies were assessed using an on-line calculator. ⁷

Results

Between 2013 and 2022, a total of 790 619 radiographs and 508 950 CTs were performed across the 4 emergency departments and there were a total of 602 heat exposure days and 552 air pollution exposure days.

Heat exposure days and air pollution exposure days were associated with increased utilization of radiographs (excess absolute risk of 5.4 and 2.6 imaging studies per 1 million people at risk per day, respectively) and CT (excess absolute risk of 4.1 and 3.4 imaging studies per 1 million people at risk per day, respectively).

Excess medical imaging attributed to heat exposure generated excess GHG emissions of 1450 kg CO₂e/year locally (209 kg CO₂e/year from radiographs and 1241 kg CO₂e/year from CT) and 36 261 kg CO₂e/year when extrapolated nationally (5230 kg CO₂e/year from radiographs and 31 031 kg CO₂e/year from CT). National excess GHG emissions attributed to heat are equivalent to 148 608 km driven by an average gasoline-powered passenger vehicle or 18 270 kg of coal burned (Figure 1).

Figure 1.

Study summary highlighting the interconnectedness of radiology and planetary health. Ambient heat and air pollution exposures adversely impact human health leading to higher utilization of radiography and CT in the emergency department. Excess medical imaging generates greenhouse gas emissions which are the primary driver of climate change, worsening environmental exposures including heat and air pollution. Excess greenhouse gas emissions attributed to ambient heat and air pollution are equivalent to 18 270 and 20 481 kg of coal burned nationally, respectively.

Excess medical imaging attributed to air pollution exposure generated excess GHG emissions of 1626 kg CO₂e/year locally (147 kg CO₂e/year from radiographs and 1479 kg CO₂e/year from CT) and 40 648 kg CO₂e/year when extrapolated nationally (3664 kg CO₂e/year from radiographs and 36 984 kg CO₂e/year from CT). National excess GHG emissions attributed to air pollution are equivalent to 166 588 km driven by an average gasoline-powered passenger vehicle or 20 481 kg of coal burned.

Discussion

Increased imaging utilization associated with climate-related exposures exacerbates the environmental impact of delivery of radiology services in a negative feedback loop. Excess imaging attributed to heat and air pollution across Canada generate excess greenhouse gas emissions of 36 261 kg CO₂e/year and 40 648 kg CO₂e/year, respectively, thus contributing to the worsening climate crisis and highlighting the interconnected relationship between radiology and planetary health.