A very large number of population-based observational studies have reported a positive association between ambient concentrations of air pollution and hospitalizations for respiratory and cardiac disease; however, there exist few studies assessing the health benefit of an intervention which reduces community exposure to air pollution. Improvements in both air quality and health effects have been documented following a number of large-scale changes in local air pollution emissions, including copper smelters in the Southwestern United States [1
], bitumous coal burning in Dublin, Ireland [2
], lowered sulfur content for fuel oil and gasoline in Hong Kong [3
], closure of pollution-emitting industries in East Germany [4
], reduction of traffic during the 1996 Summer Olympic Games in Atlanta [5
], and reduction of traffic during the Summer Asian Games in Busan, South Korea [6
]. Studies have also been done following the closure of the Utah Valley Steel Mill [7
] and on the impact of the air pollution-lowering steps adopted prior to the 2008 Beijing Olympics [9
]. In many of these studies the intervention led to significant reductions in negative health effect metrics for the affected populations.
The present study assesses the health impact of the closure of an oil refinery in Oakville, Canada on residents’ hospitalizations. The refinery was designed for production of consumer-grade gasoline and by-products such as asphalt and kerosene. It was located near the shore of Lake Ontario and produced 13,200 cubic meters of gasoline per day (approximately 90,000 barrels) [11
]. The refinery was built in 1958 [12
] and closed and decommissioned over a six-month period from October 2004 to March 2005. There remains a small-scale oil terminal at the location, but air pollution emissions, in particular SO2
, have been almost completely eliminated after the refinery closure. Ambient measurements of air pollution for the city were more complete than site-specific emissions data for the study period, as the site-specific monitor was removed before the refinery closure. Considering the relatively small population size of Oakville, we examined respiratory-related morbidity, as there were more hospital admissions than deaths, providing more statistical power. Thus, in this study we focused on the changes in ambient air pollution in relation to those in morbidity records to measure the impact of the refinery closure on public health.
In this study, we found that the closure of the oil refinery located in the city of Oakville, Ontario was associated with measurable reductions in wind-direction-adjusted ambient SO2 in Oakville. We additionally found that there was a significant reduction in respiratory-related hospitalizations in Oakville, with the reduction occurring sharply after the refinery closure and persisting. Moreover, we found no other explanatory or confounding factors which influenced the reduction in hospitalizations for Oakville, such as changes in socio-economic status, traffic counts, or traffic-related air pollutants such as NO2. Taking these findings together, the reduction in SO2 emissions from the Oakville refinery closure and the subsequent decrease in SO2 concentrations in ambient air concentrations appear to have occurred simultaneously with a significant reduction in cold-season respiratory hospitalizations in Oakville.
Natural experiments represent a powerful tool in establishing a causal link between exposure and response. In many cases, the experiment acts as an intervention, with correspondingly large changes: the Utah Valley steel mill closures [7
] being one of the most clear and famous examples. In our study the evidence suggests that even closures of smaller-scale industrial sites like the Oakville refinery, if the sites are emitters of pollutants associated with health effects, can have immediate and measurable effects on the health of the surrounding community.
There were several limitations of our study. Data were lacking from the Refinery Station (61602), which was closed at the end of 2002, and the replacement Oakville station (61603) did not begin operation until April 2003, although data from the NPRI indicated that there was little change in the emissions from the refinery up to 2003, so the 1996–2002 span of available data from 61602 should give reasonably accurate estimates of the ambient air quality before closure. Data from Oakville station provided us a view into ambient air quality after closure. However, no SO2 data were available after 2007 for the Oakville Station. In addition, VOC data (which would normally be of great interest when examining the emissions from a refinery) were sparse or unavailable for the period of the study.
The NPRI data used as a gauge of pollution emissions from the refinery are not entirely reliable, as the data are self-reported by industry, rather than observed by a third party. In addition, regulations only require coarse aggregate measures. Self-reported data on air pollution emissions are available from 2002–2014, and emissions of specific chemicals (e.g., toluene) are available back to 1994. As well, yearly NPRI reporting requirements, including addition/removal of substances, reporting thresholds and reporting exemptions for specific industrial sectors have changed over time [14
]. In 2001, new release groupings were created, including on-site pollutant release to air, and 7 criteria air contaminants were added in 2002, including SO2
, NOx, CO, and VOCs.
There are no limitations to the health-related data, as they are complete due to mandatory reporting regulations, with complete morbidity data available back to 1996. The seasonal age-standardized SHRs based on the GTA should account for seasonal, demographic and population changes through the study period, and as demonstrated in the Online Supplement
, are resistant to variation in parameter choices for the SHR.
By contrast, our study has several strengths. Use of SO2
as a proxy for overall refinery emissions is a sensible choice, as SO2
is known to be related to morbidity (hospitalizations), both in general [27
] and specifically for the Canadian population [33
]. While associations between SO2
and morbidity are positive and significant, they are small in magnitude, so any association between refinery closure and health outcomes cannot be necessarily directly attributed to this pollutant, however use of SO2
as a representative proxy of the whole seems reasonable. At the same time, no other ambient air pollutants with available data showed statistically significant reductions of step-function nature after the refinery closure, despite the clear reduction (6000 tons per year for SO2
, Table 2
) in emissions, so again, the use of SO2
The closure of the refinery coincided with a measurable reduction in hourly ambient SO2 levels in the city of Oakville—a reduction that was greater than what would be expected from the refinery closure, which we estimated through evaluation of similar monitoring stations in the neighboring city of Toronto using wind-direction-restricted analyses. Comparing the before- and after-closure periods, we found a statistically significant (step-function) reduction of ambient SO2 concentration levels in Oakville only, not in Toronto. This is another strength of the study, as with the local nature of SO2 ambient concentration we would not expect to see step-function reductions of SO2 concentration outside of the immediate region surrounding the refinery.
The closure of the refinery came soon after the introduction of a stringent sulfur content regulation for gasoline in Ontario: as of 1 January 2005, all gasoline sold in Ontario was limited to an annual average sulfur level of 30 ppm (30,000 ppb) or 30 milligrams per-kilogram (mg/kg), with a never-to-be-exceeded limit of 80 ppm (Government of Canada, 1999). From July 2002 to 2005, there was an interim annual average sulfur content of 150 ppm. The ambient concentration reduction happened quite sharply in 2002–2003, despite the regulation rolling out in phases, as most fuel manufacturers moved their facilities to the new standard in time for the initiation of the regulation. Similar regulatory changes were implemented in June 2006 for diesel fuel, with a reduction from 500 to 15 ppm [35
]. These changes, together with more restrictions on power plants and industry, led to a decrease in the Ontario average annual ambient concentration of sulfur dioxide (SO2
) from approximately 6 ppb to 2.2 ppb across the 2000–2013 period [36
]. The step-wise decrease in ambient SO2
levels observed in Oakville appears to be in addition to the background decrease in SO2
levels associated with the reduction in allowable sulfur content in gasoline, as seen in ambient concentrations of nearby municipalities.
Regarding other commonly available air pollutant measures, NO2
concentrations have also been previously linked to morbidity [33
]; however, examination of the present data revealed neither a significant decrease in 2001–2003 such as was observed in SO2
with the roll-out of the Canadian Environmental Protection Act (1999) [35
] regulations, nor any sudden decrease in Oakville levels at or around the closure of the refinery. As NO2
is most commonly linked to automobile traffic, this fits available evidence, supporting the NPRI records which indicate that NO2
was not a significant emission from the refinery.
While the Census Division of Halton (which contains CSD Oakville) experienced rapid population growth through the 2001–2011-time period, much of the growth occurred in newly-built subdivisions well north of Lake Ontario, away from the refinery and north of the highway system [22
]. The area directly co-located with the refinery saw very little population growth (0–3%) during this time. In addition, the age distribution skewed toward retirees through this period, with the demographic profile aging over the decade; much of this aging should have been compensated for by the standardization of hospitalization records. Any residual effect not compensated for by this modeling (due to population demographics being temporally coarse owing to census patterns) should have been in the direction of an aging population, which should result in increased levels of hospitalizations rather than the opposite.
In conclusion, despite limitations in data availability for the region and the study, we have demonstrated measurable reductions in ambient SO2 levels as would be experienced by the residents of Oakville. We similarly demonstrated a sharp decrease in cold-season age-standardized hospitalization rates, which occurred immediately following the refinery closure. No other contributory factor was found which could explain this decrease. Thus, we present in this study another piece of evidence in the field, showing concurrent measurable reductions in both SO2 concentrations and respiratory-related hospitalizations when a local emission source was removed.