The Donora Smog Revisited: 70 Years After the Event That Inspired the Clean Air Act

Abstract

At a storefront museum approximately 25 miles southeast of Pittsburgh, Pennsylvania, a sign reads, “Clean Air Started Here.” This is not hyperbole. At the end of October 1948, the communities of Donora and Webster in Pennsylvania were visited by a smog that changed the face of environmental protection in the United States. Conservative estimates showed that 20 individuals died, while an additional 5900—43% of the population of Donora—were affected by the smog.

This event led to the first large-scale epidemiological investigation of an environmental health disaster in the United States. Questions remain about the long-term effects of the smog, because higher rates of cardiovascular disease and cancer than were expected were observed in the region in the decade following the smog.

Recent work has suggested that environmental contaminants from a bygone era in Donora might have an impact even today. In addition, reports regarding air pollution have indicated that levels of pollutants similar to those estimated to have occurred in Donora are currently present in some rapidly industrializing regions of China and India. Seventy years after the smog, this event still resonates.

Approximately 4000 miles away from Donora, Pennsylvania, on December 3, 1930, there was a warning of what was to come. Over a distance of roughly 12 miles along the Meuse River Valley in Belgium, doctors began to receive urgent calls.^1,2 The reported symptoms, at first mysterious and sudden, began to assume a pattern. There was hoarseness and irritation of the larynx, chest pain, coughing, nausea and vomiting, and even foaming at the mouth.^2,3 The symptoms worsened, and within 24 hours, more than 60 people were dead.^1,3,4 In the terror and confusion after the event, citizens of the Meuse Valley and outside observers speculated that the cause could be anything from a mustard gas attack to sand from the Sahara Desert having blown into the region.¹ The response by the medical and scientific community was swift, concluding that the event was caused by air pollution from the numerous factories along the river, combined with a temperature inversion and unique geography, which together trapped smoke from the industrial plants at ground level.³ In leading medical journals, strongly worded articles were published, warning that despite the unusual conditions of the Meuse event, the same amalgamation of factors was likely to occur elsewhere, with disastrous results.^1,4,5 This prediction was roundly ignored. Eighteen years later, it happened again.

THE DONORA SMOG OF 1948

As residents of a township that relied on two major industrial plants for their livelihood, the citizens of Donora were no strangers to heavy pollution from the American Steel and Wire plant and the Donora Zinc Works. At the time, smoke in the air was often considered to be a sign of progress and prosperity, whereas clear skies meant economic depression and unemployment.⁶ However, the smog that occurred in October 1948 was exceptional even by the standards of the region.⁷ At first, to the residents of Donora, the conditions did not appear to be markedly unusual. The smog did not stop the annual Halloween parade from going forward on October 29, when children displayed their costumes as they walked down Main Street.^8,9 The next day, the Donora Dragons played a high school football game despite extremely poor visibility,⁸ a testament to the fighting spirit of a high school that produced such athletes as Stan Musial and Ken Griffey. As conditions worsened, telephones at the offices of the town’s eight doctors began to ring, with reports of respiratory distress becoming widespread.^9,10

The first responders of Donora, which included an ambulance and a firetruck, began to answer calls. Because of the darkness, these emergency vehicles had to be guided by a man walking in front with a flashlight. When this procedure later became impossible, firemen began going door-to-door to provide oxygen to Donora residents.^9,11 Doctors warned those with chronic health conditions to evacuate, but as the fog grew more dense, the roads became impossible to traverse.¹¹ At approximately 2:00 am on Saturday, October 30, the first death occurred,⁷ and within 12 hours, 17 citizens of Donora and Webster were dead.^10,11 Physicians, firefighters, and other first responders did not stop visiting the homes of the sick for days. When it was over, 20 had died within Donora and Webster, with an additional 1440 affected by serious illness and another 4470 individuals who had mild or moderate symptoms, totaling nearly half of the working class population of Donora.¹⁰

Immediately afterward, much wrangling and debate commenced regarding who could be trusted to objectively investigate this public health crisis, until requests from borough leaders in Donora, the United Steelworkers Union, the state of Pennsylvania, and American Steel and Wire itself, convinced the United States Public Health Service (USPHS) to investigate the smog.¹¹ The first large-scale epidemiological study of an environmental health disaster ever conducted in the United States then began. The group of 25 investigators was led by H. H. Schrenk, who was the Chief of the Environmental Investigations Branch of the USPHS at the time, after having served with the United States Bureau of Mines for 20 years in Pittsburgh, Pennsylvania.¹² The USPHS conducted an extensive study that included house-to-house surveys, autopsy reviews, veterinary investigations, air pollution monitoring stations, and analyses of weather conditions.¹⁰ In its preliminary report released in 1949 (a final report was never published) the USPHS investigators were circumspect, but concluded that the Donora smog was caused by a combination of three primary factors.

The first major contributing factor was the pollution emitted by American Steel and Wire plant and the Donora Zinc Works, which covered miles of riverfront land. These mills regularly emitted billowing plumes of smoke, and in particular, the Zinc Works had been identified as a major polluter because of its emissions of hydrogen fluoride, carbon monoxide, nitrogen dioxide, multiple sulfur compounds, and heavy metals within fine particulate matter.^7,11 The USPHS report also acknowledged the contribution to pollution by the voluminous river traffic and by residential use of coal-burning furnaces.¹⁰ The second major factor identified by the USPHS was an unusual weather system. The smog first settled throughout the town on October 26 and 27, when a temperature inversion occurred.¹⁰ A cold front moved in, after which there was very little wind. As the air stagnated, cold air became trapped below warmer air in the inversion layer, which, in turn, acted as a lid over the valley. Air entrapment was enhanced by the unique geography of Donora, which was the third major contributor to the smog. The borough was captured within the confines of a horseshoe bend in the Monongahela River, and the region was surrounded by hills and cliffs that rose to a minimum of 400 feet.¹¹ Effluent from the local coke ovens, coal stoves, and plants’ smokestacks lingered for five days within this geographical bowl, trapped by the inversion at 150 feet—an altitude below which numerous people lived.^7,11

Ultimately, although the USPHS research team positively identified neither a single contaminant that caused the illnesses during the smog nor the precise source, they were able to clarify the contributing factors, which were markedly similar to those that had occurred in the Meuse Valley two decades previously. They offered several recommendations for preventing another event from occurring in the future, including reducing plant effluent and creating a system whereby weather alerts could be used to warn the region of conditions favorable to another smog.¹⁰ However, there were some gaps in the investigation. Clarence Mills, a professor of experimental medicine from the University of Cincinnati, had conducted his own study of the event, and was straightforward in his conclusion that there could well be long-term effects among individuals in the community that were not addressed by the USPHS investigation.¹³ The American Journal of Public Health published an editorial in 1950 highlighting the key research gaps that remained after the investigation.¹⁴ In this prescient work, the authors specifically emphasized the continued threat to public health from air pollution, even at lower exposures. The article went on to include the important findings of the USPHS regarding disparities in health effects caused by air pollution that are still seen today, including the higher death rate of non-Whites than Whites in Donora, and the key impact of poor housing quality on the degree to which residents were affected.¹⁴ Another editorial published in the New England Journal of Medicine in 1950 stated the USPHS report was a missed opportunity for conducting a more detailed investigation of the health effects of both long-term pollution and severe, acute events.¹⁵ Because of the timing and nature of their study, the USPHS focused largely on proximal health effects, whereas only one research group conducted analyses of long-term health outcomes in Donora.^16,17

LONG-TERM EFFECTS OF THE SMOG

The task of investigating the longitudinal effects of the smog was performed by two biostatisticians at the University of Pittsburgh.^16,17 In their 1961 study, Ciocco and Thompson assessed deaths from cancer and cardiovascular disease (CVD) in Donora from 1948 to 1957 and compared observed and expected disease-specific rates as calculated for each age group using the cause-specific mortality of the entire study sample from Donora.¹⁶ Their data showed a consistently higher number of deaths than expected from CVD in the decade following the smog for those who had reported having heart or respiratory disease in 1948.¹⁶ Among men and women collectively, a total of 70 deaths from CVD were observed in Donora for those who had reported heart disease, asthma, pneumonia, or bronchitis in 1948. This figure was substantially higher than the expected number of 39 CVD deaths,¹⁶ although these findings garnered little attention since their publication in 1961.

Thompson and Ciocco also conducted a study of cancer deaths in Donora from 1948 to 1957, as well as those in Arsenal, Pennsylvania, a district near Pittsburgh.¹⁷ In this work, they did not compare the proportion of cancer deaths in Donora during the period following the smog with that of Arsenal during the similar time period. We adapted data from the analysis by Thompson and Ciocco,¹⁷ and as shown in Table 1, there was a statistically significantly higher proportion of cancer deaths in Donora compared with Arsenal (odds ratio = 1.97; 95% confidence interval = 1.34, 2.90). Therefore, in the decade following the smog, higher than expected CVD and cancer mortality rates were observed in Donora, which suggested that the smog, in conjunction with long-term pollution overall, had longer term effects than was commonly acknowledged. It is possible that one of the central contributors to the smog—pollution by the Donora industrial plants—could affect environmental and public health even today, as addressed in a recent analysis of sediment in a lake in the region.¹⁸

TABLE 1—

Odds Ratios for Cancer Mortality in Donora, PA, Compared With Arsenal, PA, After the 1948 Smog

Characteristics	Number of Cancer Deaths/Total Participants
	Arsenal (1951–1956)	Donora (1948–1957)
Age, y
21–34	3/2004	1/917
35–49	11/2079	12/803
50–64	29/1476	23/723
≥ 65	20/746	17/269
Total	63/6305	53/2712
OR (95% CI)	1 (Ref)	1.97 (1.34, 2.90)

Note. CI = confidence interval; OR = odds ratio.

Source. Adapted from Thompson and Ciocco.¹⁷

Rossi et al.¹⁸ reported on a study of the sedimentary record of an unnamed lake approximately six miles northeast of Donora. The research team recovered three cores from the lake bed to measure the concentration of contaminants during the last 200 years. They were able to combine their findings with the historical record of industry in the region, and discovered that after the opening of the Zinc Works in 1915, there were substantially increased concentrations of cadmium, lead, and zinc.¹⁸ Although a sharp increase in these heavy metals was detectable immediately after the opening of the Zinc Works, cessation of operations did not result in a concomitant marked reduction in these contaminants. Rather, these contaminants have remained above the recommended concentrations for cadmium and lead 70 years after the smog.¹⁸ The authors pointed out that environmental events, such as human disturbance or resuspension from flooding, could ultimately release these contaminants from the sediment back into the water, resulting in increased environmental and human exposures. Therefore, the pollution that contributed to the smog of 1948 remains a risk even to the present day.

AIR POLLUTION TODAY

In 2018, 70 years after the Donora disaster, air pollution continues to be a global threat to public health. Recent news articles have highlighted air pollution challenges that remain both within the United States and throughout the world. A recent study of more than 60 million Americans who use Medicare demonstrated that higher exposure to air pollution was significantly associated with increased rates of all-cause mortality.¹⁹ In India, both household and outdoor exposure to particulate matter are significant health concerns. As reviewed by Pant et al.,²⁰ developing countries contend with multiple contributors to increasing air pollution, including population and industrial growth. Air pollution has been estimated to be the cause of more than 100 000 premature deaths in India alone.²⁰ Another country facing severe air pollution challenges is China. In an analysis of mortality related to exposure to particulate matter, Hu et al.²¹ reported that 1.3 million premature deaths, primarily from chronic obstructive pulmonary disease, as well as CVD and cerebrovascular disease, were attributable to air pollution.²¹ Hence, despite major efforts to curb air pollution, it remains a significant public health threat globally, particularly in developing countries.

CONCLUSIONS

Despite strong warnings from the medical and scientific community following the Meuse Valley disaster in 1930,^1,4,5 Donora did not implement the smoke-control measures that began with vanguard efforts throughout the United States at the municipal, county, and state levels.^6,22 This lack of environmental protection resulted in the tragedy of 1948. Effects of the smog were detectable even during the following decade, with higher rates of cancer and CVD deaths than were expected. The smog disaster, in turn, was one of the events that catalyzed the first steps taken nationally to reduce the effects of pollution. In the ever-increasingly industrial United States, efforts to curb pollution had been under way within cities, counties and states, finally culminating with the passage of the Clean Air Act.^22–24 As reviewed in detail by Stern,²² many factors dovetailed to ultimately create an environment in which federal legislation was passed. These included a 1962 smog event in London, England, a full decade after the 1952 Great Smog that was estimated to have resulted in the deaths of 4000 people,²⁵ as well as the impact on the general public of the release of Rachel Carson’s book The Silent Spring, which raised awareness of the risks of pollution and helped launch the environmental movement in the United States.²² The resultant federal laws reduced the risk of countless communities from experiencing harms such as those that had occurred in Donora.^23,24 Nonetheless, work remains to be done as air pollution continues to threaten the health of the public. Thus, the specter of the 1948 smog incident and its precipitating causes remains to this day. The potential exists for weather events that could again unleash contaminants that are part of the smog’s legacy. In addition, developing countries in particular continue to face major public health threats from air pollution and smog. As with the warnings that took place after the Meuse Valley disaster, we ignore these smog incidents at our peril.