Do Israel’s congested roads increase cancer risks?
High exposure to nitrogen oxide significantly increases risk of prostate, breast and lung cancer
High exposure to air pollution from transportation vehicles is correlated with a 50% increase in prostate, breast and lung cancer risks among cardiac patients, a new study from Tel Aviv University has found.
Diesel exhaust, which consists of a diverse mixture of gases and particles, is classified as a human carcinogen by the International Agency for Research on Cancer. Previous epidemiological studies have suggested that the pollutants have a relatively small effect on cancer and mortality, but determining an exact relationship between the two proves difficult because of the vast differences in exposure to diesel exhaust among different populations.
In Israel, where according to a 2016 OECD report average traffic density per square kilometer is higher than that of any other OECD country, there has been a particularly strong effort to understand the impact of traffic-related air pollution on vulnerable populations.
A December 2018 study by Israel’s Central Bureau of Statistics found that the biggest killer of Israelis is cancer, followed by heart disease and diabetes. The disease results in some 177.1 deaths for every 100,000 people, according to the report.
A team at TAU, led by Prof. Yariv Gerber and PhD student Gali Cohen from the Department of Epidemiology and Preventive Medicine, hypothesized that exposure misclassification, a major challenge in air pollution epidemiology, may have led to understated estimates of the carcinogenic nature of traffic pollution in previous studies.
Because it is not feasible to provide personal monitors to a large study population, the researchers developed a novel approach to exposure assessment by cross-referencing two mathematical models that measure transfer pollutants at the study participants’ site of residence. One model was developed at the Technion, the other at Hebrew University.
The researchers integrated the two monitoring systems to capture different aspects of exposure, which may be accounted for by one model but not by the other.
“The models are based on data from dozens of pollutant-monitoring stations across the country, and each model also takes into account additional data, such as transportation volumes, meteorology and geographic variables,” Cohen said. “We used them to estimate as accurately as possible the level of exposure at each patient’s home to nitrogen oxide (NOx) concentrations in the air, which is considered a reliable measure of the level of transport pollution.”
The subjects of the study included just under 9,500 patients who underwent cardiac catheterization at Rabin Medical Center from 20042014. At baseline, this population was free of cancer, on average 69 years old, and largely residents of central Israel. Notably, 34% reported being smokers, 74% had hypertension and 44% had diabetes, meaning that the study group was already a population with vulnerable health.
The TAU researchers used the National Cancer Registry database to check the cancer status of the study’s participants up until 2015, a follow-up period whose median length was seven years.
In that time, there were 741 new cases of cancer, and by 2017, about 3,000 deaths.
When the researchers correlated this data with data on exposure to air pollution from vehicles, they found that those with high exposure to NOx concentrations (above 25 parts per billion) had a significant increase – up to 1.56 times more – in their risk of prostate, breast and lung cancer. The researchers adjusted their calculations for patients’ clinical and demographic data, including sex, smoking status, hypertension, diabetes and neighborhood socioeconomic status.
“The higher the exposure, the higher the risk,” Cohen stated. But he acknowledged that there is still more work to be done to truly understand the health impacts of diesel exhaust.
“This is an observational study that does not allow a definite conclusion about the existence of a causal link between air pollution and the health outcomes studied, as there may be other explanations,” he said.
Moreover, the study only accounted for its participants’ exposure at home. The lack of information on participants’ exposure to vehicle exhaust while not at home is a gap in the analysis, but the authors note that previous studies show older populations spend an average of 80% of their time at home, and the median age of the study cohort was 69.
The results of the study will be published in the September issue of the Scientific Journal of Environmental Research. The article concludes with a call for further use of its unique model for exposure assessment in future epidemiological studies: “Its adaptation may considerably change the perception of patients, clinicians and policy-makers regarding the magnitude of the threat of air pollution on public health,” the authors stated.