Effect of Diesel Exhaust Exposure on Railroad Worker Health and Mortality

Hazardous work conditions expose employees to health and safety risks, and employers to potentially higher expenses including the possibility of a prolonged series of expensive litigation. Indeed, recognition of this in individual and organized (collective) bargaining over higher pay and health benefit coverage, and of course, government regulation involving improved safety measures and equipment design is common. It is easier for all to deal with such risks when they are recognized, and the extent of that risk known. Often, though, risks may appear uncertain, with contradictory evidence supporting opposing views. Such is the case for the exposure of railroad workers to diesel exhaust, a subject that has been investigated for decades with considerable disagreement. This paper contains a focused survey of published studies in the past thirty-five years using observational data and epidemiology (laboratory studies on animals) to review the extent to which disagreement has or not been abated.

Effects of Short-Term Exposure to Diesel Exhaust on the Ecophysiology, Growth, and Fecundity of Soybean (Glycine max (L.) Merr.) and Chicory (Cichorium intybus L.)

Plants growing along roadways are often exposed to vehicle exhaust containing both particulate matter (PM) and various gases that could affect gas exchange and thus plant reproduction. To investigate effects of diesel exhaust exposure on plant ecophysiology, growth, and fecundity, individuals of soybean (Glycine max (L.) Merr.) and chicory (Cichorium intybus L.) were exposed to either exhaust from a diesel generator or ambient air. Exposure occurred daily over a 5-day period (beginning 18 June 2013) using open-top chambers in an agricultural field in southwestern Ohio, United States. Plants were evaluated at 3 times (before, directly after exposure, and following a 5.5-week post-treatment recovery period) for photosynthetic rate (A), stomatal conductance (g), water use efficiency (WUE), stomatal clogging due to PM deposition, and number of nodes. Aboveground biomass, fruit number, mean seed number, and seed mass were measured for soybean after the recovery period. In soybean, A minimally decreased with exposure to diesel exhaust (compared to the control), but an increase in g and a decrease in WUE were detected after the exhaust treatment. Chicory exhibited a relatively low increase in A after the treatment, but there were no clear differences in g or WUE. Growth and fecundity were similar among all soybean plants directly after treatment, but after 5.5 weeks plants exposed to diesel exhaust had increased vegetative biomass while exhibiting no difference in fecundity. These plant species reacted differently to short-term diesel exhaust exposure, suggesting that the impact of diesel exhaust will depend on both the plant species and its physiology.

Determinants of citation in the literature on diesel exhaust exposure and lung cancer: a citation analysis

ObjectivesEpidemiological research on the association between diesel exhaust exposure and lung cancer risk has some methodological challenges that give rise to different conclusions and intense debates. This raises the question about the role of selective citation and of citation bias in particular. Our aim was to investigate the occurrence and prevalence of selective citation in this field.DesignCitation analysis.SettingWeb of Science Core Collection.ParticipantsWe identified 96 publications in this network, with 4317 potential citations. For each publication, we extracted characteristics such as study conclusion and funding source. Some of these characteristics are related to the study content: study design, sample size, method of diesel exposure assessment, type of diesel technology under investigation, and whether smoking had been adjusted for.Primary and secondary outcome measuresWhether a citation occurs or not, measured and analysed according to the preregistered protocol. Exploratively we analysed the association between funding source and study conclusion.ResultsMethodological content of a study was clearly related to citation, studies using more sophisticated methods were more likely to be cited. There was some evidence for citation bias: supportive publications had a higher chance of being cited than non-supportive ones, but after adjustment for study quality, this effect decreased substantially (adjusted OR 1.3, 95% CI 1.0 to 1.7). Explorative analyses indicated that three quarters of non-profit funded publications had a supportive study conclusion against only one quarter of the industry-funded publications.ConclusionsThere is evidence for selective citation within this field, but the evidence for citation bias was weak. It seems that factors related to the methodology had more impact on citation than the conclusion of a study. Interestingly, publications that were funded by industry were more skeptical about a causal relationship between diesel exhaust and lung cancer compared to non-profit-funded publications.