The minefield of diesel emissions

The carcinogenic effects of diesel emissions/exhaust are widely known. In 1988, the US’ National Institute for Occupational Safety and Health labelled diesel exhaust as a potential occupational carcinogen and, in June 2012, the IARC will be revisiting their existing labelling of diesel particulates as potential carcinogens.

Particulate Matter (PM) in diesel emission
The problematic component of diesel emissions is particulate matter, a topic which yours truly has worked on rather extensively; also, many are the research papers on the morbidity and mortality of PM. PM is an aggregated mixture of salts, inorganic, and organic compounds, generally characterised by aerodynamic diameter. The PM in diesel emissions are collectively very fine (less than 1 μm in diameter) and carbonaceous; but its specific composition depends on the engine characteristics, type of fuel used, and any filtering devices utilised.

Effect of PM on human health
Nonetheless, the end result is that due to their small size, they can penetrate deeply and cause inflammation. Scientists have analysed PM’s distribution in the human lung and sites with PM deposition were predicted to be future sites of lung cancers. On the whole, short-term effects are usually respiratory related. Long-term effects includes respiratory illnesses (ranging from pulmonary inflammation to allergies), cancer, cardiovascular, and cardiopulmonary disease (for more information/references on all statements: contact me)- and even altering of gene expression. But many are the studies associating traffic with increased incidences of respiratory and cardiovascular problems.

Furthermore, the particle’s surface adsorbs polycyclic aromatic compounds, often with metals and acidic components (some examples being chlorobenzene, quinines, acids, benzo-a-pyrene, mercury, lead, phenols). In fact, is there a need to refer to published research when our old elementary chemistry lessons should suffice in deducing what happens if those compounds enter into our body via our nostrils? (for more information/references: contact me).

Diesel exhaust and miners
In this backdrop, consider the situation of those working in underground mines. Miners are the occupational group most exposed to high levels of diesel since they use diesel-powered heavy equipment and breathe in the exhaust on a daily basis. Despite the presence of ventilation (if any), in such an enclosed environment, the exhausts culminates in a very high level. Consequently, researchers at the National Cancer Institute (NCI) and the National Institute for Occupational Safety and Health, via their ‘Diesel Exhaust in Miners Study’, aimed at evaluating the risk of diesel exhaust-associated death in miners, with a sample of 12315 US miners at eight non-metal (to minimise confounding variables such as exposure to carcinogens such as radon, silica, and asbestos) mining facilities (1 limestone mine in Missouri, 3 potash mines in New Mexico, 1 salt mine in Ohio, and 3 trona mines in Wyoming).

Four methodology papers were published in the Annals of Occupational Hygiene in 2010. Subsequently, the results were published in March 2012 via two papers. Paper 1 presented the risk of death from any cause (with an emphasis on lung cancer), using data from the full study population (the cohort study). Paper 2, the case-control study, reported the lung cancer deaths in the cohort study, controlling for smoking and other risk factors (such as prior employment in high-risk jobs, history of respiratory diseases, etc). The dose-response results were illuminating and statistically significant, generally illustrating an increasing risk of lung cancer death with increasing levels of diesel exhaust exposure:

1. Those exposed to high levels of diesel exhaust had three-fold risks of lung cancer (than those exposed to low levels)

2. Those exposed to high levels of diesel exhaust underground faced a five-fold risk.

3. In non-smokers, the risk of lung cancer death increased with increasing exposure to diesel exhaust. Those with the highest level of diesel exposure were 7-times more likely to die from lung cancer than non-smokers in the lowest exposure category.

4. In heavy smokers, the effect of diesel exhaust exposure was attenuated (decreased risk for lung cancer death- decreasing with increasing levels of exposure). It is hypothesised that smoking clears the diesel particulates from the lungs. Furthermore, carcinogens in diesel exhaust and cigarette smoke may operate in the same metabolic pathway in the body and compete with each other, resulting in a saturation of the pathway, thus diminishing the effects of either component (NCI, 2012).

Industry’s ire

Let’s take a detour and visit the mining industry queen bees in their comfy airconditioned offices, far away from the worker bees languishing in an environment of PM-emitting machines. In around 1995, a coalition of mining firms (the Mining Awareness Resource Group) commenced a 17-year legal, legislative, and political battle from conducting and publishing the afore-mentioned epidemiological studies. Their first strategy was to stop the study before it began (after all, is there truly any causal link between diesel exposure and lung cancer incidences?). Their next was to control the release of the study findings using quite a many gimmicks, such as asking for reviewing the data before publication, holding the researchers in contempt of court for withholding data, and writing vaguely threatening letters to journals which may potentially publish the studies.

Potential impacts

The publication of these studies could have the following consequences which affects the industry’s existence and market performance: (rational)investors may withdraw, concerned stakeholders could kick up some troubles, new regulations and standards on diesel emissions, cleaning up, and finding alternatives (all which contributes to compliance costs), and, potentially, miners and their families could sue.

Corporate Human Responsibility, anyone?

What puzzled me was the effort which the coalition put into preventing the studies from being published. In all probabilities, they deduced that the results would not be conducive to their existing status quo. What certainly doesn’t seem to have been considered, by these interested parties (comprising of humans), was the health of their workforce (also comprising of humans). Surely even the rational profit-maximising decision-maker should have deduced that the well-being of the human capital would contribute to long-term firm performance? Politicians too seem to have stood with the industry on this matter. Hypothetically, had the study found no correlation, the studies would probably have been well-publicised by the industry.

External validity

Whilst this study focussed only on the miners, one could extrapolate this to populations/individuals elsewhere exposed to the analysed levels of diesel exhausts. Several countries in the developing world (where emission standards are practically nonexistent) widely use diesel as a vehicle fuel and there is a concentration of usage in trucking, shipping, and rail works. Even if these individuals are not immediately exposed to levels experienced by the underground miners, this could result in a cumulative accumulation. And one needn’t elaborate more on the plight of mine workers in developing countries. One must also point out that lung cancer is just one of the many worries facing a miner.

I hope that the interested parties would view this event as something which could be a source of competitive advantage. For instance, they could develop new technology which further reduces diesel emissions or switch to much more efficient and healthier technologies.

Image source: Gaetano/Corbis

Sources:
Silverman, D., Samanic, C., Lubin, J., Blair, A., Stewart, P., Vermeulen, R., Coble, J., Rothman, N., Schleiff, P., Travis, W., Ziegler, R., Wacholder, S., & Attfield, M. (2012). The Diesel Exhaust in Miners Study: A Nested Case-Control Study of Lung Cancer and Diesel Exhaust JNCI Journal of the National Cancer Institute DOI: 10.1093/jnci/djs034 Attfield, M., Schleiff, P., Lubin, J., Blair, A., Stewart, P., Vermeulen, R., Coble, J., & Silverman, D. (2012). The Diesel Exhaust in Miners Study: A Cohort Mortality Study With Emphasis on Lung Cancer JNCI Journal of the National Cancer Institute DOI: 10.1093/jnci/djs035 Stewart, P., Vermeulen, R., Coble, J., Blair, A., Schleiff, P., Lubin, J., Attfield, M., & Silverman, D. (2012). The Diesel Exhaust in Miners Study: V. Evaluation of the Exposure Assessment Methods Annals of Occupational Hygiene, 56 (4), 389-400 DOI: 10.1093/annhyg/mes020

http://www.cancer.gov/newscenter/pressreleases/2012/DieselMinersQandA http://www.washingtonpost.com/national/health-science/diesel-reports-publication-delayed-as-industry-demands-to-see-documents-first/2012/02/01/gIQA5wrFtQ_story_1.html

Controversial, Bt very common

Probably the most controversial issue in agriculture today is the use of transgenic crops. What does this mean exactly? Well, basically, it is the addition of genetic material from one species into another. Mules, for example, are technically transgenic as they are the offspring of different species, horses and donkeys. The Soviets developed a hybrid of radishes and cabbages, though unfortunately it had the leaves iof radish and the roots of cabbage (*). But what people generally mean these days is the insertion of a particular gene into a plant, which is then expressed in that plant, and it's desecndents.

Many transgenic crops include the letters Bt, which comes from Bacillus thuringiensis, a type of bacteria. Now, this bacteria produces a toxin which kills insects, but very very specifically. In other words, it will kill one type of insect, but not another, nor other animals. Put the genes for this toxin in plant cells and they will make it themselves, so that when an insect injests part of the plant, it takes in the toxin.

Although there is no reason why virtually any crop should not be engineered to include Bt genes, commercially only two have been, cotton and maize. In 2009 about half the worlds cotton was grown on transgenic plants. It is reckoned that the economic benefit from transgenic cotton globally is about $2.9 billion, 65% from increased yields and 35% from reduced expenditure on pesticides. By far the largest producers are China (3,400,000 hectares) and India (8,400,000 hectares). Bt genes are so specific that there is a growing trend to combine several in each plant, to defend against a cocktail of pests.

Of course people don´t eat cotton, whilst they do maize. Nonetheless, 16 countries around the world grow transgenic maize against 11 growing cotton, with the USA (over 17 million hectares) and Brazil (5 million ) being the largest growers. In this case, genes have sometimes been combined with those for drought resistance, allowing maize to grow where iin the past it struggled.

One of the reasons for the controversy over GM technology is the control companies such as Monsanto exert over their products. Of course any plant breeder needs to protect their investment, but the huge development costs involved here mean that not only are GM seeds normally more expensive, but the legal protection is much more stringently applied - think DRM in software. That's all very well, but once a plant is in a distant valley, it's quite hard to monitor. For example, it has been reckoned that about 60% of cotton grown in the Indian state of Gujarat in 2007 was illegal. With the best will in the world, the fate of seeds after harvest is not necessarily enforecable, and there are plenty of people willing to grow seeds for sale. Storing your own crop or buying from local producers are both traditional sources of seeds and it is hard to convince people that this is, or should be, illegal.

So, is it safe?

A recent paper (**from which some of the figures above were also culled) surveys the many papers published on this subject. It has to be said that the author tends to dismiss negative studies as either badly designed or otherwise inadequate, but anyway his conclusions are as follows.
Firstly, and most importantly, there is no evidence of any toxicity at all to mammals such as ourselves.
The advantage of Bt proteins is their specificity, and even insect predator species tested don't seem to suffer any ill effects from eating poisoned prey, but parasitoids do. These are species that parasitise pests, and though they do not suffer themselves from the toxins, weaker hosts mean fewer parasitoids. As they can be important in controlling pest populations this is something to bear in mind.
A major concern in the early days was a possible effect on honey bees, feeding on the pollen and nectar of transgenic plants. This of course would impact on growers of other crops, not getting any benefit from the transgenics themselves. Fortunately as yet there is no evidence of toxicity on honey bees, or on the butterflies tested, which might be expected as they are more related to the pests targeted.

Of course, as ever in life, there are unintended consequences. For one thing, insects are quite capable of evolving resistance to Bt proteins. It is not common, and there are ways to limit it, but Bt toxins are not foolproof. And secondly, if Bt is killing your most annoying pest you can apply less pesticide, which means other pests can fill the gap. Here the specificity of Bt is actually a handicap. Species as diverse as aphids, leaf hoppers, spider mites and thrips have all emerged to threaten the new crops, which can lead to increased insecticide use, which defeats the whole point of Bt crops. Fortunately, generally they are less severe than the original enemies, and higher levels of insect predators, not affected by Bt, help keep them under control.

*Karpechenko GD. Polyploid hybrids of Raphanus sativus L. X Brassica oleracea. L Bull Appl Bot. 1927;17:305–410.
**Transgenic Crops: An Option for Future Agriculture. Wei-Cai Yang and Jianmin Wan. Journal of Integrative Plant Biology. July 2011. Volume 53, Issue 7. Pages 510–595


Karpechenko GD (1927). Polyploid hybrids of Raphanus sativus L. X Brassica oleracea L Bull Appl Bot, 17, 305-410

Yang, W., & Wan, J. (2011). Transgenic Crops: An Option for Future Agriculture Journal of Integrative Plant Biology, 53 (7), 510-511 DOI: 10.1111/j.1744-7909.2011.01064.x