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In March 2019, the Health Council published a health-based recommended exposure limit for diesel engine emissions, as a basis for establishing a legal limit value. Recently the German government has also made a proposal for a limit value for diesel engine emissions (DME). The evaluation of the health risks or DME leads to various discussions, such as the suitability of the available epidemiological studies and animal testing studies for the derivation of a limit value, the practical significance of very low limit values ​​and the question of whether a single limit value is applicable to both old and old. newer types or diesel engines.These themes were discussed at an afternoon symposium organized by the Labor Toxicology section of the Dutch Society for Toxicology and the Health and Chemistry Contact Group.

Dick Heederik or the Institute of Risk Assessment Sciences (IRAS) or Utrecht University kicked off with an overview of what is known about the health effects of DME. It is estimated that around 3 million workers in the EU are exposed to DME. The wide application of diesel engines and the size of the exposed population implies that an intention to set a - possibly low - limit value quickly leads to discussions. All the more so since emissions from diesel engines have already been greatly reduced as a result of European regulations. The most recent European emission limit for Elemental Carbon is no less than 99% lower than in 2000, while the reduction for PAHs is around 80%. This complicates the interpretation of epidemiological studies,
In 2012, the IARC concluded that DME is a group 1 human carcinogen. There was sufficient evidence for this for lung cancer; limited evidence for bladder cancer. According to IARC, there is a genotoxic mechanism, but opinions were divided within SCOEL. It was clear, however, that on the basis of the available epidemiological data no safe threshold value could be established. A meta-analysis of epidemiological studies, from 1999, shows that in itself much more research is available than what was included in the recent Health Council recommendation. Based on 30 studies, it can be concluded that there is a consistent relationship between the level of exposure to DME and lung cancer.

Jolanda Rijnkels of the Health Council discussed the background to the health-based recommended exposure value for DME that was published by the Health Council on 13 March 2019.
The advice only applies to emissions from engines powered by petroleum-based diesel fuel. No epidemiological studies are yet available for the new types of engines.
For the derivation of a recommended exposure limit, the focus has been placed on carcinogenicity, because it concerns a effect a safe threshold value cannot be established.
DME is carcinogenic, through a stochastic genotoxic mechanism, so through damage to the DNA. A health-based recommended exposure limit is therefore risk-based.In the Netherlands, the government deduces two risk levels: the target risk level, based on an additional risk or 4 cancer cases out of every 100,000 deaths in the general population and the prohibition risk level, based on an additional risk or 4 cancer cases out or every 1,000. For work, we assume a 40-year working life. The Health Council prefers to use epidemiological studies to derive these values. In the end, only three epidemiological studies remained. Never before have there been extensive discussions about the quality of the available data.
Elemental carbon (EC) has been chosen as the measure for exposure to DME in the respirable part of the particle emissions. Elemental carbon itself is not carcinogenic, but it is a good marker for exposure.Ultimately, a health-based recommended exposure limit of 1 µg / m3 EC (prohibition risk level) and 0.01 µg / m3 EC (target risk level) was reached.
The Health Council's advice can be found on the website (click here to follow the link) , as well as the study in collaboration with the Nordic Expert Group, all comments received, and the Health Council's response.
The presentation of Matthias Möhner from Berlin concerned a risk assessment or DME in Germany. With his presentation the gift of a critical look at the epidemiology and the rationale behind the recommended German OEL. The OEL for Germany was 50 µg EC / m3 in May 2017. This is based on older diesel engine emissions. Toxicological deduction has been used.The dominant mechanism of action has been discussed. The carcinogenic effect is primarily due to the ultra-fine particles or benzo (a) pyrene, BaP. The share of PAH in DME has been quantitatively estimated on the basis of BaP. Details on www.baua.de, search term AGS diesel.
Then the question was raised whether the results of the epidemiological studies require a further reduction of the limit value, through his critical detailed consideration of the key studies.
The final conclusions of Möhner were:
The risk of lung cancer due to DME / EC appears to have been overestimated in the two key studies ;
A re-analysis of the DEMS is recommended.The two studies of underground miners give comparable results (the SMR for lung cancer in the German study is 0.73);
The SMR for lung cancer in the truck driver cohort is 1.04 (Laden, 2007), which is low against the background of smoking habits among truck drivers.

The last presentation was by Mariska Dry and Tamara Onos, both occupational hygienists at Auxilium, who were asked to check the diesel emission exposure of employees involved in the construction of a tunnel; to advise on this in the past (2016), the present (2019) and in the future.
NO, NO2 and EC were tasks as exposure measures. In 2016 the TGG were 8 hours NO (public OEL), NO2 (public OEL), and EC (private OEL), 0.2 ppm (0.25 mg / m3); 0.21 ppm (0.40 mg / m3); 16 µg / m3, (recommended exposure limit 10 µg / m3). At the end of the project in 2019, the TGG were increased by 8 hours of NO2 (public OEL) and EC (private OEL) to 0.5 ppm (0.96 mg / m3), respectively. reduced to 1.03 µg / m3, (GR).
The conclusions and advice in 2016 were that DME was a problem and that measures had to be taken; that NO exceeded the OEL and that NO had to be monitored to reduce the measurements.
The conclusions and advice in 2019 were partly the same: that DME was a problem and that measures had to be taken; but that EC exceeded the OEL and that EC had to be monitored to reduce the measurements.

Panel
discussion The discussion first of all addressed the question of whether epidemiological studies in this case were the most suitable for deriving a limit value.
Subsequently, the practical consequences that a limit value of 1 µg / m3 would have been discussed. First of all, it will be a challenge to get the measurement methods sufficiently sensitive. The background concentrations in the Netherlands are also generally higher, or at least in the same order of magnitude. On the other hand, the background concentrations in the Netherlands are therefore roughly the highest in Europe, and that they demonstrably lead to early death. In the current situation, it could be an option, for example, to select "the background + 1 µg / m3" as the limit value. It will be up to the SER to advise on this.

Herman Bartstra
Jeroen Terwoert

N / A, Work Toxicology Section.