This is no polemic for or against the car. Nor about petrolheads. Nor environmentalists. This is about the chemicals that are to be found inside cars, and the importance of good ventilation, to avoid occupants gently steeping in a cocktail not of their own making. The SIN is the ‘Substitute It Now!’¹ list developed by the International Chemical Secretariat, a largely government funded organisation in Sweden² – a list of over one thousand chemicals with harmful health or environmental effects, which they suggest should be removed from consumer products. But do we find any of these in modern cars?
This is not a new problem, but one the significance of which we are only beginning to understand. As discussed in previous newsletters, the emissions from vehicle exhausts have improved significantly over the last ten years. Initially it was mainly seen as particulate reduction, as the widespread cheating on nitrogen oxide (NOx) emissions – of which Dieselgate was emblematic – was only resolved from around 2018 when official laboratory results were validated with an on-road test called Real Driving Emissions. The remaining pollutants of most concern in the exhaust are carbon dioxide (CO2) and a range of volatile and semi-volatile organic compounds (VOCs and SVOCs).
At the same time, the construction of vehicles has become more sophisticated. While generally to the benefit of consumers in terms of utility and design, the potential impact on the health and comfort of vehicle occupants has not been fully considered. The increased use of glues in vehicle manufacture and superior construction methods creating an almost perfectly sealed cabin come with downsides. Significant hurdles in understanding the consequences have been difficulties in measuring the compounds of interest, and the lack of standards to measure vehicle interior air quality (VIAQ). This is beginning to change, led by South Korea and Japan, which collectively regulate nine different VOCs in the cabin.
Emissions Analytics has been working on this from both angles. It has been an active participant in a standardisation workshop under the Comité Européen de Normalisation (CEN)³, aiming at measuring the air quality inside light-duty vehicles in terms of particle ingress from outside and CO2 build-up. In parallel, it has been developing methods for measuring the presence of VOCs and SVOCs in cabin air, and how they might be emitted from the interior materials. The two areas are linked because the worse the ventilation and filtration system, the greater the likelihood of the accumulation of noxious organic compounds. Multiply that by the length of time typically spent in vehicles and the human exposures could be greater than to ambient air pollution.
To get a measure of the problem, if we chemically analyse the interiors of cars, do we find any of the compounds on the SIN List? We took a small sample of recent model year vehicles in Europe and analysed a range of interior materials, including dashboard plastic, seat material and carpets. Each sample was analysed using two-dimensional gas chromatography coupled with time-of-flight mass spectrometry, with sample introduction via microchamber – a system provided by Markes International and SepSolve Analytical.
One vehicle in particular gave interesting results: a top-selling, European-made small car from 2020. We tested the carpet in the boot and footwell, dashboard plastic and the seat covering material. Across these sample locations, 16 of the SIN List compounds were identified, as shown in the table below. The metric is the percentage of the peak area – in other words, the area under the compound’s peak on the chromatogram expressed as a proportion of the total peak area of all organic compounds identified. It is a reasonable approximation of the relative abundance of the SIN List compounds in each sample.
While just 1.23% of the organic compounds found in the dashboard plastic were on the SIN List, this exceeded 11% for the footwell carpet. Furthermore, its most prominent compound was diethyl phthalate. Generally, phthalates are a synthetic substance commonly used to make plastics more flexible. A growing body of research suggests that many of the compounds in this group have undesirable health effects, including reducing fertility. As a result, regulations are beginning to restrict their use, for example, under REACH in the EU, the concentration of four target phthalates cannot together exceed 0.1% by weight in consumer goods. Diethyl phthalate is not one of these four, and the research on its health effects is currently limited, but its high concentration in the footwell carpet should warrant additional focus.
Beyond phthalates, a way to assess the health dangers of the other compounds on the SIN List is to look at the ‘hazard statements’ produced under the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), an international consensus system developed by the United Nations for classifying and labelling hazardous chemicals. Hazard statements provide standardised wording as to the nature and degree of the threats. For example, ‘H350’ indicates a chemical that may cause cancer. An individual compound can have multiple hazard designations.
If each of the compounds identified in the vehicle are scored according to the number of hazard designations, and these are then grouped generically, we obtain the totals shown in the table below. Included in this assessment are those assessed as ‘persistent bioaccumulative toxic’ compounds, which is a separate hazard category. These compounds do not break down easily in the environment or living creatures and so progressively build up.
At a high level, it can be seen the most prevalent health effects are irritation or damage to the skin, eyes, throat and lungs. The boot carpet has the largest number of designations, and contains a relatively high level of octamethylcyclotetrasiloxane, which is suspected of damaging fertility. The harms are not just to humans, for example naphthalene is also highly toxic to fish and other aquatic life.
The number and extent of these compounds present in common materials in vehicle interiors points to action needed by manufacturers to address the potential toxicity to occupants. Beyond the SIN List, we have also identified a ‘PFAS’ in the same vehicle’s seat material.
Per- and polyfluoroalkyl substances (PFASs) are manmade organofluorine compounds, first created in the mid twentieth century and which became popular for their water repellent, stain resistant and non-stick features. The problem is that they do not break down readily in the environment, hence being described as “forever chemicals”, or persistent organic pollutants. This bioaccumulation means that it is believed that they are gradually building up inside most living creates as well as the wider environment.
The health effects of PFASs were brought to wide public attention for the first time in the 2019 film Dark Waters, where compounds based on perfluorooctanoic acid (PFOA), a subset of PFASs, were released from an industrial source in West Virginia, USA. The evidence as to the environmental effects has continued to accumulate. An article in December 2021 in Environmental Science & Technology shows that these persistent compounds do not simply get washed into the sea and diluted into insignificance. Rather, waves crashing on the shore recirculate the chemicals into the air and onto land⁴. This increases the human exposure and associated health effects, which include cancer, thyroid conditions and colitis.
The compound identified was 1H‚1H‚2H‚2H-perfluorooctan-1-ol – chemical formula C8H5F13O – a chain of eight carbon atoms with 13 fluorine atoms attached. The chromatogram from the seat sample below shows this compound. Of the total peak area of organic compounds, it accounted for 0.61%. The hazard classification says that it may cause damage to organs through prolonged or repeated exposure.
It should be added that it is not being claimed that exposure to this seat covering will have direct health effects. Nevertheless, by the persistent nature of these compounds, they are very likely eventually to end up in the environment, be recirculated and potentially inhaled or ingested by humans or animals. PFASs from a car seat add to this gradual and irreversible accumulation.
In the longer-term, the objective should be to engineer these compounds out of vehicles, where there are viable alternative components. Growing regulations around materials, from REACH in Europe and from the Environmental Protection Agency in the US, together with emerging regulation of vehicle interior air quality led by Korea, Japan, Russia and China, will force the pace. But how should vehicle owners mitigate the effects in the shorter run?
The concentration of VOCs in cabin air generally increases as the vehicle heats up. A car parked in the sun will see more chemicals released from the interior materials into the air, recondensing once the vehicle cools back down. To this chemical soup is added particles and NOx that enter the car through the ventilation system as the vehicle moves, plus the CO2 exhaled by the occupants.
Although not the most glamorous part of a car, a good heating, ventilation and air conditioning system is the best way to limit exposure. The benefits of maintaining fresh air in confined spaces has been brought to prominence through the Covid pandemic. The ideal is to keep the ventilation on fresh air mode – rather than recirculation – but this relies upon excellent filtration to minimise the particle and NOx ingress. In balancing this trade-off, the best vehicles are many times better than the worst, as described in previous newsletters. Therefore, rating vehicles in a fair and comparable way is urgently needed.
Fortunately, both the car and filtration industries have been actively involved in standardisation of test methods, including through CEN Workshop 103, initiated by the AIR Alliance⁵, which is due to publish its work soon. Together with the work on vehicle interior air quality through UNECE, it is quite possible to see how these new tools in measurement and evaluation can bring about healthier, and perhaps SIN-free, cars for both the occupants and the wider world.