Deep Dive

Energy Transition and Pollution – Manufacturing Impacts

When the Intergovernmental Panel on Climate Change (IPCC) made its assessment of sector contribution to climate change, transportation weighed in at 11%, much of it from cars and light trucks. The car industry, through a combination of voluntary action and regulatory mandates, has moved to reduce emissions from its products. This is more than counterbalanced by the continued increase in private car ownership in emerging markets. One need only look at the number of cars per thousand inhabitants in India (70 in 2016) versus the US (816 in 2018) to get a sense of potential increases in transportation related GHG emissions as middle class ranks swell.

The switch to battery-powered propulsion is the choice of countries (Norway, Belgium, India, the Netherlands, Canada, Sweden, Denmark, the United Kingdom, France, Spain among others) and of the state of California, which, by itself, is the tenth largest car market in the world. Car companies have taken note, with General Motors being the latest firm setting a target date for phasing out the production of combustion engines.

How does the switch to electric propulsion change the environmental impact of car making? We now have enough data from the United States to get a sense of the shifting challenges in reducing harm unrelated to climate change as the car industry goes through the energy transition.

The short answer is that some things won’t change at all or very little. Others will change quite substantially. The emission of volatile organic compounds will not be affected by the shift to electric cars, but metal contamination could spike. How a company handles its waste will remain the critical factor in minimizing damage. Like in every industry, there are differences between companies.

In compiling the analysis, we only used data reported by the companies under the industry code for Automobile Manufacturing. Car companies will report data under other headings for car assembly and car part plants depending on the type of activity that involves the handling of regulated toxic chemicals.

Paints and solvents

Of the 630 or so toxic chemicals on which the EPA has reported in the last 30 years, solvents used in paints and resins are the car industry’s biggest contributor to pollution. There is a strong correlation between the volume of solvents reported as waste, and the number of cars sold in the US. More cars need more paint, which leads to more waste.

Car sales vs waste production of solvents in car manufacturing

Some companies are better at capturing the waste than others. The rate of release to waste production varies widely and also shows that some companies have made an effort to reduce their impact, while others are less diligent.

Daimler Ford GM Honda Tesla Toyota
2014 55% 27% 41% 32% 20% 14%
2015 58% 25% 36% 20% 44% 12%
2016 53% 25% 36% 20% 71% 13%
2017 81% 25% 39% 4% 4% 13%
2018 83% 27% 42% 4% 18% 21%
2019 69% 25% 41% 29% 11% 15%

The table above only gives a partial understanding of the total environmental impact of solvent use in making cars. The industry uses different types of solvents, which are not equal in toxicity. The five main solvents are 1,2,4 Trimethylbenzene, glycol esters, n-butyl alcohol, toluene and mixed xylenes. Judging by the waste production, German manufacturers favor glycol esters – at BMW they make up 90% of the solvents used, and at Daimler it’s 63%. The Americans and Japanese favor 1,2,4 Trimethylbenzene, which makes up about a third of the solvents at GM and nearly half at Toyota. Tesla also heavily favors 1,2,4 Trimethylbenzene.

The EPA rates chemicals by toxicity, setting the toxic weight of n-hexane, a common solvent, at 1 and then assigning each chemical a score relative to n-hexane. The toxic weight of 1,2,4 Trimethylbenzene is 20, glycol ethers are at 0.107.

A better way to look at this data is to incorporate the toxicity by multiplying the waste volume and the release volume with the toxic weight and then calculating the ratio of release to waste. Looked at it this way, the date shows that some companies – Ford, GM and Toyota in particular – while using more toxic chemicals also make more of an effort to capture rather than release those chemicals.

Daimler Ford GM Honda Tesla Toyota


6% 21% 13% 21%




7% 20% 18% 3%




8% 14% 15% 41%




8% 16% 6% 1%




6% 16% 13% 64%




7% 12% 55% 1%


The data also shows that Tesla was still figuring out its production process. Waste production of toxic chemicals at the company is changing, as is the capture rate and the toxicity. Presumably this will stabilize as the production process becomes more standardized after years of rapid expansion.

Energy Transition – The Metals

The volatility in the solvents data is not the only reason Tesla stands out. The main regulated toxics the company has generated recently as waste are not solvents, they are metals, specifically manganese and zinc.

Only two other companies used as much metal in their car manufacturing, Honda and Toyota. Both Japanese companies have invested more in hybrids than others, so they need batteries.

Both Honda and Tesla seem to have moved away from manganese and toward zinc, joining Toyota in its reliance on the metal. Both companies had substantial waste production of manganese in 2017, which was severely dialed back the following year despite higher production numbers.

Manganese waste was the biggest item by wight in the regulated toxic chemicals reported by Tesla in 2018, but the company reported none in 2019. Honda also reported no manganese waste or release in 2019 after a big 2018 volume.

Metals waste production and release in 2018
Metals waste production and release in 2019

Imports of zinc, other than zinc ore, into the US peaked in 2017 at about 132,000 tons before surging to 234,000 tons in 2020 as Tesla ramped up production of its Model 3 sedan. Manganese dropped back in 2020 to 27,100 tons from 33,400 tons in the previous two years.

Metal waste production and car sales are not well correlated because companies that are not building plug-ins or hybrids don’t use these materials. The waste is heavily concentrated at Honda, Toyota and Tesla. All three companies are clearly diligent and successful at not letting these chemicals out into the environment. Zinc and zinc compounds have a toxic weight of 40, while manganese and its compounds is 103 times as toxic as n-hexane.

Ratio of release to waste production relative to the industry average by company

The metals are not cheap – zinc is around $2,800 per ton, manganese not much cheaper – so the companies have a strong incentive to recycle and reuse rather than dump metal in a landfill. Still, with that kind of toxicity, even small releases can cause big problems. As more companies make the energy transition, metal pollution will require special attention.