A study reveals that brake dust poses a greater health risk than diesel exhaust.

      Peter Nelson

      Over the past few years, governments globally have made considerable efforts to cut down on tailpipe emissions. European Union lawmakers aim to prohibit the sale of new piston-engine vehicles by 2035, and modifiers who circumvent emissions control measures are facing fines in the millions. Nevertheless, a recent study reveals that brake pad dust poses a greater health risk than exhaust emissions.

      Published in the UK in February 2025, the study examines the effects of non-exhaust emissions, such as road, tire, and brake pad particles, on lung health. It highlights that brake dust, the dark residue accumulating on wheels as brake pads wear, accounts for up to 55% of non-exhaust emissions by mass. The issue is that this dust does not just settle on wheels; it pollutes water and becomes airborne. The chemical makeup of the dust varies depending on the brake pad type, but typically contains iron, copper, and zinc, along with different abrasives, lubricants, and reinforcing fibers. The study points out that there are currently no regulations governing the materials used in brake pads.

      Copper is particularly concerning; ironically, it was introduced in brake pads as a replacement for asbestos, which is a known carcinogen among other health risks. Now, copper is often found in non-asbestos organic (NAO) brake pads, the most common type in the U.S., and poses health risks similar to those of asbestos. The study indicates that the fine particles released from these pads during wear are associated with diseases like pulmonary fibrosis, cancer, and pulmonary adenocarcinoma. According to the authors, the fine particles produced by NAO brake pads may be more detrimental to health than those from a diesel engine.

      It is important to note that "diesel engine" is a rather ambiguous term, and we are left wondering which specific model serves as a benchmark. Are we referring to a 1970s Mercedes-Benz 300D, a 1990s Freightliner FLD120, or a Euro 6-compliant BMW 320d? The variation in exhaust emissions can be substantial.

      Mandating electric vehicles, as the European Union intends to do, will not mitigate pollution from brake pads; it may even exacerbate the issue. "This trend is expected to elevate over time, as there is a transition to heavier battery-electric vehicles which produce greater amounts of these friction-induced, non-exhaust emissions," states the study. While many EVs utilize regenerative braking and rely less on traditional hydraulic brakes, the brake pads still make contact with the rotors. Heavier vehicles also experience more frequent tire changes.

      In the EU, the Euro 7 emissions standards set to be implemented in November 2026 will restrict the fine particles emitted by brake pads. While the regulations establish different thresholds for various powertrains, they do not specifically address copper. The authors of the study suggest that legislative changes to decrease copper levels in brake pads would benefit public health.

      California and Washington, among other states, are already tackling the issue of copper content in brake pads. The Brake Pad Law, finalized in 2017, limited copper content to a maximum of 5% in 2021 and will further reduce it to 0.5% by 2025 for all new vehicles sold in California. Washington's Better Brakes Law implemented the same restrictions and noted that around 66 metric tons of copper from brake pads enter the Puget Sound marine environment each year. Several suppliers, including Akebono from Tokyo, already offer a selection of low-copper and copper-free brake pads.

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