Are Asphalt Millings Toxic?

Asphalt millings aren't harmless dirt, but the research that exists generally rates them as a low-risk material in ordinary use. Millings contain the same compounds as the pavement they came from, mainly polycyclic aromatic hydrocarbons, or PAHs, from the asphalt binder, plus trace metals from traffic and from the stone itself. Studies of recycled asphalt have generally found that these substances leach into water at low levels under normal conditions. The main cautions are dust and loose particles, runoff toward wells and surface water, strongly acidic ground, and material from unknown or contaminated sites. Good placement and good compaction reduce those risks further.

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Are Asphalt Millings Toxic? What's in Them

Millings are ground-up asphalt pavement, which is mostly crushed stone and sand held together by a few percent of asphalt binder. Our explainer on what asphalt millings are covers how they're made. The main substances people ask about:

• PAHs. A large group of compounds found in asphalt, smoke, soot, and many petroleum products. The EPA classifies several PAHs as probable human carcinogens. Whether they cause harm depends on how much reaches a person and how. PAHs tend to cling to particles rather than dissolve in water.
• Metals. Pavement picks up traces of metals from tire and brake wear and from vehicle fluids, and the stone contains natural minerals too.
• Site-specific contaminants. Pavement removed from a particular site, such as an old industrial lot, could carry spills or residues from that site.

What Research Has Found

• New Jersey's environmental agency. A review by the NJDEP Science Advisory Board concluded that the potential for recycled asphalt pavement to leach PAHs and metals is relatively low, partly because PAHs don't dissolve easily and because weathering has usually removed the more leachable compounds from old pavement. It also noted that grinding creates finer particles, which can work against that, and that loose, unbound millings can produce dust. The agency's own guidance states a policy of encouraging the reuse of recycled asphalt.
• A New Jersey Department of Transportation research project tested recycled asphalt from three plants. The researchers recommended that unbound recycled asphalt could be used in most settings, including parking lots, farm roads, and pathways, but not in highly acidic environments such as some mine sites or landfills. In weak-acid lab tests meant to mimic landfill conditions, some samples released lead above the federal drinking-water benchmark, which is why they advised testing before use in acidic settings.
• A Minnesota Department of Transportation study from the 1990s measured runoff from a stockpile of bituminous millings and found PAH concentrations near or below detection limits. The study's main concerns were sediment and pH in runoff, and it recommended ordinary construction-style runoff controls around stockpiles.

These findings don't mean millings are risk-free. They suggest that ordinary use, especially compacted millings on well-drained ground away from water supplies, is unlikely to cause significant contamination.

Where the Real Cautions Are

Dust and Loose Particles

The New Jersey review treated dust and fine particles as the main exposure route to think about for loose millings, especially on unpaved surfaces with more traffic, while noting that these scenarios haven't been studied much. It suggested that binding or sealing the surface is worth considering where children play often. At home, that means compacting well, wetting the material lightly while you spread it, wearing a dust mask during handling, and not letting kids play in loose piles.

Drinking Water Wells

If you have a private well, keep millings well back from the wellhead and don't direct runoff toward it. Shallow wells, very permeable soil, and fractured rock all raise the stakes.

Streams, Ponds, and Wetlands

Loose millings can wash into ditches and waterways as sediment. Keep them away from the water's edge and give runoff a vegetated strip to pass through first.

Acidic Ground

Research points to much higher metal leaching when water is strongly acidic. Ordinary rain and most soils aren't that acidic, but it's a reason not to use millings on land affected by mining runoff or other acidic sources.

Unknown Sources

Millings from a normal road resurfacing job are different from material scraped from an old industrial site. Buy from established suppliers who can tell you where the material came from.

Coal-Tar Sealer Is a Separate Issue

Much of the concern about PAHs on driveways traces to coal-tar-based sealcoat, not to asphalt itself. According to the U.S. Geological Survey, coal-tar-based sealcoat typically contains roughly 1,000 times more PAHs than asphalt-based sealcoat, and pavement dust from coal-tar-sealed lots can carry far higher PAH levels than dust from unsealed pavement. If you decide to seal a millings surface or a paved driveway, an asphalt-based product avoids that particular problem. Some states and cities restrict or ban coal-tar sealers.

How to Reduce the Risk

1. Check local rules. States handle recycled asphalt differently, so ask your state environmental agency or local officials before using millings near water.
2. Keep a buffer from wells and waterways. Ask your local health or environmental office what distance they recommend.
3. Compact the millings. A tight surface sheds less dust and fewer loose particles.
4. Control drainage. Direct runoff to vegetated areas that can filter it, not into streams or storm drains. Our post on driveway runoff and drainage has practical ideas.
5. Don't burn or heat them. Heating asphalt releases fumes.
6. Skip diesel and waste oil. They're sometimes sprayed on millings as a binder, and they add pollution of their own.
7. Wash up. Wash hands after handling millings, and keep kids from playing in piles.

Compacted vs Loose Millings

How millings are installed matters as much as what's in them. A thick, well-compacted layer over a stable base sheds fewer loose particles, makes less dust, and holds up better in heavy rain. A thin, loose layer on bare ground wears faster and can wash onto lawns and into ditches. The same steps that make a millings driveway last longer also keep exposure low: a good base, enough depth, thorough compaction, and water directed off to the side.

Should You Test Your Well?

If you have a private well near a millings driveway and want peace of mind, periodic water testing is reasonable. Your local health department can suggest a lab and a test panel.

Bottom Line: Are Asphalt Millings Toxic?

Millings contain PAHs and trace metals, but the studies that exist generally find low leaching under ordinary conditions. The practical cautions are dust, runoff toward wells and water, acidic ground, and material of unknown origin. Compact them well, keep them away from wells and waterways, avoid coal-tar sealers, buy from reputable suppliers, and check local rules before you order.