Asphalt shingle roof runoff is not clean water. Rain leaving a typical shingle roof carries dissolved zinc at roughly 14 to 17 times a common water quality reference threshold, plus lead and copper above guideline levels, alongside eroded mineral granules, bitumen particles, and polymer fibers. Because asphalt shingles cover more than 80% of United States homes and the country installs over 12.5 billion square feet of them each year (Atlas Roofing / ARMA industry figures, 2024), that runoff is one of the most widespread and least discussed diffuse pollution sources in the built environment. This report synthesizes federal and peer reviewed data into a single picture of what leaves a shingle roof and how much of it there is.
What actually washes off an asphalt shingle roof?
Four distinct pollutant streams leave an asphalt shingle roof during rain: eroded mineral granules and fine sediment, dissolved metals (zinc, copper, and lead), polycyclic aromatic hydrocarbons (PAHs) leached from the bitumen, and polymer microparticles from the shingle surface and its modifiers. Each has a different source inside the shingle, and each behaves differently once it reaches a gutter, a storm drain, and eventually a stream.
The shingle is a layered product: a fiberglass mat, a bitumen (asphalt) coating, and a surface layer of ceramic coated mineral granules that makes up about one third of the shingle’s weight (industry composition data, 2024). Every layer contributes something to runoff. The granules shed as sediment, the bitumen leaches organic compounds, and the biocidal metals dosed into modern granules dissolve out over the roof’s life.
How polluted is asphalt shingle roof runoff?
Runoff from asphalt shingle roofs exceeds standard water quality reference thresholds for zinc, lead, and copper, in several cases by more than an order of magnitude. The clearest synthesis comes from Degenhart and Helmreich (2022, Frontiers in Environmental Chemistry), which compiled measured metal concentrations in roof runoff against Germany’s GFS reference values (insignificance thresholds for groundwater).
| Pollutant | Asphalt shingle runoff (reported median) | Reference threshold (German GFS) | Approximate exceedance |
|---|---|---|---|
| Zinc | 859 to 1,000 µg/L | 60 µg/L | ~14 to 17x |
| Lead | 25 to 43 µg/L | 1.2 µg/L | ~21 to 36x |
| Copper | 2.1 to 30 µg/L | 5.4 µg/L | up to ~5.6x |
Source: Degenhart and Helmreich (2022). Values are medians compiled across field studies and vary with roof age, rainfall pH, dry period length, and whether the granules are algae resistant. The consistent finding is that zinc and lead in shingle runoff sit well above the reference levels used to judge whether water is meaningfully contaminated.
Where do the metals in shingle runoff come from?
The metals come from three places: biocidal granules dosed with copper or zinc to resist algae, trace lead and zinc in the shingle and its atmospheric dust load, and legacy contamination near roads. A United States Geological Survey study by Van Metre and Mahler (2003, Chemosphere) sampled particles washed from asphalt shingle and galvanized roofs in Austin, Texas, and found zinc, lead, pyrene, and chrysene concentrations that exceeded sediment quality guidelines for probable toxicity to bottom dwelling aquatic life. That study identified asphalt shingles specifically as a lead source and estimated rooftop washoff contributed roughly 55% of the zinc load in the particle fraction studied.
Modern algae resistant shingles add copper on purpose. A four and a half year weathering study of 14 roofing materials (Winston and colleagues, 2019, Environmental Pollution) found that algae resistant asphalt shingles with copper containing granules leached copper at a steady rate with no measurable decline across the study, because the granules are engineered to dissolve slowly and keep releasing biocide. In that basin (Puget Sound, where asphalt shingle made up 71% of roof area), copper granule shingles were the second largest roofing copper source after chromated copper arsenate treated wood shakes.
This is the same chemistry homeowners buy on purpose to fight roof algae. The copper and zinc that kill Gloeocapsa magma on the shingle do not stay on the roof; they leave in the first flush of the next storm. Our guide to roof moss and algae killers covers the zinc and copper products involved, which are the same metals that show up downstream.
Do asphalt shingles leach PAHs from the bitumen?
Yes, but at lower and more variable concentrations than the metals. Bitumen is a petroleum residue, so it carries polycyclic aromatic hydrocarbons that can leach into water on contact. Brandt and de Groot (2001, Water Research) measured aqueous leaching from bitumen and asphalt and found PAHs with more than two rings at 4 to 50 ng/L, with naphthalene, a two ring PAH, reaching up to 4.5 µg/L in leachate. The USGS Austin study separately flagged pyrene and chrysene, both PAHs, in rooftop particle samples above sediment toxicity guidelines.
PAH leaching depends heavily on the bitumen’s oxidation state and age. Weathered, oxidized roofing bitumen tends to release less freely dissolved PAH than fresh material, and some standardized leaching tests of roofing bitumen membranes detect no regulated PAHs at all. The defensible reading is that shingle bitumen is a real but secondary PAH source in roof runoff, smaller in exceedance terms than the zinc and lead signal.
Are asphalt shingles a microplastics source in stormwater?
Asphalt shingles are a plausible but under quantified microplastics source, because most modern shingles are polymer modified. Manufacturers add styrene butadiene styrene (SBS) or atactic polypropylene (APP) to the bitumen for flexibility, and these polymers can erode into runoff as the surface weathers and granules detach. Stormwater microplastics research consistently finds that fibers dominate urban runoff, with one review reporting roughly 66% of stormwater microparticles were fibers.
The direct evidence is still thin. Most quantified roadway and stormwater microplastic work isolates tire wear and pavement wear (for example, Jarlskog and colleagues, 2024, Journal of Hazardous Materials, on pavement generated microplastics), not shingle surfaces specifically. No published study yet gives a clean national mass estimate for shingle derived microplastics. That gap is stated plainly here rather than filled with a fabricated number.
How much sediment do America’s shingle roofs shed?
America applies roughly 6 million tons of mineral granules to new and replacement asphalt roofs each year, and an order of magnitude estimate puts the granule and bitumen sediment mobilized toward storm drainage at somewhere around 100,000 to 300,000 tons annually. These figures are an original synthesis built from industry production data and shingle composition, and they are presented as bounded estimates, not measured totals.
| Mass stream | Estimated annual mass (US) | Basis |
|---|---|---|
| Mineral granules applied to new and replacement roofs | ~6 million tons | 12.5 billion sq ft/yr (about 125 million squares) at roughly 100 lb of granules per square (one third of shingle weight) |
| Granules landfilled inside tear-off shingles | ~3.7 to 4.3 million tons | 11 to 13 million tons of shingle tear-off per year (EPA) at about one third granule fraction |
| Granule and bitumen sediment mobilized toward storm drainage | ~100,000 to 300,000 tons (order of magnitude) | Assumed 2% to 5% lifetime washoff of in-service granule throughput |
The headline number to hold onto is the applied mass: at 12.5 billion square feet of shingle produced yearly (Atlas Roofing / ARMA, 2024), with granules at about one third of shingle weight, roofs receive on the order of 6 million tons of crushed rock surfacing every year. Most of that mass stays embedded until tear-off and then goes to landfill, since less than 10% of the 11 to 13 million tons of annual shingle waste is recycled (EPA). The fraction that erodes into gutters and storm drains during the roof’s service life is the part that becomes a chronic sediment and metals load in urban waterways.
Methodology and limitations
The concentration data here are measured values from peer reviewed studies, cited inline to source and year. The national mass estimates are original calculations combining three independent inputs: industry shingle production volume, the widely reported one third granule mass fraction, and EPA shingle waste tonnage. Each input is sourced; the arithmetic combining them is ours.
Three limitations bound what these numbers can show. First, roof runoff concentrations are highly site specific: rainfall pH, the length of the preceding dry spell, roof age, and slope all change the result, so the ranges above should be read as typical bands, not fixed values. Second, the German GFS thresholds are a European reference standard used for comparison; United States water quality criteria differ by state and by receiving water, so the exceedance multiples indicate relative severity, not a specific regulatory violation. Third, the 100,000 to 300,000 ton sediment mobilization figure rests on an assumed 2% to 5% lifetime washoff fraction, which is not directly measured at national scale; it is offered as an order of magnitude bound, and the applied and landfilled masses are the firmer figures. No individual field measurement in this report was invented, and where a national number is not findable, the gap is stated rather than filled.
How can roof runoff pollution be reduced?
Runoff pollution from shingle roofs can be reduced at the roof, at the downspout, and at the ground, and the mitigation options carry very different price and performance profiles. None of them make shingle runoff drinkable without treatment, so rainwater harvested from an asphalt roof should be used for irrigation or non potable uses unless it is filtered and tested.
- Choose lower leaching surfaces where practical. Unpainted or inert roof surfaces leach fewer metals than copper granule algae resistant shingles or bare galvanized metal. Weigh this against the algae resistance you give up.
- Intercept the first flush. A first flush diverter sends the initial, most contaminated runoff of each storm away from any collection system, since metals and sediment peak early.
- Add a green roof or bioretention. Vegetated assemblies and rain gardens capture sediment and adsorb metals before runoff reaches storm drains. See our green roof cost, types, and load guide for the structural and budget tradeoffs.
- Be cautious with rain barrels. A gutter rain barrel is fine for garden water, but asphalt roof runoff is not a safe drinking source untreated given the zinc, lead, and PAH data above.
For the broader waste and carbon picture behind these roofs, see our shingle waste and recycling report and the 2026 roofing material carbon report, which together frame where those 11 to 13 million tons of torn-off shingles actually go.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.
Frequently asked questions
Is rainwater from an asphalt shingle roof safe to drink?
Not without treatment. Runoff from asphalt shingle roofs commonly carries zinc at roughly 14 to 17 times a standard water quality reference threshold, plus lead and copper above guideline levels and trace PAHs from the bitumen (Degenhart and Helmreich, 2022). Harvested shingle roof water is suitable for irrigation, but it should be filtered and tested before any potable use.
Do asphalt shingles pollute stormwater?
Yes. Asphalt shingle roofs shed mineral granules, dissolved zinc, copper, and lead, PAHs from the bitumen, and polymer particles into runoff. A USGS study (Van Metre and Mahler, 2003) found rooftop washoff particles exceeded sediment quality guidelines for zinc, lead, pyrene, and chrysene, and estimated roof washoff contributed about 55% of the zinc load in the fraction studied.
What are the black or colored granules I find in my gutters?
They are the ceramic coated mineral granules that surface asphalt shingles, which make up about one third of a shingle’s weight. Some granule loss is normal weathering, but heavy accumulation can signal an aging or hail damaged roof. Those granules are also a sediment source in storm drainage, and on algae resistant shingles they carry copper or zinc biocide that dissolves into runoff.
Do asphalt shingles contain microplastics?
Most modern asphalt shingles are polymer modified with SBS or APP plastics for flexibility, so they are a plausible microplastics source as the surface weathers. Stormwater studies find fibers dominate urban runoff (about 66% of particles in one review), but no published study yet gives a clean national mass estimate for shingle derived microplastics specifically, so the figure remains unquantified.
Why does my roof runoff contain so much zinc and copper?
Because those metals are added on purpose. Algae resistant shingles use copper or zinc granules dosed to slowly dissolve and suppress roof algae. A four and a half year study (Winston et al., 2019) found copper granule shingles kept releasing copper at a steady rate with no decline, meaning the biocide that protects the roof leaves in each storm’s runoff.
How much shingle sediment reaches waterways each year?
America applies roughly 6 million tons of mineral granules to roofs annually, based on about 12.5 billion square feet of shingle produced (ARMA/industry, 2024) at one third granule weight. Most stays embedded until tear-off, but an order of magnitude estimate puts granule and bitumen sediment mobilized toward storm drainage at around 100,000 to 300,000 tons per year, a bounded estimate rather than a measured total.