On the Appalachian Trail, hikers have a name for what they find behind rocks near popular campsites in spring: the toilet paper bloom. It is the most visible failure of Leave No Trace ethics in the American backcountry, and the one most hikers misunderstand the worst. The standard advice, bury it six inches down at least two hundred feet from water, assumes the soil will finish the job. In most places people actually backpack, it will not.
325 million visits, no formal accounting
The National Park Service recorded 325.5 million recreational visits in 2023, and that figure does not include the millions more on USFS, BLM, and state-managed land where dispersed backcountry use is common.[1] The Park Service does not publish a backcountry-specific volume estimate for human waste or toilet paper, but the math is simple. An average adult produces around half a kilogram of solid waste per day. A typical thru-hiker uses around three standard rolls of toilet paper over a five-to-seven-month trip.[2] A standard roll weighs around 110 grams. Across the roughly 3,000 hikers who complete the Appalachian Trail in a given year, the math comes out to somewhere near a metric ton of toilet paper buried in the soils along that one corridor each season.
The reason this matters is not that buried paper is inherently dangerous. It is that the model most hikers carry in their heads, the cathole as a slow compost bin where paper turns to soil over a season or two, does not match the science.
The cathole prescription, and why it fails in practice
Leave No Trace Principle 3 (Dispose of Waste Properly) is straightforward. Bury solid human waste in a cathole 6 to 8 inches deep, located at least 200 feet (roughly 70 adult paces) from water sources, campsites, and trails.[3] The Pacific Crest Trail Association and the National Park Service both reinforce this guidance. Toilet paper, the guidance says, can be buried with the waste or packed out, with packing-out increasingly preferred in arid and alpine zones.[4]
The prescription has three failure modes that are well documented in the field.
The first is geometry. Most alpine and subalpine soils in the western US, in western Tasmania, and across glaciated mountain ranges in general do not contain 6 inches of diggable substrate. A 2005 survey of Tasmanian backcountry sites found that achieving the prescribed 15 cm burial depth was "impossible to severely challenging at most sites" using the plastic trowels commonly sold in outdoor stores.[5] Hikers compensate by burying shallow, by placing waste under rocks (which actively slows decomposition, see Section 03), or by not burying at all.
The second is animal disturbance. In the same Tasmanian study, 34 of 750 buried sample bags were exhumed by native or introduced animals during the observation period, with 88 percent of those excavations occurring at the shallower 5 cm depth.[5] Frost heave excavated additional samples in alpine sites without any animal involvement.
The third is the assumption that the paper itself breaks down on a useful timescale. This is the part that the data contradicts most clearly.
Two years, nine environments, one definitive answer
In 2000, Kerry Bridle and Jamie Kirkpatrick at the University of Tasmania buried 750 mesh bags of toilet paper, facial tissue, and tampons at depths of 5 cm and 15 cm across nine plant communities representative of the Tasmanian backcountry. Half of the bags received a nutrient solution simulating human urine and feces. Bags were retrieved at 6, 12, and 24 months and scored on a five-point decay scale (1 = no decay, 5 = fully decayed). The study, published in the Journal of Environmental Management in 2005, is the most rigorous decomposition study of its kind.[5]
The results across all nine sites at the 24-month mark are below. Anything under 3.0 means more than half the original mass of toilet paper was still intact two years after burial, with simulated waste added.
Figure 1. Western alpine sites showed essentially no decay (1.37 of 5) after two full years, even with simulated human waste added to accelerate decomposition. By contrast, coastal eucalypt forest was 80 percent broken down. Mean annual rainfall and soil pH were the strongest predictors of decay rate in the regression model.
Two findings from this study deserve emphasis.
First, the alpine sites showed almost no measurable breakdown after two years. The Western Alpine site in the Tasmanian Wilderness World Heritage Area had a decay score of 1.37 of 5 even with nutrient enrichment, meaning the paper was still substantially intact, recognizable, and identifiable as toilet paper two full years after burial. Bridle and Kirkpatrick concluded that hikers should not be advised to bury toilet paper in any treeless vegetation above 800 m in western Tasmania, full stop.[5]
Second, the trajectory matters as much as the endpoint. Below is the same decay data tracked over time at three representative sites.
Figure 2. The alpine line is essentially flat. After 24 months of burial with simulated human waste added, the Western Alpine sample bags were within 0.4 points of where they started. The Lowland Rainforest sites, despite high rainfall, also lagged because their soils were cold and acidic.
The regression model that Bridle and Kirkpatrick fit to their data identified mean annual rainfall, temperature, and soil pH as the three variables that mattered most. Their predictive index runs from 3 (slow) to 6 (fast) and reconstructs the observed decay ordering across all sites. We have built that index into the calculator at the end of this article so you can check your own home range.
Thirty months later, 100 percent of catholes still contained paper
The Tasmanian work is the most controlled study, but it is not the only one. In an independent field experiment in alpine areas of Montana, Wyoming, and Colorado, researcher Andrew Skurka GPS-marked a series of catholes and returned to them on a rolling basis over a period of several months to thirty months. In his published account in Backpacking Light, he reports finding "evidence of both human feces and toilet paper in 100 percent of the catholes" when he returned, regardless of how long had elapsed.[6]
The implication is uncomfortable but clean. In a meaningful fraction of the backcountry that hikers most want to spend time in, the high country, the desert, anywhere cold or dry or acidic, burial is not a disposal method. It is a delay. The current Leave No Trace Center for Outdoor Ethics guidance increasingly recommends packing out toilet paper in these zones, and the PCTA explicitly recommends carrying it out in dry sandy soils and high elevation areas.[4]
Cellulose, plus the parts that do not biodegrade
The "it is just paper, it will compost" intuition treats toilet paper as if it were a leaf. It is not. Modern toilet paper is engineered to maintain structural integrity when wet, and that engineering involves chemistries that persist long after the cellulose fibers are gone.
A typical sheet of commercial bath tissue is roughly 95 to 98 percent cellulose pulp by mass. The remainder consists of additives whose function is to give the sheet the wet-strength, softness, and visual whiteness consumers expect.
Biodegradable wood or recycled fiber. The part most people imagine when they think about toilet paper.
Polyamide-epichlorohydrin. A synthetic cationic polymer that forms covalent bonds with cellulose to prevent the sheet falling apart when wet.[7]
Quaternary ammonium compounds, silicones, occasionally lotions and fragrances.
Chlorine-dioxide bleaching byproducts, fluorinated processing aids, recycled-feedstock contaminants including BPA.[8][9]
The most important of these additives, for backcountry purposes, is PAE.
PAE: the polymer that holds the sheet together
Polyamide-epichlorohydrin resin (CAS 68583-79-9) is the dominant wet-strength chemistry used in tissue manufacturing worldwide. It is dosed into the pulp slurry at 5 to 30 kilograms per metric ton of dry fiber, or roughly 0.5 to 3 percent of the finished sheet by mass.[7][10] Without wet-strength additives, paper retains only 3 to 5 percent of its dry tensile strength when soaked. With PAE, it retains 10 to 50 percent. This is what makes a wet sheet of toilet paper hold together long enough to do its job.
PAE works by forming irreversible covalent crosslinks with the cellulose fibers and with itself. It is, in materials terms, a thermosetting polymer. Once cured, it does not melt, does not redissolve in water, and resists hydrolysis. Wet-strength papers must be subjected to elevated temperatures, mechanical agitation, and aggressive chemistry just to be repulped at the mill where they were made.[11] In a cathole, none of those conditions exist.
The peer-reviewed literature has not yet quantified what happens to the PAE fraction of buried toilet paper after the cellulose breaks down. What is established is that PAE is a synthetic polymer that resists the biological and chemical pathways by which cellulose biodegrades. The cautious reading is that the synthetic resin fraction persists in soil as polymer residue after the visible paper is gone. Whether that residue meets the conventional 5 mm particle-size definition of "microplastic" depends on how it fragments, and that has not yet been measured in field conditions. The conservative claim, fully defensible: a sheet of toilet paper buried in a cathole leaves behind a small mass of engineered synthetic polymer that the surrounding soil cannot biologically process.
PFAS: the contamination that does not depend on what brand you buy
The second persistent fraction of a tissue sheet is the one almost no one outside of paper chemistry knows about until they read about it. In 2023, a team led by Timothy Townsend at the University of Florida tested 21 commercial toilet paper brands sourced from North America, Western Europe, Central and South America, and Africa, screening for 34 different per- and polyfluoroalkyl substances (PFAS). They found a fluorotelomer phosphate diester known as 6:2 diPAP in every sample tested, regardless of region or whether the paper was made from virgin or recycled fiber.[8] 6:2 diPAP accounted for 91 percent of the total PFAS detected in the paper samples and 54 percent of PFAS in matched wastewater sludge samples from Florida treatment plants.
A separate study in France attributed up to 89 percent of certain 6:2 diPAP loadings in wastewater to toilet paper alone.[12]
The recycled-paper aspect deserves attention because it inverts the usual eco-intuition. Recycled tissue is often marketed as the more sustainable choice. From a forest-conservation standpoint that is correct. From a PFAS standpoint it is at best neutral and may be worse, because recycled feedstock has been exposed to fluorinated processing chemistries twice. First, when it was made into paper (typically printing or packaging stock, where PFAS coatings are widely used for grease and moisture resistance). Second, when it is reprocessed into tissue.[8][13] Recycled tissue made from post-consumer thermal receipts has also been shown to carry measurable BPA into the finished product.[9]
What one season actually deposits
Below is a per-hiker accounting for a typical Appalachian Trail thru-hike, using the most commonly cited usage figures from the long-distance hiking community.[2]
That figure is the per-individual contribution. Of the roughly 3,000 hikers who complete the Appalachian Trail in a given year, plus the much larger population of section hikers and overnight backpackers using the same corridor, the cumulative mass of buried paper deposited along the trail comes out conservatively near one metric ton per year.
The trail itself runs from Georgia to Maine. A non-trivial fraction of its length passes through montane forest and exposed alpine zones (the Smokies, the White Mountains, Mount Katahdin) where the decay rates from Section 03 apply. The paper buried in those zones in a given season may still be there when the next season's hikers arrive.
Water you are already carrying
The bidet argument is mechanically simple. Hikers already carry water. A bidet uses around 100 to 150 mL per use. A typical hiker carries 1 to 2 liters between sources. A single liter is enough water for roughly seven to ten bidet uses, more than enough for a full day. The actual cleaning is better, not just lighter. There is no paper to bury, no paper to pack out, no zinc-oxide skin barrier needed to prevent chafing because the skin is rinsed clean rather than abraded.
The case from a Leave No Trace standpoint is even simpler. The rinse water itself is, by EPA wastewater categorization, greywater. The pathogenic content is in the cathole, where it belongs. Nothing of consequence is left on the surface. There is no paper, no PAE resin, no PFAS trace, no recycled-fiber BPA. Just water and what the body has already produced, buried at the correct depth.
A bottle cap bidet replaces the existing cap on a 28-410 threaded narrow-mouth bottle (the Smartwater bottle is the most common example) with a 4-gram nozzle that produces a directed stream when the bottle is squeezed. The 28-410 thread standard is the same specification used on the majority of single-use drinking water bottles produced in the Americas, Europe, Australia, China, and Japan, which means the device works with most bottles a hiker is likely to encounter on resupply. The replacement cap weighs less than a single sheet of toilet paper. It does not require batteries, priming, or a separate dedicated bottle.
This is not a moral argument for a different product. It is a structural one. The toilet paper problem in the backcountry is not a behavioral problem solvable by more careful burial. It is a materials problem. The materials we are using do not decompose on a timescale that matches our use of the landscape, and they carry persistent synthetic chemistries we cannot easily filter back out. Replacing the materials with water removes the problem at the source.
How fast does buried toilet paper break down where you hike?
Select a value in each row above to see the predicted decomposition index for that environment.
Cold, wet, acidic soils. Western alpine. Montane moorland. Tasmanian World Heritage type sites.
Expected outcome: essentially no measurable decomposition over 24 months, even with human waste added to accelerate microbial activity. In Bridle's study, sites in this category had decay scores between 1.37 and 2.52 of 5 after two full years. Recommendation: do not bury toilet paper in this environment. Pack it out, or eliminate it from the system entirely.
Cold, wet, near-neutral soils. Subalpine and montane forests with reasonable organic content.
Expected outcome: partial decomposition over 24 months. Decay scores in this category ranged from 2.65 to 3.85 of 5. Roughly half the buried paper mass remains identifiable two years later.
Warm, wet, acidic soils. Lowland rainforest and heavy-organic forest sites.
Expected outcome: partial decomposition. The acid-loaded soil chemistry slows microbial breakdown even when temperatures are warm.
Warm, wet, near-neutral soils. Most temperate forest backcountry.
Expected outcome: most of the toilet paper mass decomposes within 12 to 24 months. Visible fragments may still be present at the one-year mark. The PAE and PFAS fractions persist beyond the visible cellulose.
Cold, dry, acidic soils. High-elevation pine forest and dry-glaciated alpine.
Expected outcome: slow decomposition. Dryness and low temperatures together suppress microbial activity even where the soil is otherwise compositionally favorable.
Cold, dry, near-neutral soils. Higher-elevation dry forest.
Expected outcome: moderate breakdown over 12 to 24 months. Better than acidic alpine, worse than warm forest.
Warm, dry, acidic soils. Mediterranean and chaparral type sites.
Expected outcome: moderate. Warm temperatures help, but low moisture and acid soil chemistry slow microbial digestion of cellulose.
Warm, dry, near-neutral soils. Coastal eucalypt and grassy forest type sites at low elevation.
Expected outcome: most of the toilet paper mass decomposes within 6 to 12 months when nutrients are added. This is the most favorable case in Bridle's nine-site study, with decay scores above 4.0 of 5 after two years. The PAE and PFAS fractions still persist regardless.
How to read this. The index reproduces the order of observed decay rates across all nine of Bridle and Kirkpatrick's Tasmanian sites. It is calibrated to their study and is not a substitute for site-specific guidance from your local land manager. The index speaks to the cellulose fraction only. The synthetic polymer (PAE) and fluorochemical (PFAS) fractions of modern toilet paper do not biodegrade meaningfully in any of these environments.
The principle behind the principle
Leave No Trace was written in an era when "biodegradable" was treated as a self-evident category. The category was always shakier than that, and modern toilet paper has drifted further from it than most users realize. The reasonable response is not to defend the current practice harder. It is to update the toolkit.
A water bottle and a four-gram bottle cap bidet do the same work as a roll of toilet paper, with less weight, no waste, no buried polymer, no trace fluorochemicals deposited in alpine soils, and a cleaner result. The data does not require the change. But it makes the case as cleanly as data can.
