Mycoremediation and the Decomposition of Human Waste

This write-up addresses the hypothesis that mycoremediation is a safe and effective approach to dealing with human waste in the backcountry based on an extensive review of existing literature.

The review tackles this question by breaking the topic down into several components such as:

(1) comparison to alternative “status quo” backcountry waste management practices

(2) why fungi?

(3) why fungi for human waste in the backcountry?

(4) introduction of the PACT species of mycelium into new environments (invasiveness)

(5) PACT species safety

(6) What happens to the fungi after decomposition is complete?

Comparison to current practices

PACT Outdoors’ product adds a fungus to break down the specially formulated wipe and human waste in the ground. Common practices rely on existing soil microbes to break down waste (human feces, urine, and toilet paper) left in the backcountry. While some visitors pack out their waste (Manning et al, 2012; Apollo, 2017), frequently, visitors leave it dispersed throughout the backcountry. More “flushable wipes” may also wind up in the backcountry since they are conveniently packaged. These wipes often have plastics to make them stronger than toilet paper when wet (Durukan 2019). Folks who leave waste in the backcountry rely on sufficiently active soil microbes to break down this waste and used toilet paper although growing efforts have been made to educate people on packing out their paper waste.

Problems ensue when the microbes cannot keep up and when people leave their waste at the surface (Cilimberg et al, 2000). The problems here are twofold: 1) pathogens persist from human sewage itself, 2) toilet paper persists and litters the wilderness in popular wilderness areas. Studies suggest that bacteria from buried waste may be found up to a year later in buried waste (Temple et al, 1982). People enjoying the outdoors often leave human waste and toilet paper unburied. This exposes the waste to wild animals (van Keulen et al, 2002), contaminates water sources, and creates an unpleasant experience for other outdoor enthusiasts (Stevenson et al, 2019). Depending on the soil conditions, bleached and unbleached toilet paper can take over two years to break down in the backcountry (Bridle 2004). As of this review, no academic studies have been done on the fate of synthetic wet wipes in the backcountry, but since they are stronger than toilet paper and contain anti-microbial additives, it is unlikely that they break down in under two years.

Soil microbes are often unable to keep up with buried or surface level waste (Bridle 2004). There is a lot of variability because ecosystems have different environmental conditions that impact soil microbe activity. When left at the surface, toilet paper persists. Alpine and montane environments have relatively little background decay capacity when compared to well drained lower elevation forests (Bridle 2004).

Why fungi?

A huge body of work supports mycoremediation: our use of fungi to solve pollution problems (Harms 2011). Fungi are nature’s recyclers and upcyclers. Fungi link ecosystems and organisms (Bahram 2022). Fungal metabolisms involve external digestion- key to their natural resiliency and their usefulness in mycoremediation. External digestion means that they produce clouds of enzymes that contact their food and then they wait for the half-broken up food to drift back to their cells. Wood rotting fungi have the most research on their mycoremediation capacity, partially due to their mushroom-forming habit, and partially due to their longstanding and highly observable habit of thwarting efforts to make wood products unrottable (Zabel 1983). However, fungi serving different ecological roles share mycoremediation capacity due to their shared external digestion method. Fungi from across the kingdom have been shown to break down various pollutants spanning explosives to pesticides and PCBs (Harms 2011). Since the 80s, there has been interest in using fungi to address pollution and help our society in different ways. Many efforts involved adding wood rotting fungi to polluted soil and these unadapted strains likely failed to establish in the non-wood environment (Harms 2011). It is important to align the ecological demands of fungi with the application. In industrially polluted soils, it is often the case that capable fungi live on site (D'Annibale 2006, Germain 2021).

Beyond pollution, fungi have helped control many pathogens. Plant pathogens, commonly called blights, are often caused by parasitic fungi, bacteria, and viruses. The fungal Trichoderma species are common agricultural biocontrol agents, living organisms used to control pest populations (Joo 2022), applied to soils to control pathogens and increase crop yields.

Why fungi for human waste in the backcountry?

There is a lot of evidence supporting mycofiltration: the process of using fungi to filter out pollution from waterways. Regarding the pathogen aspect of human waste disposal, there have been no direct studies in the literature on breaking down human waste in soils-all use mock waste made of standardized materials. There are few studies showing that fungi remove pathogens from real human waste, due to the dearth of studies using real human waste in general. However, there have been studies on fungi and their impact on pathogens.

✓ The Environmental Protection Agency funded work by Paul Stamets’ company Fungi Perfecti, to investigate filtering out E. coli from runoff after a rain (Stamets, 2013).

✓ Others have looked at mycelium as a way to reduce pathogens from wastewater lagoons. Researchers at the University of New Mexico, together with the city of Albuquerque, looked at floating filters using oyster mushrooms. They found that the filters reduced surface level E. coli reliably, week after week (Martinez, 2016).

✓ The Dungeness watershed built a wetland to treat cow manure and incorporated a layer of mycelium with wood-like supplements to help it grow and the fungi helped to consistently remove E. coli.

The PACT system currently delivers fungal mycelium with a wood substrate, a product commercialized as PACT Tabs. PACT instructs users to only use the product in locations where waste burial is approved practice, add three PACT Tabs to the cat-hole and fill with dirt. This is consistent with similar use-case success stories!

Introducing the PACT mycelium species to new environments

The main concern is the question: Is your chosen species of fungi invasive?

The PACT species has been observed across the world (see figure below). Notice that it has been observed frequently in highly populated areas across the US.

Note the following when interpreting the map:

1) Fungi are not documented to the extent that plants are and therefore maps are far less complete and origins much more difficult to discern.  

2) The map’s observations are based on our fungus’ mushroom form, a behavior done only under certain growing conditions.  

3) Fungi like our species spend most of their lives as threads beneath the ground or inside wood in their mycelial form. This form is not reflected in the map as this state is rarely observed or tracked.

4) It is highly likely that this species spans greater areas than those where we happen to see their mushroom form.

5) This map reflects a select number of locations where PACT’s species have been found, not the entire habitat of the fungus.

 

There is an initiative that tracks invasive species in the European Union: The Global Register of Introduced and Invasive Species. It was created with the goal of identifying and prioritizing invasive alien species, controlling or eradicating prioritized species, and putting measures in place to manage pathways and prevent invasive species spread. They report that the PACT species has been introduced in Austria, Poland, Czech Republic, Norway, Germany and Slovenia with no evidence of impact.

The initiative tracks reports from authoritative sources describing environmental impacts, rapid spread, or presence in high abundance, and found that the species has been introduced to countries with various dominant ecosystems similar to the U.S. and it has not become invasive or caused environmental impacts.

 

PACT mycelium species safety

It is natural to be cautious of the risks of handling any organism. The PACT species is widely regarded as a safe fungus, not pathogenic to humans. In the U.S., the Department of Health and Human Services publishes the Biosafety in Microbiological and Biomedical Laboratories which catalogs various microbes of interest (ATCC 2018). They assigned the species a biosafety level of 1, meaning it presents minimal hazard to people and the environment and it is not known to consistently cause disease in healthy adults.

Not only is the species not pathogenic to humans, but it is widely cultivated for food. The mushrooms are quite tasty. It is in the top ten mushrooms traded commercially across the world. The UN’s Food and Agriculture Organization recommends it to developing countries as a mushroom for them to cultivate.

What happens to the soil?

With so much cultivation outside, folks wondered about the impact to soil communities. In China, the government recommends that nurseries grow it along with their plants to improve the economic benefit of a plot of land. Research found that it had an overall positive impact on the forest soils, since it increased soil organic matter and available phosphorus content to the soil microbes and plants. They grew the mycelium to produce mushrooms and also saw benefit after the mushrooms finished fruiting, when the mycelium stage is still active. They found that it improves soil nutrient content and that the mycelium stimulated soil microbial life. The studies on the impact to soil communities in Chinese forests found that, even when grown on a large-scale, the mycelium disappears if not provided with more food after a time.  This is consistent with findings from a field-scale study on a farm in New York, introduced a year prior, did not recolonize a year later.