# The Quirky Rot Fungi: Underexploited Potential for Soil Remediation and Rehabilitation
## 1 Soil Ecology, Health, and Erosion Control
### Slag Stabilization and Mining-Affected Soil  
There is a consensus that mining activities have been and will continue to be one of the most important activities for the extraction of heavy metals. Despite this, it is also agreed that this is one of the activities that leaves the greatest pollution legacy in the environment [9; 10; 11; 35; 36]. There are two major problems associated with ore mining activities: the large amount of slag produced, and the on-site and off-site pollution caused by slag (Figure 2). The slag itself is inherently loose and poorly aggregated, rendering it highly susceptible to erosion and dust formation, and with practically no water retention. The permanence of slag under weathering conditions facilitates the mobility of potentially toxic elements through the frequent release of acid drainage and the transport of dust. Mining activities (even at a small scale) can thus contribute, in the short- and long-term, to an increase in heavy metals in the air, water, and soil in the vicinity of the mining site or several kilometers away [9; 10; 37; 38]. Because of these characteristics of mine spoils, studies focusing on this type of pollution, in a cross-sectional way, have reported that the levels of potentially toxic elements are, as expected, higher in the vicinity of mines, decreasing with distance; but, even at a distance, they remain high, sometimes well above the permissible limits established by international standards such as the World Health Organization [9; 36]. Therefore, the implementation of stabilization and rehabilitation strategies for these mine spoils close to the mine sites could have a very significant off-site contribution, whether to the environment or to the population. The application of rot fungi as a first amendment can address three important aspects and is in line with the primary functional role of these fungi in the environment. Rot fungi are pioneer species; unlike other types of fungi commonly used in rehabilitation processes (such as mycorrhizal fungi), these fungi do not require a biotrophic link. They can better support themselves in aggressive environments than other microorganisms because of their higher tolerance and more efficient use of resources, partly overriding the negative impacts of heavy metals [38; 39]. In this way, rot fungi can shape these environments, helping to establish other microorganisms by creating microhabitats with a hyphal network (e.g., as in [6; 40]), and with the same network, allowing the translocation of nutrients and fostering a more hospitable environment for subsequent colonization by plants (e.g. [4]). In turn, the root system of established plants can also help stabilize debris. On the other hand, when they establish themselves in the soil or in these harsh environments, the hyphae network has a physical function, aggregating particles (through the production of natural glues based on polysaccharides), thereby improving water retention and aeration [41; 42]. For instance, under simulated rainfall events, mushroom residue-amended tailings were found to outperform all erosion metrics (lower runoff volume, decreased sediment yield, or the minimization of rill formation) compared to untreated tailings or other tailing treatments such as soil incorporation [41]. The use of mushroom-based amendments has been useful in other cases where the objective is to stabilize degraded and eroded soil. [PERSON] et al. [42] reported that a 10 ton per hectare application of mushroom residues would greatly increase the proportion of 0.5 mm macro-aggregates, and that the upgrade in microaggregates leads to positive feedback on organic matter storage and a 2-fold increase in saturated hydraulic conductivity [42]. Finally, as part of their natural function, rot fungi (responsible for the degradation of recalcitrant natural materials) secrete organic acids and chelating compounds that can bind heavy metals, thereby reducing their bioavailability and toxicity through three main pathways: biosorption, bioaccumulation, and precipitation.