# Effects of Microbiota on the Soiling Process of PV Modules in Arid Zones of the Atacama Desert
## 3 Results and Discussion
### Soiling Mechanism
The observed difference in the microbial diversity found at the UA and PSDA biofilms was highly interesting, as the soiling at the UA demonstrated a high concentration of toxic heavy metals, such as Cd, Hg, and Pb, none of which play any known biological role (Figure 3). In contrast, these elements were found in lower proportions in the soiling at the PSDA. It would be reasonable to deduce that the toxicity of these elements could reduce the microbial diversity at the UA compared with the PSDA. However, greater microbial diversity was observed in the UA biofilms than in those from the PSDA (Figure 8A,B). Therefore, the microbial diversity appears to be unaffected by this factor, which suggests that the microorganisms isolated from the UA soiling may have developed mechanisms of homeostasis, tolerance, and even resistance to toxic heavy metals. On the other hand, the results reveal that the microbial diversity in biofilms found in the soiling at the UA and PSDA was determined by the TOC factor found in both soilings, with 0.9 and 0.1 ppm, respectively, and other factors related with weather conditions: high UV radiation, salinity, arid condition, etc. The significance of assessing biofilm growth lies in their composition of microorganisms that adhere to surfaces, whether inert or living. These microbial films attach to surfaces by creating a matrix composed of polysaccharides, proteins, and nucleic acids, which not only facilitates their adhesion but also provides protection. This matrix, which is known as \"Extracellular Polymeric Substances\" (EPSs), plays a crucial role [64]. Therefore, soiling cemented on PV panels is also affected by biofilm formation, thus potentially intensifying this phenomenon. Moreover, biofilm formation not only promotes adhesion but can also lead to material corrosion due to microbial metabolism, thereby accelerating the degradation of metallic materials [65]. Based on the results obtained in our research, which demonstrate the capability of biofilms formation from microbiota in the soiling samples from the UA and PSDA, it was possible to propose a fouling mechanism that incorporates the contribution of microbiota, as illustrated in Figure 9. This proposed mechanism is divided into three stages:  
* Transport and deposition of microbiota: This is the process by which microbiota present in the soil is transported by wind action and subsequently deposited on the surfaces of photovoltaic (PV) modules. Wind-transported dust can be colonized by microbial communities that originated from inoculates containing organic matter [6]. A distinctive feature of the Atacama Desert is that the mineralogical composition of soils and rocks provides specialized ecological niches for microbial communities [66; 67]. * Microbial colonization: In this stage, microbial colonization begins with the initial adhesion of microorganisms to the surface of the photovoltaic (PV) module. This process is directly related to the accumulation of dust particles on the PV glass. The microorganisms that colonize the surface are the most adapted and capable of withstanding the extreme conditions inherent to solar panels, which are characterized by low levels of organic matter and limited water availability [49]. * Biofilm formation: In this stage, biofilms are generated, which contributes to greater dirt adhesion on the solar panel [10]. This process involves non-living extracellular polymeric substances (EPSs) that create ecological niches and provide protection against environmental factors, such as desiccation and solar radiation [64]. Additionally, biofilm colonization on outdoor solar panels acts as an adhesive for particle deposition, which strengthens the cementation process [65]. According to [PERSON] et al. [8], the strong adhesion produced by EPSs on the PV module surface can withstand even torrential rains.