# Evaluation of _Aspergillus flavus_ Growth on Weathered HDPE Plastics Contaminated with Diesel Fuel
## 1 Introduction
Bioremediation emerges as a viable, cost-effective, and environmentally sustainable alternative to traditional physico-chemical treatment methods [11]. In particular, filamentous fungi such as white-rot fungi (WRF) are noted for their ability to penetrate solid matrices, secrete ligninolytic enzymes, and degrade petroleum hydrocarbons [10]. The concept of fungal-based biocleaning involves using fungal strains to degrade organic contaminants directly on solid surfaces, with minimal water use. This method reduces the generation of contaminated effluents and water consumption, although it presents technological challenges such as maintaining suitable environmental conditions, preserving surface moisture, and selecting strains capable of effective colonization on weathered and contaminated substrates. Fungal genera such as _Aspergillus_ and _Penicillium_--both from the Aspergillusillanceae family--are recognized for their resilience to extreme environmental conditions and their versatility in industrial and bioremediation applications. However, their application in closed-system biocleaning remains unreported [12; 13]. Fungal biodegradation of high-density polyethylene (HDPE) has garnered increasing attention due to the pressing need for sustainable solutions to plastic pollution. Various fungal taxa have demonstrated notable potential in degrading HDPE under laboratory conditions. Among them, _Aspergillus_ species, such as _A. niger_, _A. flavus_, _A. terreus_, and _A. fumigatus_, have been widely reported to colonize polyethylene surfaces and induce chemical and morphological changes consistent with biodegradation, including weight loss and oxidation of polymer chains [14; 15]. _Penicillium_ species, notably _P. citrium_, _P. chrysogenum_, and _P. oxalicum_, have also been identified as effective agents in HDPE degradation, capable of reducing polymer mass and inducing visible cracks and microstructural damage on plastic films [16]. Similarly, members of the genus _Fusarium_, such as _F. oxysporum_ and _F. solanti_, have exhibited enzymatic capabilities to attack polyethylene matrices, resulting in measurable mass loss and alterations in infrared spectra. Recent investigations have even isolated effective HDPE-degrading fungi from unique ecosystems, such as mangrove soils (_Aspergillus niger_, _Penicillium citrium_) and insect gut microbiota (e.g., _Cladosporium haltolerans_ from _Galeria mellonella_ larvae), underscoring the adaptability and metabolic diversity of fungi in plastic degradation [14; 17]. These fungi secrete a wide range of oxidative enzymes, including laccases, peroxididases, and cutinases, which facilitate the breakdown of recalcitrant polymers into metabolizable oligomers. Collectively, these findings highlight the potential of _Aspergillus_, _Penicillium_, _Fusarium_, and related genera in advancing fungal-based strategies for mitigating HDPE pollution. In the context of fungal biodegradation studies, radial growth rate has been widely used as a kinetic parameter to assess colonization capacity on various substrates [18; 19]. Additionally, the formation of halos surrounding the fungal colonies has been recognized as a complementary indicator of metabolic activity, likely associated with the diffusion of extracellular enzymes or secondary metabolites, thus offering insights into their biochemical potential for surface degradation [18]. Since petroleum derivatives such as diesel undergo physicochemical transformations during weathering that alter their toxicity and bioavailability, the development of fungal-based biocleaning technologies must begin by evaluating microbial strains capable of colonizing and growing on contaminated plastics under these conditions. Accordingly, this study aims to assess the growth capacity of the filamentous fungus _Aspergillus flavus_ on HDPE surfaces retrieved from discarded diesel storage tanks contaminated with diesel fuel weathered for more than two years.