# Evaluation of _Aspergillus flavus_ Growth on Weathered HDPE Plastics Contaminated with Diesel Fuel
## 1 Introduction  
Plastic waste generated from the use of tanks for the storage of fuels, lubricants, additives, and other petroleum-derived products represents an increasingly pressing yet underexplored environmental challenge. While specific data on such waste streams are often not disaggregated, it is estimated that a significant proportion of the more than 460 million metric tons of plastics used annually is associated with the energy and transportation sectors, including high-density polyethylene (HDPE) containers for petroleum derivatives. This figure is projected to exceed 1231 million metric tons by 2060 [1]. Among these applications, HDPE tanks used for diesel storage are notable for their chemical resistance, durability, low weight, and ease of manufacturing. They are commonlyemployed in agriculture, mining, and transportation, with capacities ranging from 200 to over 5000 L. In Chile, these tanks are regulated under Decree No. 160 [2] issued by the Superintendence of Electricity and Fuels. However, after up to two decades of contact with diesel fuel, their recycling becomes highly complex due to the adsorption and diffusion of hydrocarbons into the polymer matrix, compounded by long-term environmental weathering [3]. Conventional cleaning methods for these tanks typically involve washing with water and detergents, which generates hydrocarbon-laden wastewater requiring subsequent treatment. This merely transfers the contamination from the plastic to the effluent, posing additional environmental risks. Diesel fuel is a complex mixture comprising hundreds to thousands of compounds, including aromatic hydrocarbons (15-40%), linear alkanes (25-50%), and naphthenes (20-40%), with carbon numbers between C9 and C22 [4]. Among these, aromatic compounds such as toluene are particularly persistent and problematic, and are considered representative of this fraction [5]. These substances are chemically stable and tend to accumulate in plastic matrices. Weathering, driven by prolonged exposure to environmental factors such as UV radiation, atmospheric oxygen, temperature fluctuations, and humidity, induces substantial chemical transformations in diesel residues adhered to HDPE surfaces [6; 7]. These changes include progressive increases in viscosity, reductions in aqueous solubility, and declines in bioavailability [8]. For example, photochemical weathering of petroleum at 5 \({}^{\circ}\)C has been reported to increase its viscosity more than sixteenfold and decrease its water-soluble fraction by a factor of seven compared to petroleum at 30 \({}^{\circ}\)C, with direct implications for its dispersion and treatability [3]. Under the temperate, semi-arid climate of Santiago, Chile--characterized by high seasonal solar radiation--significant changes in the chemical structure of diesel residues on exposed HDPE tanks begin to manifest within 6 to 12 months. During this period, lighter aliphatic hydrocarbons (C10-C14) tend to evaporate, while heavier components (C15-C22) and aromatic compounds undergo partial oxidation, yielding intermediate products such as carboxylic acids and alcohols. Between 12 and 24 months, the chemical profile of the adhered contaminants diverges markedly from that of fresh diesel, becoming dominated by recalcitrant residues, oxidized polar fragments, and low-volatility compounds, thereby altering their environmental behavior and microbial interactions [9]. Moreover, the simultaneous exposure of HDPE to diesel and sunlight may trigger photoxidative processes within the polymer itself, modifying its surface topography, oxidation state, and affinity for microbial colonization and enzymatic action [10]. This combined effect has direct implications for fungal adhesion and metabolism in bioremediation settings involving _Aspergillus flavus_. Diesel-contaminated plastic waste also poses environmental and human health risks due to emissions of volatile organic compounds and the potential for leaching into soils and aquatic systems.