Long-Term Use of Agrochemicals: Mycological and Physicochemical Indices Suggest Shifts in Bio-Physicochemical Patterns

Introduction: Agrochemicals used over time reshape soil, with fungal and physicochemical signals marking shifts in bio‑physicochemical patterns Aim: This study investigated fungal diversity and abundance in agrochemical contaminated soil from Kwale, Delta State, Nigeria, emphasizing their tolerance to heavy metals. Methodology: Soil samples were collected from contaminated and uncontaminated sites. Soil physicochemical parameters were assessed. Heavy metal concentrations were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) while fungal isolation and enumeration were carried out on Rose Bengal Chloramphenicol agar and Potato dextrose agar following standard protocol. Results: Results showed that the contaminated soil differed notably from the control in physicochemical composition. The pH values were 4.56 (uncontaminated soil) and 5.63 (contaminated soil), indicating acidification. Essential macronutrients such as calcium and magnesium content were 111.24 mg/kg and 32.95 mg/kg in control while in the contaminated soil the values were 223.83 mg/kg and 60.58 mg/kg, respectively. Heavy metal concentrations were substantially higher in the contaminated soil, with values of 159.06 mg/kg (cadmium), 2.911 mg/kg (mercury), 4.37 mg/kg (copper), and 0.46 mg/kg (arsenic), following the trend Cd > Cu > Hg > As. Correspondingly, the total heterotrophic fungal count was 6.70 × 10⁴ CFU/g in the control and 4.36 × 10⁴ CFU/g in the contaminated soil, representing approximately 35% decrease in fungal abundance. Dominant fungi in the control soil included Aspergillus, Mucor, Fusarium, Trichoderma and Penicillium, while the contaminated soil was dominated by stress-tolerant Aspergillus, Fusarium, Rhodotorula, and Trichoderma species. Conclusion: The findings demonstrate that heavy metal contamination disrupt soil microbial balance, reducing fungal abundance and diversity. However, the persistence of tolerant genera highlights their potential for mycoremediation and soil restoration in contaminated farmlands.