Perhaps not distance but significance - which might have the longest exposure, conditions seemingly favorable to fungal growth and adaptation (organic material, limited amount but constant oil exposure, etc.), exclusion of possibly limiting factors such as direct heating/sunlight, sea water (unless you want marine fungi - prob limited in that), absent water.

In my experience, the age of contamination is the most important thing. In a contaminated environment, microbial populations, including fungi, also adapt. Adaptation increases with the length of exposure to the contaminant. I know from experience (I have worked in the bioremediation field for 30 years) that over time the microbial population of a contaminated area increases in the proportion of microorganisms capable of degrading the pollutants/pollutants present. Therefore, I recommend sampling areas with the oldest contamination.

Best regards

Vit