# Evaluation of _Aspergillus flavus_ Growth on Weathered HDPE Plastics Contaminated with Diesel Fuel
## 3 Results
### Fungal Growth Dynamics on Plastic Substrates
#### 3.3.4 Analysis of Experimental Variability Across Treatments  
To complement the evaluation of _Aspergillus flavus_ behavior on the different plastic matrices, coefficients of variation (CV) were calculated for colony area in each experimental combination (matrix \(\times\) temperature). This allowed for quantification of relative data dispersion and the identification of patterns of homogeneity or heterogeneity among replicates.  
At 30 \({}^{\circ}\)C, the treatment involving weathered and diesel-contaminated gray plastic exhibited a CV of 35.2%, indicating moderate variability among replicates, likely attributable to microenvironmental differences or heterogeneity in the aged plastic substrate. In contrast, the unweathered diesel-contaminated white plastic presented a high CV of 58.3%, reflecting considerable data dispersion and a potential sensitivity of the fungus to this specific matrix. The control treatment--uncontaminated gray plastic--showed an intermediate CV of 40.4%.  
At 25 \({}^{\circ}\)C, a similar trend was observed: weathered diesel-contaminated gray plastic maintained moderate variability (CV = 33.8%), while the white unweathered plastic again demonstrated high variability (CV = 55.1%), reinforcing its erratic behavior. The control group displayed the lowest CV in this series (24.0%), indicating greater consistency among replicates.  
At 20 \({}^{\circ}\)C, the pattern was again consistent: the CV was 29.8% for weathered diesel-contaminated gray plastic, 50.2% for unweathered diesel-contaminated white plastic, and 34.2% for the control. These values suggest that even under less favorable thermal conditions, the weathered and contaminated matrix promotes more predictable fungal growth compared to commercial diesel-contaminated white plastic.  
These findings indicate that experimental variability is influenced not only by incubation temperature but also by the matrix type and the degree of contaminant weathering. The most heterogeneous conditions were consistently associated with the white plastic containing commercial diesel, whereas weathered or uncontaminated substrates offered more stable environments for _A. flavus_ growth.  
The coefficient of variation (CV) is a statistical metric that expresses the relative dispersion of a dataset with respect to its mean, enabling the comparison of variability across experimental conditions with differing absolute magnitudes. It is calculated as the ratio of the standard deviation to the mean, expressed as a percentage. In microbiological studies, CV values below 30% are typically interpreted as indicative of high experimental homogeneity, whereas values between 30% and 50% represent acceptable variability. CVs exceeding 50% reflect substantial data dispersion, often associated with complex interactions or non-uniform responses by the organism under study.  
In the present work, the highest CV values were systematically observed in treatments involving non-weathered, diesel-contaminated white plastic, consistently exceeding 50% at all tested temperatures. This finding suggests a combination of physiological sensitivity of the fungus to commercial diesel and potential interference from physicochemical characteristics of the white polymer, such as the presence of antioxidant additives or pigments, which may hinder mycelial colonization in a heterogeneous manner across replicates.  
These results reinforce the importance of considering both the composition of the contaminant and the plastic substrate in the design of fungus-based biocleaning strategies.