Towards a broadly applicable soil algal bioassay using the paper-disc method: Influence of pH and clay fraction in natural soils

Long-term soil contamination poses significant ecological risks, necessitating practical tools for comprehensive soil quality assessment. This study introduces the paper-disc method utilizing the soil alga Chlorococcum infusionum to evaluate both natural and historically contaminated soils. This innovative method employs a paper disc interface, facilitating the diffusion of bioavailable contaminants from soil to algae, thereby enabling non-destructive toxicity assessments. In controlled experiments, algal growth responses were analyzed across a gradient of pH levels and clay fraction. Results indicated optimal growth in soils with slightly acidic to near-neutral pH (4.88–5.70) and clay fraction below 50%. Comparative analyses with traditional soil-based assays demonstrated that the paper-disc method effectively mirrors contaminant bioavailability, as evidenced by consistent algal growth inhibition patterns. Furthermore, the method's alignment with global soil pH and texture distributions underscores its broad applicability. By providing a non-invasive, ecologically relevant tool, the paper-disc method enhances current soil quality monitoring techniques and supports sustainable soil management and restoration efforts.