Paper-disc method: An efficient assay for evaluating metal toxicity to soil algae.

Area of Science:

• Environmental Toxicology
• Soil Ecology
• Algal Bioassays

Background:

• Probabilistic ecological risk assessment often relies on micro/mesofauna toxicity data.
• Soil algae, a food source for soil fauna, offer an alternative for toxicity assessment.
• Current soil algal bioassays lack standardized guidelines and face sample collection challenges.

Purpose of the Study:

• To introduce and validate the paper-disc method as an accessible alternative for soil algal toxicity screening.
• To adapt the paper-disc method for evaluating copper (Cu) and nickel (Ni) toxicity to Chlorococcum infusionum.
• To assess the efficacy of the paper-disc method using multiple endpoints including growth zone, chlorophyll fluorescence, and photosynthetic activity.

Main Methods:

• Adapted the established paper-disc method, commonly used for antibacterial assays, for soil algal toxicity testing.
• Utilized Chlorococcum infusionum as the test alga and exposed it to copper and nickel contaminated soils.
• Evaluated toxicity through measurements of algal growth zone, chlorophyll fluorescence, and photosynthetic activity.

Main Results:

• Decreased chlorophyll fluorescence and photosynthetic activity were observed with increasing concentrations of Cu(+2) or Ni(+2).
• Visual analysis of the algal growth zone corroborated findings from chlorophyll fluorescence measurements.
• Both direct ethanol extraction and indirect culture medium extraction methods proved effective, with the direct method being simpler.

Conclusions:

• The paper-disc method is a user-friendly and effective assay for screening soil toxicity.
• This method demonstrates efficacy in detecting toxicity from heavy metals like copper and nickel.
• The paper-disc assay correlates with indirect soil quality indicators, enhancing its utility in ecological risk assessment.