Toxicity screening of metals with special reference to quantitative approach

Area of Science:

• Environmental Toxicology
• Ecotoxicology
• Analytical Chemistry

Background:

• Assessing heavy metal toxicity is crucial for environmental protection.
• Existing toxicity testing methods vary in sensitivity and quantitative accuracy.
• Standardized and sensitive methods are needed for reliable ecotoxicological assessments.

Purpose of the Study:

• To compare the sensitivity and quantitative accuracy of three ecotoxicity testing systems: Microtox, Motility Test, and Growth Zone Inhibition Test.
• To evaluate the toxicity of various metals (Cr(6+), Al(3+), Cd(2+), Pb(2+), Cu(2+), Zn(2+), Hg(2+)) using these systems.
• To establish a quantitative Growth Inhibition Test as an alternative to the qualitative Growth Zone Inhibition Test.

Main Methods:

• Metals tested: Cr(6+), Al(3+), Cd(2+), Pb(2+), Cu(2+), Zn(2+), and Hg(2+).
• Toxicity assessment systems: Microtox assay, bacterial motility test, and Growth Zone Inhibition Test.
• Development and application of a quantitative Growth Inhibition Test using Bacillus cereus.

Main Results:

• Toxicity varied across systems, with Microtox being the most sensitive.
• Mercury (Hg2+) exhibited the highest toxicity (EC50 = 0.08 mg/L in Microtox).
• Cadmium (Cd2+) and Chromium (Cr6+) were the least toxic (EC50 values 19.4 and 21.0 mg/L, respectively).
• The quantitative Growth Inhibition Test determined MIC for Hg2+ at 0.03 mg/L, contrasting with the Growth Zone Inhibition Test.

Conclusions:

• Microtox is the most sensitive system for evaluating metal toxicity among the tested methods.
• Mercury (Hg2+) is consistently the most toxic metal across different ecotoxicological assays.
• A quantitative Growth Inhibition Test provides reliable MIC and MAC values, serving as a valuable alternative to qualitative methods.