Toxicity Screening of Metals with Special Reference to Quantitative Approach

Abstract

A series of metals Cr⁶⁺, Al³⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, and Hg²⁺ were tested in three systems–-Microtox™, Motility Test, and Growth Zone Inhibition Test. Toxicity endpoint of each metal was variable from system to system. Of the three systems, Microtox™ was the most sensitive system. In this system, Hg²⁺ reacted as the most toxic element having EC₅₀ value 0.08 mg/L while Cd²⁺ and Cr⁶⁺ were least toxic with their EC₅₀ values 19.4 and 21.0 mg/L respectively. MEC₉₀ value of Motility Test was always needed more concentrations of toxicant in comparison to other systems. In comparison to Microtox™, ten times more concentration of Hg²⁺ (1.4 mg/L) was required to find out its MEC₉₀ value. Growth Zone Inhibition Test was very simple method from handling point of view. The usual practice of evaluation of toxicity screening in this system is either qualitatively or semi-qualitatively. Hence a study was designed to establish a quantitative technique, Growth Inhibition Test, as an alternative to this test using the same sensor organism B. cereus, which allows determination of MAC as well as MIC. MIC for Hg²⁺ was found to be 0.03 mg/L in Growth Inhibition Test while the same element was needed more concentration (1.0 mg/L) in the case of Growth Zone Inhibition test to produce halo. However, all these systems including Growth Inhibition Test showed Hg²⁺ was the most toxic element.

Keywords :

• Growth Inhibition Test
• Metals
• Motility Test
• Growth Zone Inhibition Test
• Three Systems Microtox™
• Toxicity Screening