Rapid assessment of xenobiotic toxicity : a dissertation submitted in partial fulfilment for a Bachelor of Science with Honours at Lincoln University

Abstract

Conventional analytical techniques for monitoring toxicity offer high precision but are disadvantaged by the high cost of specialised equipment, the need for trained personnel and the observation that measured levels do not necessarily reflect bioavailability. Lincoln Technology has researched a 'co-substrate replacement' BOD biosensor, MICREDOX, which has the potential to rapidly assess the toxicity of xenobiotics. This dissertation reports on the validation of the standard MICREDOX methodology for rapidly determining estimates of biotoxicity. The results presented show that microelectrode amperometry can adequately replace bulk electrolysis as a detection method and that analyte volumes can be reduced to less than 1 ml. Microelectrode amperometry also facilitated the collection of time course information and the development of toxicity profiles. The response of two soil bacteria, Bacillus subtilis (B8) and Pseudomonas putida (ATCC 49128) to 3,5-dichorophenol was examined using this revised methodology. EC50 values of 7.5 ppm and 18 ppm were determined for B. subtilis and Ps. putida, respectively, and are in line with ECso values reported in the literature. The MICREDOX biotoxicity assay was also used to determine the toxicity of copper (II), chromium (VI), and arsenic (V), one binary mixture [Cu (II) + Cr (VI)], and one ternary mixture [Cu (II) + Cr (VI) + As (V)] to Bacillus subtilis at pH 7.4. EC₅₀ values of 61ppm for Cu (II), 68 ppm for Cr (VI), and 154 ppm for As (V) were determined. The EC₅₀ value for the binary mixture was 116 ppm Cr (VI) when Cu (II) is held at 79 ppm. No EC₅₀ value for the ternary mixture could be derived. The values derived for Cu (II) and Cr (VI) align well with those reported in the literature; no published data was found to compare the values determined by this study for As (V) and the ternary mix.