A direct contact bioassay using sulfur-oxidizing bacteria (SOB) for toxicity assessment of contaminated field soils

Abstract

In this study, 11 low/uncontaminated (including Lufa 2.2) and 9 contaminated field soils with varying geophysical and physicochemical characteristics were evaluated for toxicities based on oxygen consumption of sulfur-oxidizing bacteria (SOB). Oxygen consumption of the low/uncontaminated soils ranged between 7.9 mL and 9.5 mL, while contaminated soils ranged between 0.4 mL and 5.4 mL. Inherent test variability (CVi), variation due to soil natural properties (CVns) and minimal detectable difference (MDD) values ranged 1.2%–3.9%, 3.5%–16.9%, and 2.1%–4.3%, respectively. The toxicity threshold of 20% was established for soil toxicity based maximal tolerable inhibition (MTI). All the contaminated soils were found to be toxic and showed inhibition between 42% and 100% above the 20% threshold value. Increased proportions of clay and slit enhanced the of inhibitory effect of contaminants on SOB by reducing the oxygen consumption. Current study provides a suitable method for the rapid toxicity assessment of contaminated field soils with the advantages of ease of handling and rapidity without employing elutriates and sophisticated equipments and tools.