A solid-phase direct contact bioassay using sulfur-oxidizing bacteria (SOB) to evaluate toxicity of soil contaminated with heavy metals

Abstract

The current study tested the employment of sulfur-oxidizing bacteria (SOB) in a direct contact bioassay to evaluate toxicity of soil contaminated with heavy metals. SOB were directly exposed to soil spiked with arsenic, nickel, hexavalent chromium, zinc, mercury, copper, lead, or cadmium for 12 h in a kit-type bioassay. Oxygen consumption by SOB was used as the end-point for toxicity assessment. The results demonstrate that oxygen consumption by SOB decreased as the doses of spiked heavy metals increased. Oxygen consumption in the tests spiked with arsenic, nickel, hexavalent chromium, or zinc was less than that spiked with mercury, copper, lead, or cadmium at the same concentrations. The 12 h half-maximum effective concentrations (EC50) of SOB for arsenic, nickel, hexavalent chromium, zinc, mercury, copper, lead, and cadmium were analyzed to be 12.7, 13.3, 19.1, 20.8, 40.1, 67.2, 101.5, and 105.4 mg/kg, respectively. These EC50 values are largely within the regulatory standards of heavy metals in agricultural soil, suggesting that the SOB kit test is sufficiently sensitive for use in on-site soil toxicity tests. The findings from the current study show that the SOB kit test is a suitable tool for evaluating heavy metal-induced toxicity of soil.