Response of MICROTOX organisms to leachates of autoclaved cellular concrete

The MICROTOX bioassay, a toxicity test involving bioluminescent microorganisms, was conducted on aqueous leachates derived from a construction material made using coal fly ash as the key siliceous ingredient. The material is known as autoclaved cellular concrete (ACC). The test indicated an absence of toxic effects attributable to soluble species, which included the priority heavy metals in the filtered leachates. Toxic or inhibitive effects on the test bacteria were observed for the toxicity characteristic leaching procedure (TCLP) leachates, but this was probably due to acetic acid in the extractant rather than the solubilized metals. The ASTM (distilled-deionized water extractant) and simulated acid rain leachates, by comparison, produced a repeatable stimulative effect. Stimulation observed in the form of enhanced light ouput may be a manifestation of hormesis, a phenomenon reportedly caused by exposure to extremely low concentrations (part-per-billion range) of otherwise toxic agents such as heavy metals.