A direct solid-phase assay specific for heavy metal toxicity. I. methodology
Résumé
We have developed a direct toxicity assay for soils, sediments and sludges that is specific for heavy-metal toxicity. In the assay, a β-galactosidase-producingstrain of Escherichia coll is mixed with the solids sample together with a small volume (1.0 ml/0.5 to 1.0 g of solids) of eluent Extraction of metals from the solids sample is not required. Controls run with the assay eliminate interference due to indigenous β-ga-lactosidase activity or interaction between the solid matrix and the chromaphore. Use of 0.1 M sodium nitrate as eluent was found to yield somewhat higher sensitivity to heavy metals in solid-phase samples than MilliQ water. Application of the assay to a diverse array of soils, sludges, and sediments indicated that samples from industrial sites were generally more toxic than those from residential or commercial sites. Heavy-metal toxicity was correlated with the copper and zinc content of solids samples, but toxicity varied considerably at the lower range of metal contents. The proposed solid-phase assay should prove useful as a screening test for heavy-metal toxicity in soils, sediments, and sludges. It can also help distinguish between heavy metals and organic chemicals as the cause of toxicity in solid-phase samples.