Application of plant and earthworm bioassays to evaluate remediation of a lead-contaminated soil.

Abstract

Earthworm acute toxicity, plant seed germination/rootelongation (SG/RE) and plant genotoxicity bioassays were employed to evaluatethe remediation of a lead-contaminated soil. The remediation involved removalof heavy metals by a soil washing/soil leaching treatment process. A portionof the soil after remediation was rinsed with water in order to simulateexposure to rainfall. The bioassay results showed that the soils beforetreatment (BT) and after treatment plus water rinsing (RT) were not toxic toearthworms in a 14-day exposure, while after treatment (AT) showedsignificant toxicity. The LC50 values for Eisenia fetida andLumbricus terrestris were 44.04 and 28.83 (as % AT soilsupplemented in artificial soil), respectively. The phytotoxicity dataindicated that all three test soils significantly inhibited lettuce SG/RE ina dose-related manner, with AT being the most phytotoxic. In oats, RT had noeffect on SG/RE and AT was more toxic than BT. For the two local site grassseeds tested (blue grama and sideoat grama), the AT soil was the mostphytotoxic followed by BT and RT. In Allium cepa (common onion), BTand AT induced similar levels of genetic damage to root tip cells, whereas RTwas not genotoxic. High salt levels generated during the remediation processappeared to be responsible for the increased toxicity of AT soil for bothplants and earthworms. The rinsing of the AT soil with water effectivelyremoved both acutely toxic and genotoxic components of the soil.