Duckweed Lemna minor as a tool for testing toxicity of coal residues and polluted sediments

Duckweed was grown in controlled aseptic conditions in petri dishes illuminated for 16 h per d in the presence of single elements and nitric acid extracts of pulverized coal fuel ash (PFA), coal gasification slag (CGS) and polluted canal sediments. Toxicity was judged by expressing duckweed growth as surface coverage. The EC50 for cadmium, copper, zinc, arsenic(III), arsenic(V), selenium(IV), selenium(VI) and selenium dioxide were estimated at 0.86, 2.2, 4.4, 8.4, 297, 21, 67 and 37 uM, respectively. The concentrations of trace elements in low nitrogen oxide ash were higher than for conventional PFA. All PFA leachates were less toxic than those from the polluted sediments. Minimal leaching occurred from CGS. The canal sediment leachates strongly inhibited Duckweed growth probably because of a high zinc content. There are 32 references.