DUCKWEED LEMNA-MINOR AS A TOOL FOR TESTING TOXICITY OF COAL RESIDUES AND POLLUTED SEDIMENTS

Duckweed, Lemna minor, was used for testing single elements and leacha tes of coal ashes and sediments by expressing growth as surface covera ge. The EC50 for the elements Cd, Cu, Zn, As(III), As(V), Se(IV), Se(V I), SeO2 were 0.86, 2.2, 4.4, 8.4, 297, 21, 67, 37 muM, respectively. Leachates were tested of pulverized coal fuel ash (PFA), including ''l ow NOx'' ashes, coal gasification slag (CGS), and, as a reference, the polluted sediments of a canal. The concentrations of elements in leac hates of ''low NOx'' PFA were higher than those in leachates of conven tional PFA. The leaching of anions from PFA was more quickly than the cations. CGS showed an absolutely minimal element leaching. Comparison of the effects of conventional PFA with sediments from Rotterdam harb or, River Rhine, and the canal shows PFA to be the far less toxic one. The sediment samples from the canal demonstrated strong growth inhibi tion, probably due to high zinc concentrations originating from indust rial activity.