BIOLOGICAL MONITORING OF LANDFILL LEACHATE USING PLANTS AND LUMINESCENT BACTERIA

Landfill leachates were evaluated using assays with plants and luminescent bacteria as indicators of toxicity. Four tests were conducted with several dilutions of untreated leachate samples from two Landfills (Braunschweig and Hannover), and untreated and treated samples from a third landfill (Schwicheldt). The experimental variables were growth rate of the aquatic plant Lemna minor, root lengths of the terrestrial plants Brassica rapa and Lepidium sativum after a 72 hour germination period, root elongation of Lepidium sativum over 8 days, and light emission by Photobacterium phosphoreum. Chemical analyses of the leachates were also made. At concentrations of 100 ml/L and higher, all untreated leachate samples exhibited severe toxicity, resulting in plant death or substantially poorer root growth compared to controls. EC(50) values obtained from the bacterial toxicity test were 350 and 180 ml/L for the Braunschweig and Hannover samples respectively. Plants grown in treated samples from the Schwicheldt landfill demonstrated negative responses only with undiluted leachate, indicating that this sample was less toxic than the untreated one. Chemical analysis showed substantial differences between untreated and treated samples, which may explain the decreased toxicity observed in biological tests with the treated sample. Results of the different tests were similar for all the leachates evaluated, increasing the reliability of these assays. Analytical techniques can elucidate the chemical characteristics of an environmental sample, but give little information regarding its potential ecological effects. In contrast, the bacterial and phytotoxicity assays used in this study provided inexpensive and consistent, ecologically relevant information on the toxicity of landfill leachates.