COMPARISON OF 3 CLONES OF LEMNA IN A STATIC TOXICITY TEST OF ATRAZINE.

Abstract

Bioassays have become increasingly important indicators of environmental pollution. Lemnaceae (duckweeds) include a variety of species which are unique for bioassay application. This research tested three clones of duckweed; Lemna gibba, Lemna obscura, and Lemna minor for sensitivity and applicability to detect atrazine [6-chloro-N-ethyl-N'-(1- methylethyl)-1,3,5-triazine-2,4-diamine (C8H14C1N5)] in the environment. Nine biological parameters selected for evaluation were in two major categories: the first group included biomass; dry weight, frond number, frond production and dry weight/frond. The second group of parameters included measurement of pigments produced by the duckweeds; chlorophyll a, chlorophyll b, total chlorophyll, anthocyanin and the ratio of chlorophyll a to chlorophyll b. Regressions of parameter responses to atrazine concentrations were strongest in Lemna obscura. However, Lemna gibba was found to have the lowest IC50 (0.6-0.7 uM atrazine) for most of the nine variables measured. The small size of Lemna minor and Lemna obscura permitted these two species to be grown in small (8.5 x 12.5 cm), 24-well tissue culture plates. Bioassays in culture plates enabled tests with adequate replication and minimal costs. Lemna gibba was too large to be grown in culture plates and hence was grown in 125 mL erlenmeyer flasks which limited its efficiency of time, laboratory equipment, and materials.