Saturated water solutions of calcium chloride, calcium bromide and their 1:1 mixture are commonly used as ``high
density brines'' for pressure control in oil wells. To compare the eect of these chemicals of technical grade with the
eect of the chemicals of analytical grade the Lemna test was used. The multiplication rate, fresh weight, dry to fresh
weight ratio, area covered by plants and chlorophyll content were measured as toxicity parameters. The concentrations
of tested chemicals were 0.025, 0.05, 0.075 and 0.1 mol dmÿ3. Generally, the chemicals of both technical and analytical
grade in concentrations of 0.025 mol dmÿ3 stimulated the Lemna minor growth, while tested chemicals in concentrations
of 0.05 mol dmÿ3 did not aect the growth signi®cantly. The exceptions were results obtained by measuring fresh
weight. Most of tested chemicals in concentrations of 0.075 mol dmÿ3 and all chemicals in concentrations of 0.1 mol
dmÿ3 reduced the growth. No major dierences between eects of tested chemicals of technical and analytical grade on
plant growth were observed, except that tested chemicals of analytical grade in concentrations of 0.1 mol dmÿ3 increased
dry to fresh weight ratio much stronger than chemicals of technical grade. All tested chemicals in all concentrations
increased chlorophyll content. After treatment with chemicals of analytical grade much higher increase of
chlorophyll a concentration in comparison to increase of chlorophyll b was noticed, while chemicals of technical grade
caused more prominent increase of chlorophyll b. Ó 2000 Elsevier Science Ltd. All rights reserved.