Calcium chloride and calcium bromide aqueous solutions of technical and analytical grade in Lemna bioassay

Saturated water solutions of calcium chloride, calcium bromide and their 1: 1 mixture are commonly used as "high density brines" for pressure control i n oil wells. To compare the effect of these chemicals of technical grade wi th the effect of the chemicals of analytical grade the Lemna test was used. The multiplication rate, fresh weight, dry to fresh weight ratio, area cov ered 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 mo l dm(-3). Generally, the chemicals of both technical and analytical grade i n concentrations of 0.025 mol dm(-3) stimulated the Lemma minor growth, whi le tested chemicals in concentrations of 0.05 mol dm(-3) did not affect the growth significantly. The exceptions were results obtained by measuring fr esh weight. Most of tested chemicals in concentrations of 0.075 mol dm(-3) and all chemicals in concentrations of 0.1 mol dm(-3) reduced the growth. N o major differences between effects of tested chemicals of technical and an alytical grade on plant growth were observed, except that tested chemicals of analytical grade in concentrations of 0.1 mol dm(-3) increased dry to fr esh weight ratio much stronger than chemicals of technical grade. All teste d chemicals in all concentrations increased chlorophyll content. After trea tment with chemicals of analytical grade much higher increase of chlorophyl l a concentration in comparison to increase of chlorophyll b was noticed, w hile chemicals of technical grade caused more prominent increase of chlorop hyll b. (C) 2000 Elsevier Science Ltd. All rights reserved.