The effect of oil industry “high density brines” on duckweed Lemna minor L

Duckweed Lemna minor L. is a suitable plant model for toxicity evaluation of many substances due to its small size, rapid growth and ease of culture. Saturated water solutions of calcium chloride and calcium bromide and their 1:1 mixture are commonly used as “high density brines” for pressure control in oil wells. These solutions were added in Hoagland's nutrient medium in amounts appropriate to achieve 0.5%, 1.0%, 1.5% and 2.0% (v/v) dilutions and after two weeks of exposure the effect of tested chemicals on growth was estimated by counting fronds, measuring fresh and dry weights and determining total surface area of plants. Chlorophyll and carotenoid content in Lemna minor was also measured. Additionally, anthocyanin content in Spirodela polyrrhiza (L.) Schleiden was determined. During 14 days of exposure tested chemicals in lower concentrations (0.5%, 1.0% and 1.5% v/v) promoted the growth of Lemna minor, but they inhibited it in the highest (2.0% v/v). With increased concentration of tested solutions the concentrations of chlorophyll a and chlorophyll b were correspondingly higher in comparison with the control. Total carotenoid content and chl a/chl b ratio were also increased. The highest anthocyanin content in lower epidermis of Spirodela polyirhiza was noticed after the treatment with media containing 2.0% (v/v) CaCl 2 and 1:1 mixture of CaCl 2 and CaBr 2, but lower concentrations of all three tested solutions also resulted in anthocyanin content increase.