Abstract
The toxicity of six potassium inorganic salts: potassium carbonate (K2CO3), potassium hydrogen carbonate (KHCO3), potassium sulfate (K2SO4), dipotassium hydrogen orthophosphate (K2HPO4), monopotassium phosphate (KH2PO4) and potassium aluminum sulfate (KAl(SO4)2.12H2O) towards duckweed (Lemna minor L.) was studied. The results showed that all tested chemicals were with low toxicity but similar salts as potassium carbonate and potassium hydrogen carbonate or dipotassium hydrogen orthophosphate and monopotassium phosphate can express different toxic action towards the tested object. Potassium aluminum sulfate, was toxic to duckweed at very narrow ranges: up to 0.8 % concentration but the salt did not cause any damage to the plants. At 1 % concentration, the first phytotoxic symptoms appeared and at 1.44% concentration LC50 was established and LC90 was reached at concentration of 1.65%. The most toxic chemical was potassium carbonate due to the higher pH of its solutions, but KH2PO4 was found to be more toxic than K2HPO4 although its solutions were with neutral pH, while a pH of solution of K2HPO4 over 1 % concentration was slightly alkaline.
Keywords: Lemna minor L., potassium carbonate, potassium hydrogen carbonate, potassium sulfate, dipotassium hydrogen orthophosphate, monopotassium phosphate, potassium aluminum sulfate