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Toxicity to aquatic plants other than algae

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Simmons (2012) investigated the effects of potassium in form of KCl and K2SO4 on duckweed Lemna minorafter a 7-days static exposure; the overall lowest 7-day EC10 and EC50 values (frond number) amount to 375.3 and 1681.2 mg K/L, respectively, and are above the OECD test limit (Simmons, 2012).

Potassium is an essential macronutrient and most abundantly absorbed cation that plays an important role in the growth, metabolism and development of e.g. macrophytes. Plants suffering of potassium therefore show different symptoms (e.g. wilting, decolouration and growth disorders). It is among others involved in water balance, photosynthesis and the assembly of vegetable cell walls and is therefore present in media used for macrophyte tests (e.g. Modified Swedish Standard (SIS), 20X AAP (U.S. EPA) and modified STEINBERG medium (ISO 20079)). These media require the addition of potassium in form of K2HPO4, KH2PO4 and KNO3, resulting in final elemental concentrations of 3.9, 10.3 and 17.9 mg K/L, respectively. Potassium concentrations of the OECD test media are above the median background concentrations of potassium in European stream water of 1.60 mg K/L (FOREGS) indicating a high potassium demand of macrophytes and the corresponmding lack of a toxic potential. In sum, potassium as essential element has a very low potential for toxicity to aquatic plants.

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