Growth response of Lemna minor L. to paracetamol

Surface water and groundwater is contaminated with pseudoperistent xenobiotics present in the environment. The risk associated with an increase in the consumption of drugs and their permanent occurrence especially in the aquatic environment falls on non-target organisms. The aim of this thesis was to assess the effect of increasing concentrations of paracetamol (0.1; 10; 100 μg/l) on the growth and selected physiological parameters of the model organism Lemna minor (L.). Duckweed, as an important model plant for ecotoxicological research, has been subjected to a semichronic exposure to paracetamol. The presence of a stressor – paracetamol – after ten days of cultivation significantly influenced some growth and physiological parameters. It has been shown to significantly reduce the content of photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids), increase the value of non-photochemical quenching of chlorophyll fluorescence (NPQ), and lower the relative decline of chlorophyll fluorescence (Rfd). The results show that the increased load of paracetamol in the environment may negatively affect the growth of duckweed. Key-Words: -chlorophyll fluorescence, duckweed, growth, Lemna minor, paracetamol, pharmaceuticals, photosynthetic pigments, phytotoxicity tests Introduction Plants have the ability to accumulate in their tissues toxic metals and organic pollutants, which can cause changes in growth and morphology. At present, drugs or pharmaceuticals include among the substances hazardous to living organisms [1, 2]. It is primarily about environmental contamination and wastewater sludge. It was found that in addition to acidification and eutrophication of soils and water may also indirectly contribute to the loss of plant and animal species. Paracetamol, often used as a representative of analgesics and antipyretics, is among the candidates for an analysis of the effect on a model organism Lemna minor (L.). Pharmaceutically active substances are detected in surface water, groundwater and soil, wherein their concentration ranges from ng/l in μg/l [3], to small flows to 1 mg/l. These mobile elements of pollution enter the environment continuously [4] and their effect depends on the time during which the organism operates [5]. Studies also demonstrate that due to the high polarity and low volatility drugs bioaccumulate and are persistent in the environment [6]. Paracetamol is in 75% excreted as conjugates and in the remaining percentage the original substance persists [7]. The active paracetamol in these environments is easily transformed from conjugates thanks to the activities of microbial metabolism. It is assumed that paracetamol pseudo-persistent in the environment [8]. The concentration of analgesics which include paracetamol in the aquatic environment varies between 0.0016 and 373 μg/l [9]. The average concentration of paracetamol was calculated in this study at 246 μg/l. Paracetamol and ibuprofen at the same time showed the highest mean values of the inflow to municipal wastewater treatment plants (38 and 37 μg/l respectively). Other researchers have found that the highest concentration reaches paracetamol in Europe compared with other continents (influent concentrations ranged from 59220 ng/l, the concentration in rivers range from 12 to 777 ng/l) [10]. Removal of paracetamol in the WWTP is very effective in the order of 95% [11], yet the gate is paracetamol into the environment continuously. The concentration of paracetamol, which are normally determined in surface water can cause serious chronic effects on aquatic organisms [12]. Paracetamol has compared to ibuprofen a very low Kow value (0.40), is more accessible and therefore more toxic [13]. In particular, induction of oxidative stress may reduce the ability of effective degradation of paracetamol and other xenobiotics [14]. Hydrophyte communities aquatic plants form an important ecological element in the nutrient cycle.