engleski

The effects of isoproturon on the common duckweed in continuous and pulsed exposures

Modern agriculture almost entirely relies on the use of synthetic herbicides. After treating the crops, herbicides can easily reach aquatic ecosystems due to rainfall, surface drainage and soil erosion. Consequently, herbicides are often present in aquatic ecosystems in pulses, or in relatively high concentrations over a short period after which their concentration is diluted. In such cases, non-target organisms are faced with short-term high levels of toxicant, followed by a recovery period that may be followed by a repeated toxicant pulse. Standard environmental risk assessment tests do not take into account such exposure scenarios, as they tend to maintain the constant exposure conditions, especially concentration of the toxicants. This study aimed to determine the effects of multiple pulse exposure of non- targeted species to the pesticide. Common duckweed (Lemna minor L.) was used as a model organism, and isoproturon was applied as a toxicant. Isoproturon is a selective and systemic phenylurea herbicide for the pre- or post-emergence control of annual grasses and broad-leaved weeds. It is one of the most commonly used herbicides, and it is often detected in surface water. Plants were treated with different concentrations of isoproturon (50, 100, 150 and 200 μg/L) in nutrient solution during 21 days. We compared the effects of multiple pulse exposure (2d-puls: 2 days of treatment and 5 days of recovery and 3d-puls: 3 days of treatment and 4 days of recovery) with the effects of continuous exposure of the same concentrations. Isoproturon is toxic to the common duckweed which is evident from the decrease of growth rate, as well as reduced fresh and dry biomass of plants. The significant toxic effects were determined at all tested concentrations in continuous exposure, while the same concentration had a lower impact when applied in multiple pulses. Since growth recovery was evident in pulse exposures, the recovery period was included in IC50 calculations. The most sensitive growth indicator was the dry mass accumulation for which IC50 values were 108.56 ± 9.14 μg/L in continuous, 221.7 ± 22.6 μg/L in 3d-puls and 240.5 ± 56.9 μg/L in 2d-puls regime. Aquatic macrophytes are an essential component of freshwater food web and any change in growth rate of these plants can result in modification of the ecosystem. Reduction of the abundance of more susceptible species may clear the environment for the growth and development of resistant or even invasive species which may affect the entire food chain.

Herbicides ; Isoproturon ; Lemna minor ; Continuous and pulsed exposures ; Growth inhibition

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