Inhibition and Recovery of Aquatic Macrophyte Lemna gibba Exposed to a Combination Pesticide

Abstract

Ecotoxicological effects of mixture pesticides are studied less on aquatic plants though they have an important role in environment. Lemna sp. is adopted for natural attenuation for both organic and inorganic pollutants and widely studied for their potential application in phytoremediation, waste water treatment facilities and constructed wetlands. The primary objective of this semi-static study is to quantify pesticide related growth inhibition effect to freshwater aquatic plant Lemna gibba during 7 days of exposure followed by a 7 days recovery period. It was exposed to Chlorpyrifos 50% + Cypermethrin 5% EC in 20X AAP growth medium. Ten fronds from pre-culture were exposed to a series of 3.1, 6.3, 12.5, 50 and 100 mg/L concentration. Inhibition and yield was found to be reversible during the recovery period in 3.1, 6.3, 12.5 mg/L except 50 and 100 mg/L. Morphological changes such as gibbosity, chlorosis, short roots, broken roots, small fronds and necrosis were observed in 50 and 100 mg/L. Growth rate inhibition and yield in the exposed concentrations was found to be dose dependent. Recovery of Lemna gibba exposed to 3.1, 6.3, 12.5 mg/L in medium without pesticide is attributed to its rapid growth rate and its ability to withstand the impact of the pesticide caused by the acute exposure. Phytostatic fronds in 50 and 100 mg/L did not grow during recovery period and it could be due to suppression of cellular activity. Yield EyC50 based on frond number and dry weight was 12.19 mg/L and 8.56 mg/L. Growth rate ErC50 based on frond number and dry weight was 47.69 mg/L and 14.79 mg/L. Agilent QQQ GC-MS/MSElectron Impact Ionization mode was used for active content analysis. 13.4 μg/L stock solution of the pesticide was prepared in 20 X AAP growth medium and checked for stability. At 0 hour Chlorpyrifos and Cypermethrin recovery was 90.6%, 82.0% and at 48 hour it was 83.7%, 61.2%. There is no published data related to the mixture toxicity of Organophosphorus and Pyrethroid pesticide to macrophyte Lemna gibba. Pesticide mixtures can extirpate the macrophyte thereby affect the biodiversity of the ecosystem. This is the first study to report the combination pesticide toxicity effect to aquatic macrophyte; it contributes to fill the ecotoxicity data gap to determine the potential impact of the pesticide for environmental risk assessment.