Effects of 2-methyl-4-chlorophynoxyacetic acid (MCP A) on Lemna valdiviana.

Abstract

Aquatic macrophytes play an important role in the structure and functioning of aquatic ecosystem while facing an array of disturbances. Among those disturbances, exposure to agrochemical is significant due to intensive applications of these chemicals. Howerver, the impacts of agrochemicals on non''target aquatic plants are not well documented. Thus, present study was designed to assess the responses of non- target aquatic plants against herbicide (2-methyl-4-chlorophenoxyacetic acid 2-methyl-4-chlorophynoxyacetic acid (MCPA) using morpho-anatomical and physiological biomarkers. The numerical values of the stress responses were used for assessing the environmental risk of MCPA to the non-target environment using the model plant of Lemna valdiviana. There were two experiments where the first experiment examined the MCPA induced biochemical responses of L. valdiviana after exposing it to different MCPA concentrations (10, 100, 500, 1000 µg L·1) and control (0 µg L·1). Each treatment with (N=4, 800-820 plants per replicate ) was randomly allocated into 20 experimental units ( 4 L glass tanks) and experiment lasted for 120 hours. Plant pigment content, peroxidase (POD) activity and H2O2 content were compared. Growth and generation of new plants were also observed for two weeks under the same conditions using triplicates per treatment (5 plants per replicate). MCPA exposure significantly reduced pigment content of L. valdiviana where the total chlorophyll content was approximately 1.5 fold higher in unexposed plants (395.1 ± 28.1 µg/gFW) than that of plants (268.9 ± 20.9 µg/gFW) grown in the highest MCPA level. Although the H2O2 content was not significantly different among treatments, increased peroxidase activity indicated the MCPA induced oxidative stress in L. valdiviana. PEC:PNEC ratio was 5.5, the risk to the non-target environment was considerable and thus further assessment on exposure to MCPA is essential. In the second experiment, total number of plants after two weeks in the control, 10, 100, 500 and 1000 µg L·1 treatments were respectively 104 ± 4, 104 ± 7, 69 ± 19, 36 ± 11 and 33 ± 5 while the plant generation rates of the same treatments were respectively 7, 7, 4, 2 and 2 plants day. The present findings of the overall experiment showed the impairment of new plant generation, pigment destruction and induction of oxidative stress in non-target aquatic plant, L. valdiviana against MCPA exposure. These findings may probably useful for clarifying the interaction between agrochemicals and non-target aquatic plants.