Metsulfuron-methyl induced physiological, behavioural and biochemical changes in exotic (Eisenia fetida) and indigenous (Metaphire posthuma) earthworm species: Toxicity and molecular docking studies

Abstract

In modern agricultural practices, Metsulfuron-methyl (sulfonylurea herbicide) is widely employed to inhibit the weeds and grasses. The current study revealed that Metaphire posthuma was more sensitive than Eisenia fetida against Metsulfuron-methyl (MSM). The LC50 values for Eisenia fetida were 2884.08 mgkg−1 and 1871.18 mgkg−1after 7 and 14 days, respectively. Similarly, the LC50 values for Metaphire posthuma were 2449.34 mgkg−1 and 1673.10 mgkg−1for 7 and 14 days, respectively. Reproduction parameters were significantly decreased at 400 (T3), 800 (T4) and 1600 (T5) mgkg−1 MSM in E. fetida whereas at 200 (T2), 400 (T3), 800 (T4), 1600 (T5) mgkg−1 MSM in M. posthuma. EC50 of avoidance response for 20% MSM by E. fetida and M. posthuma was recorded 901.76 mgkg−1and 544.21 mgkg−1 respectively. Malondialdehyde (MDA) content along with guaiacol peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) activities were initially increased up to 21st day by MSM, inducing a slight oxidative stress in earthworms and recovered to control level on 28th day. The GST activities were continuously stimulated throughout the exposure period and enhance the detoxification effect thereby preventing the earthworms from toxins. Molecular docking studies indicated that hydrogen bonding and hydrophobic interactions are key forces in binding between MSM and SOD/CAT/POD/GST. As a result, this is the first study to be reported on physiological, behavioural and biochemical changes in two different earthworm species under the exposure of sulfonyl urea herbicide.