Dichlorvos and Paraquat induced avoidance responses in tadpoles (<i>Amietophrynus regularis</i> reuss, 1833) and their contribution to population decline

Umeokeke, Hilary C.; Amaeze, Henry N.; Ehiguese, Friday O.; Ogunfeitimi, Olusola O.; Soriwei, Evelyn T.; Labinjo, Suuru A.

doi:2022.37.2.e2022017

Environ Anal Health Toxicol > Volume 37:2022 > Article

Original Article

Published online June 22, 2022

Environmental Analysis Health and Toxicology 2022;37(2):e2022017-0. doi: https://doi.org/10.5620/eaht.2022017

Dichlorvos and Paraquat induced avoidance responses in tadpoles (Amietophrynus regularis reuss, 1833) and their contribution to population decline

Hilary C. Umeokeke¹

, Henry N. Amaeze¹

, Friday O. Ehiguese²

, Olusola O. Ogunfeitimi¹

, Evelyn T. Soriwei¹, Suuru A. Labinjo¹

¹Ecotoxicology Laboratory, Ecotoxicology and Conservation Unit, Department of Zoology, University of Lagos, Akoka-Yaba, Lagos, Nigeria
²Physical Chemical Department, University Institute of Marine Research (INMAR), International Campus of Excellence of the Sea (CEI.MAR), University of Cadiz, República Saharaui s/n, 11510, Puerto Real, Cadiz, Spain

Corresponding Author: Hilary C. Umeokeke ,Email: hilaryumeokeke@gmail.com

Received: April 17, 2022; Accepted: June 13, 2022.

ABSTRACT

Pesticides notwithstanding their benefits in agriculture pose threats to non-target fauna such as amphibians. This study examined the avoidance responses of tadpoles of the African common toad, Amietophrynus regularis, exposed to Dichlorvos and Paraquat under a non-forced multi-compartmented exposure system (NFS) and estimated the Population Immediate Decline (PID) by integrating avoidance and lethal responses. The NFS was designed to allow the free movement of tadpoles across six compartments in order to elucidate the ability of aquatic organisms to detect and potentially avoid contaminated environments at will. The tadpoles (n=3 per compartment/concentration; 18 per system) were exposed to gradients of Dichlorvos (0, 0.3, 0.5, 0.7, 1.0 and 2.0 mg/L) and Paraquat (0, 1.0, 5.0, 10.0, 15.0, and 20.0 mg/L) in quadruplicates with their distribution recorded every 20 mins for 3 h. 48 h acute toxicity tests under forced exposure system (FS) was performed using the same range of concentrations. Acute toxicity (48 h) response in the FS tests was dose dependent with LC₅₀ values of 0.79 mg/L and 6.46 mg/L recorded for Dichlorvos and Paraquat, respectively. The mean percentage distribution of tadpoles recorded for Dichlorvos and Paraquat was about 11% and 0% in the highest concentrations (2.0 and 20.0 mg/L) to 58% and 69% in compartments with no contaminants (control), respectively. PID was primarily driven by avoidance responses rather than mortality. These findings are of conservation interest as it elucidates the potential of both pesticides to impair local distribution of amphibians and cause biodiversity loss.

Keywords: amphibians, ecological risk assessment, forced exposure, non-forced exposure, pesticides, PID