Influences of herbicides on health of rice frog Fejervarya limnocharis populations in Nan Province, Thailand

Abstract

Intensive and continuous herbicide use in agriculture may pose a risk to health of environment and non-target organisms, including amphibian. Prior research conducted between 2010-2011 using the rice frog, Fejervarya limnocharis, as a sentinel revealed an accumulation of herbicides (atrazine, glyphosate, and paraquat) in environmental samples and frog tissue, as well as adverse effects on the health status. This study aims to determine the potential influence of herbicides on population health of the rice frog. Between July 2020 and February 2021, frogs were collected from two paddy fields with varying degrees of herbicide use in Nan province, Thailand. The results of the herbicide residue analysis in water samples indicated that detectable amounts of atrazine were found only in the contaminated site. These three herbicides were detected in frog tissues from both sites, with the contaminated site exhibiting a higher level of paraquat residue. The results on organismal parameters indicated that frogs from the contaminated sites had a greater ovarian weight, indicating a possible effect of xenoestrogen exposure, a significant difference in liver weight, possibly due to xenobiotic exposure, and a significant difference in body weight. The results on population parameters indicated significant differences in growth patterns, fluctuating asymmetry on five appendage bones of frogs, and size-frequency distribution with disproportionate distribution of the contaminated site population, indicating a possible herbicide effect on growth, development and population structure. Site-related differences in herbicide residue, organismal and population parameters indicate that herbicide use may have adverse effects on the health of the rice frog F. limnocharis population, resulting in subtle and persistent changes to paddy field ecosystems. The findings of this study may serve as a warning about potential environmental health hazards for vertebrates that live near herbicide utilization areas, including human.