Influence of herbicides on morphology and population of rice frog Fejevarya limnocharis (Gravenhost, 1829) in paddy fields, Nan province

Herbicide utilization in agricultural area can lead to an environmental contamination and adverse effects on non-target organisms including amphibians. Screening for herbicide contamination (atrazine, glyphosate and paraquat) in paddy fields of Nan Province showed contamination of atrazine in water at the field with intensive herbicide utilization. The rice frog Fejervarya limnocharis living in agricultural area was thus used as a sentinel species to test for herbicide influence on non-target organisms. Frogs were field collected from a paddy field with intensive herbicide usage (a potential contaminated site) and a reference paddy field with no history of herbicide usage. Results of herbicide tissue residue analysis showed that detectable levels of these three herbicides were found in frogs from both sites with a significantly higher level of paraquat in the contaminated site animals. Results of morphometry and gravimetry of liver, kidney, gonad and body showed that frogs from the contaminated site had a significantly lower condition factor indicating potential impact on overall health of the frog, a significantly higher liver weight indicating potential exposure to xenobiotics detoxification, and a significant increase in ovarian weight compared to those of the reference site possibly due to effects of herbicide on ovarian growth. The results of fluctuating asymmetry analysis of four appendage bones showed that FAs of frogs from the contaminated site were significantly higher than those of the reference site indicating exposure to environmental stressor during developmental process of frog. Overall, site-related differences in health status, gravimetric parameters and fluctuating asymmetry indicate that herbicide utilization could pose adverse effects at different levels to this non-target organism. These results could be used as an early warning of environmental health hazards for other vertebrates living near the herbicide utilization area, including human.