Effects of diazinon on larvae of the Asian common toad (Bufo melanostictus, Schneider 1799)

Abstract

Continuous subchronic exposure experiments were conducted to assess the effects of diazinon, an organophosphate pesticide, on the survival, growth and activity of larvae of the Asian common toad Bufo melanostictus. Two larval stages, the gill stage (Gosner stages 21 and 22) and gill-atrophy stage (Gosner stages 24 and 25), were continuously exposed to 4 microg/L, 400 mirog/L, and 10 mg/L of commercial-grade diazinon for 30 d. Treatments and untreated controls were maintained in triplicate with water changed and pesticide concentrations renewed every 3 d. Observations showed that subchronic exposure to 400 microg/L and 10 mg/L diazinon caused a significant dose-dependent increase in mortality compared to the control, regardless of the age at which larvae were exposed. One hundred percent mortality was observed in larvae exposed to 10 mg/L. No clear age-related sensitivity was evident in this study. The lethal concentrations at which 50% of the tadpoles (LC50) died during 30 d of continuous exposure were 6 and 7.5 mg/L for gill stage and gill-atrophy stage larvae, respectively. Diazinon impaired larval growth and activity. Tail abnormalities were apparent in larvae exposed to 400 microg/L and 10 mg/L of diazinon. This investigation provides the first empirical evidence of the negative effects of diazinon on the survival, growth and activity of B. melanostictus. The high degree of diazinon toxicity in this study highlights the need to consider important nontarget groups when recommending safe levels of pesticide application.

Cadmium-Induced Toxicity on Larvae of the Common Asian Toad Duttaphrynus Melanostictus (Schneider 1799): Evidence from Empirical Trials

“…Lefcort et al (1999) reported such abnormal swimming in tadpoles of R. luteiventris exposed to heavy metals. Sumanadasa et al (2008) observed that diazinon also impaired swimming activity in tadpoles of the same species of toad as was used in the present study. Reduced swimming in tadpoles exposed to Cd could be attributed to several factors; Cd accumulation has been shown to occur in muscles, probably resulting in muscle damage (Vinodhini and Narayanan 2008).…”

“…The 10-day exposure trials were conducted in glass tanks of 22 9 15 9 15 cm containing 2 L of aged tap water (Sumanadasa et al 2008). Appropriate volumes of the stock solution were added to each tank to obtain the relevant test concentration and mixed well to ensure homogeneity.…”

“…The one-way ANOVA and Tukey's tests were used to determine the influence of pesticide concentration on mortality and the Pearson's Correlation test was used to examine the nature of the dose-dependent response (Sumanadasa et al 2008). The developmental stage of the surviving tadpoles was also recorded at the end of the trial.…”

“…The developmental stage of the surviving tadpoles was also recorded at the end of the trial. The swimming activity of tadpoles was assessed every other day according to a method described in Sumanadasa et al (2008) and Wijesinghe et al (2011). Each tank was placed over a white paper on which a cross had been drawn, and the number of times that tadpoles crossed the lines was counted for 5 min between 0800 and 1200 hours.…”

Solar Radiation Alters Toxicity of Carbofuran: Evidence from Empirical Trials with Duttaphyrnus melanostictus

“…Mortality in each tank was monitored daily and body length measurements, staging (according to Gosner, 1960) and recording of swimming activity were conducted on Day 1 and Day 4. Swimming activity was assessed using a protocol described by Sumanadasa et al (2008). Qualitative assessments were made of the abnormalities observed in the tadpoles.…”