Differential toxicity and uptake of Diazinon on embryo-larval development of Rhinella arenarum

ARONZON C.M; MARINO D.J.; RONCO A.; PÉREZ COLL C.S

CHEMOSPHERE

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2014 vol. 100 p. 50 - 56

0045-6535

Diazinon is an organophosphate extensively used pesticide. The main objective of this work was to assess the lethal and sublethal effects of Diazinon and its correlation with the uptake by embryos and larvae of the common South American toad Rhinella arenarum by means of standardized bioassays during acute (96 h), short-term chronic (168 h) and chronic (504 h) exposures. Toxicity resulted time- and stage-dependent, thus the Lethal Concentration 50 for acute, short-term chronic and chronic exposure were 27.2; 20.1 and 6.8mg Diazinon/L for embryos and 8, 6.7 and 1.9 mg Diazinon/L for larvae. It is noteworthy the remarkable differences found in the concentration which caused lethality with those causing teratogenic effects. Therefore, the Teratogenic Index from 144 h was greater than two; the main adverse effects were axial flexures, irregular borders, wavy tail, microcephaly, malformed mouth and adhesive structures, gut miscoiling, underdeveloped gills, cloacal edema, desquamation and severe hydropsy. Moreover, the characteristic sublethal effect of Diazinon on larvae was abnormal behaviour related to neurotoxicity with a NOEC-168 h of 4.5 mg Diazinon/L. Uptake of Diazinon was time-dependent and significantly related to exposure concentration for both embryos and larvae. Uptake was also stage-dependent, as it was up to 27 times higher for organisms exposed from blastula stage onwards than early larvae. These facts and the Hazard Quotients of 2.73, which is above USEPA´s Level of Concern, showed the threat that Diazinon represents for R. arenarum populations.