STAGE-DEPENDENT SUSCEPTIBILITY OF 2,4-D AND ITS COMMERCIAL PRODUCT, ESTERNON ULTRA®, ON AMPHIBIAN EMBRYOS

C.S. PÉREZ-COLL; SANDOVAL M.T.; ARONZON, C. M.; HERKOVITS, J.

Simposio; Third International Symposium on Recent Advances in Environmental Health Research; 2006

Amphibians are considered highly susceptible to noxious agents, including pesticides. The identification of the most susceptible developmental stages could be of high value for biodiversity conservation objectives.Regarding pesticides for regulatory purposes the toxicity data reported is on the active ingredient (a.i.) while in the agroecosystems the commercial product is applied. The main purpose of this study was to evaluate the stage-dependent toxicity of 2,4-D (butylic ester of 2,4- dichlorophenoxyacetic acid) and its commercial formulation Esternon Ultra® (EU) on Bufo arenarum embryos from early blastula up till the end of embryonic development. For this aim, batches of 10 embryos (by triplicate) were treated during 24 hr with 2,4-D in the range of 8 to 32 mg.L-1 and EU® from 0.1 to 8 mg.L-1 of 2,4-D, starting at the following developmental stages: blastula (S.4), gastrula (S.11); neuromuscular activity (S.18), gill circulation (S.20), open mouth (S.21), opercular folds (S.23) and complete operculum (S.25). After pesticide treatments, the embryos were thoroughly washed with AMPHITOX solution (AS) and maintained in AS recording lethality, malformations and ethological alterations up to 96 hr post exposure. The results for 2,4-D expressed as NOEC and LC 100-96h were (in mg.L-1): 16 and 32 (S.4 and S.11), 16 and 18 (S.18); 12 and 16 (S.20 and S.21); 12 and 18 (S.23); 15 and 18 (S.25). The NOEC and LC100-96h for EU® (in mg.L-1 2,4-D) were: 2 and 8 (S.4 and S.11); 1.2 and 3.0 (S.18 and S.20); 0.5 and 2.0 (S.21); 2.0 and 3.5 (S.23);2 and 4.5 (S.25). Among malformations, it was appreciated for both substances: yolky plugs, delayed development, reduced body size, hydropsy, microcephaly, underdeveloped gills or gill agenesia, irregular surfaces (folds), vaulted cells followed by dissociation. Among neurological alterations, embryos exhibited abnormal swimming and spasmodic movements. Taking into account lethality, the results show that S.21 is the most susceptible stage to the herbicide, specially for its commercial product (EU®) which was about 7 times more toxic than the a.i. Therefore the stage-dependent toxicity data for amphibian embryos is of high relevance for hazard and risk assessment for the active ingredient as well as the commercial product, in particular, taking into account that amphibians are endangered species.