(Objective)

The objective wasto determine which of the two hydra species (Hydraattenuata or Hydraviridis) was more sensitive to two pesticides, and the nuse the most sensitive species as part of the battery of testorganisms of the Ecotoxicological Studies Laboratory (ECOTOX).

(Methodology)

For this purpose, dilutions of two of the most comm only used pesticides in pineapple cultivation in CostaRica which were detectedin water samples were used: the herbicide diuron and the insecticide ethoprophos. Toxicity bioassays were conducted with each of the sesubstances and with amixture of the sesubstances.Themorphological state of the hydras was recorded. Inaddition,the mean effective concentration (EC50), mean lethal concentration (LC50) andtoxicity interactions wer evaluated interm sof three possibilities: antagonistic, additiveor synergistic.

(Results)

H. attenuata as the most sensitive species to both pesticides,withan LC50sof16.84mg/Land103.01mg/L, and an EC50sof4.24mg/Land23.4mg/L for diuronan dethoprophos, respectively. Furthermore, H. viridishadan LC50sof36.94mg/Land103.01mg/L, withan EC50sof13.64mg/Land53.12mg/L, also for diuronande thoprophos, respectively. Exposure to the pesticide mixture only caused mortality in H.viridisandhadas y nergistic effect on both species.

(Conclusions)

These results suggest that H. attenuata is the most appropriate species for the evaluation of pesticide effects, but fur the rstudies should be conducted on the interactions of contaminants in mixtures, since these may modify their toxicity for different species.

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