Assessing the toxicity of pesticides used in temporary crops for aquatic organisms allows to
elucidate newly installed or aggregated disturbances over time. Thus, this ecotoxicological
study aimed to evaluate the acute toxicity of the 48% chlorpyrifos pesticide (Klorpan® 480EC)
in order to determine the mean lethal concentration (LC50-96h) for tambaqui (Colossoma
macropomum) fingerlings. Toxic sensitivity of the test organism was preliminarily assessed
using the reference substance “potassium dichromate”. Acute toxicity tests were performed
under controlled laboratory conditions for 96 hours of exposure under static system. The
medium weight of juveniles was 1.02 ± 0.06g were distributed in groups (n = 15), formed by
triplicates of 5 individuals per aquarium for each concentration of the established lethality
range: 2.5, 10, 15, 25 and 45 µg / L, plus one control (white). The lethality data were processed
by the Trimmed Spearman-Karber® method, which by Probito analyzes determined the LC50-
96h of 16.42 µg / L of the chlorpyrifos for tambaqui juveniles. Fast and severe effects caused the
animals to die within 48h of the test, and behavioral changes were observed up to 96h of
exposure. Prior to inducing death in animals, this pesticide caused some behavioral changes at
all concentrations, such as: accelerated operculum movement, continuous swimming, surface
breathing, loss of swimming balance, erratic swimming, paralysis, spasms, seizures, and others.
The Exploratory qualitative / quantitative methodological analyzes of these behavioral effects
demonstrated a possible concentration-response relationship. The results suggest that the
chlorpyrifos pesticide has been shown to be very toxic to fish, and poses a major threat to the
survival of aquatic biota.
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