Abstract:
Herbicides, when not applied following standards of use, contribute to environmental
degradation, mainly water quality, and can disrupt the ecological balance of non-target species.
The aim of this study is to evaluate the acute toxicity of two herbicides (ammonium salt of
glyphosate and paraquat) frequently used by the farmers of Ngaoundere, on the fry of
Oreochromis niloticus. Surveys were undertaken to estimate the frequency of sold herbicides and
their use in the fields, respectively, with the sellers of plant protection products and farmers in
Ngaoundere. A static acute toxicity test was carried out, to determine the LC50 of commercial
formulations of glyphosate (Super Machette 888 WSG) and paraquat (Supraxone Royal) on the
freshwater Oreochromis niloticus and its behaviours, during the exposition. The fishes were
exposed to increasing concentrations of the two herbicides, in a non-renewed oxygenated
microcosm medium. The numbers of dead fishes were recorded, after 24, 48, 72 and 96 h and the
behaviours observed, during the exposition. Surveys results indicate that glyphosate (64.99%)
and paraquat (15.77%) herbicides are the most commonly used herbicides in Ngaoundere and
that 56 % of the respondent farmers do not use the herbicides according to the recommended
standards. The 96h-LC50 values, estimated by probit analysis, were of 8.78 and 14.87 mgL-1
, for
glyphosate ammonium salt and paraquat, respectively. Lowest Observed Effect Concentration
(LOEC) means were of 6 mg.L-1
for ammonium salt of glyphosate and 10 mg.L-1
for paraquat.
The cocktail glyphosate ammonium salt + paraquat showed no mortality at the concentration of 3
+ 5 mg.L-1
, while the mortality rate was of 100% at the concentration of 5.25 + 9.5 mg.L-1
. The
fry showed unbalanced behaviours as concentration increased: erratic swimming, increased
surfacing activities and opercular movements, loss of balance, immobility and finally death. The
ammonium salt of glyphosate was found to be moderately toxic, while paraquat is slightly toxic |
