Authors :
Gaius-Mbalisi, V. K; Asiwe, E. S; Nlemolisa, O. R; Kemka, U. N; Onyeukwu, U. R
Volume/Issue :
Volume 8 - 2023, Issue 4 - April
Google Scholar :
https://bit.ly/3TmGbDi
Scribd :
https://bit.ly/40PCEQ7
DOI :
https://doi.org/10.5281/zenodo.7879787
Abstract :
The present study assessed the experimental
and predicted toxicity of pesticides and heavy metals
binary mixtures to Rhizobium species. The experimental
toxicity response was assessed using the inhibitory effect
of the individual and binary mixtures of glyphosate
(Gly) with cadmium (Cd (II) and lead (Pb (II)); and 2, 2
Dichlorovinyl dimethyl phosphate (DDVP) with Cd (II)
and Pb (II) to Rhizobium species total dehydrogenase
activity using 2,3,5 triphenyltetrazolium chloride (TTC)
as the artificial electron acceptor. The binary mixtures
were composed using fixed percentage ratios of 50% :
50%, 60% : 40% and 80% : 20% mixtures of Gly + Cd
(II), Gly + Pb (II) and mixtures of DDVP + Cd (II),
DDVP + Pb (II). The Half maximal effective
concentration (EC50) of the toxicants were estimated
using monotonic logistic dose-response model.
Prediction of binary mixture toxicity effect was carried
out using Concentration Addition (CA) and
Independent Action (IA) models. Results obtained
showed that Cd (II) and Pb (II) ions inhibited
Rhizobium sp. dehydrogenase activity in a logistic
concentration dependent manner; glyphosate and
DDVP exhibited a biphasic toxicity effect to Rhizobium
sp. Glyphosate and DDVP at concentrations below
5000mg/L and 1000mg/L respectively stimulated the
total dehydrogenase activity of the isolate. Using EC50
ranking, the order of toxicity was Cd (II) >Pb (II) >
DDVP > glyphosate. The binary mixtures of glyphosate
and Pb (II) in ratios of Gly (50%) : Pb (II) (50%) and
Gly (80%) : Pb (II) (20%) stimulated total
dehydrogenase activity of Rhizobium sp. at
concentrations below 1000 mg/L and 500mg/l for the
respective mixtures. Prediction of binary mixtures
toxicity using the CA and IA model differed in their
outcome of toxicity interactions. The CA and IA model
predicted additive interactions for the mixtures of Gly
50% + Cd (II) 50%, DDVP 60% + Cd (II) 40%, DDVP
50% + Cd (II) 50% and DDVP 80% + Cd (II) 20%,
which differed from experimentally observed
synergism. The CA model underestimated the toxicity
of binary mixtures of DDVP + Cd (II) and glyphosate +
Pb (II), while overestimating the toxicity of the DDVP +
Pb (II) and glyphosate + Cd (II) binary mixtures.
Furthermore, the IA model predicted mostly additive
interaction for binary mixtures of glyphosate + Cd (II)
and DDVP + Cd (II) ions mixture across the ratios;
which was a gross overestimation of toxicity in most of
the binary mixtures studied. The joint action of the
mixtures on test organism predicted with concentration
addition (CA) and independent action (IA) models may
present varying interactions dependent on the relative
amount of the heavy metals present in the binary
mixtures and their relative mode of action.
Keywords :
Prediction, Toxicity, Pesticides, Heavy Metals, Concentration Addition, Independent Action
The present study assessed the experimental
and predicted toxicity of pesticides and heavy metals
binary mixtures to Rhizobium species. The experimental
toxicity response was assessed using the inhibitory effect
of the individual and binary mixtures of glyphosate
(Gly) with cadmium (Cd (II) and lead (Pb (II)); and 2, 2
Dichlorovinyl dimethyl phosphate (DDVP) with Cd (II)
and Pb (II) to Rhizobium species total dehydrogenase
activity using 2,3,5 triphenyltetrazolium chloride (TTC)
as the artificial electron acceptor. The binary mixtures
were composed using fixed percentage ratios of 50% :
50%, 60% : 40% and 80% : 20% mixtures of Gly + Cd
(II), Gly + Pb (II) and mixtures of DDVP + Cd (II),
DDVP + Pb (II). The Half maximal effective
concentration (EC50) of the toxicants were estimated
using monotonic logistic dose-response model.
Prediction of binary mixture toxicity effect was carried
out using Concentration Addition (CA) and
Independent Action (IA) models. Results obtained
showed that Cd (II) and Pb (II) ions inhibited
Rhizobium sp. dehydrogenase activity in a logistic
concentration dependent manner; glyphosate and
DDVP exhibited a biphasic toxicity effect to Rhizobium
sp. Glyphosate and DDVP at concentrations below
5000mg/L and 1000mg/L respectively stimulated the
total dehydrogenase activity of the isolate. Using EC50
ranking, the order of toxicity was Cd (II) >Pb (II) >
DDVP > glyphosate. The binary mixtures of glyphosate
and Pb (II) in ratios of Gly (50%) : Pb (II) (50%) and
Gly (80%) : Pb (II) (20%) stimulated total
dehydrogenase activity of Rhizobium sp. at
concentrations below 1000 mg/L and 500mg/l for the
respective mixtures. Prediction of binary mixtures
toxicity using the CA and IA model differed in their
outcome of toxicity interactions. The CA and IA model
predicted additive interactions for the mixtures of Gly
50% + Cd (II) 50%, DDVP 60% + Cd (II) 40%, DDVP
50% + Cd (II) 50% and DDVP 80% + Cd (II) 20%,
which differed from experimentally observed
synergism. The CA model underestimated the toxicity
of binary mixtures of DDVP + Cd (II) and glyphosate +
Pb (II), while overestimating the toxicity of the DDVP +
Pb (II) and glyphosate + Cd (II) binary mixtures.
Furthermore, the IA model predicted mostly additive
interaction for binary mixtures of glyphosate + Cd (II)
and DDVP + Cd (II) ions mixture across the ratios;
which was a gross overestimation of toxicity in most of
the binary mixtures studied. The joint action of the
mixtures on test organism predicted with concentration
addition (CA) and independent action (IA) models may
present varying interactions dependent on the relative
amount of the heavy metals present in the binary
mixtures and their relative mode of action.
Keywords :
Prediction, Toxicity, Pesticides, Heavy Metals, Concentration Addition, Independent Action
