The impact of
short term exposure to the commonly used herbicides, glyphosate and propanil on Clariasgariepinus juveniles was evaluated using standard
methods that assessed fish behavior and mortality.
Fish exhibited some behavioral abnormalities such
as hyperactivity, hitting of tails against the walls of the holding medium
and abnormal swimming. The herbicides caused mortality of fish in a
concentration dependent manner for the duration of exposure to acute
concentrations of both herbicides for 96 hrs. However, the LC50 value for
glyphosate by probit method/analyses was 2.09 mg/L
while that of propanil was 4.57 mg/L, hence glyphosate was more toxic than propanil.
A
great number of the Nigerian populace are into
agriculture, the vocation accounting for a portion of the nation’s gross
domestic product (GDP) (Ayandaet al., 2021). Some groups of pesticides are toxic to non-targeted
organisms. Herbicides are one of the main methods for controlling noxious weeds
in agricultural and non-agricultural lands all over the world and it presented
more than 60% of total pesticides used in agricultural sectors (Elalfyet al.,
2017). Herbicide is an agent that has
the ability to cause death to plants. They are chemicals that are used for
agricultural and industrial purposes, and are effective against humans, plants
and aquatic organisms such as fish because of their toxicity (Adedeji and Okocha, 2012). Herbicides can be found in large amount in
the environment including soil, aquatic and biotic environments. Many
herbicides are toxic to fish at very minimal concentration. Several herbicides
are recognized for causing renal and hepatic lesions in fish (Hogan,
2014). Therefore, the mass killing of
fishes can be attributed to pesticides and herbicides (Adedeji and Okocha, 2012). Similarly, the effects of herbicides are
based on solubility of herbicides, magnification of concentration upon entry
into the food chain and persistence of herbicides and transformation to other
harmful metabolites upon entry into soil, water and biota (Hogan, 2014). Hence, the application of herbicides is
reported to have a negative effect on aquatic organisms such as fish. Previous
studies describe the wide application of glyphosate as a threat to aquatic
environment due to negligence, non-adherence to instructions, lack of knowledge
about the negative implication of herbicides and laws that govern the use of
herbicides. Clarias gariepinus is an
important fish in Nigeria (Ayandaet al., 2021). It is highly prized by
both farmers and consumers and distributed throughout all freshwater
ecosystems. It is also being widely used as a sentinel organism in toxicity
studies. Hence, this study was conceived to examine the toxicity of acute
concentrations of two commonly used herbicides Glyphosate and Propanil in the African catfish, C. gariepinus.
MATERIALS
AND METHODS
Experimental
Fish
Juveniles of Clarias gariepinus of mixed sexes and fairly uniform sizes were obtained from a fish farm in Zaria, Kaduna State,
Nigeria. The
Clarias species averaging 11.99 ± 1.56cm standard length and body weight of
4.25 ± 1.17g were used for the study. The fish were then transported in oxygenated
polythene bags to the Fisheries Laboratory, Department of Biology, Ahmadu Bello
University, Zaria, Kaduna State, Nigeria. They were
fed on a commercial pellet diet (3 % of body weight per day) and acclimatized
for three weeks in 800 L rectangular tanks containing dechlorinated
tap water (conductivity 2000 µs/cm; pH ≈ 7.5; Oxygen 90-95 % saturation;
temperature 25 ºC; photoperiod 12:12 Light: Dark). The feeding stopped 24 hours
prior to the commencement of the experiment.
Preparation
of herbicides Test Solution
Two herbicides were used in the
investigation. Both herbicides were purchased from a commercial outlet in
Kaduna. Out of 360g/L glyphosate, a stock solution (5mg/L) of the toxicant was
prepared by adding 1mL of the toxicant to 999mls of water (Reish
and Oshida, 1987). Similarly, out of 276g/L propanil, stock solution of 1mg/L was prepared in the same
way as glyphosate. The stock solutions were used for preparing different
concentrations of the test solutions by diluting measured volumes (i.e. 0.36mL
in 999.64mL of dechlorinated tap water for 0.36mg/L
concentration). The dechlorinated tap water used had
the same physical and chemical properties with the one used in acclimatizing
the fish. The control solutions were made up of only dechlorinated
tap water.
Experimental
Design
Static bioassay was conducted in the
Laboratory between July and November, 2020 following OECD (1992) guidelines to
determine the toxicity of glyphosate and propanil to C. gariepinus. From freshly prepared
stock solutions, five concentrations of 0.90, 1.80, 2.70, 3.50, 4.50 mg/L for
glyphosate and 3.96, 4.32, 4.68, 5.04, 5.40 mg/L for propanil
were dispensed with a 100mL measuring cylinder and 5mL syringe respectively for
each concentration containing dechlorinated water of
20L to 25L tanks and control. Ten fishes were randomly distributed into each
test tank in 3 replicates. The physicochemical parameters of the diluting water
(temperature, pH, dissolved oxygen, total hardness, total alkalinity and
conductivity) during the acute test were measured. The opercular
ventilation count (OVC) and tail fin movement rates (TMR) were counted manually
per minute, for three minutes and the mean recorded using a stop watch. The OVC
and TMR were observed and recorded at 12, 24, 48, 72 and 96hr. Survival and
mortality were noted during this period. Fishes were considered dead when the opercular movement ceased and there was no response to
gentle probing. This was used as a measure of mortality. The LC50
was determined by plotting a graph of the different concentrations of the
toxicants against the number of dead fishes using the probit
method. One fish species (C. gariepinus)
was used for the study. Each of the herbicides was administered at five levels
of concentration and a control. That is, 6 treatments, three replicates 18
experimental set ups or tanks for each herbicide.
Data
Analysis
Probit analysis was used to determine the LC50 value
for the herbicides using minitab 15 statistical
packages.
RESULTS
Diagnostic Behavioural Responses of
C. gariepinus Juveniles Exposed to Acute Concentrations of Glyphosate
Opercular Ventilation Counts
Results
of the opercular ventilation counts of C. gariepinus juveniles exposed to acute
concentrations of glyphosate is presented in figure 1. At 12 hours, opercular ventilation counts of the exposed group of fish
were higher than that of the control. The increase in opercular
ventilation counts was dose-dependent. On the other hand, at 24, 48, 72 and 96th
hours the OVC of the control group was higher than that of the exposed group.
Decrease in OVC with increased in concentration of toxicant was observed from
24 to 96 hours (Figure 1).
Tail Fin Movement Rate
Results
of the tail fin movement rate of C.
gariepinus juveniles exposed to acute concentrations of glyphosate is
presented in figure 2. At 12th and 24th hours, tail fin movements of the
control were lower than the exposed group. This increased and decreased of tail
fin movement rate was time and dose-dependent (Figure 2).
Mortality/96-hr LC50
Values
The mortality and probit
values for fishes exposed to acute concentrations of glyphosate are shown in
Table 1. Mortality was observed to increase with increasing concentrations of
both herbicides, glyphosate, and the highest mortality was recorded against the
highest concentration 4.50 mg/L. The 96hr LC50 value for the
herbicide (glyphosate) was calculated based on these values, and the mean value
from the probit and log of concentrations was found
to be (0.320197) (Figure 3). Taken the antilog of the mean,
gives an LC50 value of 2.09 mg/L (Table 1).
Diagnostic Behavioural Responses of C.
gariepinus Juveniles Exposed to Acute Concentrations of Propanil.
Opercular Ventilation Counts
Results of theopercular ventilation count of C.
gariepinus juveniles exposed to acute concentrations of propanil
is presented in figure 4. At 12th and 24th hours, opercular
ventilation counts of the control were lower than the exposed group. However,
at 48, 72 and 96 hours, the opercular ventilation
count of the control group were higher than that exposed group to 4.32 mg/L to
5.40 mg/L respectively. This increased and decreased opercular
was time and dose-dependent (Figure 4).
Tail Fin Movement Rate
Results of thetail
fin movement rate of C.
gariepinus juveniles exposed to acute concentrations of propanil
is presented in figure 4.7. At 12 and 24 hourstail
fin movement rate of the exposed group of fish were higher than
that of the control. The increase intail
fin movement rate was dose-dependent. On the other hand, at 24,
48, 72 and 96th hours thetail
fin movement rate of the control group was lower than that of
the exposed group. Decrease in Tail fin
movement rate with increase in concentration of toxicant was observed
from 24 to 96 hours (Figure 5)
Mortality/96-hr LC50 Values
The
results of propanil acute toxicity bioassay showing
mean mortality of C. gariepinus juveniles
are presented in Table 2. Mortality of fish was observed in all the treatment
groups except the control. Mortality was first observed in concentrtions
3.96, 4.32, 4.68, 5.04 and 5.40mg/L concentrations respectively. The highest
mortality of 25 was recorded in the highest concentration 5.40 mg/L of propanil while the least mortality of 8 was observed in the
3.96 mg/L treatment.Similarly, the
total mortality, percentage mortalities, probit kill
values and the LC50 in mg/L of C.
gariepinus exposed to acute nominal concentrations of propanil
are presented in Table 2. Mean mortality was observed to be
concentration-dependent. The 96-hour median lethal concentration (LC50)
of propernil for C.
gariepinus juveniles using the minitab was found
to be 4.57 mg/L from the antilog of the mean (0.659770) from Table 2 and Fig. 6 respectively.
Acute and sublethal toxicity tests are
commonly used to assess the toxicity of chemicals on non-target animals (Santos
et al., 2013). The 96 h LC50 is one of the most important factors for
evaluating the toxic effects of contaminants. The 96h LC50 value of
Glyphosate and Propanil in this study was found to be
2.09 mg/L and 4.57 mg/L respectively. This is proportional to increase in glyphosate and
propanil herbicides concentration and duration of
exposure. Hence, mortality is dose dependent, which suggest that the herbicides
are toxic to fish. Varying LC50 values have been obtained from
different investigation on exposure of the same organisms to different
herbicides. The differences in the values may be as a result of variation in
the concentration of herbicide, age of organism and environmental condition Olorunfemiet al.
(2014). A steady trend was generally observed in the percentage mortality rate
of C. gariepinus which increases with
an increase in concentrations of glyphosate and propanil
which is consistent with observation from (Sani
and Idris, 2016). Similarly, less mortality was found
at 0.90mg/L concentration and higher mortality was found at 4.50 mg/L
concentration of glyphosate, while for the fish exposed to propanil
concentration, lower mortality was recorded at 3.96 mg/L while higher mortality
was recorded at 5.40 mg/L. However, with highest concentration of glyphosate
and propanil, various behavioural
changes occur such as erratic swimming, gulping of air, loss of equilibrium and
resting motionless at the bottom of the aquaria were observed, which was
similar to observations made byYajiet al.
(2018). The erratic swimming, restlessness, gulping of air and resting
motionless at the bottom of aquaria observed in the investigation are not only
as a result of impaired metabolism but could be due to nervous disorder. This
was because the behavioural changes were unnoticed
before the application of glyphosate and propanil.
This was also in line with previous studies of Ayandaet al. (2021). Low concentration of
glyphosate and propanil herbicides (0.90mg/L and
3.96mg/L respectively) did not produce any serious change in the fish behaviour within 24 h. Meanwhile, higher concentrations of
glyphosate (4.50 mg/L) and propanil (5.40 mg/L) at 96
h showed loss of response to stimulus and death. At the early stage of the
toxicant introduction, all the fish survived the initial attack. This may be
owing to their defensive adaptations as the respiratory mucosa on the inner
walls of the air-sacs is thrown into folds and ridges for increasing the
surface area for gas exchange. In contact with low oxygen level, C. gariepinus breathe through their skin
and even use their air bladder as an emergency lung by gulping surface air.
During the 48, 72, and 96 h of exposure, the fish displayed physiological
malfunctions such as hyperventilation, motionless State, increase opercular ventilation, general body weakness, skin
discoloration, loss of reflex, erratic swimming which were noticeable
particularly among some fish in the highest concentrations of Glyphosate (4.50
mg/L) and Propanil (5.40 mg/L) in
which 80% and 90% mortality was recorded. The physiological malfunctions are
believed to weaken the organism’s resistance to toxins and consequently
resulting in the significant death of almost 50% at the highest concentration.
With progressive exposure, deaths become inevitable even at a lower
concentration. This could be owing to stress and the cumulative impact of
Glyphosate and Propanil toxicity. The mortality pattern
recorded in this study agrees with that observed by Rand and Pectrocelli (1985) which stated that there should be less
than 35% mortality in one of the concentrations and at least more than 65%
mortality in the highest concentration. The mortality observed in the study was
considered a result of stress-induced on the immune system of fish. Thus, slow
toxic progress and long continuance can result in a chronic toxic response. The
haematological parameters have been used as a
sensitive indicator of stress in fish exposed to different aquatic contaminants
and toxins of various types. Sub lethal concentrations of toxicants in the
aquatic ecosystem will not certainly result in the outright death of aquatic
organisms. However, the bioaccumulation of these contaminants over an era of
time may create potential health threats not only to the aquatic animals like
fish but also on higher trophic level particularly man. In the present study,
the behaviour of C.
gariepinus juveniles exposed to both herbicides Glyphosate and Propanil were observed to be similar. This could be as a
result of the fact that both chemicals have the same mode of action since they
belong to the same group of pesticides called herbicides. However, in the
present study, Glyphosate was found to be twice more toxic than propanil, sincer LC50
of glyphosate was found to be 2.09 mg/L and that of propanil
was found to be 4.57
mg/L respectively.
CONCLUSION
The
present study shows that mortality of C. gariepinus juveniles increases with increase in concentrations of Glyphosate and
Propanil herbicides which has manifested in
behavioral changes. Therefore, the higher the concentrations, the higher the
mortality rate and change in behaviour. More so, the
lower the concentrations, the lower the mortality rate and change in behaviour. Hence, Glyphosate and Propanil
herbicides can induce mortality in Clarias
gariepinus juveniles.
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Cite this Article: Yerima, R; Jacob, LT; Nazeef,
S (2023). Acute Toxicity of Glyphosate and Propanil
on Clariasgariepinus
Juveniles. Greener Journal of
Biological Sciences, 13(1): 16-23, https://doi.org/10.5281/zenodo.8141211.
