Applied Biology and Biochemistry

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An Assessment of the Extent of Bovine Milk Pollution by DDT used in Public Health in Zimbabwe
(Scientia Research Library, 2016) Basopo, N.; Brock, Gerome; Mnkandla, Sanele
Indoor residual spraying of dichlorodiphenyltrichloroethane (DDT) has been widely used in the control of malaria, and has been appreciated for its low cost and high effectiveness. Prolonged use, however, has adverse effects as DDT and its metabolites persist for long in the environment, resulting in human and animal contamination. Contamination in animals such as cattle may result from consuming contaminated water, feed and fodder. The aim of the study was to evaluate the extent of contamination of DDT and its metabolites in cow’s milk from five towns in Zimbabwe. Samples were collected from farms around Bulawayo, Chiredzi, Esigodini, Harare and Mutare with a total of n=24 samples. The pesticide residues were extracted using the quick, easy, cheap, rugged and safe (Quechers®) method and solid phase extraction and analysed using gas chromatography with electron capture detector. Total DDT was detected in all samples at levels higher than the maximum allowable residue limit. Harare and Mutare samples had the highest DDT levels of 0.38 μg/ml and 0.26 μg/ml respectively, as compared with samples from other regions (0.08-0.13 μg/ml). The DDT metabolite residues,1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) and 1,1-dichloro- 2,2-bis(p-dichlorodiphenyl)ethylene (DDE), were also detected at varying levels in the samples. The results show the presence of DDT and its metabolite contaminants in bovine milk, posing a serious health risk to consumers. Alternatives to DDT may therefore need to be employed in the control of the malaria vector.
Carbaryl and Dimethoate Induced Alterations of the Antioxidant Defense System in Two Freshwater Pulmonate Snails Helisoma Duryi and Lymnaea Natalensis
(Scholars Research Library, 2016) Basopo, N.; Naik, Yogeshkumar S.
Organophosphates and carbamates are extensively used to increase the quality and quantity of field crops. These pesticides may indirectly enter water bodies where they affect aquatic organisms. Once absorbed by aquatic organisms the pesticides are metabolised and normal metabolic processes may produce reactive oxygen species that have adverse effects on the aquatic organisms. The effects of exposure to carbaryl and dimethoate pesticides on antioxidant enzymes of two freshwater snail species Helisoma duryi and Lymanea natalensis were evaluated. Groups of snails were exposed to 25 ppb of carbaryl and/or dimethoate for 72 hours. After the exposure duration they were then analysed for their effects on the oxidative defense systems of the snails. Increased thiobarbituric acid reactive substances levels and activities of catalase, superoxide dismutase, glutathione peroxidase and glutathione S-transferase in both snail species were observed, probably as a means of combating oxidative stress due to pesticide poisoning. Increased lipid peroxidation, coupled with altered levels of oxygen free radical scavenging enzymes in snail homogenates are discussed in relation to oxidative stress.
The Effect Of Three Species Of Schistosomes On Hepatic Drug Metabolism In Male BALB/ Mice
(Elsevier, 1990) Naik, Yogeshkumar S.; Basopo, N.
Schistosomiasis is a parasitic disease that affects over 200 million people in the world. S.mansoni and S.haematobium are of medical importance while S.mattheei is primarily of veterinary concern. It is important to know the effect that the disease has on elimination of xenobiotics. The effect of S.mansoni infection on thiopental sleeping times and zoxazolamine paralysis times has previously been reported by other workers as well as by us. Similar work on S.mattheei and S.haematobium infected animals, however, has not been reported in the literature. The effect of S.mattheei and S.haematobium on thiopental sleeping times was therefore studied and compared to results obtained for animals infected with S.mansoni. Thiopental sleeping times and egg loads of infected animals are shown in Table 1. Although S.haematobium infected animals did not have detectable levels of parasite eggs in their livers at 8 weeks post-infection, significant numbers of eggs were detectable at 12 weeks post-infection. This is in agreement with the observed delayed maturation of S.haematobium schistosomulae in rodents as compared to S.mansoni or S.mattheei. The number of worm pairs in each group was as follows: S.mattheei 20-25, S.mansoni 8-10, and S.haematobium (both 8 and 12 weeks post infection) 3-10 pairs. The sleeping times of all infected animals were prolonged when compared to their respective controls. The reasons for this are not clear but it is likely that the parasite egg-induced granulomas as well as the physical obstruction to portal blood flow caused by migration of•worms from mesenteric to portal veins play a significant role. Data obtained in this laboratory on drug metabolism in vitro in S.mansoni infected animals indicate that the activity of hepatic drug metabolising enzymes is also altered, but generlllly only in animals that have developed parasite egg-induced granulomas in their livers.
Effects of chronic exposures of selected heavy metals on the glutathione S-transferase activity of freshwater snails Lymnaea natalensis in Zimbabwe
(Taylor & Francis, 2019) Mnkandla, S.M.; Siwela, A.H.; Basopo, N.
The effect of the heavy metals (cadmium, copper, mercury and lead) on snail glutathione S-transferase (GST) was investigated in 2015. Groups of Lymnaea natalensis snails were exposed to heavy metals for 28 days at concentrations reportedly found in the Mguza Dam. Water and food were changed daily. Samples were collected at days 1, 7, 14, 21 and 28 post exposure. Inhibition of GST activity, following cadmium exposures, ranged between 58 and 60%, with a decrease of 30% on day 28. When snails were exposed to copper, inhibition significantly decreased by 16%, 29%, 49% and 72% inhibition when tested on days 1, 7, 14 and 21, respectively. Inhibition on day 28 was 44%. Mercury exposures resulted in significant increases in GST inhibition, namely, 47%, 62% and 79% inhibition on days 1, 7 and 14, respectively. Inhibition on day 21 was 82%, whereas on day 28 it was significantly lower, at 29%. Concerning lead exposures, inhibition levels on day 1, 7 and 21 had mean inhibition of 60%. Inhibition on days 14 and 28 was significantly lower, with a mean inhibition of 30%. These results suggest that chronic exposures could inhibit GST activity for a certain period, after which inhibition is reduced, possibly as a result of adaptation.
Effects of Industrial Effluent on Aquatic Organisms: A Study Using Zebra Fish (Danio Rerio) as a Model Of Evaluation
(African Journal of Science and Research, 2016-09-24) Mnkandla, Siphile; Ndebele, Donald; Teta, Charles; Basopo, N.
Industrial and municipal wastewaters are among the major contributors of chemical pollutants that enter aquatic bodies and affect aquatic biota, accounting for several thousand types of chemicals released into the environment. We exposed adult zebrafish (Danio rerio) to 3 dilutions of effluent (0.1 %, 0.5% and 1.0%)v/v and tap water (control) for 14 days to assess potential effects of industrial effluent on aquatic vertebrates. Antioxidant enzyme activities namely; superoxide dismutase, catalase, glutathione S-transferase and glutathione peroxidase were determined to evaluate oxidative stress effects in effluent exposed fish. The endocrine disrupting capability of the effluent was also investigated using vitellogenin assay. The results showed highest enzymatic antioxidant activity in fish exposed to the lowest industrial effluent concentration of 0.01% and increasing industrial effluent concentration reduced the antioxidant enzyme activity in exposed fish. A significant vitellogenin induction was observed in male fish that were exposed to the 0.01%, 0.1 %, 0.5% and 1.0% effluent concentrations compared the control. A non-linear dose response curve in vitellogenin induction was observed in male fish exposed to increasing effluent concentrations, indicating that complex interactive effects associated with high levels of chemicals in mixtures. The results showed that industrial effluent contain potent oxidative-stress-inducers and endocrine-disrupting-substances which affect the well-being of aquatic organisms.
The Effects of Sub Lethal Levels of Lead on Acetylcholinesterase Activity in the Rock Pigeon, (Columba Livia)
(Zimbabwe Journal of Science & Technology, 2017) Muusha, Yeukai; Mnkandla, Sanele; Basopo, N.
Lead is one of the most abundant heavy metals that has become widely distributed and mobilised in the environment. It exists in various forms which are bioavailable to many organisms including birds, causing physiological changes upon exposure. The aim of this study was to investigate the effects of sub lethal levels of lead on acetylcholinesterase activity in the Rock pigeon (Columba livia). Twelve free range and two pen reared (control) pigeons were collected from breeders around the city of Bulawayo and placed in separate cages. Six free range and one pen reared birds were exposed to 1.25 ppm lead acetate spiked feed and water for 72 hrs, whilst the remaining birds served as the unexposed control. Spiked feed and water were changed daily. Both the exposed and unexposed birds were sacrificed and the muscle, heart and liver tissues isolated and assayed for acetylcholinesterase activity. There was significant inhibition of enzyme activity in all tissue samples obtained from lead exposed free range birds when compared to their unexposed counterparts. In the lead exposed free range birds, muscle and liver acetylcholinesterase activity was below 0.005 μg/min/mg protein while that of the heart was in the 0.02-0.07 μg/min/mg protein range. Enzyme activity was greater than 0.1 μg/min/mg protein in the unexposed free range birds. Comparing the acetylcholinesterase activity of the lead exposed pen reared control, with that of the lead exposed free range birds, the latter demonstrated significant inhibition (p<0.05). The results therefore highlight the inhibitory effect of sub lethal levels of lead on acetylcholinesterase activity which could also be possibly enhanced by prior exposure to other environmental contaminants.
Esterase Activity of Two Aquatic Snail Species Helisoma Duryi And Lymnaea Natalensis
(2013-03-12) Nyathi, C.B.; Naik, Yogeshkumar S.; Basopo, N.
Previous work has shown that inhibition of esterase activity is likely to be a useful parafrieter to develop as a biomarker of organophosphate pollutants. We have extended our preliminary study and have now tested for esterase activity with two new substrates (five in total) while measuring the esterase activity in a newly established colony of the aquatic snails Lymnaea natalensis and Helisoma duryi. Post mitochondrial fractions prepared from whole body homogenates were used to measure esterase activity with the following 5 substrates: p-nitrophenyl acetate ( PNPA), (-naphthyl acetate (ANA), phenyl acetate (pHA), carboxylic esterase activity and acetylthiocholine iodide (Ach!) and S-butyrylthiocholine iodide (BthI) cholinesterase activity. Our data shows that the carboxylic esterase (CbE) activity measured in our new stock of snails was decreased (depending on the substrate used a range from 30% to 50%) compared to values obtained previously. Since the cholinesterase (ChE) activity was measured for the first time in these two species a comparison could not be made. In general, the esterase activity was found to be slightly higher in H. duryi than in L.natalensis. The reasons for the altered activity in the new snail colony is not clear but nutrient and climatic factors are likely to be responsible.
In Vitro Effects of Carbaryl and Dimethoate on Esterases of Lymnaea Natalensis.
(2013-03-12) Basopo, N.; Naik, Yogeshkumar S.; Nyathi, C.B.
Agrochemicals have adverse biochemical and physiological effects on organisms and can ultimately cause disturbances in ecosystems. It is therefore important that sensitive techniques are available to monitor their presence and persistence in the environment be monitored. We are pursuing the possibility of developing modified esterase activity in aquatic snails as a potential biomarker for the detection of organophosphate and carbamate pesticides in contaminated waters. We have previously reported that exposure in vivo of the aquatic snail Lymnaea natalensis to a number of organophosphorus and carbamate pesticides causes inhibition of esterase activity to varying degrees in a pesticide and esterase substrate specific manner. Here we report on the effects of two commonly used pesticides, dimethoate and carbaryl in vitro, on the esterase activity of an aquatic snail L. natalensis. Post mitochondrial fractions were prepared from adult L. natalensis bred in outdoor cement aquaria. Esterase activity was measured in the presence of various concentrations of dimethoate or carbaryl. Our results showed a non-linear, but dose dependent, inhibition of esterase activity with both pesticides using 5 different substrates which were used to differentiate (choline and non-choline) esterase activity. Esterase activity was reduced significantly, depending on the substrate used, in the presence of both dimethoate (11 "10 - 78'Yo) and carbaryl (l5'Yo-93"1o). Both dimethoate and carbaryl showed similar IC50 values but variations were noted depending on the substrate used to determine esterase activity. Dimethote was, however, the mor'e potent of the two pesticides as shown by the its lower IC50 values when compared to carbaryl. Our data suggests there is a potential for the use of esterase activity in L. natalensis as a biomarker of organophosphorus and carbamate pesticides
Inhibition of Esterases of the Freshwater Snails Helisoma duryi and Lymnaea natalensis by Mixtures of Pesticides.
(World Academic Publishing., 2012-02-02) Basopo, N.; Naik, Yogeshkumar S.
Pesticides indirectly reach aquatic reservoirs via aerial drifts and as runoffs where they affect aquatic organisms. Aquatic reservoirs receive different pesticides from the different fields which usually surround them. However, studies i investigating effects of pesticide mixtures on aquatic biota is limited. The effects of six pesticides and their mixtures on esterase activity of two freshwater snail species were investigated. Groups of snails were exposed to individual as well as mixtures of the pesticides for 96 hours before analysing for esterase activity. All pesticides inhibited esterase activity in exposed snails. Binary mixtures of pesticides caused additive or synergistic inhibitions of esterase activities when compared to effects of individual pesticides. The results indicated the importance of chemical interactions on the overall effects of pesticides on aquatic organisms
Molluscan Esterase Activity As a Biomarker of Aquatic Pollution Caused By Monocrotophos.
(2013-03-12) Naik, Yogeshkumar S.; Basopo, N.; Nyathi, C.B.
There are many analytical protocols for detecting levels of agrochemicals~inaquatic systems. Methods of analytical chemistry can provide information of the exact concentrations in water samples. However they do not provide information on the potentially harmful effects on the organisms in the aquatic environment as biological markers have been shown to. Biomarkers of environmental quality should be tested under field situations if they are to be accepted outside academic circles and become part of national policies in environmental monitoring programs. We have previously shown that exposure of Lymnaea natalensis to organophosphates caused dose and time dependent inhibition of esterase activity. Here we report on the effects of monocrotophos on esterase activity in L. natalensis under field simulated conditions.Juvenile snails reared outdoors were exposed to single dose (5, 12, 15, 20 and 25ppb) of monocrotophos dissolved in either Matopos (pristine) or Umguza (polluted)dam water for 1, 7 or 14 days. Water was not changed for the duration of exposure. Post mitochondrial supernatants of whole snail homogenates were used to measure esterase activity. Cholinesterase activity was measured using acetylcholine iodide while carboxylesterase activity was measured using a-naphthyl acetate and 4nitrophenyl acetate. Esterase activity was significantly reduced in a dose responsive manner for aIr substrates. The degree of inhibitioll. varied depen,ding on the water source. Our results also indicated a decrease with time in degree of inhibition of esterase activity, suggesting a recovery with time of the snails from pesticide poisoning. On comparing data from the two dams higher inhibitions were observed in snails exposed to Matopos dam water than those exposed to Umguza dam water. Umguza dam water is highly contaminated with industrial effluents and therefore expected to have a higher microbial load and increased pesticide decomposition rate when compared to Matopos dam water, which is relatively pristine. Our results have shown that esterase activity is very sensitive to presence of organophosphates with inhibitions of up to 92 % observed within 24 hours of exposure. Altered esterase activity therefore has a potential use as a biomarker for detecting organophosphatepollution in water samples.
Pollutant mixtures as stressors of selected enzyme activities of the aquatic snail Halisoma duryi
(Academic Journals, 2014-07) Basopo, N.; Mumbamarwo, L. T; Mkandla, D; Naik, Yogeshkumar S.
This study involves an investigation on the effects of a pesticide, metal and a detergent as individual and mixtures on esterase and antioxidant enzyme activity of the freshwater snail Helisoma duryi. Adult snails were exposed to sublethal concentrations of copper (5ug/L), industrial detergent, oxyfoam (15ug/L), carbaryl (25ug/L) as well as mixtures of these pollutants for 96hours. Carboxylesterase and cholinesterase activities were measured using 4-nitropheny/acetate and acetylthiocholine as substrates respectively. The activities of superoxide dismutase, catalase, glutathione perioxidase and glutathione S-transferase were also measured as indices of oxidative stress. Esterase activity was inhibited in snails exposed to carbaryl, copper or detergent. Mixtures of the different chemicals also caused inhibitions of esterase activity when compared to the controls. All the chemicals individually antioxidant enzyme activity alteration of enzyme activity in the mixture-exposed snails though the increase was less than sum of effects of individual pollutants. More studies on the effects of a wider range of pollutant mixtures on aquatic organisms are needed however, for the full appreciation of reactive interactions that take place in complex mixtures which ultimately affect the health of aquatic biota.
Pollutants, Snails, Oxidative-Stress, Organophosphates, Metals.
(Advances in Biological Chemistry, 2015-01) Basopo, N.
Aquatic reservoirs remain the ultimate sink of chemical pollutants emanating from anthropogenic activities such as agriculture, mining and industry. Freshwater biota undoubtedly is at risk from the adverse effects of these water pollutants and there is therefore, a need to monitor effects of these chemical pollutants in order to safeguard the health of aquatic biota. We investigated the oxidative stress effects of chlorpyrifos and lead on the freshwater snail Helisoma duryi to assess the potential of using this enzyme system as a biondicator of exposure to environmental pollutants. Groups of snails were exposed to 5 ppb lead acetate and 25 ppb chlorpyrifos for 7 days after which half of the snails were sacrificed and the other half were allowed to recover in clean water and sacrificed after another 7 days. Post mitochondrial fractions were used to measure the activities of the following antioxidant enzymes: superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase and diphosphotriphosphodiaphorase. Both pollutants enhanced the activities of all the antioxidant enzymes suggesting a defensive mechanism by the snail to combat the oxidative stress due to the organophosphate chlopryrifos and metal pollutant lead. There was a significant recovery of the antioxidant defense system of the snails allowed to recover in clean water shown by the reduced alteration of the antioxidant enzyme activities of the snails allowed to recover for 7 days. This suggests the need to minimize exposure of aquatic biota to chemical pollutants and remediate the polluted water reservoirs in order to safeguard the health of aquatic life.
Potential Use of Esterases As Markers of Aquatic Pollution By Organophosphate and Carbamate Pesticides
(2013-03-12) Naik, Yogeshkumar S.; Basopo, N.
Potential Use of Esterases As Markers of Aquatic Pollution By Organophosphate and Carbamate Pesticides Pesticides are used to widely in agriculture in Southern Africa. Many of these pesticides fall into the category of either organochlorines, pyrethroids, organophosphates or carbamates. We have been interested in the possible use of esterase is as biomarkers of environmental water pollution. Amongst the compounds we have studied are dimethoate, pirirniphos, malathione and monocrotophos. We have studied the effects of these pesticides on the esterase of aquatic molluscan species such as Lymnaea natalensis and Helisoma duryi and Physa acuta. The esterases studied include choline and non-choline esterases and activity was measured using different substrates namely, a-naphthyl acetate, phenyl acetate, 4-nitrophenyl acetate, acetyl thiocholine and S-butyryl thiocholine. Our data indicates that there is a marked species difference in the response to these pesticides. In addition we have found that carbamate pesticides inhibit esterase activity to a lesser extent than do organophosphates and that this inhibition is time and dose dependent. In general esterase activity has been shown to be inhibited by as little as one ppm within eight hours of exposure. Our date supports the results of studies conducted elsewhere in freshwater, estuarine, as well as marine organisms that suggest inhibition of esterase activity in aquatic organisms is a potential biomarker of water pollution. A review of the literature will be provided in addition to data generated in our laboratory.
Recovery Of Choline And Non-Cholinesterase Activity Of The Freshwater Snail Lymnaea Natalensis Following Exposure To Six Pesticides
(2013-03-12) Naik, Yogeshkumar S.; Basopo, N.; Nyathi, C.B.
Organophosphates and carbamates are the most widely used insecticides mainly because they are readily biodegradable in the environment. We investigated the recovery of esterase activity of an aquatic snail L. natalensis following a 24-hour exposure to 6 different pest.icides. A third of the snails were sacrificed after 24 hours while another third was allowed to recover in clean water for 14 days and the remainder for 28 days. All pesticides caused significant inhibition of esterase activity. Aldicarb caused the highest inhibition in esterase activity 98 % while thiamethoxam caused the least 61 %. Esterase activity improved significantly in the recovery period and 14 days in the recovery period, aldicarb and thiamethoxam exposed snails had recovered to 57 % and 67 % of control. After 28 days of recovery, aldicarb exposed snails had only 62 % esterase activity in comparison to controls. The results show that even after 28 days of recovery, esterase activity was still reduced by up to 38 % depending on the pesticide, an indication that recovery of the snails depends on the pesticide. From the results we suggest that where pesticides need to be applied more than once, a time gap between applications should be allowed to enable non-target organisms in soil and aquatic systems to recover from effects of previous applications thereby ensuring the good health of non-target organisms.
Thionphosphate Inhibition Of Esterase Activity In Freshwater Snail Hellsoma Duryi
(2013-03-14) Basopo, N.; Naik, Yogeshkumar S.; Nyathi, C.B.
Organophosphorus insecticides (OP's) are among the most commonly used pesticides in most African countries. These compounds are esters, amides or thiol derivatives of either phosphoric acid or thiophosphoric acids. The majority now in use such as azinphos methyl, chlorpyrifos, pirimiphos methyl and malathion contain the thiono moiety (=8) for (=0) on the phosphorus atom which increases the toxicity of the insecticide. There are six different chemical classes of OPls namely orthophosphates, thionphosphates, thiolphosphates, dithiophosphates, phosphonates and pyrophosphoramides (Hassall, 1990). When used in the vicinity of aquatic ecosystems the insecticides may enter in water bodies as a result of erosion and leaching in concentrations that I may affect non-target species such as fish and snails. Also the diversity in chemical structure of OP's that exist, results in variability in their toxicity. There is a need therefore to constantly monitor effects of these organic compounds on non-target organisms: The effects'of pirimiphos methyl, a thionphosphate on esterase activity in a freshwater snail Helisoma duryi was investigated with the aim of assessing its potential as a bioindicator of presence of OP's in water. Juvenile snails reared outdoors were exposed to pirimiphos methyl in either Matopos (pristi':le) dam water or Umguza (highly contaminated with industrial waste) dam water for 1, 7, or 14 days: Esterase activity determined in post mitochondrial supernatants was significantly depressed in',a dose dependent manner. Carboxylesterase activity measured using a-naphthyl acetate and'lpnitrophenyl acetate was reduced in the range (6-90 %) and (18-79 %) respectively while cholinesterase measured using acetylthiocholine iodide was inhibited in the range (19-85 %) depending on the water source. A decrease with time in degree of inhibition of esterase activity was also observed, suggesting a recovery with time of the snails from pesticide poisoning. This recovery of the snails was probably due to both natural and microbial decomposition of the pesticides with time. It's also possible that newly synthesized esterases replaced the inhibited ones. On comparing data from the two dams, higher inhibitions were observed in snails exposed to Matopos dam water than those exposed to Umguza dam water. Probably the higher microbial load in the contaminated Umguza dam resulted in increased pesticide decomposition and hence reduced inhibition of the snails in those waters whel} compared to those snails in Matopos, a pristine dam. Our results have shown that esterase activity altered by up to 90% is sensitive, to presence of pesticide pollutants and hence has a potential as a bio-indicator for detecting organophosphate pollution in water samples.
Toxicological Effects of Chlorpyrifos and Lead on the Aquatic Snail Helisoma duryi
(Scientific Research Publishing, 2015-10) Basopo, N.; Ngabaza, Thamsanqa
Aquatic reservoirs remain the ultimate sink of chemical pollutants emanating from anthropogenic activities such as agriculture, mining and industry. Freshwater biota undoubtedly is at risk from the adverse effects of these water pollutants and there is therefore, a need to monitor effects of these chemical pollutants in order to safeguard the health of aquatic biota. We investigated the oxidative stress effects of chlorpyrifos and lead on the freshwater snail Helisoma duryi to assess the potential of using this enzyme system as a biondicator of exposure to environmental pollu- tants. Groups of snails were exposed to 5 ppb lead acetate and 25 ppb chlorpyrifos for 7 days after which half of the snails were sacrificed and the other half were allowed to recover in clean water and sacrificed after another 7 days. Post mitochondrial fractions were used to measure the activi- ties of the following antioxidant enzymes: superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase and diphosphotriphosphodiaphorase. Both pollutants enhanced the ac- tivities of all the antioxidant enzymes suggesting a defensive mechanism by the snail to combat the oxidative stress due to the organophosphate chlopryrifos and metal pollutant lead. There was a significant recovery of the antioxidant defense system of the snails allowed to recover in clean water shown by the reduced alteration of the antioxidant enzyme activities of the snails allowed to recover for 7 days. This suggests the need to minimize exposure of aquatic biota to chemical pol- lutants and remediate the polluted water reservoirs in order to safeguard the health of aquatic life.
Toxicological Effects of Differently Polluted Dam Waters Spiked with Pesticides on Freshwater Snails Lymnaea Natalensis
(Canadian Center of Science and Education, 2016) Mnkandla, Sanele; Basopo, N.; Tapfuma, Donald; Delfina, Majaya Rachel
Pesticides extensively used in agricultural fields to ensure high quality crop yields indirectly find their way to aquatic bodies where they affect aquatic biota. We investigated the effects of pesticides in different dam waters on esterase enzyme activity of the freshwater snail species Lymnaea natalensis. Groups of adult snails were exposed to 0.006 ppm chlorpyrifos and 0.003 ppm aldicarb in polluted water from Umguza dam and relatively pristine water from Hillside dam for 14 days. Carboxylesterase, acetylcholinesterase and arylesterase activities were measured. Both pesticides caused significant inhibition of esterase activity after the 14 day exposure period, with exposures to Umguza dam water showing higher inhibition as compared to exposures to Hillside dam water. Aldicarb and chlorpyrifos both showed a time-dependent inhibition of enzyme activity, the former causing a higher inhibitory effect as compared to the latter. Acetylcholinesterase was inhibited up to 80% following exposure to aldicarb while exposure to chlorpyrifos in Umguza water caused only 40% inhibition. Carboxylesterases were similarly inhibited with higher inhibition observed in snails exposed to Umguza dam water when compared to snails exposed to Hillside dam water, while arylesterases were inhibited in the range 80-90%, with an exception of chlorpyrifos spiked Hillside dam water which caused 45% inhibition. Contaminated Umguza dam water also appeared to enhance the effects of pesticides when compared to the relatively pristine Hillside dam water. Alteration of esterase activity can be used as an early warning signal indicating exposure to environmental pollutants. The results of this study therefore, highlight the adverse effects of pesticides on non-target aquatic organisms, evidenced by the inhibition of esterase activity.

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