Browsing by Author "Nyathi, C.B."

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    A comparison of metal levels and antioxidant enzymes in freshwater snails, Lymnaea natalensis, exposed to sediment and water collected from Wright Dam and Lower Mguza Dam, Bulawayo, Zimbabwe
    (Elsevier Inc., 2010-08) Siwela, Andrew H.; Nyathi, C.B.; Naik, Yogeshkumar S.
    We compared the bioaccumulation of lead (Pb), cadmium (Cd), zinc (Zn), copper (Cu), nickel (Ni) and iron (Fe) with antioxidant enzyme activity in tissues of the snails, Lymnaea natalensis, exposed to elements of two differently polluted dams. 45 snails were exposed to sediment and water collected from Wight Dam (reference) whilst another 45 snails were also exposed to sediment and water collected from Lower Mguza Dam (polluted dam). Except for Fe in sediment and Pb in water, metal concentrations were statistically higher in sediment and water collected from Lower Mguza Dam. Lead, Cd and Zn were two times higher in tissues of snails exposed to Lower Mguza Dam elements. On one hand, superoxide dismutase (SOD), diphosphotriphosphodiaphorase (DTD) and catalase (CAT) activities were significantly lower whilst malondialdehyde (MDA) levels were significantly higher in tissues of snails exposed to Lower Mguza Dam sediment and water. On the other hand, selenium-dependent glutathione peroxidase (Se-GPX) activity was significantly elevated in tissues of snails exposed to Lower Mguza Dam sediment and water. Snails exposed to Lower Mguza Dam elements seem to have responded to pollution by increasing CAT and Se-GPX specific activity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress.
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    A comparison of metal levels and antioxidant enzymes in freshwater snails,Lymnaea natalensis, exposed to sediment and water collected from Wright Dam and Lower Mguza Dam, Bulawayo, Zimbabwe.
    (Elsevier Inc., 2010-08-02) Siwela, Andrew H.; Nyathi, C.B.; Naik, Yogeshkumar S.
    We compared the bioaccuniulation of lead (Pb), cadmium (Cd), zinc (Zn), copper (Cu), nickel (Ni) and iron (Fe) with antioxidant enzyme activity in tissues of the snails, Lymnaea natalensis, exposed to elements of two differently polluted dams. 45 snails were exposed to sediment and water collected from Wight Dam (reference) whilst another 45 snails were also exposed to sediment and water collected from Lower Mguza Dam (polluted dam). Except for Fe in sediment and Pb in water, metal concentrations were statistically higher in sediment and water collected from Lower Mguza Dam. Lead. Cd and Zn were two times higher in tissues of snails exposed to Lower Mguza Dam elements. On one hand, superoxide dismutase (SOD), diphosphotriphosphodiaphorase (DTD) and catalase (CAT) activities were significantly lower whilst malondialdehyde (MDA) levels were significantly higher in tissues of snails exposed to Lower Mguza Dam sediment and water. On the other hand, selenium-dependent glutathione peroxidase (Se-GPX) activity was significantly elevated in tissues of snails exposed to Lower Mguza Dam sediment and water. Snails exposed to Lower Mguza Dam elements seem to have responded to pollution by increasing CAT and Se-GPX specific activity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress.
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    Cytosolic glutathione s-transferases of ostrich liver.
    (2015-04-09) Naik, Yogeshkumar S.; Kanyepi, R.; Ndiweni, N.; Hasler, Julia A.; Nyathi, C.B.
    Chemicals consummumed by the ostrich are likely to be metabolised by liver detoxifying enzymes such as the cytosolic glutathione Stransferases (GST). We have studied the affinity purified GST from male and female ostrich livers. 1-chloro-2, 4-dinitrobenzene (CDNB) proved to be the best of several substrates tested to measme activity. Activity with this substrate was inhibited by sulphobromoptgnalein and cibamon blue which are well established inhibitors for the m ammalian enzyme. A number of pesticides and environmentai pollutants were also found to be strong inhibitors of the enzymes. Our data indicates that ostrich liver enzymes behave similarly to the mammalian liver enzyme in terms of substrate requirements and inhibition characteristics.
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    The effect of schistosomiasis on the activation of aflatoxin B1
    (1986-03) Hasler, Julia A.; Siwela, Andrew H.; Nyathi, C.B.; Chetsanga, C.J.
    This study examined activation of aflatoxin Bl (AFB1) in livers of Schistosomamansoni-infected and noninfected mice by measuring covalent binding of ('H]AFBl to cellular macromolecules in vivo and in vitro. During a one week time period after AFB1 treatment of animals, maximal binding of ('H]AFB1 to DNA, RNA and protein in liver occured during the 1 - 6 hour period after treatment, with less binding throughout of AFB1 to macromolecules of infected mice. Experiments performed in vitro to determine the capacity of liver microsomes to mediate the binding of AFB1 to calf thymus DNA showed that microsomes from infected mice mediated the binding of less ('H]AFB1 to DNA than those from noninfected animals.
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    The effect of schistosomiasis on the covalent binding of 2-acetylaminofluorene to mouse liver macromolecules in vivo and in vitro
    (Elsevier, 1990-07-15) Siwela, Andrew H.; Nyathi, C.B.; Chetsanga, C.J.; Hasler, Julia A.
    The covalent binding of [14C]acetylaminofluorene (AAF) to macromolecules in vivo and in vitro was measured in Schistosoma mansoni-infected and in non-infected mice. Liver microsomes from infected mice demonstrated a 42% decreased capacity to mediate covalent binding of AAF to DNA. In addition, the extent of binding of AAF to liver macromolecules in vivo was generally less in infected than non-infected mice.
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    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.
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    Hepatic Cytosolic Glutathione S- Transferases of ostrich (struthio camelus): partial characterisation and interaction with xenobiotics.
    (2015-04-09) Naik, Yogeshkumar S.; Kanyepi, R.; Ndiweni, N.; Nasler, J.A.; Nyathi, C.B.
    The glutathione S-transferases (GSTs) in affinity purified pools of male and female ostrich liver were studied. The GSTs were purified from crude liver cytosols by S-hexylglutathione sepharose affinity chromatography with yields comparable to those reported for GST from mammalian livers. The K, for both glutathione (GSH) and 1-chloro-2,4-dinitroSenzenzene (CDNB) were determined and found to be within the range of values known for mammalian and invertebrate species. 1- chloro-2,4-dinitrobenzene proved to be the best of nine substrates tested to measure activity. Activity was inhibited by bromosulphophthalein and cibacron blue which are well known inhibitors of the mammalian enzyme. Our results indicate that the ostrich liver enzymes behave similarly to the mammalian liver enzyme in terms of substrate requirements and inhibition characteristics.
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    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
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    Metal Accumulation and Antioxidant Enzyme Activity in C. gariepinus, Catfish, and 0. mossambicus, Tilapia, Collected from Lower Mguza and Wright Dams, Zimbabwe
    (Springer Science+Business Media, 2009-08-28) Siwela, Andrew H.; Nyathi, C.B.; Naik, Yogeshkumar S.
    The aim of this study was to measure antioxidant enzyme activities as biological indicators of pollution in tissues of two species of fish. Five Clarius gariepinus and three Oreochromis mossambicus were collected from Umguza Dam (polluted dam) whilst seven C. gariepinus and eight 0. mossambicus were collected from Wright Dam (relatively pristine dam). Diphosphotriphoshodiaphorase and catalase activities were consistently lower (42 f 2% and 78 f 20%, respectively) in liver whilst malondialdehyde levels were two times higher in muscles of both species of fish collected from Umguza Dam. However, seleniumdependent glutathione peroxidase (Se-GPX) activity was elevated four-fold in liver and gills of 0. mossambicus collected from Umguza Dam. Metal levels were two to five times higher in muscles of both species of fish collected from Umguza Dam. Fish from Umguza Dam seem to have responded to pollution by increasing Se-GPX specific activity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress. Keywords Antioxidant enzymes . Heavy metals . 0. mossambicus . C. gariepinus High levels of trace metals in freshwater may occur as a result of natural weathering of minerals in the sediments and bed rocks or as a result of anthropogenic activities such as mining, industrial, municipal and agricultural discharges (Winston 1991). Most trace metals are essential in small concentrations for normal metabolic processes in mammals including fish and humans. At abnormally high concentrations, metals can cause death in fish. Metals such as lead (Pb), cadmium (Cd), copper (Cu) mercury (Hg), silver (Hg) and cobalt (Co) have been shown to be extremely toxic when they bind to fish gills (Tao et al. 2000). Fish are exposed to metals through contaminated food and the water column in chronically contaminated aquatic ecosystems, the main routes of accumulation being through gills (Tao et al. 2000). Sublethal and chronic concentration of metals exerts their toxicity on fish by generating free radicals such as the hydroxyl radical ('OH), peroxyl-radical (Roo2) and superoxide (Oo2-) and some non-radical ROS such as hydrogen peroxide (H202). These ROS can trigger oxidative damage to proteins, nucleic acids and lipids (Winston 1991). However, defensive antioxidant enzymes, which detoxify reactive oxygen species, are present in the liver, kidneys, gills and intestine (Buhler and Williams 1988). Antioxidant enzymes have been used as biomarkers of pollution by metals and organic compounds that generate oxidative stress in molluscs (Cossu et al. 2000) whilst MDA levels have also been shown to be affected by oxidative stress (Rodrigues-Ariza et al. 1993). As antioxidant enzyme activities and MDA levels can be used as biomarkers of pollution, this study was undertaken to determine the relat~ onship between concentration of metals, antioxidant enzyme activities and MDA levels in two species of fish collected from Mguza Dam (which receives domestic and industrial effluent from Bulawayo City sewage works) and from Wright Dam with no history of pollution.
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    Metal accumulation and antioxidant enzyme activity in C. gariepinus, Catfish, and O. mossambicus, Tilapia, collected from lower Mguza and Wright dams, Zimbabwe
    (Springer Science+Business Media, LLC, 2009-08) Siwela, Andrew H.; Nyathi, C.B.; Naik, Yogeshkumar S.
    The aim of this study was to measure antioxidant enzyme activities as biological indicators of pollution in tissues of two species of fish. Five Clarius gariepinus and three Oreochromis mossambicus were collected from Umguza Dam (polluted dam) whilst seven C. gariepinus and eight O. mossambicus were collected from Wright Dam (relatively pristine dam). Diphosphotriphoshodiaphorase and catalase activities were consistently lower (42 ± 2% and 78 ± 20%, respectively) in liver whilst malondialdehyde levels were two times higher in muscles of both species of fish collected from Umguza Dam. However, seleniumdependent glutathione peroxidase (Se-GPX) activity was elevated four-fold in liver and gills of O. mossambicus collected from Umguza Dam. Metal levels were two to five times higher in muscles of both species of fish collected from Umguza Dam. Fish from Umguza Dam seem to have responded to pollution by increasing Se-GPX specific activity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress.
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    Metal Accumulation and Antioxidant Enzyme Activity in C. gariepinus, Catfish, and O. mossambicus, Tilapia, Collected from Lower Mguza and Wright Dams, Zimbabwe.
    (Springer Science+Business Media, 2009) Siwela, Andrew H.; Nyathi, C.B.; Naik, Yogeshkumar S.
    The aim of this study was to measure antioxidant enzyme activities as biological indicators of pollution in tissues of two species of fish. Five Clarius gariepinus and three Oreochromis mossambicus were collected from Umguza Dam (polluted dam) whilst seven C. gariepinus and eight O. mossambicus were collected from Wright Dam (relatively pristine dam). Diphosphotriphoshodiaphorase and catalase activities were consistently lower (42 ± 2% and 78 ± 20%, respectively) in liver whilst malondialdehyde levels were two times higher in muscles of both species of fish collected from Umguza Dam. However, seleniumdependent glutathione peroxidase (Se-GPX) activity was elevated four-fold in liver and gills of O. mossambicus collected from Umguza Dam. Metal levels were two to five times higher in muscles of both species of fish collected from Umguza Dam. Fish from Umguza Dam seem to have responded to pollution by increasing Se-GPX specific activity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress.
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    Metal Levels and Antioxidant Enzyme Activities in Freshwater Snails Exposed to Sediments From Polluted and Pristine Dams in Zimbabwe
    (2013-03-12) Naik, Yogeshkumar S.; Nyathi, C.B.; Siwela, Andrew H.
    The aim of this study was to determine the metal and antioxidant enzyme activities (AGE's) in the freshwater snail Lymnaea natalensis, exposed to sediments form a polluted (Umguza) and pristine (Wright) dams around Bulawayo City, Zimbabwe with a view to developing a biomarker of freshwater pollution. Adult lab reared snails (10-15 mm) were exposed for 4 weeks to water and sediment cofiected from 4 different sites of Umguza Dam (a sink of domestic and industrial effluent) and Wright Dam (privately owned -and considered to be relatively pristine). Antioxidant. enzymes, heavy metals and malondia1dehyde (MDA) analyses were performed using the S-9 fraction of whole snail soft tissue. Catalase and glutathione peroxidase activities were significantly elevated in snails exposed to Umguza Dam water and sediment (Student t-test, p < 0.01 and p < 0.001) when compared to snails exposed to Wright Dam. DT- diaphorase activity was significantly reduced in snails exposed to Umguza Dam water and sediment (p < 0.001) when compared to snails exposed to Wright Dam water and sediment. Snails exposed to Umguza Dam water and sediment bad a higher total metal load compared to those exposed to Wright Dam elements and the MDA levels were correspondingly elevated in snails exposed to polluted water and sediment (p < 0.01). The higher MDA levels and altered AGE activities suggest that the snails exposed to Umguza Dam elements are under higher oxidative stress.
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    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.
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    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.
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    Species and Sex Related Differences in Antioxidant Enzymes in Fish Collected From Umguza and Auchmacoy Wright Dams, Bulawayo, Zimbabwe.
    (2013-03-12) Nyathi, C.B.; Siwela, Andrew H.; Naik, Yogeshkumar S.
    Agricultural and industrial activity results in the pollution of our environment by pesticides and metals usually causing deleterious effects on both humans and other animals in the environment. We are interested in the effects of pesticides and metals on non-human targets, such as fish, in the environment. Literature reports suggest that there are species and sex differences amongst fish in the metabolism of foreign compounds (xenobiotics) on the detoxifying enzymes of aquatic organisms. The aim of this study was to assess whether there are any species and sex differences in antioxidant enzyme activities of local fish. Catfish (Clarius gariepinus) and bream (Oreochromis mossambicus) collected from two dams, one polluted (Umguza) and one pristine (Auchmacoy Wright) in the Bulawayo area. Gills, liver and kidneys from captured (gill netted) fish were excised, homogenized and centrifuged to obtain S-9 fractions. The S-9 fraction was used to assay for activities of the antioxidant enzymes, catalase, glutathione peroxidase and DT- diaphorase. Significant sex-related differences in the activity of catalase in liver and gill but not in kidney of catfish collected from Umguza Dam were noted (Student t test, P< 0.05). No sex-related differences in catalase activity were observed in bream tissues collected from Umguza Dam. Catalase activity in female bream collected from Umguza Dam was/significantly higher when compared to female catfish catalase from the same dam. Glutathione peroxidase activity in catfish collected from Umguza Dam were Seen to be sex dependent in gill and liver but not in kidney (Student t test, P < 0.05) whilst species differences were noted only in liver, with higher activities in catfish. Umguza bream showed significant sex differences in glutathione peroxidase activity onfy in the gills. DT- diaphorase activity in catfish collected from Umguza Dam was shown to be sex dependent in gill and kidney but not in liver. In Umguza bream, DT-diaphorase activity was seen to be sex dependent only in gills. Species differences in DT-diaphorase activity were only seen when male catfish and male bream were compared. DT-diaphorase activity was shown to be significantly higher in male catfish compared to male bream but there were no differences in activity when female catfish were compared to female bream in all the tissues. For fish collected from Auchmacoy Wright Dam, significant differences in bream catalase activity was seen in all the three tissues studied. Species difference in catalase activity were noted in liver and gill but not in kidney. Significant sex differences in the activity of glutathione peroxidase were noted only in the kidneys of the bream. Species differences in glutathione peroxidase activity were noted only in the gills of female fish. No significant diffe.rences in DT-diaphorase activity either by sex or species were noted in all the tissues of fish collected from Auchmacoy Wright Dam. Our data indicates that enzyme activity is species, sex and tissue dependent in fish and that enzyme activity is also affected by the presence of pollutants.
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    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.