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.
Anthropogenic activities undertaken by man in his quest to improve his livelihood have resulted in the production and release of chemicals in quantities that the environment cannot cope with. Increase in urbanization and industrial activities as well as uncontrolled exploitation of arable land has undoubtedly resulted in significant discharge of chemical pollutants and their byproducts which find their way into aquatic reservoirs which are the ultimate sink for environmental pollutants. Thousands of organic and inorganic materials such as pesticides, fertilizers, detergents and metals contaminate natural aquatic ecosystems daily and affect aquatic biota such as snails and fish. Many developing countries, including Zimbabwe, depend on agriculture to boost their economies; thus pesticides are likely to represent an important source of xenobiotics in contaminated rivers. Pesticides such as organophosphates, carbamates and pyrethroids are extensively used in agriculture and public health. In agriculture pesticides such as chlorpyrifos are used in the control of pests of cotton, corn and fruit trees such as apples and oranges [
Mining and industrial activities also release byproducts such as metals and organic compounds which have stressful effects on the environment. In aquatic ecosystems these pollutants affect the wellbeing of aquatic biota. Netpae et al. [
The objective of this study was to evaluate in laboratory conditions the oxidative stress effects of an organophosphorus insecticide, chlorpyrifos and the metal lead, as single entities on the aquatic snail species Helisoma duryi.
All enzymes, substrates, pesticides and chemicals were bought from either from Sigma Chemical Company or Aldrich Chemical Company, Germany. All other laboratory reagents, used in this study, were of analytical (ANALAR) grade.
Snails were bred in outdoor cement aquaria containing tap water and fed on fresh garden lettuce according to the method of [
Six whole snails from each experimental group were pooled and homogenized in (5X weight of soft tissue) ml of ice-cold homogenization buffer (0.1 M potassium phosphate pH 7.4). The homogenates were centrifuged at 10,000 × g for 10 minutes and the resultant supernatant (S-10) fraction stored at −80˚C until analyzed. Protein content in post mitochondrial fractions of the snails was determined using the method of [
All enzymes assays described below were performed on S-10 fractions of the whole snail homogenates.
Superoxide dismutase (E.C.1.15.1.1) activity in the S-10 fractions was measured following the method of [
Catalase (E.C. 1.11.1.6) activity was measured in S-10 fractions according to the method of [
Glutathione peroxidase (EC.1.11.1.9) activity was determined in S-10 fractions according to the method of [
Glutathione S-transferase (EC.2.5.1.18) activity was measured in S-10 fractions according to the method of [
NAD(P)H quinone oxidoreductase (EC.1.6.99.2) activity was measured in S-10 fractions following the method of [
Statistical differences between control and experimental groups were analyzed using the Dunnet test. Differences were considered significant at *p < 0.05.
Superoxide dismutase activity was significantly increased (p < 0.05) in both lead and chlorpyrifos exposed snails when compared to the controls, unexposed snails (
Catalase activity was significantly increased (p < 0.05) in all pollutant exposed snails when compared to the controls (
Glutathione peroxidase activity was significantly increased (p < 0.05) in lead and chloryrifos exposed snails
when compared to the controls (
Glutathione S-transferase (GST) activity was significantly increased (p < 0.05) in lead and chloryrifos exposed snails when compared to the controls (
The activity of NAD(P)H quinone oxidoreductase was significantly increased (p < 0.05) in pollutant exposed snails when compared to the controls (
Pollutants such as metals occur naturally in the environment. However, due to man’s daily activities to improve his livelihood, their levels in ecosystems increase to levels that cause adverse effects to other organisms. Metals like lead are introduced in aquatic ecosystems as effluent from mining and industrial activities. Pesticides which are used by man to improve the quality and quantity of crops find their way in aquatic environments via aerial drifts during spraying, leaching and as runoffs after heavy rains. In fact literature shows that of the pesticides applied by farmers only 50% gets to the target organisms [
Metals like lead probably cause production of reactive oxygen species (ROS) which if not eliminated effectively attack macromolecules such as lipids, proteins and carbohydrates in living organisms. The induction of oxidative stress in biological systems by lead is reported by several researchers however, mechanism of ROS induction is unknown [
Our results also showed activations of CAT and GPX of 227% and 30% respectively in snails exposed to lead (
Activated GST activity shows the important role of this enzyme in protecting cells against oxidative stress [
Activation of NAD(P)H quinone oxidoreductase, a detoxification enzyme, that reduces reactive quinones and quinone-imines to less reactive and less toxic hydroquinones in living organisms has been shown to be a defense strategy by living organisms to guard against the oxidative effects of reactive quinones which can be formed during detoxification reactions. In the present study we observed significant (p < 0.05) activation of NAD(P)H quinone oxidoreductase in all snails exposed to chlorpyrifos or the heavy metal, lead (
The organophosphate chlorpyrifos is an insecticide, acaricide and miticide used to control foliage and soil- borne insect pests on a variety of food and feed crops. It controls pests such as cutworms, aphids, root borers, beetles, armyworms, spider mites and pink bollworms in crops that include cotton, soya beans, wheat, corn, citrus and tree nuts [
In the present study chlorpyrifos activated the activities of SOD, CAT, GPX, GST and DTD in all pesticide treated snails. Activation ranges of 22% - 155% were observed depending on the antioxidant enzyme analyzed. Chlorpyrifos is a degradable pesticide, and a number of environmental forces may be active in its breakdown. In soil, water, plants and animals, the major pathway of degradation involves cleavage of the phosphorus ester bond to yield 3,5,6-trichloro-2-pyridinol (TCP). This conversion to TCP is a detoxification step and the TCP can be further degraded via microbial activity and photolysis to carbon dioxide and organic matter. During normal metabolism of chlorpyrifos ROS may be produced and biological systems use antioxidant enzyme systems to protect themselves from effects of ROS. The results observed in the present study imply that probably in the metabolism of chlorpryifos in the freshwater snails H. duryi, ROS were indeed produced and probably that caused the defense mechanism of the snails to be activated (indicated by activation of CAT, GPX and GST) probably as an adaptive mechanism to overcome the oxidative stress induced effects of chlorpyrifos. Our results are supported by Khalil [
All exposed snails significantly recovered from the effects of the two pollutants chlorpyrifos and lead when allowed to recover in clean water for 7 days. The antioxidant enzymes of snails exposed to chlopryrifos recovered by 18% - 90% depending on the antioxidant enzyme. While, the snails exposed to lead recovered by 49% - 88% depending on the antioxidant enzymes in the recovery period. There are few studies that have shown how contaminated aquatic organisms can recover their biochemical status when the pollutants are removed. Ma et al. [
In the present study there was no significant recovery observed in the NAD(P)H quinone oxidoreductase activities for all pollutant exposed snails. The results suggest that probably NAD(P)H quinone oxidoreductase is an active enzyme in the scavenging of ROS during the detoxification of environmental pollutants. Our results are supported by Siegel et al. [
Our results have shown that the antioxidant enzyme system of H. duryi snail’s is sensitive to the studied pollutants indicated by the consistent activations of the studied antioxidant enzymes and as such has a potential of being used as a non-specific biological indicator of exposure to environmental pollutants.
This research was supported by the International Programme in Chemical Sciences (IPICS), Uppsala University, Sweden and the Research Board, NUST, Bulawayo, Zimbabwe.
NorahBasopo,ThamsanqaNgabaza, (2015) Pollutants, Snails, Oxidative-Stress, Organophosphates, Metals. Advances in Biological Chemistry,05,225-233. doi: 10.4236/abc.2015.56019