|M.Sc Student||Levy Ella|
|Subject||Early Contamination Detection in Water Supply Systems|
through Enhancement of Bio-sensors by Chlorpyrifos
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Barak Fishbain|
|Full Thesis text|
Rapid water quality monitoring in water supply systems can Prevent immediate exposure to harmful substances and avert adverse health effects.
Rapid contamination detection and warning of an acute toxicity event could be achieved by monitoring the reaction of living organisms exposed to a continuous water flow in a biological early warning system (BEWS). Not all toxic substances influence organism used in BEWS in a short period of time and thus cannot be detected rapidly.
A common toxic substances that penetrate water systems are Organophosphorus (OP) pesticides. In BEWS, in toxic concentrations, OP pesticides might affect fish after a long time period which not suitable for real time detection. The reaction of the test organism could be in shorter time and at lower concentration by enhancing the toxicity of the substance. In the case of OP the substance has higher toxicity after oxidation. In this work we developed a concept for enhancing fish bio-sensors for detecting OPs by applying chemical manipulation, so in the event of an OP contamination it transforms to a more toxic form.
Chlorpyrifos (CP) was used in this research as a representative pesticide of the OP group. The work is divided in to two parts. Part one is the Oxidation of CP to Chlorpyrifos oxon (CPO) in water in order to increase its toxicity. Part two is the comparison of CP and CPO influence on fish that are used as biosensors in BEWS.
Oxidation of CP in water was achieved by using bromine, chloroperoxidase enzyme and chlorine. Most of the experiments were performed with chlorine and inspected for different residence times and molar ratios. The oxidation yield increase with time and as chlorine to CP molar ratio increased.
The test organism selected for the toxicity experiments was the striped bass. The fish weighed about 1 gr and were 4-6 cm long. The experiments were performed in concentrations between 0.02 to 4 mg/l of CP and CPO for 5 hours. CPO was found to be more toxic by at least two orders of magnitude when compared to CP. The fish behavioral change and mortality when exposed to CPO was significantly faster and at lower concentrations in comparison to CP. When exposed to 0.03 mg/l of CP and CPO, the maximum CP concentration allowed by the health ministry of Israel, only the fish exposed to CPO showed a reaction which occurred after about an hour of exposure.