Detection & Monitoring of Carbamate Pesticides
Content Objective Case study background
Introduction - Why use carbamate pesticides?
Health impacts of carbamate pesticides.
Measurement method
Results and comments Advantages & disadvantages of systems
used
Objective
A case study of two flow-injection biosensor systems using semi disposable enzyme reactor have been developed to determine the presence and amount of Carbaryl, a type of Carbamate pesticide.
Case Study Background
Water samples collected from wells located in the Songkhla Province of Thailand.
There are various vegetation farm found in that area.
The six sampling wells that were chosen are
all located near vegetable growing areas.
Introduction - Why use carbamate pesticides?
Increased use of Carbamate pesticides due to
its ability to kill of wide range of pest.
lower environmental persistence
economically viable
past results visible
While Organochlorine pesticides are
environmentally persistent
bio-accumulative pesticides
genotoxic – (deleterious action on a cell’s genetic material affecting its integrity)
endocrine disruptors – ( interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body)
Health impacts of Carbamate pesticides
Acetylcholinesterase, is an enzyme that degrades the neurotransmitter, acetylcholine.
Carbamate pesticides causes a inhibition/retardation of acetylcholinesterase(AChE) enzymatic activity when ingested.
Thus when there is a inhibition of AChE activity, there will tend to be an increase amount of acetylcholine
In there is high level of acetylcholine, it can cause convulsions, epilepsy and tremors.
Measurement method
Test was done with 2 different type of flow-injection biosensor systems:
- Potentiometric ( ion analyzer – measures pH level)
- Conductimetric (conductivity meter – measures conductivity level)
The acetic acid dissociated further to release hydrogen ions as shown:
The released hydrogen ions are then used by both the potentiometric & conductimetric system, which respectively uses pH electrode to detect the increase of hydrogen ions, and a lab-built conductivity meter to detect the increase of conductivity due to the increased number of ions.
Measurement method Step 1 : Immobilization of acetylcholinesterase on activate silica gel.
Step 2: Injection of Acetylcholine solution to determine initial enzymatic activity.
Step 3: Injection of water sample which may be containing carbamate pesticides.
Step 4: Stop flow when sample solution reaches enzyme reactor. ( Incubation period )
Step 5: Wash out of pesticide containing solution,from system .injection of Acetylcholine solution again, and determine the enzymatic activities.
%Inhibition can then be calculated for the before & after results.
Inhibition, I (%) = [ (Ho - H1) / Ho ] x 100
Ho – Height difference given by enzyme reactor before
Hi – Height difference given by enzyme reactor after
Results and comments
Only samples from sampling site 1 and 2 contains carbaryl by using the two biosensor systems
Standard carbaryl was analyzed by the GC-MS first.
Incubation time is 5 and 10min for the potentiometric and conductimetric system respectively.
Results and comments Potentiometric system: Inhibition values 7.2% and
2.9%
Conductimetric System: Inhibition values 5.9% and 2.8%
Detection limit of system 10% inhibition 0.3ppm
US EPA standard 12% inhibition 0.7ppm
Results and comments Presence of carbaryl in water samples were double
confirmed with gas chromatography–mass spectrometric (GS-MS) system
Reasons for given results
two wells were nearer to the vegetable patches than the rest
vegetable patches near these two sites were just recently sprayed, a few days before the water collection
As half-life of carbaryl in surface water is about 8 days
Advantages & disadvantages of systems used
Advantages Both systems are simple to construct and easy to operate
- The potentiometric system uses pH electrode that is readily available
- The conductivity cell in the conductimetric system is very easy to make, using a small section of a glass tube with two stainless steel tubes glued to the ends as electrodes
Both systems allow the analysis of a large number of samples
Can be used as a monitoring or a screening method for pesticides
Disadvantages Although the enzyme reactor is specific to one particular type
of compound, the detection sensitivity is still not high enough to detect low concentrations of Carbaryl in the water sample.
THE END http://detectionandmonitoring.wordpress.com/
Prince of Songkla University, Hat Yai, Songkhla
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