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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