Studies on the rapid detection of pesticides on stored grain


Cereals & Oilseeds
Project code:
01 June 1989 - 31 May 1990
AHDB Cereals & Oilseeds.
AHDB sector cost:
£52,956 From HGCA (Project No. 0011/2/89)
Project leader:
W A Matthews and N R Price CSL-Slough



About this project


1. The EnzyTec Pesticide Detection Program was investigated as a rapid field test for the detection of pesticides on stored grain in the UK. It was concluded that it would only be useful for testing UK treated grain for the compounds chlorpyrifos-methyl, malathion, methacrifos or etrimfos at doses of 5ppm or more and if the testing was carried out within 8 weeks of the treatment.

2. The test depends upon the formation of a blue colour. If pesticides which react with the enzyme acetylcholinesterase are present, ie organophosphates or carbamates, the enzyme becomes blocked and no colour develops. The organophosphorus pesticides used as grain protectants in the UK only react with the enzyme if present in an oxidised form. The kit therefore contains ampoules of an oxidising agent which is used before the test is carried out.

3. Equal volumes of the grain to be tested and water are shaken together for 1 minute and the test is carried out on 20 ml of the water extract.

4. In tests carried out at the Central Science Laboratory, Slough on grain treated with commercial formulations at the recommended doses, only methacrifos and malathion were detected; pirimiphos- methyl, chlorpyrifos-methyl, etrimfos and fenitrothion were not. This is because these compounds are not very soluble in water and the concentrations present in the extracts were not high enough to react with the EnzyTec ticket.

5. A method was developed, using a detergent solution and multiple extractions, which enabled sufficient chlorpyrifos-methyl, malathion, methacrifos and etrimfos to be extracted from the grain to give a positive response at a dose on the grain of 5ppm. At doses below this the test was found to be unreliable.

6. Pirimiphos-methyl and fenitrothion did not react with the enzyme on the detector ticket at all. In the case of pirimiphos-methyl this was found to be because oxidation did not proceed. It did not prove possible to overcome this problem. Therefore, the EnzyTec kit, or any other based upon the use of the acetylcholinesterase enzyme, may not be suitable to detect pirimiphos-methyl. The problem with fenitrothion was not investigated.

7. The amount of pesticide extracted with water from grain decreased with time after the treatment, so much so that by 8 weeks after treatment a positive response with the ticket could not be relied upon.

8. The tickets purchased from EnzyTec were found to vary considerably in terms of performance. Tickets which would have given uneven responses were removed after visual inspection but replicate tests were required to obtain a reliable result, thus increasing the cost of the tests.

9. The performance of the tickets deteriorated four fold over a storage period of two years at room temperature. The best responses were obtained in the first 4 months.