14 Nov Insight into 2,4-D during the 2018 citrus season – Key Point Summary
Please find below our key point summary regarding our insights into 2,4-D during the 2018 citrus season.
WHAT IS 2,4-D?
2,4-D (2,4-Dichlorophenoxyacetic acid) is a systematic herbicide, that kills most broadleaf weeds by causing uncontrollable cellular growth of the cells and tissues that carry water within the weed via the action of the herbicide mimicking the plant growth hormone auxin.
2,4-D IN THE SA CITRUS INDUSTRY?
2,4-D in the South African citrus industry is applied as a post-harvest drench active, in the form of the 2,4-D Sodium salt, to assist in the prevention of stem-end rot by keeping the buttons or calyx of the fresh fruit alive whilst in storage.
Furthermore, 2,4-D has also recently been registered as a pre-harvest active to aid with the reduction of the navel ends and control of navel-end rot in combination with other fungicide actives.
HOW IS 2,4-D ANALYSED AT MICROCHEM?
2,4-D is typically included in the scope of analysis under the multi-residues pesticide QuEChERS method in the free acid form of the herbicide; however this conventional method cannot be applied to detect the full 2,4-D concentration which incorporates the sum of the free acid, esters, salts and conjugates.
When the active is applied to the fruit, especially over prolonged times of exposure, 2,4-D tends to form esters of the compound (the active alters its chemical structure) which covalently binds to the fruit matrix.
If the citrus sample were to be analysed with the QuEChERS method with the 2,4-D esters compounds present on the fruit as well as the 2,4-D free acid, only the 2,4-D free acid would be detected with the QuEChERS method and reported being positive omitting the additional 2,4-D esters and thus underestimates the true concentration. The reason that the active is underestimated in terms of the concentration is that covalently bonded compounds cannot be broken from the fruit matrix with the conventional QuEChERS method as there is no drastic pH change in the sample to perform this task.
Therefore, in order to report the full concentration of 2,4-D in citrus samples an additional step to the QuEChERS method was introduced to convert the 2,4-D esters into the free acid, via a process called alkaline hydrolysis which alters the pH to convert the covalently bonded esters into the free acid form, which would then report the full 2,4-D concentration as“2,4-D (Sum of free acid, salts, esters and conjugates)”as per European regulations.
The Alkaline Hydrolysis QuEChERS method would then also apply to other pesticide actives that tend to form ester compounds of the free acid whilst present on the fruit or tree such as the commonly applied active Dichlorprop.
It should be noted that Microchem has incorporated the Alkaline Hydrolysis step in the QuEChERS method of extraction for all citrus samples so as to report the full concentration of -D as “2,4-D (Sum of free acid, salts, esters and conjugates)”as we strive to conform to the European standard of pesticide reporting.
WHAT WE DISCOVERED IN TERMS OF 2,4-D?
Towards the beginning of the 2018 citrus season Microchem noticed an increase in the levels of 2,4-D found on samples submitted to the laboratory, and in most instances the concentration exceeded the default export MRL of 1 mg/kg.
This matter was investigated in-house by performing multiple re-checks of the Alkaline Hydrolysis QuEChERS method, 2,4-D pesticide standards as well as all the quality control measures used for this specific active, which were all within specification as they were when releasing the results to the industry. Furthermore, inter-laboratory testing was carried out with another SANAS accredited laboratory as well as an internationally recognized German laboratory which yielded identical 2,4-D concentration levels of the test samples. Citrus Research International (CRI) additionally conducted a ring-test with laboratories in South Africa in order to determine the degree of accuracy and precision of reported post-harvest actives in which Microchem achieved excellent results for the reporting of 2,4-D (Sum of free acids, salts, esters and conjugates).
Under further investigation it was found that 2,4-D is applied in the fruit drench tanks in the form of the 2,4-D sodium salt which is supplied by various suppliers, however one should pay careful attention when following the active application note from the supplier as they vary from supplier to supplier.
In this particular case, with regards to 2,4-D, we picked up on the fact that the starting concentrations of the actives from different suppliers were the same but the dosage values when preparing the drench/fungicide bath differ in the sense that the volume per 100 litres of water have inconsistent values, hence yielding lower or higher 2,4-D concentrations on the citrus fruit.
POINTERS ON 2,4-D
One needs to take into account that this active is not a conventional active due to its mode of action on fruit and cannot be analysed with the normal QuEChERS method if the full concentration is required depending on the destination country of the fruit in question. Therefore, special attention should be focused on the method utilized by the laboratories and how the active is reported in order to comply with export MRL values set out by various regions so as to avoid differences in manner of reporting which could ultimately lead to consignment rejection if the South African laboratories under-estimates the concentration based on the normal QuEChERS method.
The application notes of the actives in question should be followed, however one should keep in mind that the final concentration found on the fruit could differ from product to product as they have different preparation instructions in terms of volumes and/or concentrations.
Microchem incorporates leading-edge GC-MS/MS and LC-MS/MS analytical instruments as well as sample tracking LIMS software to offer pesticide analysis at competitive low prices by reducing the time it takes to get results. As a result our clients enjoy a streamlined experience, shorter lead times, easy-to-read reports and certificates of analysis.
Microchem is also able to offer sample receipt notifications when samples arrive in the laboratory and preliminary results for Dithiocarbamates, Ethephon, Heavy Metals and Microbiological analyses. We can also provide you with value adding summary reports of analyses performed over a specific period/season for all products analysed at Microchem as well as ARfD evaluation reports for individual samples analysed at Microchem.
Microchem strives towards being locally and internationally compliant in terms of pesticide reporting by abiding to DAFF pesticide regulations, as we are a DAFF officially recognized laboratory, as well as incorporating European regulations in how pesticide actives are reported in terms of pesticide naming, sums and conversion factors.
Microchem is SANAS accredited for pesticide analyses on the following fresh fruit matrices:
- Pome Fruit
- Stone Fruit
- Citrus Fruit
- Grapes and Small Berries
Should you have any queries or would like additional information with regards to the pesticide active 2,4-D please feel free to contact Rogan Van Kerpel and Stephen Newborn at the Microchem Pesticides Department:
Telephone: (021) 465 6996