pesticide residues in citrusYou may have celebrated the festive period with a cocktail or two. If you did, which pesticides did you possibly consume? The answer may depend on whether or not your cocktail was embellished with slices of citrus fruit. At least that was the inference from a lecture titled Effective Food Safety Control: Pesticide Residues and More Within a Single Run, which was presented by  Professor Jana Hajšlová  (UCT, Prague) at the the 1st International Symposium on Recent Developments in Pesticide Analysis . Prof. Hajslova reported that alcohol facilitates the transfer of residues from limes into the drink, transferring between 20-40% of incurred residues of azoxystrobin, imazalil and carbofuran in one hour. She lightheartedly noted that her students concluded that drinking mojito (white rum, sugar, lime juice, sparkling water, and mint) at a faster rate would decrease the intake of pesticides.

Perhaps a mocktail would be a better alternative to reduce pesticide intake, or would it? Professor Hajslova also reported multiple residues (3-5 different pesticides) in fresh home-made citrus juices, but most at concentrations below the permitted maximum residue levels (MRLs).

Pesticide Residues in Citrus

A number of different classes of pesticides, including plant growth regulators (used to promote fruit thinning in heavy years, fruit set in light years and to reduce pre-harvest fruit drop), herbicides, insecticides and fungicides are used in multiple treatments in the pre-harvest production of citrus.  Fungicides are then applied post-harvest to prevent spoiling during storage and transport.

Not surprisingly, analytical data often show a high frequency of detection of multiple pesticide residues in citrus fruit and juices. The results of a European survey of oranges in 2011  showed that 1,173 samples (80%) contained residues from a total of 73 different pesticides, with MRL exceedances of 16 different pesticides in 36 (2.5%) samples. The results for a survey of orange juice in 2012 showed that 217 samples (31%) contained residues of a total of 17 different pesticides and 37 samples contained multiple (2-3 pesticides). An official report by the UK Pesticides Residues Committee on a survey including citrus in 2009 showed that 100% of samples of grapefruit, 80% of lemons and 44% of limes contained multiple pesticide residues.

The high percentage of residues detected in citrus are typically fungicides such as thiabendazole or imazalil, which are incorporated into wax and sprayed onto the fruit after harvest. Post-harvest residues of carbendazim were once common, but carbendazim is now banned for use in orange production in the U.S. and the E.U. due to its potential as an endocrine disruptor. Most residues are below MRLs, and individually not considered to be of toxicological concern.

Pesticide Cocktails

However, for many years researchers have been discussing the possibility of greater risks associated with consumption of multiple residues of pesticides and chemical contaminants even at low concentrations. The so-called ‘cocktail’ effects refer to the synergistic interaction of two or more different chemicals to produce an enhanced additive biologically toxic effect that is greater than the calculated sum effects of the individual chemicals. Synergistic activation is not well understood because the experiments needed to provide robust evidence are by their nature complex and scientifically challenging. A recent study by Delfosse et al  that provides some insight into a possible explanation has been published in Nature Communications. An insight into the risk assessment of multiple residues has been published by the European Food Safety Authority (EFSA) in an article titled International Frameworks Dealing with Human Risk Assessment of Combined Exposure to Multiple Chemicals.

It is obviously important to consider all of the available information in context. The main purpose of pesticide monitoring programmes is to ensure that pesticides are being used in accordance with the label instructions so the analysis of citrus includes the peel. As pesticides applied post-harvest are mostly retained on and within the peel (81% in the case of thiabendazole), peeling will remove the majority high proportion of these residues. Peeling will not remove pesticides with systemic action, but  the vast majority of residues are below MRLs, which are not safety levels but trading levels, and are set at concentrations much lower than concentrations considered safe. The ‘cocktail’ effect of multiple residues creates some uncertainty, but pending more information, I will continue to enjoy my cocktail, preferably embellished with citrus slices from produce grown organically. It would be wise to consider other precautions, such as the use of non-treated, non-waxed citrus for zest, and organically-produced citrus for the preparation of citrus fruit preserves. Seville oranges, which are bitter tasting due to high levels of pectin, are not waxed specifically for this purpose.

Citrus – A Difficult Matrix for Analysis of Pesticides

Citrus fruits are among the most difficult matrices to analyse for pesticide residues. The high number of matrix co-extractives can cause suppression of ionization in LC-MS and chemical interferences in both LC-MS and GC-MS, as described in a lecture titled Evaluation of Q Exactive LC-MS for Pesticide Residues in Fruits and Vegetables, presented by Prof. Amadeo Rodríguez Fernández-Alba (EU Reference Laboratory for Residues of Pesticides, Fruits and Vegetables, University of Almeria) at the 1st International Symposium on Recent Developments in Pesticide Analysis. These matrix effects impact the accuracy and precision in quantitative analysis and the detection rates in screening analysis.

Like what you are learning?

Sign up to stay connected with all Thermo Scientific resources, applications, blog posts and promotions.
Keep Me Informed!

In LC-MS analysis of citrus, the use of hybrid quadrupole high resolution accurate mass (HRAM) mass spectrometry operating at 70,000 resolving power in full scan (at m/z 200) and at least 17,500 in MS/MS only provided by orbitrap technology is required to minimize the impact of the matrix effects. In a recent publication that included the analysis of oranges, the authors, Gómez-Ramos et al, concluded that LC/Q-Orbitrap MS working in full scan, together with an MS/M scan, is a powerful tool for routine analysis of pesticide residues in fruits and vegetables, especially to obtain accurate identification and quantitation.

Other derived products, including citrus oils and citrus molasses (used in animal feeds) are also analytically challenging and would also benefit from the use of Q-Exactive GC (GC-HRAM) technology.

Additional resources

Application note: High Efficiency, Broad Scope Screening of Pesticides Using Gas Chromatography High Resolution Orbitrap Mass Spectrometry

Analytical Scientist Article: Introducing the Pesticide Explorer Collection

Always what’s next.

During 2015 we added a lot of information to our Food and Beverage Community . Analytical Sciences are continually evolving, and along with developments in instrumentation, they create possible new solutions to food safety and quality challenges. Never wanting to standstill the question is Always what’s next? Well, going into 2016, we have a number of collaborations with world-renowned institutes, especially in the areas of pesticides and beverages. To follow the progress of these collaborations along with in-house applications, webinars, publications, events, and more, including a Round Table discussion (Live Podcast, mid-February 2016) with Katerina Mastovska, Hans Mol, Walter Hammock, Amadeo Rodríguez Fernández-Alba and Richard Fussell, please visit the Food and Beverage Community, which will have a new look and feel in early 2016.