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Addressing Pesticide Residue
Fast, efficient and cost-effective analysis will assure the quality of agricultural products.
by Jennifer Larson and Ned Purdom
The European Union, through the newly formed European Food Safety Authority (EFSA), is widely recognized as one of the strictest regulatory agencies in the world governing the production and distribution of consumable agricultural products. Whether its zeal is driven by France’s long standing claim as the birthplace of gastronomy or the fact that many countries with different food traditions share patch-worked borders or by consumer concern for food safety fueled by well- publicized scares over BSE in beef, Salmonella in eggs and dioxins in pâté, it is clear that the policies the EFSA has set forward leave little room for missteps in the assurance of food quality.
One of the key areas regulated by the European Commission and the EFSA is the use of plant protection products – insecticides, fungicides and herbicides. In 1991, a harmonized authorization system was established to ensure that these active substances could be evaluated, controlled and made public on an EU-wide basis with the idea that an active substance cannot be used unless it is included on a positive EU list. At the time the directive was adopted, there were over 800 such substances authorized for use in the member states.
In 1992, the EU embarked on a total review of all plant protection products that is expected to be completed in 2008. The fate of the products in question rests almost entirely with the manufacturers who must “defend” their substances (i.e., prove that they meet the required safety standards). The scrutiny has led to a number of the older active compounds being withdrawn either for reasons of toxicity, efficacy or environmental impact, or simply because the regulatory hurdles and financial burden of providing adequate scientific data to support an approval were too onerous. As a result, by 2003 almost 50 percent of the original plant protection substances had been deemed unsuitable to remain on the market and have already been withdrawn or will be shortly.
When a compound is de-listed, its maximum permitted residue level (MRL) in food reverts to the limit of detection (LOD) which in the EU is typically set at 0.01 mg/kg (10 mg/kg or 10 parts per billion(ppb)). Proposed new MRL legislation being considered is to set a common LOD of 10 mg/kg for any commodity/pesticide combination for which a higher level cannot be justified.
MRLs reflect levels of pesticides that are expected to be found in produce that has been treated in accordance with good agricultural practices. Where pesticides do not give rise to readily detectable residues, or are not approved for use on particular commodities, MRLs are set at the lowest level that can be identified in routine laboratory analysis – effectively a zero. Although MRLs are not safety limits, generally being set well below a level that could cause concern for consumers’ health, they remain the statutory tool used to ensure legal compliance.
In an effort to internationalize their efforts and level the playing field for member states to participate in the increasingly global market for agricultural products, the EFSA consults with the World Trade Organization (WTO) on all new MRLs before they are issued. This doesn’t necessarily ensure that standards are the same from country to country, but does signal that harmonizing production is still the goal.
One example of how the MRLs remain country-specific, however, is the proscribed limits on chlorpropham – a growth regulator used in potatoes to suppress sprouting during storage. The MRL in the UK and throughout most of the EU is 0.5 mg/kg, while in Sweden the limit is 10 times less at 0.05 mg/kg and the U.S. Environmental Protection Agency (EPA) has set the limit at 50 mg/kg. This indicates not only the ongoing inconsistencies, but the very strict limits allowed (in the U.K. and across the continent) by the European authorities.
In addition to de-listing existing compounds, the EFSA has the responsibility to ensure that new plant protection products are fully evaluated for safety, efficacy and environmental impact prior to being made available to growers.
In 1993, a survey by the National Resources Defense Council found that worldwide there were 71 pesticides used on food crops that have been found to cause cancer in animals and humans. Similar concerns regarding organo phosphorus and carbamate compounds are being expressed in campaigns led by Greenpeace and Friends of The Earth. A number of these compounds, developed as many as 50 to 60 years ago, have been taken off the markets both in the U.K. and the U.S., and replaced by compounds, which have better activity or less environmental or potential human health impact. The list of approved pesticides, herbicides and fungicides is long and growing as new compounds are introduced and used (or misused) by growers looking for more effective options.
Against this background, the requirements for reliable, sensitive and comprehensive analysis of pesticide residues in food has never been more crucial to ensure compliance with national and international law and to assure consumers that their fruits and vegetables are healthy.
New Detection Techniques
Traditionally, pesticide residues in foods were monitored with multi-residue methods such as gas chromatography (GC) coupled with either selective detectors or mass spectrometry (MS). But the newer substances, while safer, have proved difficult to monitor because they are either not amenable to GC or are not detectable at sufficiently low levels to assess their compliance with statutory maximum levels.
In order to keep up with the changing landscape, companies providing agricultural analysis in Europe have had to shift to new detection techniques to measure the residue of the recently approved pesticides. One response has been for the produce testing labs to assay compounds separately with individualized methods for each class; but this results in lengthy analysis times with high staff and consumables cost.
With the emergence of new compounds on the market and a reduction in allowed MRLs throughout Europe, companies that provide full-scale analysis and consulting on food products, such as Law Labs, (Birmingham, England) have seen an increase in the demand for their services. Law Labs works with a number of the largest worldwide agricultural suppliers as well as supermarket retailers to independently test and validate the pesticide levels in traded and marketed produce and other foodstuffs.
“This isn’t just about needing to test for many more compounds, it’s also about being able to test them at lower and lower levels,” says Don Brown, pesticide services manager for Law Labs. “The challenge is being able to achieve these detection levels with a high degree of confidence so you are certain that what you have identified is genuinely a pesticide, not a co-extracted artifact.”
Brown, who belongs to the Royal Society of Chemistry, the Institute of Food Sciences and Technology and the British Mass Spectrometry Society, been testing food for pesticides for more than 20 years. He is a stickler for both accuracy and validity and emphasizes that “for routine testing it is necessary to be able to detect to a level that is at least half of what is set for compliance so you know that you are well within the maximum limits.”
He notes that until recently, the company had established systems for detecting common pesticides, but only a piecemeal approach for the analysis of novel substances that were not amenable to identification by GC-MS. One approach used was to apply different GC conditions or combined liquid chromatography (LC) with UV or fluorescence detection on these odd samples, but this would often require separate extractions of the same sample and was not an efficient solution.
“It was no longer cost effective to create a specific targeted analysis technique each time a new substance crossed our desks or was given a lower MRL,” Brown adds.
Instead, the company decided to look to new approaches. The idea was that a comprehensive technique would allow the company to benefit from a single, “generic” approach to achieving very low detection levels.
Key acronymn letters include: Q(quick), E(easy), C(cheap), E(effective), R(rugged) and S(safe). Taking advantage of the selectivity provided by the relatively new triple quadrupole mass spectroscopy (GC and LC) instrument and the recent development of the QuEChERS extraction technique, Law Labs developed a multi-class, multi-residue procedure for the routine monitoring of pesticides at or below U.K./EU maximum residue levels.
To improve efficiencies and streamline the process, they turned to a new detection solution, a triple quadrupole MS system from Varian, Inc. (Palo Alto, Calif.) “The Varian system we’re using now minimizes potential interference from co-extractants.” Brown says. This allows for less stringent sample clean up and reduces the need for extra confirmation of residue identity. Law Labs uses both triple quad systems to determine a wider range of compound types. And for compounds that run on both types of systems, they are able to obtain additional confirmation of identity and quantification.
During the selection process for new analysis systems, the company tested instruments from each of the five leading manufacturers by spiking samples with a range of outdated and newly approved pesticides and performing a series of detection runs. Law Labs selected the Varian, Inc. system based on consistent performance, ruggedness and price and because Varian was the only company that had developed and offered a triple quad GC as well as an LC system. Law Labs needed the versatility offered by both the GC and LC methods with MS/MS but wanted the commonality found in a single supplier system.
In addition to benefiting from the improved instrumental capability, Law Labs employs the QuEChERS method for extraction developed by the USDA Wyndmoor Research Centre. Brown explained that Law Labs are the first in the UK to routinely use the technique.
“We were looking for an extraction which would save time and still be capable of extracting the widest possible range of compound types – QuEChERS is already widely used in Germany and the U.S.,” he adds.
With this method, the company has achieved significantly higher outputs while using 90 percent less solvent than with traditional methods. The pesticide residue determination is then performed using both the GC and LC with MS/MS calibrated with Matrix Matched Multiple Pesticide Standards at 4 levels.
Law Labs has validated the technique for around 160 compounds. Even pesticide classes like carbamates, macrocyclic lactones, morpholines and benzimidazoles that were traditionally difficult to analyze, can now be detected with a single extract.
Especially in Europe where the public continues to view GMO foods and pesticide residue as very significant issues, the large retail chains are choosy about their fruit and vegetable suppliers and the analysis process used to determine MRLs. Ideally the retailers are looking to turn this data into a competitive advantage but are also acutely aware of the damage adverse residue findings can have on their reputation and brand identity.
Companies like Law Labs have their work cut out for them. As consumers become more knowledgeable, detection limits in many countries are lowered further, and the WTO becomes more involved with the flourishing near-borderless market for produce.
“We are used to receiving weird and wonderful things from unusual locations,” Brown says. “One of our customers sends us dragon fruit from Vietnam, physalis from Columbia and native figs from Saudi Arabia. This customer also re-exports these same products through a distribution center in Belgium to Holland and Sweden. For good reason, we take our role in the supply chain very seriously and need to employ the most up to date and sophisticated instrumentation and methodologies available.”
Brown expects continued interest on the part of the public and regulatory authorities around pesticides and an increasing demand for fast, efficient, and cost- effective analyses to assure the quality of more wonderful agricultural products from around the orld.
Jennifer Larson is a freelance writer with a background in molecular biology. She previously held positions at BMS, Chiron and Novartis. Ned Purdom is a freelance technical journalist working in the San Francisco Bay Area.