Producing agricultural commodities for consumers around the world has many challenges, and compliance with pesticide regulations is one of them. An example of this challenge occurred last November in Europe. Testing by official and private laboratories indicated the presence of fosetyl-Al residues on tree nuts in excess of the EU Maximum Residue Limit (MRL) of 2 mg/kg.
The California nut industry was puzzled by these findings; no state or federal residue tolerance (MRL) exists for fosetyl-Al in almonds, walnuts or pistachios. The use of this pesticide on nut-bearing trees is not permitted and could not account for the laboratory findings in Europe. Why were these residues being detected?
An examination of the European MRL itself provided a partial answer to this question: the EU had defined the MRL to be the sum of fosetyl, phosphorous acid and their salts, expressed as fosetyl. Phosphorus acid is also known as phosphonic acid (its’ salts are called phosphonates). Because phosphonates are metabolites of fosetyl-Al, their presence in food commodities is used as an indicator of fosetyl usage. A review of the European and California test results showed that phosphonates were detected, not fosetyl. Could there be other sources of phosphonates besides the breakdown of this pesticide?
The answer to this question is yes. A number of fertilizer products contain phosphonic acid or phosphonate salts as an active ingredient. These products are applied to the soil or as foliar sprays on a number of crops, including California tree nuts. It is likely that these applications were the source of the residues detected. This information was provided to the European Commission for their consideration. California producers were not alone on this issue: tree nuts and other commodities from multiple supplier nations had also tested high for phosphonates.
Because of the low risk to consumers from these residues and the potential for trade disruptions due to MRL violations, the European Commission approved temporary MRLs (t MRLs) of 75 mg/kg for tree nuts, blueberries, figs, pomegranates and other commodites. Published as Commission Regulation (EU) No 991/2014, the tMRLs are only in effect through December 31st, 2015 and are scheduled to expire on New Years’ Day, 2016. This action by the European Commission provides immediate relief from MRL violations, but a long-term solution will involve international cooperation. Governments around the world may view the same agricultural chemicals differently, with the controls on fertilizers (usage, monitoring) typically less restrictive than those for pesticides. Phosphorous acid and its ammonium, potassium and sodium salts are typically classified as fertilizers in the US and are exempt from US EPA tolerance (65 FR 59346, October 5, 2000). In contrast, the European Union classifies phosphonates as pesticides. Given these differences, how will this issue be resolved?
The tree nut industry has begun a collaboration to seek a permanent solution. The US almond, pistachio and walnut industries have partnered with DFA of California, USDA and others to conduct research into the residues and origins of phosphonates in tree nuts. INC and European laboratories are part of this collaboration. These studies will include the proper residue trials needed to establish permanent, science-based MRLs: the original 2 mg/kg level is a default limit and not based on specific commodity data. This same approach was successfully applied in radishes to derive a fosetyl-Al MRL, replacing the existing default value (EFSA Journal 2009; 7(9):1313).
As we enter the fall of 2014, there is reason for optimism on the issue of fosetyl-Al, phosphonates and tree nuts. The establishment of the temporary MRLs provides the opportunity to collect the necessary scientific data to determine a reasonable limit for these residues, while ensuring a steady supply of healthy foods to European consumers. While it is certain more time will be needed to finalize the data needed to establish an appropriate permanent MRL for tree nuts, the cooperation between regulators, scientists and industry across the globe may yet prevail over the challenges posed by MRL issues!