Forensic issues in the analysis of trace nitrofuran veterinary residues in food of animal origin

Over the past twelve years hundreds of official analyses for nitrofuran antibiotic residues in farmed shrimp and prawns have led to product recalls, border rejections, and de-listed suppliers. Positive-release testing regimes have been instigated at huge economic cost. There have been repeated occasions when new scientific information or policy clarification has led to enforcement decisions being seen in a new light and current practice continues to evolve. There remain discrepancies between results found pre-harvest and pre-export in some countries, and results from Border Inspection Posts' analyses when consignments arrive at their destination, despite international harmonisation of test methods and quality criteria. Forensic issues around enforcement decisions following laboratory results for non-compliant consignments containing nitrofurans are summarised herein, including those that have been referred for technical appeal to the UK Government Chemist. Current best practice is collated and specific recommendations and suggestions made for the decision-making process in food safety enforcement. We recommend an approach to semicarbazide analysis from core flesh, removal of ice glaze prior to analysis and that measurement uncertainty is subtracted from the mean result to yield a 'not less than' figure used for reporting purposes 'beyond reasonable doubt'. Research is needed to fill knowledge gaps with regard to sample homogeneity and sampling protocols for nitrofurans in food of animal origin. Sampling should be standardised, as has been established for mycotoxin controls and a modern toxicology risk assessment of nitrofurans and their metabolites in food appears to be warranted.