Evaluation of an immunobiosensor for the on-site testing of veterinary drug residues at an abattoir. Screening for sulfamethazine in pigs

A study was conducted to determine the feasibility of performing "on-site" screening for sulfamethazine (SMT), at an abattoir, using a rapid immunobio sensor method. This involved transfer of the biosensor technology and an as say developed in the laboratory, to the cold, humid conditions of a modern pig-processing factory. A pre-determined threshold limit of 0.4 mu g ml(-1) SMT in bile was used to identify the likelihood that corresponding tissue samples contained SMT concentrations in excess of the European maximum perm issible residue limit of 0.1 mg kg(-1). Bile samples containing SMT concent rations above the threshold limit were deemed positive and the correspondin g kidney and muscle samples were sent to the laboratory for HPLC analysis. The robustness of the biosensor instrumentation in the harsh operating cond itions was monitored throughout the project. The performance of the assay, on-site, was assessed by the regular inclusion of QA samples and by the sub mission of control 'SMT-positive' pigs to the abattoir. Sampling procedures , identification and traceability were also under scrutiny. During the project, 337 (9.35%) of the total kill were tested for SMT resid ues, representing 75% of all producers submitting pigs for slaughter. Twelv e animals, including the ten controls, gave positive bile results. HPLC ana lysis confirmed SMT residues in all 12 kidneys (11 in excess of the permiss ible level). Ten muscle samples also contained violative SMT levels. Throug hout the project, the biosensor performed reliably, with no adverse reactio n of any mechanical or electrical components. The SMT assay also performed reliably. This is the first report of a biosensor being used for 'on-site' drug screening.