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Monensin sodium is a polyether carboxylic ionophore coccidiostat agent that is authorised as a feed additive under Commission Regulations N° 2430/1999 and 1455/2004 for use in chickens for fattening (100-125 mg/kg feed, withdrawal period 3 days), chickens reared for laying (up to 16 weeks of age; 100-120 mg/kg feed; no withdrawal period) and turkeys for fattening (up to 16 weeks of age, concentration range 60-100 mg/kg feed; withdrawal period 3 days). Despite the requirements set for feed business operators in Regulation (EC) No 183/2005, it is generally acknowledged that under practical conditions during the production of mixed feeds, a certain percentage of a feed batch remains in the production circuit and these residual amounts can contaminate the subsequent feed batches. This cross-contamination may result in the exposure of non-target animal species, and hence the potential health risks for non-target animal species as well as the potential residue deposition in foods derived from these non-target species have been evaluated.

Signs of intoxication in animals are consistent with the mode of action of ionophoric coccidiostats. Cardiac effects (inotropy and raised blood pressure), necrosis of striated muscles (rhabdomyolysis) and nerves (peripheral neuropathy) are reported to occur in various non-target animal species. Other signs of intoxication include anorexia, diarrhoea, depression, leg weakness, ataxia and dyspnoea as well as growth retardation. Particularly sensitive are horses, for which fatal intoxications at dosages of less than 2 mg/kg b.w. have been reported. Dogs, small ruminants and ducks are very sensitive to ionophoric polyethers. In conclusion, accidental ingestion of feed intended for turkeys or chickens containing monensin at the maximum authorised level of 120 and 125 mg/kg feed, respectively, presents a health risk for several non-target animal species.
Cross-contamination of feed at a level of 10% (12.5 mg/kg feed) of the maximum authorised monensin level for target animal species, would result in an intake for non-target animal species of up to 0.6 mg/kg b.w. per day of monensin. This level exceeds the overall no observed adverse effect level (NOAEL) of 0.3 mg/kg b.w. per day as derived from an oral toxicity study in dogs and rabbits, and hence may induce signs of intoxication in sensitive species such as horses and possibly other species. The Panel on Contaminants in the Food Chain (CONTAM Panel) concludes that adverse health effects in non-target animals may occur if cross-contamination of feed exceeds a level of 5% of the maximum authorised level of monensin in feed for target animal species.

Kinetic studies in various animal species showed that monensin is rapidly absorbed, metabolised and excreted. Kinetic data show that the highest levels of monensin residues are found in liver. Residue levels in other tissues are negligible.
Human exposure resulting from consumption of food products from non-target animal species exposed to feed cross-contaminated up to a level of 10% of the maximum authorised level, is well below the acceptable daily intake (ADI) of 3 ?g/kg b.w. as established by the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP Panel). Therefore, the CONTAM Panel concluded that there is negligible risk to consumers' health from ingestion of monensin residues in tissues of animals exposed to feed cross-contaminated up to a hypothetical level of 10% of the maximum level authorised target animal species.

Opinion

[1] For citation purposes: Opinion of the Scientific Panel on Contaminants in the Food chain on a request from the European Commission on cross-contamination of non-target feedingstuffs by monensin authorised for use as a feed additive, The EFSA Journal (2008)592, 1-40.