The natural occurrence of chloramphenicol in crops

Unexpected findings of the banned antibiotic chloramphenicol in products of animal origin, feed and straw prompted urgent investigation. Therefore a monitoring study in straw was carried out. The monitoring showed that in 37 sample chloramphenicol was detected. In 7 samples a concentration above 0.3 μg kg-1 was found with the highest result at 6.8 μg kg-1. Next the hypothesis was studied that the chloramphenicol is naturally present in soil, through production by soil bacteria, and subsequently can be transferred to crops. First, the stability of chloramphenicol in soil was studied. The fate of chloramphenicol highly depends on soil type and showed a half-life of approximately one day in non-sterile topsoil. It was found to be more stable in sub-soil and sterile soils. Second, the production of chloramphenicol in soil was studied and it was confirmed that Streptomyces venezuelae can produce chloramphenicol at appreciable amounts in non-sterile soil. Third, a transfer study was carried out using wheat and corn grown on three different soils, that were weekly exposed to aqueous chloramphenicol solutions at different levels. Chloramphenicol was taken up by crops as determined by chiral liquid chromatography coupled to tandem mass spectrometric analysis and the levels in crop were found to be bioavailability related. It was concluded that chloramphenicol residues can occur naturally in crops as a result of the production of chloramphenicol by soil bacteria in their natural environment and subsequent uptake by crops.