Ethylene dibromide residues in stored maize grains

Ethylene dibromide (EDB) is an insecticidal fumigant used extensively in Ghana for fumigation of maize during storage. Treatment is usually done in jute bags lined with polyethylene material at a dose rate of 0.05 mL/kg. The present study was conducted using U-14C-ethylene dibromide to determine residues in maize grain from the time of fumigation to the point of human consumption. 14C-EDB (1 mCi/mmol (1 Ci = 37 GBq) was added to 10 mL cold EDB and applied to grain at a dose rate of 50 μCi/kg. As in actual practice, the grains were exposed to EDB for 7 d, soaked in cotton wool and then thinly spread at ambient temperature of 28-30 deg. C and relative humidity of 80-90%. Samples were analysed at 0 time and at regular intervals up to 40 weeks. Surface and methanol extractable residues were determined according to a standard protocol (see Annex 1, these Proceedings). Total and bound residues were determined by directly counting a powdered sample. It was shown that substantial amounts of EDB were taken up by the grains during fumigation. Total residues declined from 82 mg/kg at 0 time to about 20 mg/kg after 4 weeks and 12 mg/kg after 40 weeks. Surface and methanol extractable residues accounted for 5 mg/kg of the terminal residue after 40 weeks, the remaining being bound. The preparation of some diets as practised in Ghana removed a part of the residue (15-30%). The study demonstrates the importance of using the nuclear techniques to detect and quantify EDB residues, in particular the bound or 'hidden' portion which is not determined by conventional techniques. Data indicate the presence of high unacceptable levels of EDB and/or derivatives in maize grain at the point of human consumption. This finding would necessitate that local practices be modified, revised or changed. According to the recommendations of the FAO/WHO report FAO/WHO Pesticide Residues in Food, WHO Technical Report Series No. 417(1969), EDB may be used under the condition that no detectable residue of the parent chemical reaches the consumer. (author)