experiment ended and the farm had reverted to using antibiotic free animal foodstuff, stools from ten of the farm residents were recultured. One person had more than 80 percent tetracycline resistant organisms, one had 5 percent and in the remainder tetracycline resistance could not be detected. This paper has the hallmark of a classical study, both in design and execution. A number of interesting observations from it warrant comment. The emergence of tetracycline resistance in the tet-fed chicks was rapid, being obvious within one week, whereas the passage of resistance to control birds or the family on the farm was not evident for three to five months. The authors consider that the most probable explanation for acquisition of resistance by the controls was prolonged exposure to small amounts of tetracycline in the environment, although they also acknowledge the possibility that resistant organisms might have passed from chicken to chicken and chicken to man. The latter explanation has greater superficial plausibility but the former is favored because of the different patterns of resistance seen in the chick and human samples. The present study is also novel in being longitudinal, describing the evolution of patterns of resistance and their disappearance with time whereas earlier reports have essentially been cross-sectional in nature. An important and somewhat reassuring outcome of this approach was the demonstration of reversal from resistance strains following the removal of tet-feed. Initially tetracycline resistance was noted in both E. coli and Proteus rnirabilis but after tet-feed was in-
troduced, the dominant organism was €. coli, suggesting that it has a selective advantage over Proteus mirabilis in the gut. The development of multiple resistance patterns has been observed in hospital patients treated with tetracycline5 and in both clinical and agricultural settings is worrisome. Concern arises from the possibility that multiple drug resistance may arise in a pathogen and the potential ease with which multiple resistant commensals may transfer resistance to a pathogen. The reasons for the emergence of multiple resistance are unclear and deserve further study. Despite the disappearance of resistant strains following the removal of tet-feed the data presented by Levy and his colleagues are a potent argument against the uncontrolled use of antibiotic supplements in agricultural foodstuff. 0
1. T. Watanabe: Infective Heredity of Multiple Drug Resistance in Bacteria. Bact. Rev. 27: 87-115, 1963 2. E. S. Anderson: The Ecology of Transferable Drug Resistance in the Enterobacteria. Ann. Rev. Microbiol. 22: 131-180, 1968 3. The Use of Drugs in Animal Feeds. Publication no. 1679, National Academy of Sciences, Washington, D.C., 1969 4. S. B. Levy, G. B. FitzGerald and A. B. Macone: Changes in Intestinal Flora of Farm Personnel after Introduction of a Tetracycline-Supplemented Feed on a Farm. New Engl. J. Med. 295: 583-588, 1976 5. N. Datta, M. C. Faiers, D. S. Reeves, W. Brumfitt, F. Orskov and I. Orskov: Factors in Escherichia coli in Faeces after Oral Chemotherapy in General Practice. Lancet 1: 312-315, 1971
INSECTICIDES IN BREAST MILK Insecticides are still present in human breast milk five or more years after prohibition of of their general use in Norway. The amounts received by the infant via this route, however, are likely to b e much less than those transferred transplacentally. Key Words: breast milk, DDT, insecticides
Human breast milk has been known to contain insecticides for some time.’>* Those most commonly detected are chlorinated hydrocar72
NUTRITION REVIEWS I VOL. 35, NO. 4 I APRIL 1977
bons such as DDT and its metabolites, Dieldrin, Aldrin and related compounds. Some of these compounds have been barred from gen-
era1 use in a number of countries and the study reviewed was concerned with the persistence of insecticides in human breast milk five or more years after exposure to them had ceased in Norway.* Bakken and Seip collected 50 samples of breast milk mainly from women in the Oslo region who were not normally subject to exposure to insecticides. The specimens were analyzed by gas chromatography and thinlayer ~hromatography.~ All the samples contained hexachlorobenzol, one or more forms of benzene hexachloride, DDT and its metabolite DDE. Other insecticides such as heptachlorepoxide, Aldrin and Dieldrin were discovered in some samples. Thirty-six of the samples contained DDT at a concentration above the maximum safe level recommended by the World Health Organization for cow’s milk.4 The same was true for benzene hexachloride in 28 samples and hexachlorobenzol in seven. Making the assumption that the sample reflected the secretion of insecticide throughout the day, the total daily intake of DDT was greater than the maximum permitted by WHO in 46 of the 50 samples. Samples were collected at different times in the postnatal period. The concentration of hexachlorobenzene did not vary with time, but benzene hexachloride and DDT levels were highest in colostrum and fell progressively up to the fourth month when sampling stopped. The change may be partly due to the higher fat content of colostrum and the fact that insecticides are stored in body fat. The authors noted that samples collected at the beginning of April contained less DDT than those collected in late May and early June. They speculated that this was due to a possible relationship between this finding and the consumption of imported fruit and vegetables in late winter and spring. The idea does not seem tenable since imported produce which might have
been sprayed with insecticide would be eaten more in the earlier period when milk insecticide levels were lower. Three of the women provided more than one sample and analysis of paired or multiple specimens revealed marked variation in milk insecticide content on different days. The potential concern of the effect of insecticides on the infant is nullified by the knowledge that the maximum likely to be ingested is 1000 times less than that known to cause acute intoxication in man.2 The long term consequences are also less alarming than they might appear since the infant is exposed to insecticides not only in breast milk but also in utero. The concentration of DDT in adult adipose tissue is approximately 30 times greater than that in breast milk’ and the concentration in the tissue fat of fresh stillbirths was found to be one-third of that in the adult.5 Thus the infant is exposed to insecticides mobilized from maternal tissues prenatally and at birth already has more insecticide stored in body fat than he is likely to acquire if suckled. 0
1. H. Egan, R. Goulding, J. Roburn and J.O. Tatton: Organo-Chlorine Pesticide Residues in Human Fat and Human Milk. Brit. Med. J. 2: 66-69, 1965 2. G. H. Quinby, J. F. Armstrong and W. F. Durham: DDT in Human Milk. Nature 207: 726-728, 1965 3. K. Noren and G. Westoo: Determination of some Chlorinated Pesticides in Vegetable Oils, Margarine, Butter, Milk, Eggs, Meat, and Fish by Gas Chromatography and Thin-Layer Chromatography. Acta Chem. Scandinav. 22: 22892293, 1968 4. WHO Technical Report Series No. 41 7. Geneva, 1969 5. D. C. Abbott, R. Goulding and J. 0. Tatton: Organochlorine Pesticide Residues in Human Fat in Great Britain. Brit. Med. J . 3: 146-149, 1968
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troduced, the dominant organism was €. coli, suggesting that it has a selective advantage over Proteus mirabilis in the gut. The development of multiple resistance patterns has been observed in hospital patients treated with tetracycline5 and in both clinical and agricultural settings is worrisome. Concern arises from the possibility that multiple drug resistance may arise in a pathogen and the potential ease with which multiple resistant commensals may transfer resistance to a pathogen. The reasons for the emergence of multiple resistance are unclear and deserve further study. Despite the disappearance of resistant strains following the removal of tet-feed the data presented by Levy and his colleagues are a potent argument against the uncontrolled use of antibiotic supplements in agricultural foodstuff. 0
1. T. Watanabe: Infective Heredity of Multiple Drug Resistance in Bacteria. Bact. Rev. 27: 87-115, 1963 2. E. S. Anderson: The Ecology of Transferable Drug Resistance in the Enterobacteria. Ann. Rev. Microbiol. 22: 131-180, 1968 3. The Use of Drugs in Animal Feeds. Publication no. 1679, National Academy of Sciences, Washington, D.C., 1969 4. S. B. Levy, G. B. FitzGerald and A. B. Macone: Changes in Intestinal Flora of Farm Personnel after Introduction of a Tetracycline-Supplemented Feed on a Farm. New Engl. J. Med. 295: 583-588, 1976 5. N. Datta, M. C. Faiers, D. S. Reeves, W. Brumfitt, F. Orskov and I. Orskov: Factors in Escherichia coli in Faeces after Oral Chemotherapy in General Practice. Lancet 1: 312-315, 1971
INSECTICIDES IN BREAST MILK Insecticides are still present in human breast milk five or more years after prohibition of of their general use in Norway. The amounts received by the infant via this route, however, are likely to b e much less than those transferred transplacentally. Key Words: breast milk, DDT, insecticides
Human breast milk has been known to contain insecticides for some time.’>* Those most commonly detected are chlorinated hydrocar72
NUTRITION REVIEWS I VOL. 35, NO. 4 I APRIL 1977
bons such as DDT and its metabolites, Dieldrin, Aldrin and related compounds. Some of these compounds have been barred from gen-
era1 use in a number of countries and the study reviewed was concerned with the persistence of insecticides in human breast milk five or more years after exposure to them had ceased in Norway.* Bakken and Seip collected 50 samples of breast milk mainly from women in the Oslo region who were not normally subject to exposure to insecticides. The specimens were analyzed by gas chromatography and thinlayer ~hromatography.~ All the samples contained hexachlorobenzol, one or more forms of benzene hexachloride, DDT and its metabolite DDE. Other insecticides such as heptachlorepoxide, Aldrin and Dieldrin were discovered in some samples. Thirty-six of the samples contained DDT at a concentration above the maximum safe level recommended by the World Health Organization for cow’s milk.4 The same was true for benzene hexachloride in 28 samples and hexachlorobenzol in seven. Making the assumption that the sample reflected the secretion of insecticide throughout the day, the total daily intake of DDT was greater than the maximum permitted by WHO in 46 of the 50 samples. Samples were collected at different times in the postnatal period. The concentration of hexachlorobenzene did not vary with time, but benzene hexachloride and DDT levels were highest in colostrum and fell progressively up to the fourth month when sampling stopped. The change may be partly due to the higher fat content of colostrum and the fact that insecticides are stored in body fat. The authors noted that samples collected at the beginning of April contained less DDT than those collected in late May and early June. They speculated that this was due to a possible relationship between this finding and the consumption of imported fruit and vegetables in late winter and spring. The idea does not seem tenable since imported produce which might have
been sprayed with insecticide would be eaten more in the earlier period when milk insecticide levels were lower. Three of the women provided more than one sample and analysis of paired or multiple specimens revealed marked variation in milk insecticide content on different days. The potential concern of the effect of insecticides on the infant is nullified by the knowledge that the maximum likely to be ingested is 1000 times less than that known to cause acute intoxication in man.2 The long term consequences are also less alarming than they might appear since the infant is exposed to insecticides not only in breast milk but also in utero. The concentration of DDT in adult adipose tissue is approximately 30 times greater than that in breast milk’ and the concentration in the tissue fat of fresh stillbirths was found to be one-third of that in the adult.5 Thus the infant is exposed to insecticides mobilized from maternal tissues prenatally and at birth already has more insecticide stored in body fat than he is likely to acquire if suckled. 0
1. H. Egan, R. Goulding, J. Roburn and J.O. Tatton: Organo-Chlorine Pesticide Residues in Human Fat and Human Milk. Brit. Med. J. 2: 66-69, 1965 2. G. H. Quinby, J. F. Armstrong and W. F. Durham: DDT in Human Milk. Nature 207: 726-728, 1965 3. K. Noren and G. Westoo: Determination of some Chlorinated Pesticides in Vegetable Oils, Margarine, Butter, Milk, Eggs, Meat, and Fish by Gas Chromatography and Thin-Layer Chromatography. Acta Chem. Scandinav. 22: 22892293, 1968 4. WHO Technical Report Series No. 41 7. Geneva, 1969 5. D. C. Abbott, R. Goulding and J. 0. Tatton: Organochlorine Pesticide Residues in Human Fat in Great Britain. Brit. Med. J . 3: 146-149, 1968
NUTRITION REVIEWS / VOL. 35, NO. 4 / APRIL 1977
73
