MATERIALS AND METHODS

Milk sampling: Milk samples collected in the city of Sari and the other in the city of Babol. Both were part of a total of 10 samples collected in order to exposure study on Levels of OCPs. All samples were obtained in July 2004 and donors were selected according to the protocol established by WHO^[9]. All mothers were informed about the objectives of the study and gave their consent. At each area, 10 samples of 100 mL each were collected from breastfeeding mothers. Milk was expressed manually directly in a jar and kept frozen at -20°C. Before, each jar was cleaned with organic solvents and three tablets of potassium dichromate were added to avoid degradation during shipping. After finishing the collection of the 10 sub-samples, they were sent frozen to the central laboratory in Sari city, where they were defrosted at room temperature and pooled to give a total volume of 1000 mL. One part of 500 mL was sent to the reference laboratory in Shaheed Beheshti University of Tehran and the other aliquot was kept frozen for safety purposes (e.g., damage during transportation).

Analytical procedure: The method was followed baded on Methods in Yu^[10]. For determination of organochlorine pesticides, human milk samples were centrifuged and from the cream the compounds of interest extracted together with fat by use of sodium sulfate and light petroleum. After evaporation of the solvent the fat content was determined by weighing out the mass of the remainder. Up to 0.5 g of the fat extract was redissolved in cyclohexane ethyl acetate and the internal standards were added. For separation of fat, gel permeation chromatography was performed on Bio-Beads S-X3 with cyclohexane/ethyl acetate as eluting solvent. after concentration of the eluate almost to dryness and redissolution in iso-octane chromatography on a small column of partially deactivated silica gel was used as final clean up step using toluene as eluent.routine determination was performed with GC/ECD using generally two different GCs (Fisons Mega 2) with two columns of different polarity (fused silica No. 1: 30 m PS-088 [97.5% Dimethyl- 2.5% diphenyl siloxane copolymer], 0.32 mm i.d., 0.32 μm film thickness, fused silica No. 2: 30 m OV-1701-OH, 0.32 mm i.d., 0.25 μm film thickness, both columns custom-made). Results were confirmed routinely by GC-LRMS^[11].

RESULTS AND DISCUSSION

The age of donors in each sample was about 23 years old in average. The fat amount of fresh weight was 4.2% for Sari and 4.9% for Babol city.

Table 1:	Organochlorine pesticide concentrations in human milk from two agricultural city, Sari and Babol collected in July 2004 (μg g-1 fat)

Table 2:	Average concentrations of organochlorine pesticides from different countries (μg g-1 fat)
n.a. = not analyzed

Concentrations, based on lipid weight, of organochlorine pesticides in human milk are given in Table 1. In both samples, the highest amounts were found for p,p’-DDE, which was 0.056 μg g^-1 fat in Sari and 0.045 μg g^-1 fat in Babol , followed by β-HCH, which was 0.037 μg g^-1 fat and 0.024 μg g^-1 fat, respectively. The concentrations of the other analyzed compounds were near or, in most cases, below detection limit (0.001 μg g^-1 fat).

The high proportion of p, p’-DDE / p,p’-DDT was 5.6 for Sari and 11.25 for Babol, indicate that exposure happened through environmental contamination by former application of DDT since DDE/DDT ratio will increase when the use of DDT ceases^[5]. The exposure to its persistent metabolite DDE still occurs mainly via foodstuffs and also through metabolic conversion of p,p’- DDT. The same assumption can also be made for the HCH group, as only the more stable beta isomer was present in both samples. In 1989, the use of DDT and HCH has been restricted by the Iranian Government to public health campaigns for vector control. Until 1998, both compounds were used as insecticides, which is concentrated in the North region (98% of cases), northern part of Iran. Both sampled Cities are located in the north part of Iran.

Levels of HCB, DDT and HCH have been reported in human milk from different countries and some data are given in Table 2. Data from Germany are also from samples from the third round of WHO-coordinated exposure studies x and reflect the situation in central Europe. Comparison of the levels from the current study in Iran with those in other countries showed that HCB is at the Lower end of concentrations, whereas sum DDT and β-HCH are at the upper end^[12,13].

CONCLUSIONS

Ocs concentrations in the environment have been decreasing gradually worldwide. Legally banning of OCs can lead to low concentrations in the environment and consequently to low human exposure which can be observed by considering human milk as good indicator of general population exposure^[13,14]. This process is supported by the Stockholm Convention which is a global treaty signed now by 55 parties to take action against certain POPs, among them PCBs, PCDDs and PCDFs^[9,15]. After ratification by France as the 50th Party, the Convention entered into force in May 2004. The effectiveness should be evaluated four years after the date of entry into force and periodically thereafter at intervals^[10,16]. Therefore, a Global POPs Monitoring Programme was developed. United Nations Environment Programme (UNEP) organized a workshop to provide a scientific basis for this programme. One of the conclusions was to select the following matrices: air; bivalves; wildlife species (fish, bird’s eggs, marine mammals) and human milk^[11].Therefore, future analyses of these POPs in breast milk also from Iran are encouraged to show tendencies over time.

Levels of OCP residues in human milk from Mazandaran province were comparable to those from developed countries and significantly lower than those from developing countries. The low level of OCPs in human milk as found in the present study support the Iranian policy of encouraging breast-feeding.

ACKNOWLEDGMENTS

The authors would like to thank from all the professionals involved on selecting the donating mothers In Mazandaran province and on collecting the samples.