| Summary: | Temporal trends of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DL-PCBs) in mothers' milk are still quite rare. Data are particularly scarce when it comes to concentrations from the last decade, 2000 and onwards. The aims of the present study were to assess temporal trends of PCDD, PCDF and DL-PCB in mothers' milk from Stockholm, 1972–2011 and to compare the results with previous analysis of some of the older samples.The samples were analyzed by high resolution GC/MS and results were statistically evaluated for the periods, 1972–2011 and 2002–2011. The rate of which ∑PCDDs, ∑DL-PCBs and the ∑TEQ are decreasing (on pg/g fat WHO-TEQ2005) is higher in the last decade compared to the 40 year period, 1972–2011. A similar trend is indicated, but not confirmed, for ∑TEQ of PCDFs, probably due to too many PCDF congeners below LOQ in the period 2002–2011. Concentrations of ∑PCDDs, ∑PCDFs, ∑DLPCBs and ∑TEQ, all expressed as pg/g fat on TEQ-WHO2005-basis, show a statistically significant decline over time, 5.8–6.8% per year, 1972–2011. The last ten years the annual declines for ∑PCDDs, ∑DL-PCBs and ∑TEQ are 9.2–11% and for ∑PCDF, 5.4%. Congener specific trend analysis, 2002–2001, of PCDDs and DL-PCBs showed the same pattern, while the PCDF congeners showed no such general trend. The results from the re-analysis showed good agreement with slightly lower ∑TEQ1998 pg/g fat concentrations in six out of seven samples and mean difference of 13% in ∑TEQ1998. The study shows that time series can be elongated from previous studies, as long as the sample population remains the same. Keywords: Mothers' milk, Dioxin, PCDD, PCDF, dioxin-like PCB, Time series
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