Intra-individual variations and time trends 1991-2001 in human serum levels of PCB, DDE and hexachlorobenzene

Background: An important question is whether human serum levels of persistent organic pollutants has continued to decrease during the last decades. The aim of this study was to assess intra-individual variations over time of serum levels of 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153), 1,1-dichloro-2,2-bis(4-chlorophenyl)-ethene (p,p'-DDE) and hexachlorobenzene (HCB), considering the impact of a number of possible determinants. Methods: Blood samples were drawn for the same 39 subjects in 1991 and 2001. Interviews were made at both occasions. Lipid adjusted serum concentrations of CB-153, p,p'-DDE and HCB were determined in both sets of blood samples using gas chromatography-mass spectrometry. The fatty acid composition of the serum lipids was analyzed by means of gas-liquid chromatography. Result: The CB-153 concentrations in serum had averagely decreased with 34% in between 1991 and 2001 (p < 0.001). Of individual determinants only increasing BMI was associated with decreasing CB-153 levels (beta = -1.0, 95% CI -1.8, -0.2, p = 0.01), explaining 13% of the variation. The average decrease of p,p'-DDE was 55%, and could only weakly be associated with a relative increase of BMI (beta = - 1.0, 95% CI-2.3, 0.2, p=0.09), explaining only 5% of the variation. The average decrease of HCB was 53%, and was associated only with high fish consumption in 1991, explaining 12% of the variation. Conclusions: The results support a continuing decrease in human body burdens of PCBs, DDE and HCB during the 1990s. The explanatory factors relative change of BMI and fish consumption explained only a minor part of the time-related variations in serum levels.