Background: There is increasing evidence from epidemiological studies that some man-made chemicals present in the environment can disrupt endocrine homeostasis in exposed humans. Exposure during foetal life to e.g. phthalates has been linked to adverse effects on testicular and ovarian development, thyroid homeostasis and growth in postnatal life. Exposure to phthalates fluctuates not only from day to day but also over time which poses a major challenge for exposure classification. Urine concentrations are currently considered the best proxy of phthalate exposure. However, many longitudinal mother-child cohorts which aim to investigate long-term health consequences of the foetal environment may have biobanks with only serum samples. In serum samples, phthalate levels are generally lower and there may be an unknown contribution from post-collection contamination.
Objectives: To explore whether prenatal maternal serum samples can be used to assess phthalate exposure. Additionally, to investigate temporal and geographical differences in phthalate exposure across three different birth cohorts.
Methods: We compared phthalate metabolite levels in prenatal serum samples from an Australian (1989-91) and a Danish (1997-2001) birth cohort with levels in serum and urine samples from a recent Danish birth cohort (2012-14). Samples were analysed for 32 phthalate metabolites from 15 phthalate diesters by isotope-diluted liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the same laboratory.
Results & discussion: Significant differences in phthalate metabolite levels between the three cohorts were found with generally higher concentrations in the Australian cohort followed by the early Danish cohort. Levels in the older Danish cohort were higher than in the recent one which is in agreement with regulations on phthalate use in the EU since 1999. Due to higher serum phthalate metabolite concentrations, detection rates of phthalate metabolites were higher in the Australian cohort compared to the Danish cohorts. Large inter-individual variations in serum phthalate metabolite levels were observed. In serum from all three cohorts, and urine from the most recent cohort, primary and secondary metabolites of di-(2-ethyl-hexyl) phthalate (DEHP) correlated significantly while secondary metabolites of di-iso-nonyl phthalate (DiNP) only correlated in the older cohorts. In the Australian cohort, metabolites of di-n-butyl phthalate (DnBP) were also correlated. Secondary metabolites of DEHP in serum were positively correlated to urinary levels. Altogether, this indicates true exposure rather than post-collection contamination.
Conclusion: Serum samples are suitable to assess prenatal exposure to some phthalates. Geographical regions may differ in phthalate exposure patterns, and European regulations appear to have resulted in a decreasing exposure from the early 1990s to the 2010s in Denmark.
19 Sep 2019 - 21 Sep 2019