Background: Emerging experimental evidence shows variations in gut microbiota composition and diversity that may be affected by exposure to environmental chemicals. However, data from human studies are scarce and no previous study investigated the association of lifetime exposure to environmental chemicals, assessed at multiple timepoints, and gut microbiome diversity.

Objective: To characterize gut microbiome and identify species and pathways associated with different degrees of life-time exposure to marine pollutants in healthy young Faroese adults.

Methods: We studied 124 adults born in the Faroe Islands in 1986-1987 and periodically followed every seven years through age 28 years. Organochlorine compounds including polychlorinated biphenyls (PCBs) and pesticides, perfluoroalkyl substances (PFASs), and mercury (Hg) were measured in cord blood and participants’ blood at 7, 14, 22, and 28 years. At the age-28 examination, gut microbiome was measured using 16S rRNA amplicon and shotgun metagenome sequencing. The relations of gut microbiome with environmental exposures were assessed using permutational multivariate analysis of variance (PERMANOVA), and multivariate association with linear models (MaAsLIN) adjusting for important confounders.

Results: The most important correlations were observed between 7 and 28-years exposure indicators and microbial diversity. Certain PFASs, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, and β-hexachlorocyclohexane at 7 and 28-years each accounted for 1.2 to 2% of the variance in microbiota. After multivariate adjustment using MaAsLIN, these significant associations were mainly driven by enrichments in the escherichia, alistipes, ruminococcus, and bifidobacterium species, and depletions in bacteroides. Overall, the observed effects were similar to or stronger than the effects observed for well known predictors of microbial diversity, such as breastfeeding.

Conclusions: This study provides the first characterization of gut microbiome in a Faroese population. Findings suggest that early life and concurrent exposures may contribute to changes in the gut microbial composition.