Currently, the environmental impact of ubiquitous plastic debris triggered quite some public attention. However, the global impact of microplastic on human health is by and large either unknown or neglected. By looking at the underlying biochemical mechanisms leading to the global health threat microplastic was discovered to carry persistent organic pollutants, such as polycyclic aromatic hydrocarbons (PAH), to marine life. The effect of microplastic-ingestion in the human body remains unfortunately somewhat elusive as of yet. For this reason, we screened for compounds binding to the human estrogen receptor α (ERα) and identified the PAH compounds indeno[1,2,3-cd]pyrene (Indpy) and picene (Pice) with a high binding affinity. We applied next generation sequencing to analyze the differentially expressed genes in MCF-7 cells after treatment with Indpy and Pice. We found 8 upregulated genes: ABCC5, CCNG2, CYP1A1, DDIT4, IER3, RUNX2, STC2, and SLC7A5 and 14 downregulated genes: ADORA1, CEBPB, CELSR2, CTSD, CXCL12, KRT19, PGR, PKIB, RARA, RET, SEMA3B, SIAH2, TFAP2C, and XBP1 induced by both ligands and associated with ESR1-regulation. The altered gene expression may influence cell proliferation and metastasis, favoring cancer development with a poor response to therapy. In addition, we confirmed the binding of Indpy and Pice to ERα using molecular docking and microscale thermophoresis. ERα activation was measured with ESR1-overexpressing HEK293 (HEK-ESR1) cells and confirmed for Indpy. In conclusion, we showed an ESR1-mediated influence of the PAH compounds Indpy and Pice on the gene expression pattern of MCF-7 cells, possibly also promoting breast cancer development in patients.Copyright © 2019. Published by Elsevier Inc.