The EPOLIO project uses the expedition along the obligatory transit between Singapore and Port Louis to measure a range of pollutants in the air, surface waters and water column of the Indian Ocean to quantify anthropogenic stress and to provide a first risk assessment in the region. Furthermore, it is planned to identify the water masses their sources and element cycling processes in this understudied region. The study area represents an ideal model system as it crosses almost the entire Indian Ocean basin, starting from the highly populated regions of Indonesia, Malaysia and Singapore and extending into the open Indian Ocean. The expedition allows better understanding of the impact of megacities on the land-coast-ocean interaction and beyond, in a very sensitive and understudied marine ecosystem. In particular we are aiming (1) to map the concentrations of pollutants (e.g. estrogens) and abundance of microplastic in relation to hydrographic conditions in surface waters and vertically in water masses at selected positions; (2) to identify anthropogenic pollutants transport pathways horizontally, from land to the open ocean, and vertically, from the water surface to deeper water layers, their sources and possible sinks into Indian Ocean; (3) to assess and quantification of the anthropogenic contamination with emerging pollutants (microplastic, estrogens) by using environmental descriptors e.g. risk quotient (RQ) or estradiol equivalent concentration (EEQ) as well as (4) to understand water mass distribution and nitrogen cycling in the central equatorial and southern Indian Ocean, one of the least studied oceanic areas worldwide. The cruise is endorced Ocean Decade activity.