2. Methodology

#### 2.1 Micropollutant monitoring

All spatial analyses and mapping were conducted with ArcMap 10.4. All of the data used is freely available online including the digital elevation models used to delineate the Hudson River Estuary catchment area and tributary watersheds, land cover data, and industrial discharge sites including wastewater treatment plants, hospitals, and population data. Grab samples were collected in 1 L amber, trace clean glass bottles. The samples were shipped in a cooler to our laboratory at Cornell University at the end of each sampling campaign. Samples were stored at 4°C and in the dark until sample preparation within 24 h of arrival in our laboratory. We used a mixed-bed solid-phase extraction (SPE) method to concentrate the 1 L samples as previously described [7, 30]. The high-performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS) method was previously developed and validated for a broad range of micropollutants [30, 31]. A target screening approach was used to quantify the concentrations of 200 micropollutants in each of the samples. Detection limits are generally in the low ng L<sup>1</sup> range for the micropollutants on this list. Statistical analyses were conducted using R Statistical Software and an alpha level of 0.01 was used to determine significance. The hclust function was used to cluster micropollutants using Ward's method based on the occurrence profiles for all the detected micropollutants at each sample site during each sampling event. Paired Wilcoxon rank-sum tests were used to assess the differences between micropollutant concentration profiles across sample sites.
