Environmental officials in Oregon detected traces of 128 chemicals across all state watersheds, according to a recent report.
Researchers from the state's Department of Environmental Quality collected water samples from 177 rivers, streams and estuaries between 2008 and 2013, then tested for the presence of more than 500 chemicals ranging from industrial compounds and pesticides to banned substances and consumer products.
Most of the traces accumulated at very low levels, according to the DEQ report, although some sites reflected totals in excess of state limits or other benchmarks for human health and the environment.
The largest variety of chemicals came from the basins of the Hood and Willamette rivers, two Columbia River tributaries near population centers, industrial activities and agricultural operations.
Officials said the results would provide a baseline for the future study of pollutant levels in the state's waterways.