Do detections automatically mean that harmful effects will occur?
No. The presence of “detectable” organic compounds does not mean that harmful human-health effects will occur because detections are often at low concentrations that were well below benchmarks that are protective of human health. USGS analytical methods are designed to measure low levels of compounds—typically as low as 0.02 part per billion and sometimes as low as parts per trillion—which is commonly 100 to 1,000 times lower than drinking-water standards. For perspective, reporting limits for public drinking-water commonly are set through Federal regulations at 0.5 microgram per liter, and water utilities generally are not required to measure below this limit. Detections reported in this study, therefore, do not necessarily indicate a concern to human health, but rather provide a characterization of the low-level environmental occurrence of a wide variety of chemicals not commonly monitored in sources of drinking water. The USGS low-level approach helps to identify emerging issues; to
