Releases of TRI chemicals to water typically occur as direct discharges to streams or other water bodies. Surface water discharges are often regulated by other programs and require permits such as Clean Water Act National Pollutant Discharge Elimination System (NPDES) permits.
The following graph shows the trend in the pounds of TRI chemical waste discharged to water bodies.
Note: For comparability, trend graphs include only those chemicals that were reportable to TRI for all years presented.
From 2007 to 2019:
- Discharges of TRI chemicals to surface water decreased by 38 million pounds (-16%). Most of this decline was due to reduced releases of nitrate compounds to water.
- Nitrate compounds are often formed as byproducts during wastewater treatment processes such as when nitric acid is neutralized, or when nitrification takes place to meet standards under EPA’s effluent guidelines. More pounds of nitrate compounds are released to water than any other TRI chemical.
- Nitrate compounds alone accounted for 89% of the total quantity of all TRI chemicals discharged to surface waters.
The following graph shows the trend in the RSEI Scores for TRI chemicals released to water bodies.
- The biggest contributor to RSEI Scores for releases to water from 2007 to 2018 was arsenic compounds. For 2019, the largest contributor to RSEI Scores for releases to water was mercury compounds.
- The high RSEI Score for discharges to water in 2008 includes a large one-time release of arsenic compounds due to a coal fly ash slurry spill, and a release of benzidine, which is highly toxic (benzidine is known to cause cancer in humans).
- The increase in RSEI Score for releases to water beginning in 2017 is driven in part by an increase in discharges of mercury compounds to water by a mining facility in Florida.
- For a complete, step-by-step description of how RSEI derives RSEI Scores from surface water discharges of TRI chemicals, see “Section 5.4: Modeling Surface Water Releases” in Chapter 5 (“Exposure and Population Modeling”) of EPA’s Risk-Screening Environmental Indicators (RSEI) Methodology, RSEI Version 2.3.8.
- For general information on how RSEI Scores are estimated, see Hazard and Potential Risk of TRI Chemicals.
This page was published in January 2021 and uses the 2019 TRI National Analysis dataset made public in TRI Explorer in October 2020.