More than 500 million pounds of toxic chemicals were reported dumped into the Mississippi River between 1992 and 1996, more than the total amount of toxic chemicals dumped into all other U.S. waters combined. Most of this pollution was runoff from phosphate piles used by three fertilizer companies in Louisiana. The next five most polluted waters, in terms of toxic chemical discharges, were the Ohio River, the Brazos River in Texas, Connoquenessing Creek in Pennsylvania, the Pacific Ocean, and the Houston Ship Channel. More than 800 million pounds of toxic chemicals were directly dumped into the top 50 different rivers, creeks, and bays between 1992 and 1996. Bearing in mind the significant shortcomings with TRI data, these figures nonetheless suggest that substantial improvements in local watersheds might be possible through efforts that target a few major polluters.
Many polluters dump large amounts of toxic chemicals down the drain to sewage treatment plants.
In many cases polluters send their toxic discharges to public sewer systems because regulations governing toxic discharges to sewers are less strict than those governing direct discharges to water. Phosphoric acid, nitrate compounds, and ammonia present serious threats to the aquatic environment when discharged in large quantities such as those reported here, because they are converted to the nutrients phosphorus and nitrogen in water. Phosphorus and nitrogen are primarily responsible for the low-oxygen conditions that threaten whole ecosystems such as the Chesapeake Bay and portions of the Gulf of Mexico. The compound, however, continues to be dumped to waters in large amounts and contributes substantially to disruptions of local ecosystems. Temporary but significant increases in acidity of water bodies are likely to occur near major sulfuric acid discharge points, which can in turn create toxic conditions for aquatic life and liberate toxic metals stored in the local sediment.