More than 12.7 million pounds of toxic chemicals, such as nitrates, arsenic, benzene and mercury were dumped into the Mississippi River in 2010, according to a report released Thursday by the advocacy group Environment Missouri.
Only the Ohio River, with 32 million pounds, received more toxic discharge in 2010, according to the report based on data from the U.S. Environmental Protection Agency.
The Missouri River ranked seventh with nearly 5 million pounds of dumped toxins.
"Missouri's waterways are a polluter's paradise right now," said Sarah MacFarland, state field associate for Environment Missouri. "These toxic chemicals end up contaminating our drinking water and are absorbed by the fish that we eat."
The environmental group called on the government to improve enforcement of the Clean Water Act in an event held Thursday at Tower Grove Park.
"We need clean water now," MacFarland said.
Some of the toxins are known to cause cancer, reproductive disorders and developmental delays.
Environment Missouri also used the 2010 EPA data to determine the facility that dumped the most toxins in each state. Topping the list in Missouri was the Tyson Foods plant in Sedalia, which released 410,724 pounds into Little Muddy Creek. Tyson also came in at No. 1 in Illinois, where its plant in Joslin discharged 3.3 million pounds of chemicals into Rock River in the northwest part of the state, according to the group's calculations.