An environmental group says our major rivers are among the ten most toxic waterways in the country. Environment Missouri uses figures from the Environmental Protection Agency for its ratings. The group says almost 13-milion pounds of toxic chemicals went into the Mississpppi River in 2010 chemicals such as arsenic, benzene, mercury and nitrates. The only river with a worse record is the Ohio. The Missouri River is seventh on the list. Environment Missouri says it got about five-million pounds of toxins. The group points to the Tyson Foods plant in Sedalia as the biggest contributor of toxins in Missouri waterways.