A study showing high rates of air pollution near many schools is raising concerns and questions about the validity of the assumptions made.

USA Today’s special project “The Smokestack Effect, Toxic Air and America’s Schools” shows many Mankato schools as being among the worst in the nation for unhealthy air outside them.

The conclusions are based on emissions primarily from two large soybean-processing companies in Mankato — CHS and ADM.

CHS officials said their emissions are significantly below required government standards and they are confident they cause no risk. (See related story.)

USA Today, in partnership with several universities, conducted an eight-month study. They used the government’s own computer model simulation that predicts the path of toxic chemicals released by companies.

In Mankato, several schools ranked in the 2nd or 3rd percentile nationwide for poor outdoor air quality: Fitzgerald, Franklin, Immanuel Lutheran, Monroe, Mount Olive, Riverbend and Washington. If a school is in the 3rd percentile, it means only 2 percent of the schools in the nation have worse air quality.

Other Mankato schools ranked from the 6th to 20th percentile.

“I think we should all be concerned about it obviously,” said Mankato Supt. Ed Waltman. “But I don’t have the answer.”

The study used reports companies are required to file with the Environmental Protection Agency that show how many pounds of various toxic pollutants they release into the air.

In Mankato, four major contributors are releasing a variety of pollutants into the air, the reports show. CHS (formerly Honeymead) releases 560,250 pounds per year; ADM releases 282,488 pounds; Dotson foundry 2,186 pounds; and MGA Graphics 125 pounds.

Kari Palmer, an environmental research scientist with the Minnesota Pollution Control Agency, said she is skeptical of the report for a few reasons.

“Our general take is that the EPA model they use is a very broad-brush look at things.”

She said it is puzzling that schools near each other could have significant differences in their percentile rankings.

“We don’t exactly understand the modeling and why some schools near each other rank so differently,” Palmer said.

And she said the study was done using only “point-source” pollution — pollution coming from factories.