Chlorpyrifos is the most commonly used insecticide among Minnesota farmers, who used almost a million pounds of it last year.

The chemical has been of increasing concern to environmental and health officials in Minnesota. It’s being detected in an ever-growing number of lakes and streams.

And last year, after rural community groups raised concerns, the Minnesota Department of Health decided to include it in a study measuring contaminant levels in some 200 children.

JOSEPHINE MARCOTTY