The city of Rapid City, South Dakota has discovered toxic herbicides in compost purchased through its solid waste facility.

Clopyralid, the persistent herbicide; MCPP and Quinclorac were found. The chemicals are harmful to plants and can interrupt the growth cycle of broad leaf plants.

Rapid City Solid Waste Facility says the contamination "likely arrived in the feed stock for the yard waste compost."

The herbicides could last in soil for several months and, in some cases, several years.

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