MINNEAPOLIS — The Minnesota Pollution Control Agency opened a public comment period Monday on proposed changes to the state’s water quality standards for protecting wild rice, a long-running dispute that has pitted mining interests against American Indian tribes and environmentalists.

A 1973 state law limits discharges of sulfates to 10 milligrams per liter into waters that produce wild rice, which plays an important cultural and spiritual role in the life of Minnesota’s Ojibwe tribes. The law drew few objections until environmentalists noticed that it largely wasn’t being enforced a few years ago.

The MPCA proposed changes in March that would take a site-by-site approach based on calculations about individual water bodies. The draft also establishes criteria for designating lakes and streams as wild rice waters, and includes initial lists of about 1,300 bodies of water and of 900 more that warrant further study.

The MPCA is taking comment on the proposal through Dec. 18.

Strong objections have already been made by tribes and environmentalists, who argue that preserving the old standard would provide better protection. Industry groups don’t like the new proposal either, saying the science behind it is flawed.