WASHINGTON — The Environmental Protection Agency in January ruled that a chemical manufactured for agricultural weed control is not a carcinogen and creates no risks to human health when used as directed. At the same time the agency has compelled further mitigation measures to ensure pesticide sprays target certain pests and curb glyphosate resistance in weeds.

The E.P.A. last week re-approved glyphosate under the Federal Insecticide, Fungicide and Rodenticide Act, legislation first enacted in 1910. A 1996 amendment under the Food Quality Protection Act required all pesticides sold or distributed in the United States to undergo continuous review in order to assess and reduce risk as “changes in science, public policy and pesticide use practices will occur over time,” the agency said in its glyphosate decision. A 2006 registration review program established the periodic review frequency at 15 years.

The reregistration decision was praised by U.S. agricultural leaders, including Zippy Duvall, president of the American Farm Bureau, who said it was “a win for sustainable agriculture.

“Today’s decision means farmers can continue to use conservation tillage and no-till methods on their farms to conserve soil, preserve and increase nutrients, improve water quality, trap excess carbon in the soil and reduce greenhouse gas emissions,” he said. “That said, safety is our first priority and the science clearly shows that this tool is both safe and effective.”

Sold commercially as Roundup, glyphosate was first registered for U.S. use in 1974 to control invasive weeds in agricultural production and residential landscaping. Producers less frequently have employed glyphosate as a desiccant to kill a crop to assist with dry-down just prior to harvest.

The agency had re-examined glyphosate as part of a periodic review of pesticides to ensure each can perform as designed without unreasonable adverse effects to human health.

In its Interim Registration Review Decision for Glyphosate released last week, the E.P.A. said “... there are no risks of concern to human health when glyphosate is used according to the label and that it is not a carcinogen ...” The 36-page decision, available to the public by searching “glyphosate” at epa.gov, states both cancer and non-cancer effects were evaluated for glyphosate and its metabolites.

In its decision, the agency concurred with the findings of numerous global bodies, including the Canadian Pest Management Regulatory Agency, the Australian Pesticide and Veterinary Medicines Authority, the European Food Safety Authority, and the German Federal Institute for Occupational Safety and Health.

An earlier scientific review by the U.S. Department of Agriculture produced the same findings.

The re-approval of glyphosate came with changes to labeling, requiring a “medium” droplet size when spraying glyphosate alone, and a “fine” droplet when applying glyphosate mixed in a tank with other pesticides.