Austin, Texas-based Whole Foods has quietly added biosolids to a list of products it plans to ban suppliers from using to grow produce, beginning later this year.

The decision comes after a handful of consumer and environmental advocacy groups waged an email campaign urging the retailer to label produce items grown with biosolids, also known as treated sewage sludge.

But Kate Kurtz, a soil scientist with the King County Waste Water Treatment Division, Seattle, said prohibiting the use of biosolids is actually counter to the tenants of sustainable agriculture.

“We feel very confident of the safety and the efficacy of biosolids and the use of biosolids, especially in nourishing crops,” she said. “We see the benefits of recycling the carbon and nitrogen back into the soil. From a sustainability standpoint, it really makes a lot of sense.”

She cited the county’s 40 years of experience producing biosolids as well as numerous studies conducted by universities and state and federal agencies.

The requirements are moot for organic production since the U.S. Department of Agriculture’s National Organic Program already bans the use of biosolids.

In September 2013, Whole Foods rolled out core standards that suppliers will have to meet by September. Biosolids were missing from the initial standards but have since been added. Whole Foods did not return phone calls or emails seeking comment.

The core standards also will include a science-based rating system being developed with the input of sustainable agriculture experts and suppliers, according to a Whole Foods press release. It is designed to measure the performance of topics it considers important to sustainable farming.

Beginning in September, the retailer will display ratings of “good,” “better” and “best” on produce and floral items.

Biosolids are the product of anaerobic digestion, where millions of beneficial microbes feed on and degrade the initial organic material over a 25- to 30-day period.

The Environmental Protection Agency has strict regulations about the number of pathogens that can remain at the end, the use of those biosolids and pre-harvest intervals for various crops, said Roberta King, King County biosolids program lead.

Over the years, King County has worked with researchers from the University of Washington, Washington State University, Oregon State University and the University of Arizona to develop safe uses for its biosolids, sold under the Loop brand.

For example, WSU is looking at how a composted Loop product called GroCo could be used to replace peat in potting mixtures for nursery plants, Kurtz said.

Several decades ago, heavy metals from industrial sources were a concern in biosolids. But Kurtz said EPA regulations now require industrial sources to pretreat their waste stream and remove heavy metals before sending it to municipal wastewater treatment plants. The pretreatment has reduced heavy metals loads in biosolids to negligible levels and also enabled industrial users to capture and recycle heavy metals.