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Loop®, like biosolids across the United States, are tested, and re-tested, and then tested again. In fact, because of this extensive testing, we know more about the content and quality of biosolids than other fertilizers (both synthetic and organic) and manure (from cows, chickens, and so on) used on farms every day.

The King County Biosolids Program monitors Loop’s physical, chemical, and microbial properties every month to make sure the product meets regulatory standards and is consistently high in quality. Less than 3 percent of the flow into King County’s treatment plants is from industrial sources, but to protect Loop’s quality, King County also works with local businesses and industries to make sure metals and chemicals stay out of the sewer. As a result, Loop contains very small amounts of metalsfar less than the regulatory standards and similar to any other soil products on the market.

Regulated Metals in Loop Biosolids

What about pharmaceuticals?

It’s a fact that chemicals are everywhere in our environment—from the pills we take and the products we put on our skin to the materials in our homes. As a result, trace amounts of chemicals from pharmaceuticals and personal care products do end up at our treatment plants and in our biosolids. However, these chemicals are present in such tiny amounts that it would take hundreds and hundreds (even thousands) of years of working directly with biosolids products to match what we’re exposed to every day in most household products


View our annual Loop quality data and quality control processes.

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For more information about Loop biosolids, please contact us at: