Southwest Environment

Stories written by University of Arizona students

Department of Soil, Water and Environmental Science
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Changing perceptions on biosolids

By Ruth Hook

Using biosolids as a fertilizer for crops is a controversial issue. Ian Pepper and Charles Gerba, both professors in the University of Arizona’s Department of Soil, Water and Environmental Science, have been researching the application of biosolids to investigate whether they are a hazard to the health of the surrounding community, as some people fear.

“The concern of pathogens in the biosolids is expressed by the community, but the science shows that Staphylococcus aureus, which is the main concern, is not present in the treated products,” Pepper explained. Staphylococcus aureus is a disease-casing pathogen that can cause a wide range of illnesses such as skin infections. It is the leading cause of staph infections, including the highly dangerous Methicillin-resistant Staphylococcus aureus, or MRSA, which many people call “mersa.”

Biosolids are regulated by the Environmental Protection Agency and must meet the agency’s standards on heavy metal content and pathogens that are specified in Part 503, which contains all of the biosolids regulations.

The heavy metals that are of concern include lead, mercury and arsenic.

These three heavy metals can cause damage to the brain if ingested via food or air. The amount of these metals present in biosolids is minimal once they have gone through the treatment process, Gerba indicated.

The treatment of wastewater is an extensive process with goals of removing pathogens and contaminants that could pose harm. There are three main stages of treatment; primary, secondary and tertiary. Through these steps large solids are removed, organics are decomposed and disinfection is applied. The end products include biosolids, which head to the drying stage, and sewage effluent, which is sent somewhere else.

“Now, with increasing treatment processes, almost all metals and pathogens are not there. It’s almost to the stage where they don’t need to be regulated,” Gerba remarked.

Not only does the EPA regulate biosolids, but it also regulates the sites in which the biosolids are applied. To prevent disturbing the soil and thus releasing potential hazards to air, the EPA restricts high traffic in public areas for one year after the application of biosolids. For food crops whose edible parts do not touch the soil, harvesting of the crop must wait until at least 30 days after the application. If a crop’s edible part does touch the surface, harvesting of the crop must wait until at least 14 months after the application.

Another concern about biosolids relates to endocrine disruptors. Endocrine disruptors are present in human wastes from many sources, including residuals from birth control pills. Endocrine disruptors can interfere with a cell’s ability to reproduce and with cell metabolism. They can severely affect humans and other organisms if present in the environment.

Endocrine disruptors remain in the organisms and as the organisms are passed through the food chain, the endocrine disruptors begin to affect organisms further up. The most well-known endocrine disruptor is DDT, a pesticide used from the 1940s until 1972, when it was banned throughout the U.S. and in much of the world.

In the U.S., the most infamous effect of DDT involved its appearance in the eggs of predatory birds – including bald eagles. It would cause the eggshells to be soft and not support the weight of the nesting birds. This problem in the shells drove many birds of prey to the verge of extinction.

Research being conducted at the UA will provide a better understanding of the concerns expressed by communities, Gerba said. 

“People don’t want biosolids because of a perception issue,” Gerba said. “They believe in NIMBY – Not In My Back Yard – but what they don’t get is you’re more likely to get sick from manure than biosolids.” 


Ruth Hook is an environmental science major in the Department of Soil, Water and Environmental


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