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Composting and anaerobic digestion of food waste provide two means to recover and recycle some of the nutrients required to grow food. The use of these methods also reduces the amount of food waste going to landfill and incineration. Many communities and states are enacting programs and policies to reduce food waste and capture as much as possible for recycling. To ensure the recycled materials are safe and free from contaminants that could amplify within a circular food system, it is important to understand where and how contaminants are introduced into the system, and how policies affect the degree of contamination. 

Source separated food waste was collected from two regulatory environments (mandated food waste separation vs unregulated) and six source types (grocery, hospital, school, restaurant, retirement community, residential) to test the hypothesis, based on previous stakeholder engagement, that voluntary participation in food waste recycling would result in lower contamination rates. Physical contaminants, heavy metals, organohalogens, pathogens and antibiotic resistance genes (ARGs) were measured. Food waste processors were also surveyed about their perceptions about contamination and associated risks. 

Testing of processed food waste after removal of physical contaminants showed that mandated food waste recycling did not increase contamination rates. This finding contradicted food waste recyclers’ perception that organics recycling mandates would result in higher levels of contamination. Source type influenced carbon, nitrogen phosphorus, calcium, and copper concentrations, tet (M) abundance, and physical contamination in our samples. 

Physical contamination was high with over 80% of samples containing some non-food waste, and 57% containing non-compostable items such as plastics. The chemical composition of the processed food waste was highly variable. Most heavy metals were below the EPA method detection limit, and those that were detectable were well below any global regulatory limits on land application of compost or biosolids. Pathogens were also present, when detected, at very low levels, although microbial community analysis by high throughput sequencing showed that genera that contain pathogens were present in most of the samples tested, so care must still be taken while handling these materials. Halogenated organic contaminants were detectable by the EOX method in 14% of samples. PFBA, a perfluorinated chemical, was detected in 57% of the samples tested. Detection of these compounds is of concern due to their potential for bioaccumulation in the circular food system. Antibiotic resistance genes for beta lactams and tetracyclines were detected in almost all samples. This is cause for concern because increasing resistance is developing in pathogens, and food may be a vector for this transfer to humans. 

The level of contamination in our source separated samples was relatively low, with the exception of some antibiotic resistance genes, however our processing method might have underestimated packaging-associated contamination. This should be explored further on depackaged food waste and field-pre-processed input materials, along with studies on the fate of these contaminants during treatment. Surveys and interviews suggest food waste managers were generally more concerned about physical contamination of food waste than trace contaminants, while our results show that awareness should be raised about PFAS and potentially ARGs, which were detectable in a majority of our samples.