Understanding potential contaminants in compost helps consumers, landscapers, and agricultural producers make informed choices about the products they use on their soil.

Common Contamination Concerns

Inerts (Physical Contaminants)

Physical contaminants include glass, plastic fragments, metal, and other non-compostable materials that may enter the composting feedstock stream. Commercial composters use screening and hand-sorting to minimize inerts, but some small fragments may remain. Regulations set maximum allowable levels for physical contaminants in finished compost.

Compostable Plastics

Products labeled "compostable" are designed to break down in commercial composting facilities. However, the composting timeline and conditions needed vary by product, and some may not fully decompose during a standard composting cycle. This remains an evolving area of standards and regulation.

PFAS (Per- and Polyfluoroalkyl Substances)

PFAS are persistent chemicals found in many consumer products that can enter compost through contaminated feedstocks such as food-soiled paper products. Research is ongoing regarding PFAS levels in compost and their impact on soil and plant health. Regulatory standards are being developed at state and federal levels.

Pesticides and Herbicides

Certain persistent herbicides (such as aminopyralid, clopyralid, and picloram) can survive the composting process and cause damage to sensitive plants. Quality composters test for herbicide residues and carefully manage their feedstock sources to minimize this risk.

What Consumers Can Do

  • Request compost data sheets and review contaminant test results
  • Look for US Composting Council Seal of Testing Assurance (STA) certified products
  • Ask vendors about their feedstock sources and quality control practices
  • Report quality concerns to your local waste management authority

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