Plastic washing at recycling plants can spike phthalates in wastewater, study suggests

New research from Iowa State University's Polymer and Food Protection Consortium reveals that certain plastic washing methods used in recycling facilities can significantly elevate phthalate concentrations in wastewater. These findings highlight critical gaps in current recycling practices and underscore the need for improved chemical management protocols in the industry.

The comprehensive study, published in Advances in Materials Science and Engineering, examined standard industrial plastic-washing techniques and discovered that specific cleaning methods led to substantial accumulation of two phthalate compounds in wash water. Phthalates are chemical additives extensively used in plastic manufacturing that have been associated with cancer risks and endocrine disruption, with particular concerns for children's reproductive and developmental health.

Research Focus and Methodology

The investigation centered on polypropylene (No. 5 plastic), commonly found in dairy containers and food packaging applications. This material represents a priority target for enhanced recycling efforts due to its durability, high value, and currently low recycling rate of approximately 3%.

"We're tracking the fate of these chemicals throughout the recycling process to develop effective removal strategies," explained Greg Curtzwiler, associate professor of food science and human nutrition and the study's senior author. "Understanding how to properly manage these compounds is essential for advancing recycling technologies."

During the research, plastic samples were processed into 1-3 millimeter flakes and subjected to various washing protocols. Initial observations showed reduced concentrations of potentially harmful chemicals in the cleaned plastic, prompting researchers to investigate where these substances migrated.

Key Findings and Chemical Detection

The study revealed significant differences between washing methods. Physical agitation alone or combined with sodium hydroxide (a lye-based solution) showed no detectable phthalates or bisphenols in the resulting wastewater. However, ultrasonic cleaning and sodium hydroxide combined with industrial detergent produced concerning results.

Two specific phthalates were identified in the contaminated wash water: di(2-ethylhexyl) phthalate (DEHP) and di-cyclohexyl phthalate (DCHP). The study's most alarming finding emerged from testing the sodium hydroxide and detergent method across 15 cleaning cycles, simulating industrial water reuse practices.

DEHP concentrations increased progressively with each cycle, starting at ten times the EPA's drinking water limit after the initial wash and reaching 25 times the allowable level after 15 cycles. Additionally, declining detergent concentrations suggested plastic flakes were absorbing cleaning chemicals, introducing additional contamination concerns.

Implications for Industry and Environment

These findings expose significant gaps in the regulatory oversight and scientific understanding of plastic recycling processes. The accumulation of harmful chemicals in industrial wastewater presents potential risks to environmental and public health, particularly given the widespread reuse of wash water in recycling operations.

Keith Vorst, director of the Polymer and Food Protection Consortium and study co-author, emphasized the actionable nature of these discoveries. "While these findings raise important concerns, they represent solvable challenges that can be addressed through targeted interventions," noted Vorst, who serves as an associate professor of food science and human nutrition.

Potential Solutions and Future Directions

The research team has identified several promising approaches for mitigating chemical contamination in recycling operations. Foam fractionation, which utilizes air bubbles to capture and remove contaminants from water, represents one viable treatment option.

Additional technologies under investigation include electro-oxidation processes that use electrical current to decompose harmful chemicals, and bio-based treatments incorporating carbon nano-onions, a specialized nanomaterial with chemical remediation properties.

Water conservation strategies also show promise for reducing contamination risks. These approaches include enhanced plastic sorting systems and alternative cleaning methods that minimize or eliminate water usage entirely.

Economic Considerations and Industry Challenges

Implementing these solutions requires careful consideration of economic factors, particularly given the recycling industry's traditionally narrow profit margins and expansion goals. The U.S. Environmental Protection Agency has established an ambitious target of achieving 50% plastic recycling rates by 2030, yet current performance significantly lags this objective.

According to recent data from The Recycling Partnership, only 21% of eligible household recyclable materials are currently processed, with plastic recycling rates falling below this already modest figure.

"Balancing environmental protection with economic viability remains crucial," Curtzwiler emphasized. "Solutions must be cost-effective to ensure widespread adoption while supporting industry growth and sustainability objectives."

This research represents an important step toward understanding and addressing the complex chemical challenges inherent in plastic recycling, providing a foundation for developing safer, more effective recycling technologies that protect both environmental and human health.