Expanded polystyrene is not chemically degraded by mealworms†

Abstract

Expanded polystyrene (EPS) is a widely used plastic material that poses significant environmental challenges due to its resistance to degradation. While mealworms have been reported to degrade EPS, several critical questions remain unanswered: (1) Do mealworms actually chemically degrade the polystyrene backbone in EPS? (2) Can mealworms effectively derive nutrition from EPS consumption? and (3) What mechanisms, if any, enable EPS degradation by mealworms? This study addresses these questions by feeding mealworms two types of EPS diets: pure EPS without additives and commercial EPS containing additives. Mealworms were individually housed (to prevent cannibalism) and categorized into age-specific groups, and their growth and survival were monitored on diets of pure EPS, commercial EPS, or under starvation conditions. Our results demonstrated that, compared to starvation, both pure and commercial EPS diets failed to sustain mealworm growth, and survival rates decreased, indicating that EPS consumption is toxic to mealworms. Gel permeation chromatography and attenuated total reflectance-Fourier transform infrared spectroscopy analyses of the frass revealed partial degradation of commercial EPS, characterized by a reduction in higher molecular weight fractions and increased carbonyl group formation. Additives likely caused EPS degradation. In contrast, pure EPS was essentially unaffected by passage through the mealworm digestive tract, providing clear chemical evidence that neither mealworms nor their gut microbiota possess enzymes capable of breaking down EPS for energy. These findings reveal that previous studies overstated the ability of mealworms to digest and derive energy from EPS, while providing new insights into the chemical processes involved in limited EPS degradation. Our results emphasize the need for further research into alternative organisms, pretreatment methods, and integrated waste management strategies that can more effectively address the challenge of EPS degradation.