Relative to a Common Phthalate, Citrate-Based Plasticizers Exert Minimal Impact on Plastisphere Bacterial Community Composition during Biopolymer Biodegradation

Citrate-based plasticizers are often marketed as eco-friendly alternatives to phthalates like dibutyl phthalate (DBP). Here, we investigated these assertions by examining the response of soil microbial communities to biopolymer samples plasticized with acetyl tributyl citrate (ATBC), triethyl citrate (TEC), DBP, or nothing (control). Samples were buried in soil for 14 weeks, after which the biomass and diversity of bacterial and fungal communities associated with the biopolymer, attached soil, and bulk soil were characterized using metabarcoding and quantitative PCR. Differences between buried (incubated) and nonincubated biopolymer samples were also analyzed using X-ray microcomputed tomography, gel permeation chromatography, and 1H-nuclear magnetic resonance spectroscopy to assess biopolymer degradation and plasticizer migration. Surface degradation and plasticizer migration were observed for all treatments, with minor impacts of plasticizers on microbial biomass and alpha diversity. Critically, however, plastisphere bacterial communities formed two groups that were compositionally distinct. One group comprised the DBP samples while the other comprised the control, ATBC, and TEC samples. This indicates that DBP can impact soil bacterial community composition on release from biopolymer blends, while the effects of the citrate-based plasticizers were reduced─supporting their use as potentially less environmentally impactful alternatives to phthalates.