Microplastics in human skeletal tissues: Presence, distribution and health implications.

Although microplastics have been detected in human blood, placenta and other tissues. In this study, for the first time, we characterized the presence and variation of microplastic deposition patterns in three human skeletal tissues, namely the bone, cartilage, and intervertebral discs. Forty microplastic fragments were observed in 24 samples from the bone, cartilage, and intervertebral disc, ranging from 25.44 to 407.39 μm in diameter. The deposition abundance of microplastics in the human intervertebral disc (61.1 ± 44.2 particles/g) was higher than those in the bone (22.9 ± 15.7 particles/g) and cartilage tissue (26.4 ± 17.6 particles/g). The average sizes of microplastics in intervertebral discs (159.5 ± 103.8 μm) and bone (138.86 ± 105.67 μm) were larger than that in the cartilage tissue (87.5 ± 30.7 μm). The most frequently identified polymers were polypropylene (35 %), ethylene vinyl acetate copolymer (30 %), and polystyrene (20 %). The in vivo experiment suggested that microplastics invaded the bone, cartilage, and intervertebral discs through blood circulation after 4 weeks of exposure. Serum levels of tumor necrosis factor-α (TNF-α), Type Ⅰ procollagen amino-terminal peptide (PINP), and tartrate-resistant acid phosphatase-5b (TRACP-5b) were elevated compared with those in the control group (p < 0.05). Our study suggests that microplastics invade the bone, cartilage, and intervertebral discs through the blood supply, causing distinct patterns of microplastic accumulation in these regions. Microplastic invasion can affect skeletal health by influencing the expression of inflammatory and bone morphogenetic cytokines. These findings provide insights into investigating the impact of microplastics on human skeletal health.