<p>Although several microbial strains can metabolise poly(<i>cis</i>-1,4-isoprene), recent studies suggest that tyre and road wear particles (TRWP) persist beyond 2 years in soil or water. To understand how microbial degradation evolves with increasing material complexity, the biodegradation of various elastomers, model composites and laboratory-wear particles was evaluated over several weeks using standardised tests in soil, compost, or freshwater. Natural rubber (NR) and synthetic poly(<i>cis</i>‑1,4‑isoprene) (<i>cis</i>‑IR) showed substantial biodegradation. NR reached 50% mineralisation (%ThCO₂) at 361 days in soil and approximately 50 days in compost. <i>cis</i>‑IR half-mineralised at 55 days in compost and 44–72 days in freshwater. Comparatively, the mineralisation of poly(<i>cis</i>-1,4-butadiene) (<i>cis</i>-BR) and styrene-butadiene rubber was limited to a few percent over the investigated period. Non-stereospecific polyisoprene reached about 3% mineralisation in freshwater at 140 days, underscoring the importance of <i>cis</i>‑1,4 stereoregularity. The mineralisation of a <i>cis</i>‑IR/<i>cis</i>‑BR 30/70 blend was commensurate with the proportion of <i>cis</i>-IR phase. The data relying solely on CO₂ endpoint, they cannot rule out partial degradation of <i>cis</i>‑BR phase, but indicate that complete conversion to CO₂ was not achieved. Filling NR with 20%vol carbon black or silica led to a two-fold reduced mineralisation after 45 days compared to unfilled NR, while only 5% vol had little effect. After 28 days in sludge-inoculated water, tribometer-generated model wear particles of a carbon black filled vulcanised <i>cis</i>-IR achieved 15.5% mineralisation, compared to 3.5% for the undamaged composite, potentially due to chain scission or devulcanisation. Overall, elastomer microstructure, filler content, crosslinking density and wear history appear to be influential parameters affecting rubber nanocomposites biodegradability.</p>