Natural abundance δ13C constraints on the detection of microplastic-derived carbon in freshwater environments
Year: 2025
Type: article
Abstract: Microplastics (MPs) are increasingly recognized as emerging pollutants in freshwater systems. Detecting and tracing MP-derived carbon in aquatic food webs, however, remains unresolved, limiting our understanding of ecological impacts. Here, we evaluate the potential and limitations of natural abundance stable carbon isotope measurements ( δ 13 C) as a tool to identify MP signals in freshwater ecosystems. For this purpose, two freshwater algae, Chlorella vulgaris and Chlamydomonas reinhardtii , were exposed under controlled laboratory conditions to one non-biodegradable polymer, low-density polyethylene (LDPE), and two biodegradable polymers, polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT), to assess isotope composition and growth. Laboratory data were complemented by particulate organic carbon ( δ 13 C POC ) measurements from seasonal Danube River campaigns (2023-2024) with modelled predictions based on dissolved organic carbon ( δ 13 C DIC ). MP exposure did not inhibit algae growth, but C. vulgaris exhibited significant (p <0.05) δ 13 C enrichment (+4 to +5 ‰), whereas C. reinhardtii showed no isotopic response. These shifts were unrelated to polymer isotope values and likely reflect indirect physiological stress rather than assimilation of polymer-derived carbon. Complementary binary mixing experiments further confirmed that measurable isotopic shifts occur only at unrealistically low algae-to-MP ratios (≤10:1), underscoring the limited sensitivity of isotope mass balances. Field surveys revealed pronounced seasonal δ 13 C POC variability in the Danube, spanning 7.4 ‰ annually. Yet deviations from modeled expectations were inconsistent with MP inputs and instead reflected natural drivers such as productivity and remineralization. Overall, while natural abundance δ 13 C can capture subtle algae responses to MP exposure under laboratory conditions, its diagnostic power for tracing MP-derived carbon in complex freshwater systems appears limited. • Natural abundance δ 13 C POC tested as tracer for microplastic-derived carbon inputs • δ 13 C only detects MPs at unrealistically low biomass:MP ratios (≤10:1) • Species-specific isotope shifts hinder generalization of algal MP impacts • Strong δ 13 C POC variability masks subtle MP signals in natural settings • Study defines limits of isotopic methods and guides future MP monitoring strategies
Source: Environmental Pollution
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,090
OpenAlex ID: W4416768270