Gamma-irradiation of common biological samples for stable carbon and nitrogen isotope and elemental analyses

Rationale: Around the world biosecurity measures are being strengthened to prevent the spread of pests and diseases across national and international borders. Quarantine protocols that involve sample sterilisation have potential effects on sample integrity. The consequences of sterilisation methods such as gamma (γ)-irradiation on the elemental and chemical properties of biological samples have not been widely examined. Methods: We tested the effect of γ-irradiation (50 kGy) on the stable carbon and nitrogen isotope compositions (δ¹³C and δ¹⁵N values) and elemental concentrations (C % and N %) of common biological samples (fish, plants and bulk soils). The analysis used a continuous flow system consisting of a Delta V Plus isotope ratio mass spectrometer connected with a Thermo Flash 1112 elemental analyser via a ConFlo IV interface. Results were compared using two one-sided tests (TOST) to test for statistical similarity between paired samples. Results: There was no change in the δ¹⁵N values or N % of γ-irradiated samples, and only small changes to the δ¹³C values of consumers (range: 0.01‰ to 0.04‰), producers (−0.02‰ to 0.04‰) and sediments (0‰ to 0.07‰). The magnitude of change in δ¹³C values was greatest at low carbon concentrations but appeared negligible when measured against replicated sample analysis and the combined analytical uncertainty (i.e., 0.10‰). The C % values of irradiated samples were higher for consumers (0.23%) and lower for producers and sediments (0.04% and 0.05%, respectively) which may have implications for certain types of biological material. Conclusions: Routine γ-irradiation has little effect on the stable carbon and nitrogen isotope compositions of common biological samples and marginal effects on carbon elemental concentrations. This is unlikely to warrant concerns since the observed difference is typically of a magnitude lower than other sources of potential uncertainty.