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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 gamma irradiation (50 kGy) on the stable carbon and nitrogen isotope compositions (δ13 C and δ15 N 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 δ15 N values or N % of gamma-irradiated samples, and only small changes to the δ13 C 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 δ13 C 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 % 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 gamma 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.