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 (gamma)-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 (delta C-13 and delta N-15 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 delta N-15 values or N % of gamma-irradiated samples, and only small changes to the delta C-13 values of consumers (range: 0.01 parts per thousand to 0.04 parts per thousand), producers (-0.02 parts per thousand to 0.04 parts per thousand) and sediments (0 parts per thousand to 0.07 parts per thousand). The magnitude of change in delta C-13 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 parts per thousand). 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 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.

Automated summary

The experiment on gamma-irradiated biological samples showed that sterilization had little effect on the stable carbon and nitrogen isotope compositions of common samples and only marginal effects on carbon elemental concentrations.