Since the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) banned ivory trade in 1989, the international community has made efforts to save endangered elephants. However, mammoth ivory excavated from the Siberian permafrost is still considered a legal commodity. These two types of ivory have similar appearances but vastly different prices, leaving poachers with an opportunity to mix and transport poached elephant ivory with mammoth ivory to get away with it. To plug this potential loophole, researchers have developed stable isotope analysis techniques to quickly and inexpensively distinguish between modern elephant ivory and mammoth ivory.

1. Detection principle and advantages
Stable isotopes refer to the different atomic forms of elements that appear in varying proportions in natural environments. Due to differences in living environments, there are significant differences in the hydrogen and oxygen isotope content in the ivory of mammoths and modern elephants: mammoths living in Siberian glacial sites (high latitude cold regions) consumed water with different ratios of hydrogen and oxygen isotopes compared to modern elephants living in the tropics.
Research has found that after detecting multiple isotope ratios in ivory, 2H (hydrogen isotope) does not overlap at all in mammoth ivory and elephant teeth, and 18O (oxygen isotope) also has very little overlap. This means that using hydrogen and oxygen isotopes can effectively distinguish between the two. In addition, the detection of carbon, nitrogen, and sulfur isotopes in ivory revealed overlap between the two types of samples, making it difficult to use as a distinguishing criterion. Researchers suggest using multi-element combined stable isotope analysis, focusing on hydrogen and oxygen isotopes, to achieve identification effect.
2H (hydrogen isotope): The ivory values of elephants and mammoths do not overlap at all.
18O (oxygen isotope): There is a slight overlap between the two.
13C, 15N, 34S: The three elements overlap between the two types of ivory. The picture shows ivory samples used by the research team for analysis. A and B are modern elephant ivory carvings, C and D are mammoth ivory carvings, and E and F are unprocessed raw stone ivory. It can be seen that even in professional hands, the appearance characteristics of polished or carved samples are still difficult to accurately distinguish between mammoth ivory and elephant ivory. Stable isotope analysis can provide scientific identification basis for law enforcement agencies by leveraging the differences in drinking water sources between the two.

2. Research methods and findings
The research team tested 79 ivory samples, of which 44 were identified as modern elephant ivory and 35 were mammoth ivory. Some of these samples were seized by Hong Kong law enforcement agencies, while others were purchased from carving markets in Hong Kong and Shanghai. Researchers measured the stable isotope ratios of five elements (carbon, hydrogen, nitrogen, oxygen, sulfur) and compared their distributions in two types of ivory. The results showed that the distribution of the two types of ivory in the hydrogen and oxygen isotope maps almost did not overlap: the red dots in the figure represent modern ivory, and the blue dots represent mammoth ivory. It can be seen that the two groups of samples are clearly separated on the δ ^ 2H and δ ^ 18O scatter plots. This difference reflects the vastly different ecological environments in which the two are located: elephants consume water sources from tropical regions and have a higher abundance of hydrogen and oxygen isotopes; Mammoths are taken from cold temperate regions and have lighter hydrogen and oxygen isotopes.

In addition, research has found that there are no significant differences in carbon, nitrogen, and sulfur isotopes between elephant and mammoth ivory, and their distribution ranges are highly overlapping. This means that identification methods targeting isotopes such as carbon-13, nitrogen-15, and sulfur-34 cannot reliably distinguish between the two types of ivory. It can be seen that focusing on hydrogen and oxygen isotopes in detection is a key strategy for rapid differentiation.

3. Application prospects and benefits
Stable isotope analysis technology has the advantages of low cost and fast speed, and is considered an ideal tool for large-scale screening of suspicious ivory. Researchers suggest that law enforcement agencies can first conduct hydrogen and oxygen isotope testing on a large number of products labeled as "mammoth ivory", and for samples with abnormal isotope characteristics (close to modern elephant ivory), further expensive and time-consuming carbon-14 radiometric dating or molecular biology analysis can be used for confirmation. Such a graded screening strategy can significantly improve case handling efficiency and help plug potential illegal whitewashing loopholes.
Overall, this study provides a simple and effective identification method, offering a new tool for combating illegal ivory trade. Future research will further improve the sample collection and analysis process to ensure that this method can be used for forensic appraisal. As stated by the research team, we hope that the relevant protocols can be applied in practical testing to help countries more effectively control the circulation of ivory and protect elephant resources.