METHODS OF STABLE ISOTOPE ANALYSIS (RECONSTRUCTION OF NUTRITION)

МЕТОДЫ АНАЛИЗА СТАБИЛЬНЫХ ИЗОТОПОВ (РЕКОНСТРУКЦИЯ ПИТАНИЯ)

Жарылғасынова Бибинұр Муратбекқызы

Казахский национальный университет имени аль-Фараби, Казахстан, г. Алматы

When determining the lifestyle of ancient people, every detail of it is important. Currently, archaeologists are achieving many scientific successes with the help of the latest technologies. One of them is the definition of the diet of the inhabitants of antiquity. That is, the study of what kind of food was consumed by conducting a stable isotope analysis of human and animal bones.

An isotope is a type of the same chemical element, which differ in the mass of atoms. Conducting laboratory analyses of carbon and nitrogen isotopes, which are components of organic food, leads to many positive results. During feeding, a person collects isotopes of previous food bonds. In addition, the tooth is very important in the process of isotope analysis. By studying its isotopic composition, it is possible to determine the types of foods that it has consumed since childhood, and the bones taken for research provides information about nutrition in the last years of life.

Isotopes of radioactive carbon 14C help to determine to what date the bones belong, because as soon as the body ceases to function, there is no carbon exchange in it, and radioactive 14C begins to gradually decay. Over time, its share indicators in the remains decrease, and by the number of decays of the 14C core, as well as tree rings, it is possible to calculate the age of this bone. In general, in addition to radioactive carbon, there are two other isotopes in nature, 13C and 12C, which do not undergo decay over time [6].

In the food chain, plants are considered the first generation. They synthesize organic substances from carbon dioxide in air or water. Since the rate of chemical reactions in this environment varies, the relative amount of heavy and light carbon isotopes in plants varies.

When reconstructing nutrition from isotopic data, archaeologists rely on the principle of a trophic chain. At the beginning of the food chain are plants, then herbivores, then predators, and finally humans. The accumulation of stable carbon isotopes in freshwater bodies occurs in the same way as in seas and oceans, so fish in such lakes contain more heavy carbon isotopes. But there are more light isotopes of 12C in small lakes and rivers, and fish from there have carbon isotope values similar to plants. Therefore, in some cases it can be established that the origin of ancient fish is from a lake or river [6].

Nitrogen helps to more accurately understand whether a person has eaten fish or plants by tracking the trophic food chain. In this sense, its stable isotopes 14 N and 15 N are of great importance. Carbon isotopes also calculate their ratio to each other. The quantitative indicators obtained during the study directly reflect the position of the consumer in the food chain: the higher it is, the higher the trophic stage the organism acquires. Inhabitants of marine and freshwater reservoirs, as a rule, have a longer food chain than terrestrial animals, so their nitrogen content is higher [6].

Studies of stable carbon and nitrogen isotopes in bone collagen occupy an important place in restoring human and animal nutrition [1, 59 p.]. That is, stable carbon and nitrogen isotopes show that they can provide information about proteins in food [3, 2 p.]. According to the laboratory results of many research scientists, the isotopic composition of carbon and nitrogen in the bones and teeth of large mammals depends on nutrition – about 5 % for carbon and about 3 % for nitrogen. S.H. Ambrose reviewed the variables of nitrogen isotopes in the food chain, showing that the isotopic value of collagen depends on the climate in the region where animals lived and their physiology; in addition, he found significant changes even between their ecosystems and trophic levels [2, 293 p.].

The value of the carbon isotope composition of collagen is determined by the nutrition of herbaceous plants that absorb carbon during photosynthesis, depending on the Calvin cycles (plants C3) or Hatch–slack (plants C4). C3 plants are typical for temperate and cold natural conditions, whereas C4 plants grow best in warm and arid regions. The value of δ13C of bone collagen of herbaceous plants can reach values of - 20 % or more [4, p. 94].

Methods of stable isotope analysis. To carry out the analysis of stable isotopes on the bone, it is necessary first of all to isolate a special tissue. To analyze the bone isotope, it is first necessary to isolate a special tissue for analysis. For collagen, this includes acid mineralization of the bone (each laboratory uses different acids, concentrations and temperatures) and separation from any residual lipids [7].

In the private laboratory of Professor of Anthropological Sciences R. H. Tikot, located at the University of South Florida, bone collagen is obtained using scientifically proven laboratory methods. All bones in the laboratory are demineralized in 2% hydrochloric acid (72 hours), and pollutants soluble in alkali are removed using 0.1 M sodium hydroxide (24 hours before and after demineralization), and residual lipids are removed in a mixture of methanol, chloroform and water (24 hours) in a ratio of 2:1:0.8 [7].

One milligram of a sample of the obtained collagen pseudomorphs is placed in tin capsules and analyzed in continuous flow mode δ13C and δ15N using a CHN analyzer connected to a Finnigan MAT stable isotope ratio mass spectrometer. Samples of collagen pseudomorphs are considered a visual indicator of bone integrity. Prior to this, work is underway to burn collagen in a vacuum quartz tube at high temperature, followed by its conversion to CO2 and N2 in an autonomous mode using cryogenic distillation to separate these gases. Then each gas sample is injected into the mass spectrometer using a collector system. The CHN analyzer combines the gorenje stage with the temporary separation of CO2 and N2 formed on the path of the mass spectrometer, which is also capable of quickly switching between different ranges of measured masses (28 and 29 for N2; 44, 45 and 46 for N2. basically, one oxygen-18 weighs 46. And its measurement allows us to determine by the formula which part of the signal with a mass of 45 is oxygen-17, carbon-13). The units of measurement of gas flow and the C:N ratio are used to confirm the integrity of collagen samples [7].

For samples of bone Apatite and tooth enamel, procedures are carried out to remove non-biogenic carbon so that the values of biogenic carbon isotopes do not change [5]. Powder samples are obtained by drilling the bones or the center of the tooth enamel with a well-cleaned surface. About 10 mg is placed in a 2% solution of sodium hypochlorite to dissolve the organic components of the powder (24 hours for enamel, 72 hours for bone apatite). Then, in 1.0 M of buffered acetic acid, the process of destruction of nonbiogenic carbonates occurs within 24 hours. The integrity of Apatite and enamel samples is evaluated based on the results obtained at each stage of the pretreatment process. The obtained samples are analyzed by a second Finnigan MAT mass spectrometer equipped with a separate carbonate system in the Kiel III acid bath, which eliminates the need for autonomous CO2 production by interacting the sample with acid in a vacuum insulated glass tube and cryogenic purification of the resulting gas sample.

The samples are in addition to the measured reference gases and are confirmed by measurements of several standardized samples (samples with quantitative indicators) at the beginning of each work, and then after every six or seven archaeological samples to ensure the reliability of all results. The analytical accuracy for mass spectrometry of stable isotope ratios is usually 0.1° for δ13C and 0.2° for δ15N [7].

Thus, the analysis of stable isotopes in the study of archaeological materials is considered an additional source of information. The results of isotope analysis provide great opportunities for clarifying a sufficient number of materials about the object under study or a population group or for crossing out irrational conclusions. But in most cases, research scientists collect only bone samples without additional data. This, in turn, involves a lot of difficulties in drawing accurate conclusions.