New data on the composition and distribution of polycyclic aromatic hydrocarbons (PAHs) in thermal waters and host rocks in the Baikal Rift Zone have been obtained. It is shown that the total concentration of all identified compounds is 0.17-1.15 μg/L in the thermal springs and 0.021-1.19 μg/kg in the host rocks. Naphthalene, phenanthrene, and dibenzo[a,h]anthracene predominate in the waters. Phenanthrene, fluoranthene, and dibenzo[a,h]anthracene prevail in the rocks. It has been established that the total PAH concentration increased with TDS of water and with N2 and He concentrations in released gases. The calculated coefficients of technogenic load show a low level of pollution for all the studied thermal springs. The PAH origin was determined based on indicator ratios. On the one hand, PAHs are petrogenic in the thermal waters; they resulted from the geochemical transformations of organic matter at high temperatures, pressures, and microbial activity and were transported with aqueous and gas condensate solutions along faults and fractures. On the other hand, some compounds are pyrogenic; the pyrolysis products get into thermal waters under near-surface conditions or during the mixing of thermal water with cold groundwaters. The results obtained give detailed insight into the composition of thermal waters and the genesis of organic matter. They can be used to propose a conceptual model for the formation of thermal water composition in the region under study.
