Polyaromatic hydrocarbons in the Caspian Sea during 2017–2021

The article presents the results of study of polyaromatic hydrocarbons in the Northern Caspian and the Middle Caspian marine environment. The spatial and temporal dynamics of PAHs concentration is described on the basis of the materials gathered during 2017–2021. The study was based on the results of industrial environmental monitoring of the licensed areas of mineral resources use in the northern and middle part of the Caspian Sea. The data of industrial environmental monitoring were analyzed by standard statistical methods. It should be noted that the seasonal variability of PAHs concentrations in the Northern Caspian is characterized by the spring increase in PAHs amount for almost all period under study. A common feature of PAHs dynamics in the northern part of the sea is an upward trend from 2017 to 2020 and its decrease in 2021. No seasonal patterns in the variability of PAHs were found for the Middle Caspian. There are not found stable trends in PAHs concentrations in this region. Concentration range and fraction in the sum of all PAHs were determined for each of the PAH components. As a result of the study the dynamics of water content of marker hydrocarbons, such as pyrene, benz(a)pyrene, fenantren, acetenaften, anthracene, chrysene and naphthalene, was revealed. A redistribution of the mass share of the main components of PAHs occurred in 2019. Acetenaften, fenantren and naphthalene were the most common in the Caspian Sea water. Analysis of molecular-diagnostic ratios proves the presence of anthropogenic and natural sources of polyarenes and the mixed origin of hydrocarbon pollution in the Caspian Sea. Analysis of molecular-diagnostic ratios shows the presence of anthropogenic and natural sources of polyarenes and the mixed origin of hydrocarbon pollution in the Caspian Sea. A number of patterns have been identified through correlation analysis. There is a strong feedback between the ratios (pyrene + benz(a)pyrene)/(fenantren + chrysene) and fenantren/anthracene in the Northern Caspian. And there is also a direct correlation between the ratios naphthalene/fenantren and anthracene/(anthracene + fenantren). Analysis of correlation relationships of indicator ratios in the Middle Caspian did not reveal any dependencies, which may indicate a variety of sources of contamination by polyaromatic hydrocarbons.