MOSCOW, April 29. /TASS/. Russian scientists compared sediment layers of lakes in the Murmansk Region to understand how to distinguish natural anomalies from industrial pollution to interpret correctly environmental monitoring results, Russia's Ministry of Science and Higher Education told TASS.
Lakes' bottom sediments accumulate substances from the catchment area and from the atmosphere. Upper layers reflect the current state, while the deeper ones retain information about the time before active industrial activity has started. Without reliable data on the region's natural background, it is difficult to interpret environmental monitoring results where high concentrations of elements may be mistaken for pollution, while the true human impact, on the contrary, may remain unnoticed.
"Russia does not have any federal standards for heavy metals contents in lake sediments, thus it is most important to create a regional geochemical 'reference' system. This work has been carried out by specialists of the Institute of the North's Industrial Ecology at the Kola Scientific Center of the Russian Academy of Sciences under the Russian Science Foundation's project. The researchers were tasked to determine reference values for the content of 43 chemical elements in sediments in the Murmansk Region. Those values were to become the starting point in assessing the impact on natural objects," the Ministry of Science and Higher Education said.
The study's subject
The scientists analyzed 417 samples from 53 lakes in the Arctic Region to present the Murmansk Region's geochemical conditions, where the content of most rare elements in sediments is below or close to the average value for the Earth's crust. Higher background values have been recorded for zinc, molybdenum, cadmium, and uranium, and this fact has clear reasons. Cadmium naturally accumulates in clay minerals of sedimentary rocks - similar situations are typical for lakes in Siberia, Norway and Karelia, which confirms the anomaly's natural origin. The accumulation of uranium and molybdenum originates from the local geology. In the region's Litsevsky uranium ore district, uranium concentrations in bottom sediments can be many times higher than those for the earth's crust due to the leaching from pegmatite granites and meta-somatites. Similar processes have been registered in the Khibiny alkaline massif area.
"A separate example is the Pityevoe Lake on the Sredny Peninsula. Here, in the sediments have been found high concentrations of lead, zinc, and cadmium. However, <...> the concentration peaks are not in the upper, but in the deep layers. Results of microscopic analysis show sphalerite particles with lead and cadmium impurities. These results point to the natural origin of metals from local ore deposits. Local lakes are also naturally richer in nickel and copper, which corresponds to the distribution of deposits in the region," the ministry added.
The study results show that increased concentration of metal in lakes' bottom sediments is not equal to pollution, and quite often it reflects the drainage basin's geology. Without understanding the regional background, it is complicated to assess correctly the local pollution level. When monitoring the Litsevsky District, specialists have revealed high uranium contents, and they may interpret this as a geological feature, rather than as pollution. Whenever big amounts, above the established background, of nickel are found in an industrial zone area, this indicates a man-made influence.
The researchers intend to propose registering at the regional level the obtained background concentrations. They also plan to update the database by including new sediment samples to add and refine the obtained concentrations of 43 chemical elements. Scientists will pay special attention to lakes in insufficiently explored parts of the Murmansk Region, including western and central districts. They will also increase the number of defined elements. The data obtained in the study may be used right now as guidelines for environmental monitoring, namely while considering development of new deposits.