GEOCHEMICAL CHARACTERISTICS OF MERCURY DISTRIBUTION IN POPLAR LEAVES AND ANNUAL RINGS OF URBANIZED TERRITORIES ON THE EXAMPLE OF NOVOSIBIRSK

Abstract

Relevance of the study is determined by the necessity to provide ecological and geochemical assessment of technogenic impact on environment and population health related to urbanization and industrial development resulting in contamination of natural assets with various pollutants. The aim of the study is to assess mercury loads onto the natural components of an urbanized territory with a well-developed industrial infrastructure by studying leaves and cores of balsam poplar (P. balsamifera L.). Subjects of research are poplar leaves and annual rings. This species of poplar is very common in urban localities of temperate zone. It has a number of features allowing it to capture significant amounts of dust particles and aerosols, namely, relatively large area, wax covering and presence of both abaxial and adaxial stomata; the tree serves as an indicator of community air. Research methods were sampling of poplar leaves through the period of 2014–2018 and following a 4×4 uniform area grid with a further concentration of 1×1 km near assumed pollution sources; sampling of wood from separate trees at a distance of 0,5 to 1 km from the assumed pollution source; atomic absorption spectrometry of Hg by pyrolysis; statistical processing of data; plotting maps and graphs. Results. During the field and laboratory works, the authors have obtained the data on geochemical features of Hg distribution through the leaves and annual rings of balsam poplar (P. balsamifera L.) in the territory of the city of Novosibirsk. In the northwestern part of the city, a biogeochemical halo of Hg concentrations was identified; it is isometric in form, has an area of approximately 25 km2 and is characterized by Hg content of over 100 ng/g. In 2017, a high Hg concentration (1300 ng/g) in poplar leaves was recorded in Kalininsky district, near the industrial site of the Novosibirsk Chemical Concentrates Plant. The studies have shown a clear trend for Hg accumulation in poplar leaves throughout the vegetation period. Maximum average content was found in leaf litter at 2006 ng/g (the range is 1153–2425 ng/g). However, the average Hg content in soil is 294 ng/g, which is significantly lower than the maximum allowable concentration of 2100 ng/g. Distribution of Hg content in poplar leaves depending on leaf position in the tree crown was studies for a tree in the epicenter of biogeochemical halo of Hg concentrations. Upwind the emission source, Hg concentration in the leaves is on average 1,5 times higher than in the wind shadow. During the studies of Hg forms in poplar leaves it was established that Hg is primarily found in free and physically-bound forms, which are the most mobile, prone to increased migration, transformation and methylation under the environmental conditions. Studies of wood cores in the vicinity of the pollution source allowed establishing three periods of Hg emission: the first period, with the maximum emission covers 1967–1985, the second period of 1991–2000 shows a decrease in Hg content; the third period of 2000–2007 is characterized with a relatively low level of Hg concentration. A large biogeocheimcal halo of Hg concentrations was mapped in the city of Novosibirsk, a possible emission source was found. Dendrobiogeochemical methods applied in the epicenter of the area with the highest mercury content allowed establishing long-term dynamics in Hg content in the subjects of the study. A period with the highest technogenic impact on the urban environment was established. In residential and industrial zones in the northeast of Novosibirsk, in the territory of a large biogeochemical Hg-related halo, the authors recommend to establish environmental and geochemical monitoring with mercury metering of air samples, studies of soil and plant cover, monitoring of sanitary and hygienic indicators of population’s health.

Keywords

• hg
• urban territories
• novosibirsk
• poplar leaves
• annual rings
• dendrobiogeochemistry