Distribution and accumulation of trace elements in ecosystem components of the Tula Region, Russia, in the case of natural high Sr level conditions

Abstract

The natural excess of Sr due to unusual geological features could affect the elemental composition of the biota. This geochemical basis should be studied to analyze the possible biological accumulation and contribution in the natural protected areas and anthropogenic zones. The content of 15 elements (Al, P, S, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Ba, Pb) was determined in different components of protected areas characterized by high levels of natural strontium of rock-material origin and subjected to agricultural activity. Three key zones in the Tula region were selected due to their elevated natural strontium concentrations in surface waters and parent rocks. The content of elements in water, soils, surface sediments, organisms-biomonitors (buttercup Ranunculus repens), and freshwater bivalve shells was determined by means of inductively coupled plasma optical emission spectroscopy. Samples were collected from multiple sites within each studied zone. The bioaccumulation factors revealed the selectivity of buttercup in uptake of such elements as Sr, Ba, and essential P and S. The coupled accumulation of elements in bivalve shells and buttercups suggests biochemical mechanisms that reduce the uptake of other lithogenic (Al, V, Cr, Fe) and anthropogenic elements (Co, Ni, Cu, Zn, Cd, Pb). The calculated high values of environmental indices (bioaccumulation factors, pollution load and summarized soil pollution indices, enrichment factors) revealed the high accumulation of Sr and other lithogenic elements such as Al, V, Cr, and Co in the environmental components from the second studied zone of Bolsheberezovskoe floodplain swamp on Nepryadva River and near celestine outcrops from the first zone on the Mokraya Tabola River. At the same time, the high bioaccumulation of Sr, P, and S in plants on the second studied zone was found. The affinity for low-volatile elements (Al, V, and Fe) indicated a significant lithogenic contribution. It also revealed the higher contents of Sr and Ba near celestine outcrops (due to specific geological conditions) and higher Cd contents at a site associated with agricultural activity. This accumulation is agreed with calculated bioaccumulation and substrate enrichment levels. This study will be continued further to study the other local sources and their distribution along the river valleys in the other regions.