Metals in soils of the South Kuril Islands

The chemical composition of the volcanic soils of the southern Kuril Islands (Iturup, Kunashir, Shikotan), which are affected mainly by ash falls of the main composition during volcanic eruptions, has been studied. The total content of metals (K, Ca, Mg, Na, Ba, Cu, Co, Cd, Cr, Fe, Mo, Ni, Pb, Sc, Sr, V, Zn) and the concentrations of their mobile forms extracted by an ammonium acetate buffer at pH 4.8 were determined. Concentrations of Sc, V, Fe, Zn is 1.5–5 times higher, and the content of Cr, Ni, Sr, Ba is 2–10 times lower than clarks values. Soils are characterized by a contrasting pH distribution of 3.75–7.81, which determines the lability of metals. The maximum activity of radial and lateral migration is noted at low values of the acid-base index, leading to a sharp differentiation of the chemical composition of the genetic soil horizons in various catenary positions, the coefficients of radial and lateral migration can increase to 12 and 29, respectively. The results of factor analysis showed the leading role of soil-forming rocks in the formation of the chemical composition of soils (about 63% of the sample variance); the processes of humus formation, transformation of mineral and organic substances in soils, and hydrothermal activity have a lesser influence. Soils formed on the middle and basic rocks of the Cenozoic volcanic sequence are characterized by Ca–Mg–Na paragenetic associativity, liparite-dacite complex – Ba–K–Pb–Mo, gabbroid – Ni–Cr–Cu, psammite – V–Sc–Fe–Co. Paragenesis Mo–Pb is typical for sites of modern hydrothermal activity. The influence of placer formation processes on the chemical composition of soils in the coastal areas of the Iturup and Shikotan islands is shown. The distribution of mobile forms is associated with chelation processes, geochemical barriers of acid-base, sorption and redox types. Local soil pollution has been identified, mainly due to the operation of motor vehicles. On the territory of the settlements of Krabozavodskoye and Yuzhno-Kurilsk, there is an increase in the concentration of Ba, Sr and K associated with the activities of fish processing plants, in Kurilsk – Cr, Ni, Cu, Co, Zn and Pb, the source of which is the repair base. The calculated soil toxicity probability index (MERMQ), as well as the results of biotesting for Daphnia magna Straus. and Chlorella vulgaris Beijer showed low soil toxicity. This is explained by the low population density and low degree of economic development of the islands.