Ecological and Geochemical Assessment of the State of Soils in the City of Baikal’sk according to the Content of Polycyclic Aromatic Hydrocarbons

Abstract

The pollution of the topsoil in the city of Baikal’sk (Irkutsk oblast) under the influence of industrial emissions and wastes of the Baikal Pulp and Paper Mill (BPPM) was studied. The contents of 16 individual polycyclic aromatic hydrocarbons (PAHs) in samples of urban and background soils taken during the soil geochemical survey in the summer of 2019 were analyzed. Relatively low contents of PAHs were found in lignin sludge from the BPPM and ash from the combined heat and power station (CHPS). The concentration of total PAHs in CHPS ash reaches 46 mg/kg with a predominance of low molecular weight compounds (the proportion of naphthalene and its homologues is 24% and 34% of the total PAHs, respectively). Among high molecular weight PAHs, 5-nuclear benzo(b)fluoranthene dominates (16%). In lignin sludge, the amount of PAHs is 7.16 mg/kg with a predominance of benzo(b)fluoranthene (83%). In soils of Baikal’sk, the mean total content of PAHs (38.4 mg/kg) is five times higher than the background content. In urban soils, 4–5-nuclear fluoranthene (61.1%) and benzo(b)fluoranthene (29.4%) prevail. This enables us to assign soil pollution to the fluoranthene type. Soils of the motor traffic (total content of PAHs is 105 mg/kg) and industrial (59.5 mg/kg) zones are most strongly polluted and display contrasting geochemical anomalies of PAHs. Land use zones of the city may be arranged in the following sequence with respect to the amount of PAHs: motor traffic > industrial > residential single-story > railway transport > residential multi-story > recreational zone. Several local anomalies with increased contents of PAHs form two large pollution halos in the west and east of the city. The leading factors in the accumulation of high molecular weight PAHs in soils include acid–alkaline conditions and soil organic matter, while the accumulation of low molecular weight polyarenes is mainly controlled by pH. The environmental hazard of pollution of Baikal’sk soils with polyarenes is by 83.5% related to benzo(b)fluoranthene.