Human health risk assessment of potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) in urban topsoils of Tyumen city, Russia

Cities are the key centers of technogenesis, which leads to environmental pollution. The state of the soil cover reflects the long-term anthropogenic impact as a result of urbanization processes. In the urban environment, the priority pollutants are potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs), since they are not only an environmental hazard, but also a risk factor for the public health. Tyumen city, with a population of 807,300 people, is a large transport and trade center in Western Siberia, Russia, with a developed service sector, construction and manufacturing industries. The aim of the study is to evaluate possible carcinogenic and noncarcinogenic risks related to PTEs and PAHs in urban topsoils of Tyumen, as representative of urban environment in Western Siberia.

Topsoil samples (0-10 cm) were collected according to the regular grid at 241 sampling points. The total content of V, Cr, Co, Ni, Cu, Zn, As, Sr, and Pb was determined using X-Ray fluorescence spectrometry. Content of twelve priority PAHs was measured using high-performance liquid chromatograph Agilent 1260 Infinity. Human health risk assessment was based on the US EPA model (1989). The noncarcinogenic risk for different age groups of the population, expressed as a hazard quotient (HQ), was evaluated by comparing the average daily dose of pollutant (ADD) with a reference dose (RfD). Carcinogenic risk (CR) reflects the probability of developing cancer in an individual throughout their life, taking into account the lifetime average daily dose of a pollutant (LADD) and carcinogen slope factor (SF). Values of RfD and SF were based on toxicological data (U. S. EPA 1997, 2004, 2020; ATSDR 2020; OEHHA 2020). The combined effects were assessed using the total hazard index (THI) and the total carcinogenic risk (TCR).

Noncarcinogenic risks were more likely caused by intake of V, Co, As, Pb, Ni and Cu. For both children and adults, the risk associated with the oral intake of pollutants was the greatest. For children, significant risks arose from exposure to V, Co, As and Pb (HQ> 1). The THI values for children varied from 0.78 to 7.25, on average 2.72, for adults - from 0.08 to 0.79, on average 0.27. Most of the territory was characterized by a medium non-carcinogenic risk for children and a low risk for adults.

Significant CR was associated with long-term exposure to Co, As, Pb and benzo[a]pyrene. The TCR values under the combined effect of PTEs and PAHs ranged from 1.2 × 10^-5 to 2.2 × 10^-4, on average 6.9 × 10^-5. In general, the level of carcinogenic risk in the city was assessed as low. Medium carcinogenic risk was established in the soils of impact zones of enterprises for the production and disposal of batteries, CHPP-1 and some large transport hubs. An extensive zone of increased carcinogenic risk was established in the residential area of the central part of the city.

The research was funded by RFBR and Tyumen Region, project no. 20-45-720003, and by Ministry of Science and Higher Education of the Russian Federation, no. 0852-2020-0029.