Abstract
Former industrially contaminated sites are a burden from the past that still pose environmental risks. During the second half of the 20th century, the Pavlodar region in North Kazakhstan had been a part of Soviet Union’s industrial system that operated a chlor-alkali plant (CAP). The former CAP discharged approximately 135 t Hg into nearby Lake Balkyldak with total losses to water, soil, and air estimated around 1000 t. Pollution by potentially toxic elements (PTEs) due to former and currently active industrial enterprises is an under-investigated concern in the Pavlodar region. The present study aims to provide a much-needed update on the situation around the CAP area by evaluating the contamination by Hg and other selected PTEs (As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, Se, Zn) on the surrounding environment of the CAP and in the nearby urban zone. Soil, sediment, surface water, and groundwater samples have been collected in several sampling campaigns carried out in 2018 and 2019. Several samples had Hg concentrations exceeding maximum permissible concentrations (MPC), for soils and sediments (in mg/kg; range: 0.0006 to 24, average: 0.56) and for surface water and groundwater (in µg/L; range: 0.004 to 1340, average: 93). Critically high concentrations were mostly measured in the vicinity of Lake Balkyldak, where the majority of Hg had been discharged by the former CAP, indicating persisting Hg pollution in the studied zone. A comparison of the PTEs concentrations in soil and sediments showed less severe pollution but still some elevated values for As, Ba, Co, Cu, Mn, Ni, and Se. The inter-elemental relationship between Hg and assessed PTEs was weak, indicating the presence of sources independent from Hg emitting sources. Further research on Hg contamination on the exact territory of the former CAP is needed, and a detailed human health risk characterization to identify potential unacceptable risks is strongly recommended.
Highlights
In order to predict the migration potential of potentially toxic elements (PTEs) associated with soils, it is important to take into consideration the soil solution chemistry, as metals associated with the soil solution are able to migrate to groundwaters through the vadose zone [34]
The present study investigated soil, sediment, surface water, and groundwater contamination by 13 selected PTEs including mercury (Hg) in Pavlodar region (North Kazakhstan) around a former Hg-cell chlor-alkali plant (CAP) operated in the second half of the 20th century
Surface water and groundwater samples had similar characteristics where the majority of samples complied with the national maximum permissible concentrations (MPC) for drinking water with the exception of numerous highly contaminated samples from the impacted zone
Summary
Mercury (Hg) is a naturally occurring, volatile, highly toxic element originating below the Earth’s surface [1] and exists in elemental, inorganic, and organic forms (Table 1). The USEPA has set the minimum risk level for chronic exposure to elemental Hg (via inhalation exposure: at 3 × 10−4 mg/m3 ) and for mercuric chloride (HgCl2 ) (via oral exposure: at 3 × 10−4 mg/kg/d) [6]. Exposure to Hg and other PTEs occurs via three pathways: oral, dermal, and inhalation [7] and might cause neurological diseases (Table 1) [8], where the organic form methylmercury (MeHg) is problematic. MeHg is classified as a possible human carcinogen (Class C, weight of evidence characterization), having a reference dose of 1 × 10−4 mg/kg/d and minimum risk level for chronic ingestion of
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