Environmental Partitioning, Spatial Distribution, and Transport of Atmospheric Mercury (Hg) Originating from a Site of Former Chlor-Alkali Plant

The Legacy of Hg Contamination in a Past Mining Area (Tuscany, Italy): Hg Speciation and Health Risk Assessment

The mercury cell manufacturing process, which has been extensively used in chlor-alkali plants to produce chlorine and caustic soda by electrolysis, represents a major source of Hg environmental pollution. At Saline di Volterra (Tuscany, Italy), solution mining by pumping water into halite deposits was applied to produce brines for a mercury-cell chlor-alkali plant. The Hg-contaminated, exhausted brines were pumped back at depth into the rock salt field in order to renew the available resources. Activities ceased in 1994, following the leakage dispersion of highly contaminated Hg(0)-bearing brines into the environment. The mercury content in the soil, measured during a survey conducted in 2000, reached 334 mg/kg, highlighting diffuse contamination in the floodplain. By 2009, the Hg concentration had generally decreased and was mostly confined to the topsoil layer. In order to evaluate the present Hg soil pollution, a geochemical survey was carried out in 2023, almost thirty years after the contamination event. The obtained data indicated the occurrence of legacy Hg, which reached 25.5 mg/kg in some soil samples. Speciation analysis for the most contaminated soil revealed that Hg(0) represented about 17.3% of the total Hg and that water-soluble and organic Hg fractions were negligible. These results suggest that the originally released metallic mercury has volatilized and likely oxidized, becoming practically immobile in the soil. A risk assessment, performed by applying Hg speciation analysis, indicated that the mercury in the soil does not carry a risk of non-cancerous effects for different exposure routes in case of subsequent use of the site and that the formerly contaminated area can now be converted into a leisure area.

Mercury Dynamics in the Sea of Azov: Insights from a Mass Balance Model

The Sea of Azov, an inland shelf sea bounding Ukraine and Russia, experiences the effects of ongoing and legacy pollution. One of the main contaminants of concern is the heavy metal mercury (Hg), which is emitted from the regional coal industry, former Hg refineries, and the historic use of mercury-containing pesticides. The aquatic biome acts both as a major sink and source in this cycle, thus meriting an examination of its environmental fate. This study collated existing Hg data for the SoA and the adjacent region to estimate current Hg influxes and cycling in the ecosystem. The mercury-specific model "Hg Environmental Ratios Multimedia Ecosystem Sources" (HERMES), originally developed for Canadian freshwater lakes, was used to estimate anthropogenic emissions to the sea and regional atmospheric Hg concentrations. The computed water and sediment concentrations (6.8 ng/L and 55.7 ng/g dw, respectively) approximate the reported literature values. The ongoing military conflict will increase environmental pollution in the region, thus further intensifying the existing (legacy) anthropogenic pressures. The results of this study provide a first insight into the environmental Hg cycle of the Sea of Azov ecosystem and underline the need for further emission control and remediation efforts to safeguard environmental quality.

Mercury distribution, exposure and risk in Poyang Lake and vicinity, China

Mercury (Hg), especially methylmercury (MeHg), which is highly neurotoxic, is a global pollutant that can affect human health because of its accumulation in aquatic products. Poyang Lake, an inland lake in China, has been significantly affected by human activity, yet there is limited understanding of local mercury contamination and potential exposure pathways to humans. In this study, we explored the risks of mercury exposure by sampling sediments, plants, and aquatic organisms in the lake and surrounding areas and analyzing total Hg (THg) and MeHg levels. Sediment sampling was conducted at the main lake, rivers, rice paddies, and fishponds. Two dominant species of plants and 15 species of aquatic organisms were sampled and analyzed. We assessed the characteristics of mercury in sediments using the geo-accumulation index (Igeo), mercury exposure using the biomagnification factor (BMF) and biota sediment accumulation factor (BSAF), and risks using thresholds for adverse effects. The highest THg concentrations (137.04 ± 44.3 ng g-1 dw) were detected in the main lake sediments, whereas the highest MeHg concentrations (0.47 ± 0.6 ng g-1 dw) were detected in fishpond sediments. Mercury accumulation in the main lake sediments could be assessed as contaminated (Igeo > 0: 81.6%). Yellow catfish had the highest mercury concentration (THg 770.69 ± 199.7 ng g-1 dw; MeHg 741.93 ± 168.8 ng g-1 dw). Piscivores were adversely affected by carnivorous fish (50.8%), but all fish concentrations did not exceed the food safety standards recommend by China and the WHO. The mercury exposure results revealed significant Hg biomagnification and enrichment (BMF >1: 94.55%; BSAFmax = 1218). Long-term monitoring of aquatic organisms is warranted.

Atmospheric mercury and its deposition during the phasing out of an amalgam electrolysis plant: temporal, seasonal, and spatial patterns

Large amounts of mercury (Hg) were consumed and emitted into the atmosphere during the process of amalgam electrolysis used to produce chlorine and caustic soda since the nineteenth century. In Europe, amalgam electrolysis has been gradually replaced by advanced Hg-free technologies. In this work, we describe changes in atmospheric Hg and bulk Hg wet deposition during the phasing out of an amalgam electrolytic production line of a chlor-alkali plant in Neratovice, Czech Republic, central Europe. Bulk wet deposition Hg near the chlor-alkali plant was low at 3.6 ± 0.8 μg m-2 year-1 due in part to low annual precipitation amounts (486 ± 97 mm) in the period 2015-2021. Nevertheless, Hg deposition was elevated relative to a nearby reference site both before and after decommissioning of the electrolytic line. Switching off the amalgam electrolytic line did not notably affect bulk wet deposition Hg near the chlor-alkali plant. Levels of gaseous elemental Hg (GEM) and particle-bound Hg (PBM) monitored seasonally four times per year over 24-h time periods indicated rapid declines in four nearby settlements set in cardinal directions from the Hg emission source. Mean atmospheric GEM and PBM concentrations decreased rapidly from 9.0 ± 2.1 ng m-3 and 243 ± 255 pg m-3 in the period 2013-2017 when amalgam electrolysis was operating to 3.3 ± 0.4 ng m-3 and 32 ± 6 pg m-3 in the period 2018-2021 after its decommissioning in November 2017. Seasonal changes of GEM coincided with changes in temperature with the highest concentrations in summer, while PBM air levels were lowest in summer due to the highest seasonal precipitation amount. GEM concentrations at the four monitored settlements at Neratovice remained elevated at 2.8 ng m-3 with respect to regional background, but PBM levels decreased to background levels.

Assessment of Distribution of Potentially Toxic Elements in Different Environmental Media Impacted by a Former Chlor-Alkali Plant

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.

Potential Human Exposure to Mercury (Hg) in a Chlor-Alkali Plant Impacted Zone: Risk Characterization Using Updated Site Assessment Data

Industrial activities have resulted in severe environmental contamination that may expose rural and urban populations to unacceptable health risks. For example, chlor-alkali plants (CAPs) have historically contributed mercury (Hg) contamination in different environmental compartments. One such site (a burden from the Soviet Union) is located in an industrial complex in Pavlodar, Kazakhstan. Earlier studies showed the CAP operating in the second half of the twentieth century caused elevated Hg levels in soil, water, air, and biota. However, follow-up studies with thorough risk characterization are missing. The present study aims to provide a detailed risk characterization based on the data from a recent site assessment around the former CAP. The ⅀HI (hazard index) ranged from 9.30 × 10−4 to 0.125 (deterministic method) and from 5.19 × 10−4 to 2.54 × 10−2 (probabilistic method). The results indicate acceptable excess human health risks from exposure to Hg contamination in the region, i.e., exposure to other Hg sources not considered. Air inhalation and soil ingestion pathways contributed to the highest ⅀HI values (up to 99.9% and 92.0%, respectively). The residential exposure scenario (among four) presented the greatest human health risks, with ⅀HI values ranging from 1.23 × 10−2 to 0.125. Although the local urban and rural population is exposed to acceptable risks coming from exposure to Hg-contaminated environmental media, an assessment of contamination directly on the former CAP site on the industrial complex could not be performed due to access prohibition. Furthermore, the risks from ingesting contaminated fish were not covered as methyl-Hg was not targeted. An additional assessment may be needed for the scenarios of exposure of workers on the industrial complex and of the local population consuming fish from contaminated Lake Balkyldak. Studies on the fate and transport of Hg in the contaminated ecosystem are also recommended considering Hg methylation and subsequent bioaccumulation in the food chain.

An Integrated Investigation of Atmospheric Gaseous Elemental Mercury Transport and Dispersion Around a Chlor-Alkali Plant in the Ossola Valley (Italian Central Alps)

We present the first assessment of atmospheric pollution by mercury (Hg) in an industrialized area located in the Ossola Valley (Italian Central Alps), in close proximity to the Toce River. The study area suffers from a level of Hg contamination due to a Hg cell chlor-alkali plant operating from 1915 to the end of 2017. We measured gaseous elemental Hg (GEM) levels by means of a portable Hg analyzer during car surveys between autumn 2018 and summer 2020. Moreover, we assessed the long-term dispersion pattern of atmospheric Hg by analyzing the total Hg concentration in samples of lichens collected in the Ossola Valley. High values of GEM concentrations (1112 ng m-3) up to three orders of magnitude higher than the typical terrestrial background concentration in the northern hemisphere were measured in the proximity of the chlor-alkali plant. Hg concentrations in lichens ranged from 142 ng g-1 at sampling sites located north of the chlor-alkali plant to 624 ng g-1 in lichens collected south of the chlor-alkali plant. A north-south gradient of Hg accumulation in lichens along the Ossola Valley channel was observed, highlighting that the area located south of the chlor-alkali plant is more exposed to the dispersion of Hg emitted into the atmosphere from the industrial site. Long-term studies on Hg emission and dispersion in the Ossola Valley are needed to better assess potential impact on ecosystems and human health.