“Excessive upstream thallium discharges likely cause of intercity pollution in Lei River” 

Water quality abnormalities have recently been detected in parts of the Lei River, the largest tributary of the Xiang River in Hunan Province, impacting water safety in the cities of Chenzhou and Hengyang. According to currently available information, these abnormalities may have been caused by excessive thallium discharges in the upstream regions of the Lei River.

By Wang Kerou, Ma Mingze (intern)

File photo of the Lei River in Hunan. Credit: Visual China

[CAIXIN] Two internal company notices have recently surfaced on the internet. The first, an important notice issued by Xiangheng Salt LLC in Hunan Province on 21 March 2025 to its internal water customers, noted that “based on notifications from the municipal and district environmental authorities, for two weeks after the issuing of this notice, water sourced from the Lei River should not be used for human consumption or washing items intended for human consumption.”

The second was a notice for an emergency response to a Category IV environmental incident issued on 16 March 2025 by the Yongxing County Government of Chenzhou City. It noted that at 20:00 on 16 March, the Dahetan automated monitoring station on the Lei River between the cities of Chenzhou and Hengyang showed abnormal levels of thallium in the surface water, causing the water downstream to become unsafe for human consumption across the two cities.

Both notices were later verified as authentic. According to Jimu News, a staffer at the Yongxing County Government has noted that since abnormal levels of thallium were detected at the Dahetan monitoring station on the Lei River on 16 March, relevant authorities at Yongxing County and other surrounding regions have taken action, releasing chemical agents in the affected waters to lower thallium levels, while also investigating the causes and sources of the contamination, which currently remain unclear.

The Dahetan automated monitoring station is located in Dahetan Village, Huangshi Town, Leiyang City, which is a county-level city under the jurisdiction of Hengyang City. Liu Hongjun, the chief of Dahetan Village, told Caixin reporters in the afternoon of 23 March, a week ago, that they received a notice from the Huangshi Town Government. The notice told them to refrain from fishing due to upstream abnormalities resulting in excessively high levels of thallium in the river, and measures needed to be taken to address the issue. Following the message, the provincial government sent people to chemically treat the section of the Lei River near Dahetan Village. According to Liu, “the treatment is still ongoing, but our section of the river has already reached normal levels.” Since Dahetan Village has always used nearby groundwater for its water source, instead of relying on the Lei River, these recent events have not impacted residents’ water usage. This account was corroborated by a number of Dahetan residents, who said that their water usage was unaffected, and they had merely heard about water contamination in some areas.

The Xiang River is the river with the largest drainage area in Hunan Province, while the Lei River is its largest tributary. The Lei River is 446 km long, with a drainage basin of 11,770 sq km; the river itself flows through Guidong County, Rucheng County, Zixing City (a county-level city under Chenzhou City), Chen County Yongxing County, Leiyang City (a county-level city under Hengyang City), and Hengnan County, before finally merging with the Xiang River in Hengyang City.

Separate notices were issued by the Chenzhou City Government and Leiyang City Government on 23 March. The Chenzhou notice stated that “water quality abnormalities have recently been detected in parts of the Lei River basin,” while the Leiyang notice said that “upstream causes have led to recent water quality abnormalities in the Lei River basin near Leiyang.” Both cities activated emergency response mechanisms to tackle the issue at both upstream and downstream sites, with monitoring results subsequently indicating that the water is safe for human consumption. Further measures will continue to be implemented to ensure the safety of the water. In the afternoon of 23 March, Caixin attempted to contact relevant authorities in Chenzhou City, Hengyang City, and Yongxing County, but received no response.

On 24 March, an employee at the Yongxing County Water Bureau stated, “We’ve been in meeting after meeting, but no specifics can be disclosed.” Data from the national surface water quality real time monitoring system showed that, as of 12:00 on 24 March, water quality at the Dahetan section was rated at Category IV.  The “Environmental Standards for Surface Water Quality (GB3838-2002)” designates five categories for water quality, of which Category IV is suitable for general industrial use, and recreational use where the water does not come into direct human contact. Such water is unfit for human consumption even after treatment. Furthermore, a Class I protected zone for potable water on the Lei River lies just a few dozen kilometres downstream from the Dahetan station.

According to the 2021 revision of the “Industrial Wastewater Thallium Discharge Standards” issued by Hunan Province, thallium-related industries in Hunan include non-ferrous metal smelting, ferrous metal smelting and rolling, thermal power generation, battery manufacturing, mining, tailings management, wastewater treatment and reuse, metal product manufacturing, general equipment manufacturing, waste resources recycling, plastics manufacturing, and raw chemical materials production, in particular the production of zinc oxide and zinc hypoxide. The most common are businesses involved in lead, zinc, and steel smelting, and the manufacture of basic raw chemical materials.

Past instances of thallium pollution primarily resulted from the mining and smelting of thallium-containing ores, and from manufacturing that uses thallium-containing raw or secondary materials. Most instances were caused by the discharge of wastewater containing thallium, while some were caused by rainwater run-off carrying thallium-laden residue into rivers. If left uncontrolled, this will lead to excessive levels of thallium in rivers, especially in downstream areas.

According to the aforementioned Standards, thallium pollutants in Hunan fall into the following three main categories. First, from the mining of mineral resources: lead, zinc, pyrite, coal, and mica mines are spread across Hunan to exploit the province’s abundant mineral resources, and thallium is often released during the mining process. It is often found naturally with these minerals. In addition, thallium often leaches during secondary oxidation processes, as large amounts of the element are discharged from thallium-containing and sulphide ores.

Second, from raw minerals imported from other provinces or overseas: China currently does not regulate thallium levels in lead and zinc imports, and some imported ores contain high levels of thallium, which is released into the environment during the smelting process.

Third, from solid waste (including solid waste imported to the province): thallium contaminants may be released into the environment during resource recovery and treatment processes.

Past instances of thallium pollution have also been traced to sources other than thallium-related industries. In 2021, the Ecology and Environment Department of Hunan reported a severe case of pollution. On 10 November 2020, abnormal levels of thallium were detected in a section of the Xiang River near Hengyang, which was later traced to illegal discharges of waste water from related industries containing high levels of thallium. The suspect in this case, surnamed Wang, had an oral agreement with the owner of a chemical production company, surnamed Liu, whereby Wang leased equipment from Liu during the factory’s downtime to process hazardous waste. More than 2,700 tonnes of ferrous ash was thus processed, with the thallium-rich wastewater carried away in tanker trucks to be illegally discharged.

Due to its unique chemical properties, thallium can cause both acute and chronic poisoning. The highly toxic element can accumulate in the edible parts of plants, thus causing irreversible damage to the human body when ingested directly or indirectly. Thallium pollution has long been an issue in the main sources of water in Hunan. From 6 April to 6 May 2021, China’s Sixth Central Ecological and Environmental Protection Inspection Group conducted a month-long environmental inspection in Hunan, as part of the central government’s second round of environmental inspections.

Their report noted the large number of thallium-related businesses, thallium tailings deposits, and abandoned mines in Hunan, as well as the numerous incidents of thallium contamination in the province. Since 2020, 17 of the 22 drinking water sources along the main stream of the Xiang River were found to have abnormal levels of thallium, of which 12 were discovered in August 2020 alone. (See Caixin’s earlier report: Abnormal levels of thallium found in 17 of 22 Xiang River drinking water sources.)

In late 2020, the Hunan Provincial Government decided to launch a remedial campaign targeting thallium pollution. On 11 December 2020, Hunan Ecology and Environment Department director Den Lijia held a meeting to address the abnormal thallium concentrations in the Xiang River basin. This led to the “Remedial plan to address abnormal thallium concentrations in the Xiang River basin” to improve governance and risk management on the issue, under the guiding principle of “clearing past dues without incurring new ones.”

Green Xiaoxiang, a Hunan-based environmental protection group, has long focussed on the issue of water pollution. According to Liao Sinan, the group’s secretary general, high-risk businesses should be put under tighter regulations as a preventative measure: “Governmental authorities already have records on basically all the thallium-related businesses along the river, so they should be able to offer guidance and supervision in general, especially in terms of emergency response plans for these businesses.”

Thallium is widely used in the metallurgy and chemical industries due to its superior optical, electrical, and catalytic properties. According to the provisional “Technical Guidelines for Screening and Managing Potential Hazards from Thallium-Related Pollution” issued by the Ministry of Ecology and Environment in late 2023, five major fields are listed for screening and inspection: lead and zinc mining companies; lead and zinc smelting companies, covering both primary ore smelting businesses, and those that deal with secondary smelting using smelting waste and steel dust; steel smelting companies with sintering and pelletising processes, including standalone sintering and pelletising firms; pyrite-based sulphuric acid manufacturers; and inorganic zinc compound manufacturers that use smelting waste and steel dust as raw materials.

China’s current maximum limit for thallium in surface water is 0.0001mg/L, as defined by the “Environmental Standards for Surface Water Quality (GB3838-2002).” In 2014, Hunan Province issued the “Standards for Thallium in Industrial Wastewater,” the first codified regional regulations for discharging thallium-related waste, which specified a maximum limit of 0.005mg/L.

Hunan then revised these provincial Standards in 2021, retaining the original discharge limits, while setting additional limits on tailings deposits and for water cycled for use in the ferrous and non-ferrous metals smelting industries. At a press conference in early 2023, deputy director Huang Yu of the Ecology and Environment Department of Hunan stated that average thallium concentrations at main sections and tributaries of the Xiang River have continued to fall, decreasing by more than 50 percent compared to 2020 levels.

Responsible editor: Feng Yuding; layout editor: Xiao Zihe