Relationship between groundwater cadmium and vicinity resident urine cadmium levels in Hunan Province——a region that is both the heartland of Chinese non-ferrous mining and the home of fish and rice

Cadmium (Cd) has received widespread attention owing to its persistent toxicity and nondegradability. Cd in the human body is mainly absorbed from the external environment and is usually assessed using urinary Cd. Hunan Province is the heartland of the Chinese non-ferrous mining area, where several serious Cd pollution events have occurred, including high levels of Cd in the urine of residents. However, the environmental factors influencing high urinary Cd levels (UCLs) in nearby residents remain unclear. A research team from Central South University and Beihang University used statistical analysis models to analyze 211 nearby residents’ UCLs and the corresponding sociological characteristics from nine groundwater samples in this area.

Their analysis is published in the journal Frontiers of Environmental Science & Engineering on May 15, 2023.

Cadmium (Cd) has been identified by the World Health Organization (WHO) as one of four heavy metal contaminants of major public health concern; it has persistent toxicity and is not biodegradable. Cd in the human body is mainly absorbed from the external environment through contact, drinking, or inhalation into the body for enrichment, and is metabolized slowly. After entering the human body, Cd can be absorbed into the liver or kidney, causing damage to kidney function. Cd may also lead to cancer as a severe threat to human health. Previous studies have pointed out that the two primary sources of Cd exposure in the general population are diet and smoking. However, these studies did not integrate the relationship between the UCL and exposure to the concentration of Cd in environmental media. The groundwater factor influencing high urinary Cd levels (UCLs) in nearby residents remain unclear. There is still a lack of systematic assessment of the impact of groundwater on UCL in the vicinity of non-ferrous metal smelting sites.

Human Cd levels are mainly evaluated using urine Cd. Urine is easier to obtain and can be used to monitor very low concentrations of chemicals and to better measure the exposure level of trace element Cd in the human body. According to the survey, urinary Cd levels (UCLs) were higher in people living near mining areas than in those living in other areas. Therefore, it is necessary to explore the environmental factors that cause higher UCLs in mining areas.

Hunan Province is the heartland of Chinese non-ferrous mining, and its dominant industries are non-ferrous metal smelting, mining, and machinery manufacturing. It is also famously regarded as the home of fish and rice, cultivating over 4000 ha of rice, ranking as one of China’s most important rice-producing regions. Human activities, including non-ferrous metal smelting and uncontrolled emissions of waste gas, wastewater, and sludge from various industries, have proven to be prominent sources of Cd emissions in this area. These activities aggravate the decrease in surface vegetation, thereby accelerating the infiltration of surface water and increasing groundwater Cd pollution. Several Cd pollution events have occurred in Hunan Province, such as the Cd rice incident; the UCLs of residents along the riverbank were relatively high. Previous studies have documented the severe impacts of mining and metalprocessing activities within Hunan on rice agroecosystems. However, they did not analyze the environmental factors influencing the UCLs in the population living near the non-ferrous mining areas of Hunan Province.

To fill these gaps, the team from Central South University and Beihang University systematically examined the relationship between groundwater and UCLs near the non-ferrous metal smelting area of Hunan Province. The main objectives of this study were to: 1) identify the characteristics and current situation of Cd pollution in groundwater and urine, 2) evaluate the relationship between groundwater Cd and UCL in the non-ferrous metal smelting area, and 3) propose comprehensive management precautions according to the possible sources of UCL. This study will help clarify the environmental factors that contribute to the increase in UCLs. It will provide an essential reference for policy makers to reduce Cd exposure in areas where heavy metal industries are prevalent worldwide.

In this study, the research team found groundwater Cd concentration ranged from 0.02 to 1.15 μg/L, aligning with class III of the national standard; the range of UCL of nearby residents was 0.37–36.60 μg/L, exceeding the national guideline of 0–2.5 μg/L. Groundwater Cd levels were positively correlated with the UCL (P < 0.001, correlation coefficient 95 % CI = 9.68, R² = 0.06). There is an extremely significant positive correlation between groundwater and urine Cd in nearby heavy metal industry residents. With an increase in total Cd of 1000 μg/L groundwater, the concentration of Cd in urine will increase by 11.01 μg/L. In addition, sociological characteristics, such as smoking status and education level, also affect UCL. All results indicate that local governments should strengthen the prevention and abatement of groundwater Cd pollution.

This study is the first to systematically evaluate the relationship between groundwater Cd and UCL using internal and external environmental exposure data. Notably, the concentration of Cd in groundwater contributes more significantly to the UCL than do sociological characteristics. The relevant departments should strengthen the control and remediation of groundwater Cd and guide the population to prevent Cd pollution. These findings provide essential bases for relevant departments to reduce Cd exposure in regions where the heavy metal industry is globally prevalent.

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