Size fractionation of trace elements in the surface water and groundwater of the Ganjiang River and Xiushui River basins, China

Geochemical conditions of natural wetland and paddy fields in the Poyang Lake area, China

Abstract

During the last several decades, wetlands are losing their ecological functions due to increasing anthropogenic loads. One of these functions is the ability to bind elements forming geochemical barriers. The research aimed to study the geochemical conditions of natural wetlands and flooded paddy fields (artificial wetlands) in the Ganjiang River basin to trace geochemical barriers. The research approach was based on a comprehensive analysis of water and aqueous extracts from bottom sediments and paddy soils, including chemical and mineral composition. The samples were collected in November 2019, during the dry season at the end of harvesting. Chemical analysis was performed using standard methods for natural substances: titrimetry, photometry, ionic chromatography, high-temperature oxidation, ICP-MS, and ICP-AES. The mineral composition of the soils and sediments was determined by XRD. It was found that the main physicochemical characteristics (TDS, pH, main component concentrations) of the natural wetland water correspond to the surface water of the study area, whereas the irrigation water is similar to shallow groundwater. The content of trace elements in the irrigation water is higher than in the natural wetland water. Generally, the trace element composition of the natural wetland water corresponds to the geochemical background of the study area. Analysis of the mineral and chemical composition of the paddy soils and sediments indicates the geochemical barriers that accumulate a wide range of elements. In the natural wetland, the geochemical barrier is likely associated with a decrease in oxygen content and advective transport rate in the sediments, whereas in the paddy fields, the precipitation of clay minerals in the soil profile forms the geochemical barrier related to a decrease in filtration properties and advection–diffusion transport.

Graphic abstract

Geochemical baseline establishment, environmental impact and health risk assessment of vanadium in lake sediments, China

Lakes are essential water resources in China and their water quality is vital to the sustainability. However, the geochemical processes of trace elements, especially those of seldom-monitored trace elements, have not been adequately studied. Here, the regional geochemical baseline (RGB) of vanadium (V) was established using cumulative frequency and normalization methods. Then, the RGB was applied to quantitatively calculate the anthropogenic contribution rate in sediments of the Poyang Lake (PYL), which is the largest freshwater lake in China. The pollution level and ecological risk of V were evaluated using the geoaccumulation index (I_geo) and potential ecological risk index (EI) with respect to three different reference values, namely local soil background values (BV), the RGB, and the median value of V concentrations. The health risk of V accumulation in residents through fish consumption during sediment resuspension was assessed by combining the environmental impact assessment model and health risk assessment model. The mean concentration of V in PYL sediments was 94.37 mg/kg (33.80-148.53 mg/kg), which was slightly higher than the levels in stream sediments in China, but lower than the local BV. The calculated RGB was slightly higher than the average V content in PYL sediments, but similar to the local BV. The average anthropogenic contribution rate was calculated as 11.48%, demonstrating low anthropogenic influence. Moreover, the result of I_geo and EI showed that V in PYL sediments was uncontaminated and posed a low ecological risk. In addition, based on the calculation by the two models, the human health risk result (target hazard quotient <1) indicated that the average human health risk from fish consumption due to sediment resuspension was negligible.

Shallow groundwater quality and associated non-cancer health risk in agricultural areas (Poyang Lake basin, China)

Owing to their accessibility, shallow groundwater is an essential source of drinking water in rural areas while usually being used without control by authorities. At the same time, this type of water resource is one of the most vulnerable to pollution, especially in regions with extensive agricultural activity. These factors increase the probability of adverse health effects in the population as a result of the consumption of shallow groundwater. In the present research, shallow groundwater quality in the agricultural areas of Poyang Lake basin was assessed according to world and national standards for drinking water quality. To evaluate non-cancer health risk from drinking groundwater, the hazard quotient from exposure to individual chemicals and hazard index from exposure to multiple chemicals were applied. It was found that, in shallow groundwater, the concentrations of 11 components (NO₃^-, NH₄⁺, Fe, Mn, As, Al, rare NO₂^-, Se, Hg, Tl and Pb) exceed the limits referenced in the standards for drinking water. According to the health risk assessment, only five components (NO₃^-, Fe, As, rare NO₂^- and Mn) likely provoke non-cancer effects. The attempt to evaluate the spatial distribution of human health risk from exposure to multiple chemicals shows that the most vulnerable area is associated with territory characterised by low altitude where reducing or near-neutral conditions are formed (lower reaches of Xiushui and Ganjiang Rivers). The largest health risk is associated with the immune system and adverse dermal effects.