Ecological risk assessment of heavy metals in farmland soils in Beijing by three improved risk assessment methods

Bioavailability and ecological risk assessment of metal pollutants in ambient PM2.5 in Beijing

Metal pollutants in fine particulate matter (PM2.5) are physiologically toxic, threatening ecosystems through atmospheric deposition. Biotoxicity and bioavailability are mainly determined by the active speciation of metal pollutants in PM2.5. As a megacity in China, Beijing has suffered severe particulate pollution over the past two decades, and the health effects of metal pollutants in PM2.5 have received significant attention. However, there is a limited understanding of the active forms of metals in PM2.5 and their ecological risks to plants, soil or water in Beijing. It is essential that the ecological risks of metal pollutants in PM2.5 are accurately evaluated based on their bioavailability, identifying the key pollutants and revealing historic trends to future risks control. A two-year project measured the chemical speciation of pollution elements (As, Cd, Cu, Cr, Ni, Mn, Pb, Sb, Sr, Ti, and Zn) in PM2.5 in Beijing, in particular their bioavailability, assessing ecological risks and identifying key pollutants. The mass concentrations of total and active species of pollution elements were 199.12 ng/m3 and 114.97 ng/m3, respectively. Active fractions accounted for 57.7 % of the total. Cd had the highest active proportion. Based on the risk assessment code (RAC), most pollution elements except Ti had moderate or high ecological risk, with RAC exceeding 30 %. Cd, with an RAC of 70 %, presented the strongest ecological risk. Comparing our data with previous research shows that concentrations of pollution elements in PM2.5 in Beijing have decreased over the past decade. However, although the total concentrations of Cd in PM2.5 have decreased by >50 % over the past decade, based on machine model simulation, its ecological risk has reduced by only 10 %. Our research shows that the ecological risks of pollution elements remain high despite their decreasing concentrations. Controlling the active species of metal pollutants in PM2.5 in Beijing in the future is vital.

Assessing the ecological risk of croplands in loess drylands by combining environmental disturbance with ecosystem vulnerability

Agroecosystems suffer various ecological risks due to the intensive production of crops. However, comprehensive assessments of cropland ecological risks remain limited. This study developed an assessment method for cropland ecological risks by combining environmental disturbance with ecosystem vulnerability. Environmental disturbance reflects stresses caused by risk sources in an environment, while ecosystem vulnerability is the susceptibility of an ecosystem to adverse disturbances and its capacity to cope and adapt. The proposed method is conducive to understanding the complex exposure-response relationship between croplands and environmental stresses. Cropland ecological risk was evaluated by conducting a case study on a loess dryland region in Shaanxi. The hot spots and driving factors of risk were explored using spatial autocorrelation and quantile regression methods, respectively. Results show that overall cropland ecological risk is at medium low level. Risk hot spots are concentrated in the north of the loess dryland. Ecosystem vulnerability exerts greater effect on the distribution of hot spots than environmental disturbance in the study area. Road density (RDD), river density, and soil organic matter exert the most important effects on cropland ecological risk. Moreover, the same driving factor exhibits various effects on cropland ecological risk in different risk level areas. RDD, slope, precipitation, elevation, fertilizer application rate, gross domestic product, and distance to town center have greater effects on risk in regions with high cropland ecological risk than in regions with low cropland ecological risk. The findings of this study must be considered in formulating targeted policies for controlling cropland ecological risk in loess drylands to realize sustainable crop production.

An integrated approach for quantifying trace metal sources in surface soils of a typical farmland in the three rivers plain, China

The presence of trace metals (TMs) in agricultural soil has garnered considerable attention due to their potential migration into crops, posing a significant risk to human health. In this study, we examined the concentrations of eight trace metals (Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn) in the soil and investigated various soil physicochemical characteristics in the Three Rivers Plain region, China. The assessment of the geoaccumulation index (Igeo) for the mean concentration of all trace metals indicated that the soils were generally free from significant TM pollution. However, a noteworthy finding emerged in relation to Hg, where the maximum Igeo value suggested moderate pollution levels. Kriging prediction results further indicated that approximately 1.55% of the study area might be impacted by Hg pollution. Moreover, it is prudent to direct attention towards Cd, Cr, Cu, Mn, and Ni, as their Igeo values revealed that the region with the highest concentrations of these metals ranged from unpolluted to moderately polluted. This study employed a comprehensive approach, utilizing the Self-Organizing Map (SOM), Kriging spatial distribution, and the Positive Matrix Factorization (PMF) model to identify the sources of TMs in agricultural soil. The results unveiled that the primary contributors to TM presence were the natural parental materials, alongside industrial activities such as coal mining and coal plant operations, as well as agricultural practices. These findings provide foundational insights for future management strategies in the Three Rivers Plain, aiming to enhance agricultural productivity and promote sustainability.

Sewage sludge application stimulated soil N2O emissions with a low heavy metal pollution risk in Eucalyptus plantations

Sewage sludge (SS) has been extensively used as an alternative fertilizer in forest plantations, which are beneficial in supplying timbers and mitigating climate change. However, whether the extra nitrogen (N) applied by SS would enhance the soil nitrous oxide (N₂O) emission, an important greenhouse gas, in forest plantations have not been well understood. The objective of this study is to evaluate the ecological effects of SS application on soils, by investigating the soil N₂O emission and the toxicity of the potentially toxic elements (PTEs) in soil. A field fertilization experiment was conducted in Eucalyptus plantations with four fertilization rates (0 kg m^-2, 1.5 kg m^-2, 3.0 kg m^-2, and 4.5 kg m^-2). The soil N₂O emissions were monitored at a soil depth of 0-10 cm using static chamber method, soil chemical properties, and PTEs were determined at soil depths of 0-10 cm, 10-20 cm, and 20-40 cm. The average soil N₂O emission rate was 8.1 μg N₂O-N h^-1 m^-2 in plots without SS application (control). The application of SS significantly increased the soil N₂O emissions by 7-10 times as to control. The increased N₂O emissions were positively related to the soil total phosphorus and nitrogen and negatively correlated with copper and zinc, which increased with the SS application. However, the potential ecological risk index (E_i) and the comprehensive potential ecological risk index (RI) of PTEs were lower than 40 and 150 respectively, which indicating a low toxicity of PTEs to soil health. After seven months of SS application, the priming effects of SS on soil N₂O emissions gradually diminished. These findings suggest that the application of SS may increase N₂O emissions at the initial stages of application (<7 months) and may have a low PTEs pollution risk, even at a high SS addition rate (4.5 kg m^-2).

Pollution Characteristics, Spatial Distribution, and Evaluation of Heavy Metal(loid)s in Farmland Soils in a Typical Mountainous Hilly Area in China

Heavy metal(loid)s pollution in farmland soil is not only a serious environmental but also a human health-related issue. Accurate understanding and evaluation of heavy metal pollution levels in the soil are very important for sustainable agricultural development and food safety. Mountainous and hilly areas have the dual functions of industrial development and agricultural production, and the farmland soil in these areas is more susceptible to heavy metal pollution. In this study, the single factor index, Nemerow index, geo-accumulation index, enrichment factor index, and potential ecological risk indices, which are mainly used to assess the contamination and risk of heavy metals in farmland soils. The sources of heavy metals in agricultural soils of the study area were analyzed using correlation analysis and principal component analysis. Finally, geostatistical methods were used to map the heavy metal contamination of farmland soils. An average concentration of all heavy metals (except As) in farmland soils of the study area exceeded the corresponding background values, as indicated by the obtained results. The results of the principal component analysis showed that the heavy metal sources in the soils of the study area can be classified into two groups. The five pollutant index methods all showed the most serious Hg pollution in the study area. The integrated pollutant mapping results showed that the risk of heavy metal pollution in the study area was mostly moderate, except for the western and central parts of the region. This study enhances understanding of the pollution levers of heavy metals in Yiyuan farmland soils, and also can facilitate the monitoring of heavy metal contaminants at the primary stage of the food chain and assess the risk of the presence of heavy metal contaminants in food, thus improving the health of the residents.

Sources, transfers and the fate of heavy metals in soil-wheat systems: The case of lead (Pb)/zinc (Zn) smelting region

Heavy metals (HMs) from smelters pose severe challenges to the environmental soil quality of surrounding farmlands, and threaten human health through the food chain. This study explored the environmental effects of smelting activities on farmland soil, and additionally assessed the enrichment, transfer and health risk of HMs in soil-wheat systems. Multiple characterization results were combined to demonstrate that HMs from smelter waste were transferred to the surrounding soil. It was determined that the enrichment of HMs in soil-wheat systems is mainly controlled by the total HM concentration and pH in soil. Furthermore, the priority pollutant in soil-wheat systems was found to be Cd, and Cd affected the transfer of Cu, Mn and Pb from soil to wheat roots. Interestingly, the -OH stretching, C-H stretching, N-H amide and C-O bending were involved in detoxifying HMs in wheat. The mean values of non-carcinogenic and carcinogenic risks by consuming wheat grain were 9.1, 1.4E-02 (adults) and 11.3, 3.3E-03 (children), respectively, indicating a noteworthy health risk. This study highlighted the critical issues arising from Pb/Zn smelting activities on agricultural soils. Notwithstanding, to ensure food security, the affected regions could opt to follow up on the type of crops grown.