The causation between bioavailability of heavy metals and environmental factors are generally obtained from field experiments at local scales at present, and lack sufficient evidence from large ...scales. However, inferring causation between bioavailability of heavy metals and environmental factors across large-scale regions is challenging. Because the conventional correlation-based approaches used for causation assessments across large-scale regions, at the expense of actual causation, can result in spurious insights. In this study, a general approach framework, Intervention calculus when the directed acyclic graph (DAG) is absent (IDA) combined with the backdoor criterion (BC), was introduced to identify causation between the bioavailability of heavy metals and the potential environmental factors across large-scale regions. We take the Pearl River Delta (PRD) in China as a case study. The causal structures and effects were identified based on the concentrations of heavy metals (Zn, As, Cu, Hg, Pb, Cr, Ni and Cd) in soil (0–20 cm depth) and vegetable (lettuce) and 40 environmental factors (soil properties, extractable heavy metals and weathering indices) in 94 samples across the PRD. Results show that the bioavailability of heavy metals (Cd, Zn, Cr, Ni and As) was causally influenced by soil properties and soil weathering factors, whereas no causal factor impacted the bioavailability of Cu, Hg and Pb. No latent factor was found between the bioavailability of heavy metals and environmental factors. The causation between the bioavailability of heavy metals and environmental factors at field experiments is consistent with that on a large scale. The IDA combined with the BC provides a powerful tool to identify causation between the bioavailability of heavy metals and environmental factors across large-scale regions. Causal inference in a large system with the dynamic changes has great implications for system-based risk management.
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Causation between the bioavailability of heavy metals and environmental factors was inferred across large-scale regions using the IDA and backdoor criterion approach.
Although many previous studies have reported the soil pH and organic matter to be the most critical factors that affect the transfer of Cd in soil-crop systems in temperate zones, the behavior of Cd ...transfer is different in the Pearl River Delta (PRD), which is located in a subtropical zone with different climate and soil conditions. Therefore, we must determine the critical environmental factors that influence the transfer of Cd in the soil-vegetable system in the PRD region. Such knowledge can improve the safety of vegetables. In this study, the soil geochemical properties are investigated to explore the key soil factors that control the uptake of Cd by flowering cabbage, a popular leaf vegetable in China, from soils in the PRD region. The Cd contents in vegetables were most positively correlated to soil oxalate-Cd (p < 0.01), which indicates that amorphous Cd is the most available form for uptake into the cabbages. With the characteristics of rich in Fe oxide and Al oxide in the PRD soils, soil Fe and Al oxides were found to be the most relevant to the transfer factors of Cd from the soils to the cabbages. Soil secondary minerals are the key factor that affects the transfer of Cd, thereby influencing the migration and fate of Cd in soil-cabbage systems, with DCB-Fe significantly decreasing the Cd accumulation in cabbages. Additionally, models were developed to predict the enrichment of Cd in flowering cabbages, in which oxalate-Cd, DCB-Fe, and NaOAc-Al in soils were determined to be the most important factors that affect the Cd enrichment in flowering cabbages. In this study, we determine the important role of soil secondary minerals in affecting the transfer of Cd in soil-cabbage systems in the PRD. These observations are important to evaluate the accumulation of Cd in vegetables in subtropical zones.
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•Critical soil factors for Cd transfer are different in subtropical/temperate soils.•Soil minerals are critical for Cd transfer into cabbages in the Pearl River Delta.•Amorphous Cd in soils are most available for cabbages uptake.•Oxalate-Cd, DCB-Fe and NaOAc-Al prominently affect Cd uptake by cabbages.
Soil secondary minerals in the subtropical PRD are the critical factors that influence the transfer of Cd in soil-vegetable systems.
Soil contamination with antimony (Sb) and arsenic (As) has become a well-recognized environmental and human health issue. Consumption of vegetables, especially leafy vegetables, is one of the most ...important sources of Sb and As exposure in humans. Accordingly, it is necessary to understand the behaviors of Sb and As in the vegetable–soil system. Moreover, although Sb and As are often assumed to have similar biogeochemical behavior, identified differences in the controlling factors affecting mobility and bioavailability of Sb and As in soils need further investigation. In this study, 112 pairs of soil and flowering cabbage samples were collected from typical farmland protection areas and vegetable-producing regions across the Pearl River Delta (PRD), South China. The contamination levels of Sb and As in soils and harvested cabbages across the PRD were investigated. The main factors affecting the mobility and bioavailability of Sb and As in the cabbage–soil system were disentangled using a random forest model. The contamination levels of Sb in the cabbages and soils of the PRD were generally low, but the soils were moderately polluted by As. Increased concentrations of Fe oxides could decrease Sb accumulation in cabbages but increased the mobilization of As in soils to some extent. In contrast, Al oxides contributed strongly to the mobilization of Sb and the immobilization of As. Moreover, an increased sand content promoted the mobility of Sb and As, whereas increased silt and clay contents showed inhibitory effects. The interactions of As and Sb with Fe oxides decreased the mobility of Sb but moderately increased the mobility of As in soils. Overall, the behaviors of Sb and As in the cabbage–soil system under the effect of several important environmental factors showed some differences indicating that these differences should be considered in the remediation of co-contaminated soils.
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•Increased Fe oxide contents caused a decrease in Sb accumulation in cabbages.•Fe oxides played a moderate mobilization role in As mobility.•Soil texture was an important contributor to Sb and As mobility and bioavailability.•The interactions of As and Sb with Fe oxides affected As and Sb mobility.
Thallium (Tl), a rare metal, is universally present in the environment with high toxicity and accumulation. Thallium's behavior and fate require further study, especially in the Pearl River Delta ...(PRD), where severe Tl pollution incidents have occurred. One hundred two pairs of soil and flowering cabbage samples and 91 pairs of soil and lettuce samples were collected from typical farmland protection areas and vegetable bases across the PRD, South China. The contamination levels and spatial distributions of soil and vegetable (flowering cabbages and lettuces) Tl across the PRD were investigated. The relative contributions of soil properties to the bioavailability of Tl in vegetables were evaluated using random forest. Random forest is an accurate learning algorithm and is superior to conventional and correlation-based regression analyses. In addition, the health risks posed by Tl exposure via vegetable intake for residents of the PRD were assessed. The results indicated that rapidly available potassium (K) and total K in soil were the most important factors affecting Tl bioavailability, and the competitive effect of rapidly available K on vegetable Tl uptake was confirmed in this field study. Soil weathering also contributed substantially to Tl accumulation in the vegetables. In contrast, organic matter might not be a major factor affecting the mobility of Tl in most of the lettuce soils. Fe and manganese (Mn) oxides also contributed little to the bioavailability of Tl. A risk assessment suggested that the health risks for Tl exposure through flowering cabbage or lettuce intake were minimal.
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•Levels and spatial distributions of soil and vegetable TI were determined.•The competitive effect of rapidly available K on vegetable Tl uptake was confirmed.•Soil weathering contributed substantially to Tl accumulation in the vegetables.•Organic matter contributed little to Tl mobility in most lettuce soils.•Health risks for Tl exposure via flowering cabbage or lettuce intake were minimal.
The competitive effect of soil rapidly available K on Tl uptake by vegetables was confirmed based on field study, thereby helping to characterize the behavior of Tl.
Based on previous research, it was hypothesized that negative affect (e.g., depression, anxiety, and loneliness) and low level of emotion regulation (i.e., alexithymia) are risk factors for internet ...gaming disorder (IGD). Research utilizing a network analysis approach to psychopathology has increased rapidly, and is used to examine the pattern of interactions between causal factors of mental health disorders. Previous research has investigated the relationship between gaming disorder (GD), depression, alexithymia, boredom, and loneliness by pair-wise correlation and correlation of three or four variables. However, to date, network analysis has rarely been utilized to examine the relationship between the aforementioned multi-variables. Therefore, the present study used network analysis to examine the relationship between GD, depression, alexithymia, boredom, and loneliness among a sample of Chinese university students.
A sample comprising 1635 Chinese university students (913 males) completed a survey including the Gaming Disorder Test, Patient Health Questionnaire, and Toronto Alexithymia Scale, alongside single-item measures of loneliness and boredom.
Depression, alexithymia, boredom, and loneliness were significantly and positively associated with GD. Loneliness and boredom had the closest edge intensity, and loneliness was the strongest central node in the domain-level network. The facet-level and the item-level network analysis also showed that GD was connected with depression, alexithymia, boredom, and loneliness. The domain-level network comparison test (NCT) showed the global strengths had significant difference among gender group (males = 1.90 vs. females = 1.77, p = 0.013).
The findings indicate that there is a close relationship between GD, depression, alexithymia, boredom, and loneliness. Negative affect and low emotion regulation may induce or worsen GD, resulting in a vicious cycle. Practitioners developing interventions to overcome GD should consider aspects aimed at adjusting and improving negative emotion, especially loneliness and related negative affect as well as facilitating positive emotion.
•Loneliness and boredom had the closest edge intensity in domain-level network.•Loneliness was the strongest central node in domain-level network.•There is a close relationship between GD, depression, alexithymia, boredom, and loneliness.•There were significant differences in the global edge strength between gender groups among Chinese university students.
Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical ...phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.
Contaminated sites have become a worldwide issue because of significant environmental and health risks to users of the land. With the aim of synthesizing useful services delivered by land reuse for ...environmental, social and economic benefits, effective management measures have been taken nationally and regionally to rehabilitate contaminated sites. The unacceptable risks, large number of contaminated sites and urgent demand for land supply make it necessary to centralize limited resources within contaminated sites. In reference to the classification rationale in developed countries trying to deal with contaminated sites in an integrated, saving and timely manner, we design a conceptual framework that considers the unique context in China. We classify contaminated sites in five steps, namely: listing, investigating, filing, classifying and managing. Based on the classification results, effective suggestions are proposed for graded and classified management and further decision-making at the highest level of design. The results show that potential contaminated sites can be divided into high, medium and low priority based on four factors (social concern, redevelopment demand, health risk and ecological risk). Site-specific management strategies focusing on environmental monitoring, detailed site survey and immediate remediation, respectively, are suggested that focus on corresponding contaminated sites in different priorities. The feasibility and reliability of the proposed framework are further discussed in the final section.
Soil secondary minerals are important scavengers of rare earth elements(REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical ...phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs(La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs(LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs(HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs.The substantial fractions of REEs in soils extracted byoxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile(10 %–30 %), which were similar to the mass fraction of Fe(10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.
Soil secondary minerals are important scavengers of rare earth elements （REEs） in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical ...phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs （La to Lu and Y） associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La-Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs （LREEs） enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs （HREEs） was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile （10 %-30 %）, which were similar to the mass fraction of Fe （10 %-20 %）. Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil for- mation from REE fractionation.
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