[Integrated Analysis on Source-exposure Risk of Heavy Metals in Farmland Soil Based on PMF Model: A Case Study in the E-waste Dismantling Area in Zhejiang Province].

In order to explore the characteristics and sources of heavy metals in farmland soil and their risks to human health and to provide an important scientific basis for farmland pollution control, 133 surface soils (0-20 cm) were collected from typical agricultural production areas in Zhejiang Province, and the contents of soil Cd, Pb, Cr, Cu, Zn, Ni, As, and Hg were determined. Various methods were applied to evaluate the degree of heavy metal pollution in farmland and its ecological risks in the study area. The method of combining Kriging interpolation and positive definite matrix factor analysis (PMF) was applied to analyze the pollution sources and quantify the contribution of each pollution source. Combined with the health risk assessment model, the risk to human health of each pollution source was evaluated from the perspective of source exposure. The results showed that the average ω(Cd), ω(Pb), ω(Cr), ω(Cu), ω(Zn), ω(Ni), ω(As), and ω(Hg) were 0.76, 65.22, 92.02, 103.92, 198.49, 36.65, 5.97, and 0.20 mg·kg-1, respectively. The average contents of Cd and Cu were higher than the risk screening values of soil contamination of agricultural land, and 85.71% and 96.24% of soil was contaminated by heavy metals. The average contents of Pb, Cr, Zn, and Ni exceeded the soil background values of the Wenhuang Plain in Zhejiang Province, and the As and Hg contents were within the limit values. The potential soil ecological risks were mainly light-moderate, accounting for 90.98%, and both high and higher risk accounted for 4.51%; Cd was the main potential ecological risk element. The main sources of heavy metal pollution in the study area were the sources of the electronic waste dismantling process (26.82%), the mixed sources of coal combustion and traffic emissions (34.50%), mixed sources of natural parent materials and agricultural inputs (25.59%), and e-waste pickling runoff and solid waste leaching sources (13.09%). The health risk of heavy metal exposure to children was significantly greater than that in adults. Mixed sources of natural parent materials and agricultural inputs contributed the most to human health risks, and Cr was the element with the greatest contribution to human health risks.

Controls for phytolith accumulation in Moso bamboo leaves across China.

Phytoliths are amorphous silica formed gradually in plant tissue, which have great potential to mitigate climate change due to their resistance to decomposition and their ability to occlude organic carbon. The accumulation of phytoliths is regulated by multiple factors. However, the factors controlling its accumulation remain unclear. Here, we investigated phytolith content in Moso bamboo leaves of different ages collected from 110 sampling sites of their main distribution regions across China. The controls for phytolith accumulation were studied by correlation and random forest analyses. Our results showed that phytolith content is leaf age-dependent (16-month-old leaf >4-month-old leaf >3-month-old leaf). Phytolith accumulation rate in Moso bamboo leaves is significantly correlated with mean monthly temperature (MMT) and mean monthly precipitation (MMP). About 67.1 % of the variance of the phytolith accumulation rate could be explained by multiple environmental factors, mainly MMT and MMP. Therefore, we conclude that the weather is the major driver that regulates the phytolith accumulation rate. Our study provides a unique dataset for estimating phytolith production rate and the potential carbon sequestration of phytolith through climatic factors.

Enhancement of phytolith-occluded carbon accumulation of Moso bamboo response to temperatures elevation and different fertilization.

The accumulation of phytolith-occluded carbon (PhytOC) in Moso bamboo could be a novel long-term carbon sequestration strategy. The objective of this study was to investigate the effects of temperature change and different fertilization on PhytOC accumulation. The pot experiment was established with different fertilization (including control (CK), nitrogen fertilizers (N), silicon fertilizers (Si), and a combination of nitrogen and silicon (NSi)) under high- and low-temperature. Despite the different fertilization, the PhytOC accumulation of the high-temperature group increases by 45.3% on average compared with the low-temperature group, suggesting higher temperature is greatly beneficial to the PhytOC accumulation. Fertilization significantly increases the accumulation of PhytOC (increased by 80.7% and 48.4% on average for the low- and high-temperature group, respectively) compared with CK. However, the N treatment increased both Moso bamboo biomass and PhytOC accumulation. The difference in the accumulation of PhytOC in Si and NSi was insignificant, indicating the combination of N and Si didn't bring extra benefit to PhytOC accumulation compared to Si fertilizer alone. These results indicated the application of nitrogen fertilizer is a practical and effective method for enhancing long-term carbon sequestration for Moso bamboo. Based on our study, we conclude that global warming poses a positive effect on promoting the long-term carbon sequestration of Moso bamboo.

An integrated analysis on source-exposure risk of heavy metals in agricultural soils near intense electronic waste recycling activities.

Conducting integrated analysis of the source, exposure and health risk of heavy metals is critical for developing mitigation strategies of soil contamination. Taking the former electronic waste (e-waste) dismantling center in China as an example this study quantitatively apportioned source contribution of soil heavy metals in this area by statistical analysis and positive matrix factorization (PMF) model. Furthermore, the human health risk of identified sources were quantified by combining source profiles and exposure risk assessment. The seven heavy metals investigated were arsenic (As), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb) and Zinc (Zn). Results indicated that agricultural soils were mainly contaminated with Cd and Cu. Parent material and pesticide, fertilizer application, industrial discharge, and vehicle emission accounted for 46.6, 22.2, and 31.2%, respectively, of the accumulation of metals in the soil. Moreover, these sources contributed 52.9, 19.0, and 28.1%, respectively of the total non-cancer risk. For the total cancer risk, the contribution of these three sources was 39.2, 45.3, and 15.5%, respectively. Despite that industrial discharge contributed the least to the accumulation of metals (22.2%), it contributed the most to the total cancer risk (45.3%). Reducing industrial emission was crucial for minimizing the heavy metal input to agricultural soils and preventing potential health hazard. These findings could provide support for environmental protection authority to improve the management and risk prevention of contaminated farmland.

Apportionment and uncertainty analysis of nitrate sources based on the dual isotope approach and a Bayesian isotope mixing model at the watershed scale.

Identifying and eliminating pollutant sources of water bodies is critical for drinking water safety. In this research, river water, reservoir water and groundwater samples (n = 259) were collected from November 2015 to January 2017. Spatial Analysis was made of the isotopic compositions of potential nitrate sources (i.e., manure, sewage, chemical nitrogen fertilizer, soil organic nitrogen and rainfall) so as to obtain the site source isotopic signatures. Different sources pools and fractionation factors were loaded to a Bayesian isotope mixing model to ensure posterior estimates with less uncertainty. Results showed that the total nitrogen (TN) concentrations in Hexi Reservoir watershed were higher than the Environmental Quality Standards for Surface Water of China (GB 3838-2002), and NO3--N was the dominant form of TN (accounting for 68.63% on average). There are significant spatio-temporal variations in the isotope data (δ15N-NO3- and δ18O-NO3-) and the dominant nitrate sources, which were related to the land use types. Loading the site source isotopic signatures to the Bayesian isotope mixing model effectively improved the accuracy and precision of nitrate source apportionment. Chemical nitrogen fertilizer (NF) was the foremost largest contributor of NO3--N (38.82%), especially for Hexi North Stream (34.19%) and Yangmei Stream (44.39%), while atmospheric deposition (AD) contributed the least to NO3--N (0.47%) of river water in the watershed; soil organic nitrogen (NS) contributed more to NO3--N in the dry season than in the wet season; and manure and sewage (M&S) contributed approximately 30.22% in the whole study period, 53.60% in September 2016 and 41.33% in Hexi South Stream. This research suggests that combination of Spatial Analysis and the Bayesian isotope mixing model with the measured isotopic signatures of potential nitrate sources accurately apportion the nitrate source contributions.

A multi-medium chain modeling approach to estimate the cumulative effects of cadmium pollution on human health.

Cadmium is a highly persistent and toxic heavy metal that poses severe health risks to humans. Diet is the primary source of human exposure to cadmium, especially in China. Soil, as the main medium that transfers cadmium to rice, can be used as a helpful indicator to predict human exposure to cadmium in soils. There is, however, very little work that links a soil-rice transfer model with a biokinetic model to assess health risks. In this work, we introduce a multi-medium chain model based upon a soil-rice-human continuum to address this issue. The model consists of three basic steps: (i) development and validation of a soil-rice transfer model for cadmium based on 189 pairs of measured data in Wenling of Zhejiang province in Southeast China; (ii) calculation of weekly exposure based on the nationwide monitoring and survey results; (iii) linking the exposure model with a modified biokinetic model proposed with a classic biokinetic model to predict urinary cadmium, which is a biomarker to assess the health risks. Results indicated that the developed soil-rice-human transfer model predicted well the urinary cadmium levels in humans subjected to age and exposure uncertainties. We observed a maximum of 0.71 µg g-1 creatinine in males and 1.53 µg g-1 creatinine in females at 70 years old under median cadmium exposure, which was consistent with previous studies. Sensitive analysis was also conducted to detect the sensitive parameters that have the most significant influences on the output of the model. The new risk assessment strategy proposed in this work is beneficial for predicting the cumulative cadmium levels in various exposed populations so that we can quickly identify the critical areas from basic soil properties.

Expressing lead isotopic compositions by fractional abundances for environmental source apportionment.

Lead (Pb) isotope has been extensively used to identify sources of Pb and apportion their contributions in the environment. Conventionally, isotope ratios are used to express Pb isotopic composition. However, the linear combination of Pb isotope ratios is not consistent with mass balance. Moreover, the graphical presentations based on Pb isotope ratios are always inconsistent when different Pb isotope ratios are used. In this study, we proposed to use fractional abundance to express Pb isotopic composition to achieve more accurate and reliable source apportionment. A new method (rotation-projection method) based on fractional abundance was developed in this research. The new method compared favorably to the isotopic ratio-based method and to another fractional abundance based method using default 204Pb value (0) (Walraven's method). It allows to present four-dimensional (4-D) Pb isotope fractional abundance data in a 3-D plot. In the meantime, due to the low variation of the fractional abundance of 204Pb in the terrestrial ecosystem, the terrestrial Pb isotope fractional abundance data fell nearly on a plane, which further allows to plot the Pb isotope fractional abundance data on a two-dimensional diagram. Proper presentation of the isotopic composition data helps to achieve more accurate and reliable source identification and apportionment.

County-scale temporal-spatial distribution and variability tendency of heavy metals in arable soils influenced by policy adjustment during the last decade: a case study of Changxing, China.

The widespread "pertinacious illness" for environmental management soil contamination by toxic metals has inevitably led to announcement of gradual adjustment for the local government to curb the notorious pollution. An extensive survey was conducted in Changxing County, Zhejiang Province, to investigate the contents of cadmium (Cd), arsenic (As), lead (Pb), and copper (Cu) and characterize the spatial-temporal change pattern to elucidate the current state and performance of policy adjustment. Geostatistic methods were applied in the mapping and characterizing processes to assess the concentrations of heavy metals at unsampled sites. Enrichment factor analysis indicated obvious Cd and As enrichment in the west and northwest of the county. Ordinary kriging interpolation combined with semivariogram revealed that the four heavy metals possessed distinct spatial distribution patterns. However, the distribution patterns for the elevated Cd and Pb concentrations exhibited a similar geographic drift, corresponding primarily to industrial distribution. Compared with the investigation findings in 2003, the results indicated an uptrend of Cd and As and downtrend of Cu, while Pb was a mixture of increase and decrease. However, strengthened actions aimed at restraining heavy metal contamination are still needed to establish a mechanism to secure residents' health and livelihood.

Positive matrix factorization as source apportionment of soil lead and cadmium around a battery plant (Changxing County, China).

Chemical compositions of soil samples are multivariate in nature and provide datasets suitable for the application of multivariate factor analytical techniques. One of the analytical techniques, the positive matrix factorization (PMF), uses a weighted least square by fitting the data matrix to determine the weights of the sources based on the error estimates of each data point. In this research, PMF was employed to apportion the sources of heavy metals in 104 soil samples taken within a 1-km radius of a lead battery plant contaminated site in Changxing County, Zhejiang Province, China. The site is heavily contaminated with high concentrations of lead (Pb) and cadmium (Cd). PMF successfully partitioned the variances into sources related to soil background, agronomic practices, and the lead battery plants combined with a geostatistical approach. It was estimated that the lead battery plants and the agronomic practices contributed 55.37 and 29.28%, respectively, for soil Pb of the total source. Soil Cd mainly came from the lead battery plants (65.92%), followed by the agronomic practices (21.65%), and soil parent materials (12.43%). This research indicates that PMF combined with geostatistics is a useful tool for source identification and apportionment.