Jiulan Dai

Mercury (II) Adsorption on Three Contrasting Chinese Soils Treated with Two Sources of Dissolved Organic Matter: I. Langmuir and Freundlich Isotherm Evaluation

The behavior and fate of mercury (Hg) in soil is mainly controlled by adsorption and desorption processes with various adsorbents, particularly dissolved organic matter (DOM). This study was conducted to assess the effect of DOM from wheat straw (DOMw) and swine manure (DOMs) on Hg (II) adsorption of black, red, and fluvo-aquic soils in China. Results showed that the Hg (II) adsorption isotherms fitted well with Langmuir and Freundlich equations. The maximum Hg (II) potential adsorption capacity by the three soils followed this trend: black soil > red soil > fluvo-aquic soil. The amount of Hg (II) adsorbed on the soils significantly decreased when DOMw and DOMs were added to the soil samples. Furthermore, the extent by which DOMw affected the Hg (II) adsorption of the three soils was higher than the effect of equivalent amounts of DOMs. Therefore, DOM is important to determine the fate of Hg (II) and control Hg (II) pollution in the environment.

Multiple factors impact the contents of heavy metals in vegetables in high natural background area of China

A field survey was conducted to investigate the concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in vegetables, corresponding cultivated soils and irrigation waters from 36 open sites in high natural background area of Wuzhou, South China. Redundancy analysis, Spearmans rho correlation analysis and multiple regression analysis were adopted to evaluate the contributions of impacting factors on metal contents in the edible parts of vegetables. This study concluded that leafy and root vegetables had relatively higher metal concentrations and adjusted transfer factor values compared to fruiting vegetables according to nonparametric tests. Plant species, total soil metal content and soil pH value were affirmed as three critical factors with the highest contribution rate among all the influencing factors. The bivariate curve equation models for heavy metals in the edible vegetable tissues were well fitted to predict the metal concentrations in vegetables. The results from this case study also suggested that it could be one of efficient strategies for clean agricultural production and food safety in high natural background area to breed vegetable varieties with low heavy metal accumulation and to enlarge planting scale of these varieties.

Effect of Dissolved Organic Matter from Wheat Straw or Swine Manure on the Cu Adsorption in Three Chinese Soils

Batch equilibration experiments were conducted to evaluate the effects of dissolved organic matter (DOM) from wheat straw (DOMw) and swine manure (DOMs) on copper (Cu) adsorption and behavior in Haplic Phaeozems, Haplic Acrisol, and Eutric Fluvisol in China. Results showed that the Cu adsorption isotherms were well fitted with both Langmuir and Freundlich equations. The Cu maximum potential adsorption capacity of the three soils followed the order of Eutric Fluvisol > Haplic Phaeozems > Haplic Acrisol. DOMw and DOMs increased the Cu adsorption capacity in Haplic Phaeozems and Haplic Acrisol, and the promoting role of DOMs on Cu adsorption was obviously higher than that of DOMw. Increasing DOM concentration of DOMw and DOMs promoted the Cu adsorption in Haplic Phaeozems and Haplic Acrisol. However, this promoting effect weakened with increasing DOM concentration. Moreover, DOMw and DOMs inhibited the Cu adsorption in Eutric Fluvisol, and this inhibitory effect significantly increased with increasing DOM concentration. The results may be used to assess the potential environmental contamination of the studied soils and to control the application of organic fertilizers.

Adsorption Characteristics and the Effect of Dissolved Organic Matter on Mercury(II) Adsorption of Various Soils in China

ABSTRACT To evaluate the adsorption characteristics and effects of dissolved organic matter (DOM) from wheat straw (DOMW) and swine manure (DOMS) on mercury [Hg(II)] adsorption by soils, a series of experiments was conducted on 26 soils with different soil properties.Results showed that the values of Kd (a solid–liquid partition coefficient) of soils varied within a range of 0.768–14.386 L g−1. Kd values were mainly controlled by soil organic matter (SOM), cation exchange capacity (CEC), soil nitrogen (N), and soil sulfur (S). When DOMW and DOMS were added to the soil samples, the amount of Hg(II) adsorbed by the soils decreased significantly. Furthermore, based on the decreased percentage of adsorption of Hg(II) by soil upon adding DOMW (PDOMW) or DOMS (PDOMS), about 73.08% soils, the values of PDOMS were smaller than those of PDOMW. The PDOMW values were related to SOM, pH, free Fe oxide content, and CEC, whereas PDOMS values were related to soil free Fe/Al oxide contents. Therefore, we should pay more attention about mercury risk caused by the addition of exogenous organic matter in soils, especially for the soils with low or high pH, less SOM, low CEC, and less free Fe/Al oxide.

Long-term effects of untreated wastewater on soil bacterial communities

For 46 years (1957-2002), irrigation with wastewater has increased the amount of heavy metal and organic contaminants in soils and altered bacterial communities in Shenyang, northeastern China. There has been characterization of the different heavy metal and petroleum contaminants in two types of land uses (cornfields and paddy fields). The Nemerow composite indices of heavy metal contaminants have been higher in cornfields (1.17-4.73) than those in paddy fields (0.57-1.64). Molecular-based techniques and biochemical-based techniques were used to analyze soil microbial diversity in our study. The metabolic activity of soil microbe communities was higher in paddy sites than that in cornfields. Organic pollutants such as saturated and polycyclic aromatic hydrocarbons have significantly affected soil bacterial compositions. Heavy metals differed in how they disturbed the microbial communities. Arsenic (As) and lead (Pb) shifted the community composition and decreased microbial diversity; copper (Cu) reduced bacterial abundance in soil; and cadmium (Cd) and chromium (Cr) lowered the metabolic capabilities of bacteria.

Characteristics of Copper Sorption by Various Agricultural Soils in China and the Effect of Exogenic Dissolved Organic Matter on the Sorption

ABSTRACT To explore the effect of exogenic dissolved organic matter (DOM) on Cu(II) sorption in agricultural soils, 26 agricultural soils were collected across China. Exogenic dissolved organic matter, extracting from wheat straw (DOMW) and swine manure (DOMS), respectively, were added to the soils to conduct a series of batch sorption and characterization experiments. The solid-liquid partition coefficient (Kd) ranged from 0.02 to 76.46 L g−1, suggesting different Cu(II) sorption on various soils. PCA analysis indicated that pH, free Fe/Al oxides, carbon, and total Cu content had a significant positive relationship with the Cu(II) sorption, respectively. And the contribution rate of pH was the highest (38.15%). Moreover, DOM markedly inhibited the Cu(II) sorption in alkaline soils while promoted the Cu(II) sorption in acidic soils, which were interacted by the soil properties and DOM characteristics. The effect of DOMS on Cu(II) sorption were more obvious than DOMW, which were further confirmed by Fourier transform infrared (FTIR) spectroscopy. FTIR also showed Cu(II) was primarily adsorbed on the specific functional groups, such as CO, OH, and CO, providing direct evidences for the binding of Cu(II) with DOM. This study can guide the rational use of organic fertilizers, and also provide baseline knowledge for the prevention and control of soil pollution.

Source contribution analysis and collaborative assessment of heavy metals in vegetable-growing soils

Source quantification of heavy metals in farmland is essential for developing and implementing restoration strategies. We used various data analyses to identify and quantify sources of arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc in vegetable-growing soils. A new method of collaborative assessment, combining soil environmental quality and agricultural product safety, showed that approximately 5.20% of cultivation systems were multi-contaminated by heavy metals. The nonlinear relationship between pollution sources and the comprehensive contamination situation was established, deriving from a fitted bivariate model. The model revealed that anthropogenic sources and natural origins accounted for 65.8-86.0 and 34.2-14.0% of the comprehensive pollution, respectively. These results suggested that both human activities and natural factors contributed to the decline of local soil quality and the influence of the former was more substantial than that of the latter.

Source Analysis and Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Paddy Soils

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) are typically persistent organic pollutants with hypertoxicity and widespreading, attracting increasing attention in recent years. Six paddy land sites soils irrigated from different rivers in the Nansi Lake area of Shandong Province, China, were studied to analyze and assess the source and risk of PAHs.Analysis revealed total PAHs (TPAHs) concentrations in topsoil ranging from 57.49 to 2046.47 μg kg−1, meanwhile, Weishan County (WS) was highly contaminated primarily from coal combustion based on the Nemerow composite index and geochemical indices.Canonical correspondence analysis (CCA) suggested that bacterial species were affected by pH, TPAHs, and soil organic matter (SOM), while covariables analysis confirmed that most effects of PAHs on bacterial diversity were attributed to the PAHs effect alone rather than the combined effects of PAHs and soil properties. The average daily human exposure (ADE) in children was approximately 2 times higher than that in adults, and the exposure paths values followed a decreasing order, oral intake > skin contact > inhalation. Furthermore, the WS site and another rice test field (TF) presented potential cancer risks and required further investigation. Therefore, the study has important theoretical significance for the control of PAHs pollution in this field, providing a scientific basis for health assessment.