Urban soil amendment with organic matter can increase the steady state concentration of trace metals in urban soil. Different types of organic matter have different abilities to sorb and retain trace metals. The potential of urban soil amended with compost derived from mixed green and table waste and with maple-wood-derived biochar to retain trace metals (Cu, Zn, Cd, Pb) in the presence of de-icing salt (Na) was studied in a leaching test. Soil amended with compost retained significantly higher concentrations of Zn and Pb, as compared to soil amended with biochar, possibly due to the high cation exchange capacity of compost and its positive effect on soil pH. Indicating high ability for retaining trace metals, compost can bind contaminants originating from urban runoff water percolating through urban soil and provide a healthier medium for street tree growth.

Inadequately treated effluents from industry have serious environmental and public health concerns. Even low level discharges create problems through accumulation in water and soil. In the present work, the pollutant accumulating capacity and the general environmental health status of soil which is a repository of treated and untreated effluent discharges and solid waste dumping of a giant pulp and paper mill have been evaluated with respect to some selected physicochemical parameters. The pollutant accumulating capacity of the soil in seven well-defined sites in and around the mill was found with reference to a “control” site with no history of receiving effluent discharges or solid wastes. The changes in texture, bulk density, water-holding capacity, electrical conductivity, pH, organic carbon, cation exchange capacity, exchangeable sodium, etc. of the soil up to the normal tilled depth were observed in different seasons. In most sites, the soil organic carbon was poorly correlated to the bulk density, water-holding capacity, pH, and clay and sand contents, indicating an unhealthy state of the soil and, correspondingly, nearly exhausted pollutant accumulating capacity. Considerable differences in pH, electrical conductivity, bulk density, and water-holding capacity were observed between the soil receiving effluent discharge and solid waste dumping and the control soil. The soil had accumulated considerable amounts of the exchangeable cations (Ca, Mg, Na, and K). The work has found that industrial activities have worked against the normal behavior of the soil and reduced its capacity to serve as a natural repository of carbon.

To explore mutual relationship among soil characteristics (soil organic matter, soil texture, cation exchange capacity, and pH), land uses, toxic metal (As, Hg, Mn, and Ni) distributions and induced health risk, 156 topsoil samples (0–20 cm) were collected from farm land, forest land and construction land in a grid pattern throughout Xiandao District. Compared with Hunan soil background values, the elevated concentrations of As, Hg and Ni were found to different extent. Pearson correlation matrix suggested As-silt, Mn-Ni, CEC-Mn, CEC-Ni, and CEC-pH had significantly positive correlation, and significantly negative correlation existed in SOM-pH, CEC-clay, SOM-Ni, and SOM-pH. Results based on the soil texture analysis, analysis of variance, and Tukey test indicated the concentrations of As and Ni were higher in relatively fine textures, and the mean contents of As, Mn, Ni, pH, and SOM in construction land, construction land, construction land, forest land, and construction land, respectively, were with the significant difference from that in the other two land uses. For non-carcinogenic effects, Hazard Indexes (HIs) of Ni, Hg, Mn, and As decreased in the order of As > Hg > Mn > Ni to both children and adults. Risk contributions of each exposure pathway decreased in the order of ingestion > dermal contact > inhalation of resuspended particles for HIAₛ, HIMₙ, and HINᵢ. The inhalation of vapors was the highest contributor for HIHg, followed by ingestion, dermal contact, and inhalation of resuspended particles. As and Hg were regarded as the priority pollutants. The hierarchical risk areas were identified after comprehensive consideration of local residential population density distribution, and the different risk management measures were finally suggested for the different priority areas.

Bentonite clay was modified using quaternary ammonium cations, viz. phenyltrimethylammonium (PTMA), hexadecyltrimethylammonium (HDTMA), trioctylmethylammonium (TOMA) [100 % of cation exchange capacity of clay], and stearylkonium (SK) [100 % (SK-I) and 250 % (SK-II) of cation exchange capacity of clay]. The organoclays were characterized using X-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning electron microscopy (SEM). Atrazine adsorption on modified clays was studied using a batch method. Bentonite clay was a poor adsorbent of atrazine as 9.4 % adsorption was observed at 1 μg mL⁻¹atrazine concentration. Modification of clay by PTMA cation did not improve atrazine adsorption capacity. However, atrazine adsorption in HDTMA-, TOMA-, and SK-bentonites varied between 49 and 72.4 % and data fitted well to the Freundlich adsorption isotherm (R > 0.96). Adsorption of atrazine in organoclays was nonlinear and slope (1/n) values were <1. The product of Freundlich adsorption constants, Kf(1/n) in HDTMA-, TOMA-, and SK-I-bentonites was 239.2, 302.4, and 256.6, respectively, while increasing the SK cation loading in the clay (SK-II) decreased atrazine adsorption [Kf(1/n) − 196.4]. Desorption of atrazine from organoclays showed hysteresis and TOMA- and SK-I-bentonites were the best organoclays to retain the adsorbed atrazine. Organoclays showed better atrazine removal from wastewater than an aqueous solution. The synthesized organoclays may find application in soil and water decontamination and as a carrier for atrazine-controlled released formulations.

Accurate knowledge about factors and conditions determining copper (Cu) toxicity in soil is needed for predicting plant growth in various Cu-contaminated soils. Therefore, effects of Cu on growth (biomass production) of lettuce (Lactuca sativa) were tested on seven selected, very different soils spiked with Cu and aged for 2 months at 35 °C. Cu toxicity was expressed as pEC₅₀(Cu²⁺), i.e., the negative logarithm of the EC₅₀(Cu²⁺) activity to plant growth. The determined pEC₅₀(Cu²⁺) was significantly and positively correlated with both the analytically readily available soil pH and concentration of dissolved organic carbon [DOC] which together could explain 87 % of the pEC₅₀(Cu²⁺) variation according to the simple equation: pEC₅₀(Cu²⁺) = 0.98 × pH + 345 × [DOC] − 0.27. Other soil characteristics, including the base cation concentrations (Na⁺, K⁺, Ca²⁺, Mg²⁺), the cation exchange capacity at soil pH (ECEC), and at pH 7 (CEC₇), soil organic carbon, clay content, and electric conductivity as well as the distribution coefficient (Kd) calculated as the ratio between total soil Cu and water-extractable Cu did not correlate significantly with pEC₅₀(Cu²⁺). Consequently, Cu toxicity, expressed as the negative log of the Cu²⁺activity, to plant growth increases at increasing pH and DOC, which needs to be considered in future management of plant growth on Cu-contaminated soils. The developed regression equation allows identification of soil types in which the phytotoxicity potential of Cu is highest.