Comparison of five extraction methods for evaluating cadmium and zinc immobilization in soil.

The remediation of soil contaminated with heavy metals is an ongoing environmental concern. Paddy soils contaminated with Cd and Zn were collected from around abandoned metals mines in Korea. Limestone and steel slag were mixed with the collected soil, as amendments for Cd and Zn immobilization. Sequential extraction, lettuce cultivation and five single extraction methods were carried out to assess the effects on Cd and Zn immobilization using amendments. The exchangeable fraction of Cd and Zn was decreased and Fe-Mn oxides fraction increased by stabilization using amendments. In addition, the accumulation of Cd and Zn in lettuce decreased in treated soil and indicated the Cd and Zn immobilization effect in soil by the amendments. The extractable Cd and Zn by CaCl2 and Mehlich-3 in the untreated soils were higher than that of treated soils, whereas Cd and Zn extraction by ethylenediaminetetraacetic acid (EDTA), diethylene tetramine penta-acetic acid (DTPA) and toxicity characteristic leaching procedure (TCLP) has a small or no difference between the untreated and treated soils. The extraction results by CaCl2 and Mehlich-3 methods present reasonable results for Cd and Zn immobilization in soil than EDTA, DTPA and TCLP methods. Therefore, the choice of appropriate extraction method is very important when there is the assessment of Cd and Zn immobilization efficiency.

Human health risk assessment of cadmium exposure through rice consumption in cadmium-contaminated areas of the Mae Tao sub-district, Tak, Thailand.

The Mae Tao sub-district is located in the Mae Tao watershed, an important cadmium (Cd)-contaminated area in Thailand. This study was conducted to (i) determine Cd concentrations in rice collected from households in the area, (ii) assess the Cd exposure and potential health risk (HQ) from rice consumption in local adults and (iii) investigate how the factors of individual characteristics and consumption behavior affect the level of HQ. A total of 159 rice samples were collected from households in all 6 villages of the Mae Tao sub-district for analysis of Cd by inductively coupled plasma mass spectrometry. Biodata information and rice consumption behavior were surveyed from local residents at the same time as rice sample collection. Approximately 19.8% and 19.1% of white rice and sticky rice, respectively, contained total Cd higher than the Codex maximum standard of Cd in rice (0.4 mg kg-1). Locally grown rice contained an average of 1.5 times more Cd than retail rice. Cd exposure from consuming only sticky rice was the highest (2.26 × 10-3 mg kg-1 day-1), followed by the consumption of both types of rice (1.39 × 10-3 mg kg-1 day-1) and the consumption of only white jasmine rice (6.30 × 10-4 mg kg-1 day-1). The highest and lowest average HQ values were found in the only sticky rice consumption pattern (2.263) and the only white rice consumption pattern (0.630), respectively. The potential health risk from Cd in each rice consumption pattern was mainly influenced by the total Cd concentration in rice and the rice ingestion rate.

Reductive dissolution and sequestration of arsenic by microbial iron and thiosulfate reduction.

Iron oxide and oxy-hydroxide are commonly used for remediation and rehabilitation of arsenic (As)-contaminated soil and water. However, the stability of As sequestered by iron oxide and oxy-hydroxide under anaerobic conditions is still uncertain. Geochemical properties influence the behavior of As; in addition, microbial activities affect the mobility of sequestered As in soil and water. Microbial-mediated iron reduction can increase the mobility of As by reductive dissolution of Fe oxide; however, microbial-mediated sulfate reduction can decrease the mobility of As by sulfide mineral precipitation. This study investigated the geomicrobial impact on the behavior of As and stability of sequestered As in iron-rich sediment under anaerobic conditions. Increase in Fe(II) concentrations in water was evidence of microbial-mediated iron reduction. Arsenic concentrations increased with Fe(II) concentration; however, the thiosulfate reduction process also induced immobilization of As through the precipitation of AsFeS. Therefore, microbial-mediated iron reduction and thiosulfate reduction have opposite influences on the mobility of As under anaerobic condition.

Targeted removal of trichlorophenol in water by oleic acid-coated nanoscale palladium/zero-valent iron alginate beads.

A new material was developed and evaluated for the targeted removal of trichlorophenol (TCP) from among potential interferents which are known to degrade removal activity. To achieve TCP-targeted activity, an alginate bead containing nanoscale palladium/zero-valent iron (Pd/nZVI) was coated with a highly hydrophobic oleic acid layer. The new material (Pd/nZVI-A-O) preferentially sorbed TCP from a mixture of chlorinated phenols into the oleic acid cover layer and subsequently dechlorinated it to phenol. The removal efficacy of TCP by Pd/nZVI-A-O was not affected by co-existing organic substances such as Suwannee River humic acid (SRHA), whereas the material without the oleic acid layer (Pd/nZVI-A) became less effective with increasing SRHA concentration. The inorganic substances nitrate and phosphate significantly reduced the reactivity of Pd/nZVI-A, however, Pd/nZVI-A-O showed similar TCP removal efficacies regardless of the initial inorganic ion concentrations. The influence of bicarbonate on the TCP removal efficacies of both Pd/nZVI-A and Pd/nZVI-A-O was not significant. The findings from this study suggest that Pd/nZVI-A-O, with its targeted, constant reactivity for TCP, would be effective for treating this contaminant in surface water or groundwater containing various competitive substrates.

Competitive inhibition of cytosolic Ca2+-dependent phospholipase A2 by acteoside in RBL-2H3 cells.

The aim of this study was to investigate whether acteoside isolated from Clerodendron trichotomum Thunberg may act as a selective inhibitor of phospholipase A(2) in RBL-2H3 cells. Acteoside dose-dependently inhibited 0.5 µM melittin-induced release of [(3)H]arachidonic acid, which was due to the inhibition of cytosolic Ca(2+)-dependent phospholipase A(2) (cPLA(2)) rather than secretory PLA(2) (sPLA(2)). In Dixon plots, the apparent K ( i ) value of acteoside on cPLA(2) was 5.9 µM and the inhibitory pattern appeared to be a competitive inhibitor. The above data, suggests that acteoside acts as a competitive inhibitor of cPLA(2) in RBL-2H3 cells.

Intracellular Ca Mobilization and Beta-hexosaminidase Release Are Not Influenced by 60 Hz-electromagnetic Fields (EMF) in RBL 2H3 Cells.

The effects of extremely low frequency electromagnetic fields (EMF) on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells were investigated. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not produce any cytotoxic effects in RBL 2H3 cells. Melittin, ionomycin and thapsigargin each dose-dependently increased the intracellular Ca(2+) concentration. The increase of intracellular Ca(2+) induced by these three agents was not affected by exposure to EMF (60 Hz, 1 mT) for 4 or 16 h in RBL 2H3 cells. To investigate the effect of EMF on exocytosis, we measured beta-hexosaminidase release in RBL 2H3 cells. Basal release of beta-hexosaminidase was 12.3±2.3% in RBL 2H3 cells. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not affect the basal or 1 µM melittin-induced beta-hexosaminidase release in RBL 2H3 cells. This study suggests that exposure to EMF (60 Hz, 0.1 or 1 mT), which is the limit of occupational exposure, has no influence on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells.

Effect of Extremely Low Frequency Electromagnetic Fields (EMF) on Phospholipase Activity in the Cultured Cells.

This study was conducted to investigate the effects of extremely low frequency electromagnetic fields (EMF) on signal pathway in plasma membrane of cultured cells (RAW 264.7 cells and RBL 2H3 cells), by measuring the activity of phospholipase A(2) (PLA(2)), phospholipase C (PLC) and phospholipase D (PLD). The cells were exposed to the EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h. The basal and 0.5 µM melittin-induced arachidonic acid release was not affected by EMF in both cells. In cell-free PLA(2) assay, we failed to observe the change of cPLA(2) and sPLA(2) activity. Also both PLC and PLD activities did not show any change in the two cell lines exposed to EMF. This study suggests that the exposure condition of EMF (60 Hz, 0.1 or 1 mT) which is 2.4 fold higher than the limit of occupational exposure does not induce phospholipases-associated signal pathway in RAW 264.7 cells and RBL 2H3 cells.