Assessment of pollution of potentially harmful elements in soils surrounding a municipal solid waste incinerator, China

We assessed the contamination levels of Mn, Zn, Cr, Cu, Ni, Pb, As and Hg and the risks posed by these potentially harmful elements in top-soils around a municipal solid waste incinerator （MSWI）. We collected 20 soil samples, with an average pH of 8.1, and another fly ash sample emitted from the MSWI to investigate the concentrations of these elements in soils. We determined the concentrations of these elements by inductively coupled plasma-optical emission spectrometer （ICP-OES）, except for Hg, which we measured by AF-610B atomic fluorescence spectrometer （AFS）. We assessed the risks of these elements through the use of geoaccumulation index （/geo）, potential ecological risk index （R/）, hazard quotient （HQi） and cancer risk （Riski）. The results showed that concentrations of potentially harmful elements in soil were influenced by the wind direction, and the concentrations of most elements were higher in the area northwest of the MSWI, compared with the area southeast of the incinerator, with the exception of As; these results were in accordance with those results acquired from our contour maps. According to the I^o values, some soil samples were clearly polluted by Hg emissions. However, the health risk assessment indicated that the concentrations of Hg and other elements in soil did not pose non-carcinogenic risks to the local populations. This was also the case for the carcinogenic risks posed by As Cr and Ni. The carcinogenic risk posed by As was higher in the range 6.49 × 10 -9.58 × 10 -6, but this was still considered to be an acceptable level of risk.

Assessment of leaching behavior and human bioaccessibility of rare earth elements in typical hospital waste incineration ash in China

Leaching behavior and gastrointestinal bioaccessibility of rare earth elements （REEs） from hospital waste incineration （HWI） fly and bottom ash samples collected from Beijing and Nanjing Cities were assessed. In the same ash sample, the leaching concentrations of individual REEs determined by the Toxicity Characteristic Leaching Procedure （TCLP） were higher than those detected by the European standard protocol （EN-type test）, thereby suggesting that the low pH value of leaching solution was an important factor influencing the leacha（bility-of REE. The REE bioaccessibility results, which were evaluated using the physiologically based extraction test （PBET）, indicated that REEs were highly absorbed during fgastric phase by dissolution; and subsequently precipitated and/or re-adsorbed in small intestinal phase. The relative amounts of the total REEs extracted by the TCLP method, EN-type test and PBET test were compared. In addition to the pH value of extraction solutions, the chelating role of REEs witllt organic ligands used in the PBET method was also an important parameter affecting REE adsorption in human body. Additionally, this study showed that REEs were extracted by these methods as concomitants of heavy metals and anions （NO3^-, F^-, SO4^2- , and Cl^-） from HWI ash, which probably caused the remarkably complex toxicity on human body by the exposure pathway.

Use of flue gas desulfurization gypsum to reduce dissolved phosphorus in runoff and leachate from two agricultural soils

Controlling dissolved phosphorus(DP)loss from high P soil to avoid water eutrophication is a worldwide high priority.A greenhouse study was conducted in which flue gas desulfurization gypsum(FGDG)was applied by using different application methods and rates to two agricultural soils.Phosphorus fertilizer was incorporated into the soils at 2.95 g kg^(-1)to simulate soil with high P levels.The FGDG was then applied at amounts of 0,1.5,and 15 g kg^(-1)soil on either the soil surface or mixed throughout the soil samples to simulate no-tillage and tillage,respectively.Ryegrass was planted after treatment application.The study showed that FGDG reduced runoff DP loss by 33%and leachate DP loss 38%in silt loam soil,and runoff DP loss 46%and leachate DP loss 14%in clay loam soil,at the treatment of 15 g kg^(-1)FGDG.Mixing applied method(tillage)provided strong interaction with higher FGDG.To overall effect,the mixing-applied method performed better in controlling DP loss from silt loam soil,while surface-applied(no tillage)showed its advantage in controlling DP loss from clay loam soil.In practice it is necessary to optimize FGDG concentrations,application methods,and DP sources(runoff or leachate)to get maximized benefits of FGDG application.The FGDG application had no negative effects on the soil and ryegrass.