Heavy metal sequential extraction methods--a modification for tropical soils

Sequential extractions of metals can be useful to study metal distributions in various soil fractions. Although several sequential extraction procedures have been suggested in the literature, most were developed for temperate soils and may not be suitable for tropical soils with high contents of Mn and Fe oxides. The objective of this study was to develop a sequential fractionation procedure for Cu and Zn in tropical soils. Extractions were performed on surface (0–20 cm) samples of ten representative soils of Sao Paulo State, Brazil. Chemically reactive Mn forms were satisfactorily assessed by the new modified procedure. Amorphous and crystalline Fe oxides were more selectively extracted in a new two-step extraction. Soil-born Zn and Cu were primarily associated with recalcitrant soil fractions. The proposed procedure provided more detailed information on metal distribution in tropical soils and better characterization of the various components of the soil matrix. The new procedure is expected to be an important tool for predicting the potential effects of environmental changes and land application of metals on the redistribution of chemical forms of metals in tropical soils.     

Accumulation and Chemical Fractionation of Heavy Metals in Andisols after a Different, 6-year Fertilization Management (8 pp)

Goal, Scope and Background Andisols are widespread in Japan and have some special properties such as high anion exchange capacity, low bulk density, and high organic matter content, which might influence the accumulation or chemical fractionation of heavy metals. However, few such data exist in Japanese andisols. The primary objective of this study was to investigate the distribution and chemical fractions of Cu, Zn, Ni, and Cr in the soil profiles and subsequently to assess their potential environmental hazard. Materials and Methods Soil samples were taken from a field experiment conducted on Japanese andisols, which had received either swine compost or chemical fertilizers for 6 years. Concentrations of Cu, Zn, Ni, and Cr were determined for all of the obtained extract solutions by ICP-AES. Results and Discussion Considerably higher total concentrations of Cu and Zn were observed in the top 20 cm layer of the compost-amended soil, relative to the unfertilized soil, while chemical fertilizers had little effect. Application of the swine compost increased the concentrations of Cu and Zn, but not Ni and Cr, in all fractions in the top 20 cm layer. The greatest increase in the organically bound fraction (OM) Cu and dilute acid-exchangeable fraction (DAEXCH) Zn was observed. This suggests that Cu and Zn are potentially bioavailable and mobile in the andisol profiles after 6-year consecutive applications of the swine compost. On the other hand, distribution of Cu, Zn, Ni and Cr among various soil fractions was generally unaffected by chemical fertilizers. Conclusions We observed that 6-year consecutive applications of the swine compost led to an increase in total metals of Cu and Zn, as well as their all-chemical fractions, in the top 20 cm soil layers. Potential hazard of heavy metals, especially of Cu and Zn, as a result of the use of swine compost on andisols, must be taken into account. Recommendations and Outlook The long-term effect of the accumulation of heavy metals, particularly Cu and Zn, in various plant tissues and soils, as well as their potential risk to surface water via runoff and groundwater via leaching, needs to be carefully considered. Further investigations in the long-term experiments are therefore necessary. - Abbreviations. EXCH, exchangeable fraction of metals; DAEXCH, dilute acid-exchangeable fraction of metals; FeMnOX, iron and manganese-oxide-bound fraction; OM, organically-bound fraction; RESD, residual fraction. COMPOST, SRNF, RANF, and CONTROL stand for compost (from swine wastes), slow-release nitrogen fertilizer (coated urea), readily available nitrogen fertilizer (including NH4-N, P, and K fertilizers), and no fertilizer application, respectively.     

Levels of Lead in Urban Soils from Selected Cities in a Central Region of the Philippines (7 pp)

Background Aims, and Scope. Lead (Pb) is a naturally occurring element that poses environmental hazards when present at elevated concentration. It is being released into the environment because of industrial uses and from the combustion of fossil fuels. Hence, Pb is ubiquitous throughout global ecosystems. The existence of potentially harmful concentrations of Pb in the environment must be given full attention. Emissions from vehicles are major source of environmental contamination by Pb. Thus, it becomes imperative that concentrations of Pb and other hazardous materials in the environment not only in the Philippines, but elsewhere in the world be adequately examined in order that development of regulations and standards to minimize risk associated with these materials in urban areas is continued. The objectives of this study were: (1) to determine the levels of Pb in soil from selected urbanized cities in central region of the Philippines; (2) to identify areas with soil Pb concentration values that exceed estimated natural concentrations and allowable limits; and (3) to determine the possible sources that contribute to elevated soil Pb concentration (if any) in the study area. Methods This study was limited to the determination of Pb levels in soils of selected urbanized cities located in central region in the Philippines, namely: Site 1 – Tarlac City in Tarlac; Site 2 – Cabanatuan City in Nueva Ecija; Site 3 – Malolos City in Bulacan; Site 4 – San Fernando City in Pampanga; Site 5 – Balanga City in Bataan; and Site 6 – Olongapo City in Zambales. Soil samples were collected from areas along major thoroughfares regularly traversed by tricycles, passenger jeepneys, cars, vans, trucks, buses, and other motor vehicles. Soil samples were collected from five sampling sites in each of the study areas. Samples from the selected sampling sites were obtained approximately 2 to 3 meters from the road. Analysis of the soil samples for Pb content was conducted using an atomic absorption spectrophotometer. This study was conducted from 2003 to 2004. Since this study assumed that vehicular emission is the major source of Pb contamination in urban soil, other information which the researchers deemed to have bearing on the study were obtained such as relative quantity of each gasoline type disposed of in each city within a given period and volume of traffic in each sampling site. A survey questionnaire for gasoline station managers was prepared to determine the relative quantity of each fuel type (diesel, regular gasoline, premium gasoline, and unleaded gasoline) disposed of or sold within a given period in each study area. Results and Discussion Analysis of soil samples for Pb content showed the presence of Pb in all the soil samples collected from the 30 sampling sites in the six cities at varying concentrations ranging from 1.5 to 251 mg kg–1. Elevated levels of Pb in soil (i.e. greater than 25 mg kg–1 Pb) were detected in five out of the six cities investigated. Site 4 recorded the highest Pb concentration (73.9 ± 94.4 mg kg–1), followed by Site 6 (56.3 ± 17.1 mg kg–1), Site 3 (52.0 ± 33.1 mg kg–1), Site 5 (39.3 ± 19.0 mg kg–1), and Site 2 (38.4 ± 33.2 mg kg–1). Soil Pb concentration in Site 1 (16.8 ± 12.2 mg kg–1) was found to be within the estimated natural concentration range of 5 to 25 mg kg–1. Site 1 registered the least Pb concentration. Nonetheless, the average Pb concentration in the soil samples from the six cities studied were all found to be below the maximum tolerable limit according to World Health Organization (WHO) standards. The high Pb concentration in Site 4 may be attributed mainly to vehicular emission. Although Site 4 only ranked 3rd in total volume of vehicles, it has the greatest number of Type B and Type C vehicles combined. Included in these categories are diesel trucks, buses, and jeepneys which are considered the largest contributors of TSP (total suspended particles) and PM10 (particulate matter less than 10 microns) emissions. Conclusion Only one (San Juan in Site 4) of the thirty sampling sites recorded a Pb concentration beyond the WHO permissible limit of 100 mg kg–1. San Juan in Site 4 had a Pb concentration of >250 mg kg–1. On the average, elevated Pb concentration was evident in the soil samples from San Fernando, Olongapo, Malolos, Balanga, and Cabanatuan. The average soil Pb concentrations in these cities exceeded the maximum estimated natural soil Pb concentration of 25 mg kg–1. Average soil Pb concentration in Site 1 (16.8 mg kg–1) was well within the estimated natural concentration range of 5 to 25 mg kg–1. Data gathered from the study areas showed that elevated levels of Pb in soil were due primarily to vehicular emissions and partly to igneous activity. Recommendation and Outlook The findings of this study presented a preliminary survey on the extent of Pb contamination of soils in urban cities in central region of Philippines Island. With this kind of information on hand, government should develop a comprehensive environmental management strategy to address vehicular air pollution in urban areas, which shows as one of the most pressing environmental problems in the country. Basic to this is the continuous monitoring of Pb levels and other pollutants in air, soil, and water. Further studies should be conducted to monitor soil Pb levels in the six cities studied particularly in areas with elevated Pb concentration. The potential for harm from Pb exposure cannot be understated. Of particular concern are children who are more predisposed to Pb toxicity than adults. Phytoremediation of Pb-contaminated sites is strongly recommended to reduce Pb concentration in soil. Several studies have confirmed that plants are capable of absorbing extra Pb from soil and that some plants, grass species in particular, and can naturally absorb far more Pb than others.     

贵州丹寨县土壤-水稻中硒和重金属的积累及迁移特征

通过测定贵州丹寨县主要水稻种植区30件水稻土及对应的水稻中硒和重金属的含量,分析硒和重金属Cd、Hg、As、Pb在根系土及对应水稻中的分布特征,研究了土壤有机质和pH对硒和重金属在土壤-水稻系统中迁移的影响。结果表明：该地区水稻根系土中硒含量变化范围为0.27～0.98 mg/kg,平均值为0.65 mg/kg, 70%的样品达到富硒土壤标准,但是仅23.3%水稻籽实样品达富Se大米标准。土壤重金属污染风险较大,特别是Hg和Cd,其中80%的样品Hg超《土壤环境质量农用地土壤污染风险管控标准(试行)》(GB 15618—2018)中污染风险筛选值,但水稻籽实中尚无重金属超标现象。水稻根系对硒的富集能力相对最强,其次为茎、叶和籽实。重金属也主要积累在根系中。水稻籽实Se含量与土壤Se总量的相关性不显著,与土壤pH和有机质含量呈显著负相关。水稻籽实中Cd与土壤Se和pH呈显著的负相关关系。土壤中As和Hg向水稻的迁移则主要受总量的控制。水稻各部位Se的吸收能力与土壤重金属存在极显著负相关性,据此可采取措施如降低土壤中的重金属尤其是Cd和Hg的含量及减少有机肥的施用来提高Se在籽实中的积累。     

南方典型水稻土镉(Cd)累积规律模拟

模拟分析稻田系统镉(Cd)迁移途径和土壤Cd累积趋势有助于风险决策的科学性和合理性.本文以湖南省攸县为研究区,在多环境介质采样的基础上,构建土壤重金属污染物累积(PAM)模型,预测区域稻田土壤Cd 累积趋势,结合Monte Carlo随机模拟方法评估不同修复措施的有效性和可持续性.结果表明在当前Cd输入模式下连续耕作5...