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Fractionation and elemental association of Zn, Cd, and Pb in soils near Zn mining areas were studied using a continuous-flow sequential extraction approach. The recently developed sequential extraction procedure not only gave fractional distribution data for evaluation of the mobility or potential environmental impact of the metals, but also the extraction profiles (extractograms) which were used for study of elemental association. In addition, the elemental atomic ratio plot extractogram can be used to demonstrate the degree of anthropogenic contamination. Seventy-nine soil samples were collected in the vicinity of a Zn mine and were fractionated into 4 phases i.e. exchangeable (F1), acid soluble (F2), reducible (F3) and oxidizable (F4) phases. Most samples were contaminated with Zn, Cd and Pb. The reducible phase is the most abundant fraction for Zn and Pb (>50%) while Cd is concentrated in the first 3 extraction steps. The distribution patterns of Cd were obviously affected by soil pH. 55% of Cd appears predominantly in the F1 fraction for acidic soils while in neutral and alkaline soils, it was mostly (70%) found in the F2 + F3 fractions. The extractograms obtained from the continuous-flow extraction system revealed close association between Zn, Cd, Pb and Fe in the acid soluble phase, Cd-Pb and Zn-Fe in the reducible phase for contaminated soils. A correlation study of the 3 metals using a correlation coefficient was also performed to compare the results with the elemental association revealed by the extractograms. Atomic ratio plot extractograms of Zn/Fe, Cd/Fe and Pb/Fe in the reducible phase, where contaminated metals are predominant, can be used to evaluate the degree of anthropogenic contamination. From the elemental atomic ratio plot, it is obvious that the contaminants Cd and Pb are mostly adsorbed on the surface of Fe oxides. Zn, which is present in an approximately 1 ratio 1 ratio with Fe in contaminated soils, does not show a similar trend to that found for Cd and Pb. 相似文献
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Zarcinas BA Pongsakul P McLaughlin MJ Cozens G 《Environmental geochemistry and health》2004,26(4):359-371
A reconnaissance soil geochemical and concomitant plant survey based on 318 soil (0-15 cm) and 122 plant samples was used for the assessment of heavy metal pollution of agricultural soils and crops of Thailand. Arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) were determined in soils using aqua regia digestion, and in plants using nitric acid digestion. Organic carbon (C), pH, electrical conductivity (EC) and available phosphorus (P) were determined on the soil samples using appropriate procedures. Results indicated that concentrations of heavy metals varied widely among the different regions of Thailand. Regression analysis between the concentrations of metals in soil (aqua regia extractable) and edible plant parts indicated a small but positive relationship for Cd in all the plants sampled in the survey (R2 = 0.081, p < 0.001). There was also a positive relationship between soil and plant Cd concentrations in rice (R2 = 0.242, p < 0.010), and negative relationships for Zn in rice (R2 = 0.385, p < 0.001), and Cu (R2 = 0.355, p < 0.001) and Zn (R2 = 0.122, p < 0.026) in glutinous rice. Principal component analysis of the soil data suggested that concentrations of As, Co, Cr, Cu, Hg, Ni and Pb were strongly correlated with concentrations of Al and Fe, which is suggestive of evidence of background variations due to changes in soil mineralogy. Thus, the evidence for widespread contamination of soils by these elements through agricultural activities is not strong. On the other hand, Cd and Zn were strongly correlated with organic matter and concentrations of available and aqua regia extractable P. This is attributed to input of contaminants in agricultural fertilisers and soil amendments (e.g. manures, composts). 相似文献
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Simmons RW Pongsakul P Saiyasitpanich D Klinphoklap S 《Environmental geochemistry and health》2005,27(5-6):501-511
Prolonged consumption of rice containing elevated cadmium (Cd) levels is a significant health issue particularly in subsistence
communities that are dependent on rice produced on-farm. This situation is further exacerbated in areas of known non-ferrous
mineralization adjacent to rice-based agricultural systems where the opportunity for contamination of rice and its eventual
entry into the food chain is high. In the current study, an assessment of the degree of soil Cd and Zn contamination and associated
rice grain Cd contamination downstream of an actively mined zone of Zn mineralization in western Thailand was undertaken.
Total soil Cd and Zn concentrations in the rice-based agricultural system investigated ranged from 0.5 to 284 mg kg−1 and 100 to 8036 mg kg−1, respectively. Further, the results indicate that the contamination is associated with suspended sediment transported to
fields via the irrigation supply. Consequently, the spatial distribution of Cd and Zn is directly related to a field’s proximity
to primary outlets from in-field irrigation channels and inter-field irrigation flows with 60–100% of the Cd and Zn loading
associated with the first three fields in irrigation sequence. Rice grain Cd concentrations in the 524 fields sampled, ranged
from 0.05 to 7.7 mg kg−1. Over 90% of the rice grain samples collected contained Cd at concentrations exceeding the Codex Committee on Food Additives
and Contaminants (CCFAC) draft Maximum Permissible Level for rice grain of 0.2 mg Cd kg−1. In addition, as a function of demographic group, estimated Weekly Intake (WI) values ranged from 20 to 82 μg Cd per kg Body.
This poses a significant public health risk to local communities. The results of this study suggest that an irrigation sequence-based
field classification technique in combination with strategic soil and rice grain sampling and the estimation of WI values
via rice intake alone may be a useful decision support tool to rapidly evaluate potential public health risks in irrigated
rice-based agricultural systems receiving Cd contaminated irrigation water. In addition, the proposed technique will facilitate
the cost effective strategic targeting of detailed epidemiological studies thus focusing resources to specific ‘high risk’
areas. 相似文献
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Simmons RW Noble AD Pongsakul P Sukreeyapongse O Chinabut N 《Environmental geochemistry and health》2009,31(1):71-79
Research undertaken over the last 40 years has identified the irrefutable relationship between the long-term consumption of
cadmium (Cd)-contaminated rice and human Cd disease. In order to protect public health and livelihood security, the ability
to accurately and rapidly determine spatial Cd contamination is of high priority. During 2001–2004, a General Linear Regression
Model Irr-Cad was developed to predict the spatial distribution of soil Cd in a Cd/Zn co-contaminated cascading irrigated
rice-based system in Mae Sot District, Tak Province, Thailand (Longitude E 98°59′–E 98°63′ and Latitude N 16°67′–16°66′).
The results indicate that Irr-Cad accounted for 98% of the variance in mean Field Order total soil Cd. Preliminary validation
indicated that Irr-Cad ‘predicted’ mean Field Order total soil Cd, was significantly (p < 0.001) correlated (R
2 = 0.92) with ‘observed’ mean Field Order total soil Cd values. Field Order is determined by a given field's proximity to
primary outlets from in-field irrigation channels and subsequent inter-field irrigation flows. This in turn determines Field
Order in Irrigation Sequence (Field OrderIS). Mean Field Order total soil Cd represents the mean total soil Cd (aqua regia-digested) for a given Field OrderIS. In 2004–2005, Irr-Cad was utilized to evaluate the spatial distribution of total soil Cd in a ‘high-risk’ area of Mae Sot
District. Secondary validation on six randomly selected field groups verified that Irr-Cad predicted mean Field Order total
soil Cd and was significantly (p < 0.001) correlated with the observed mean Field Order total soil Cd with R
2 values ranging from 0.89 to 0.97. The practical applicability of Irr-Cad is in its minimal input requirements, namely the
classification of fields in terms of Field OrderIS, strategic sampling of all primary fields and laboratory based determination of total soil Cd (T-CdP) and the use of a weighed coefficient for Cd (CoeffW). The use of primary fields as the basis for Irr-Cad is also an important practical consideration due to their inherent ease
of identification and vital role in the classification of fields in terms of Field OrderIS. The inclusion of mean field order soil pH (1:5water) to the Irr-Cad model accounted for over 79% of the variation in mean Field Order bio-available (DTPA (diethylenetriaminepentaacetic
acid)-extractable) soil Cd. Rice is the staple food of countries of the Greater Mekong Sub-region (includes Vietnam, Myanmar,
Lao PDR, Thailand and Yunnan Province, China). These countries also have actively and historically mined Zn, Pb, and Cu deposits
where Cd is likely to be a potential hazard if un-controlled discharge/runoff enters areas of rice cultivation. As such, it
is envisaged that the Irr-Cad model could be applied for Cd hazard assessment and effectively form the basis of intervention
options and policy decisions to protect public health, livelihoods, and export security. 相似文献
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