Gastro-Intestinal Absorption of Lead in Children and Adults: Overview of Biological and Biophysico-Chemical Aspects

Environment International

Zhu

Cui

et al. 2006

149

Ingestion of contaminated soil has been recognized as an important exposure pathway of cadmium (Cd) for humans, especially for children through outdoor hand-to-mouth activities. The effect of ageing process following the input of Cd into soil on the bioaccessibility of Cd in five typical soils of China was investigated using physiologically based in vitro test in this study. A sequential extraction procedure was employed with attempt to identify the bioaccessible fraction(s) of Cd in soils. The bioaccessibility of Cd in strongly acidic (≈ pH 4.5) soils reached nearly steady levels (76.5-76.9% and 52.0-52.6% in the gastric and small intestinal phases, respectively) after a sharp decline in the first week of ageing. In contrast, the bioaccessibility of Cd in higher pH (N 6.0) soils was found to be much lower (53.3-72.7% and 29.9-43.4% in gastric and small intestinal phases, respectively) and took 2 weeks of ageing to reach steady levels. The freshly spiked Cd was more labile than native Cd. The main proportion of spiked Cd was found in exchangeable Cd which was higher in strongly acidic soils (68.6-71.8%) than in higher pH soils (53.4-61.4%) at day 120 after a sharp decline to the nearly steady state in the first 1 and 2 weeks, respectively. Significant correlations between Cd bioaccessibility and either water soluble and exchangeable Cd individually, or the sum of water soluble and exchangeable Cd throughout the incubation period for all soils, indicate that these forms of Cd are likely to constitute the main proportion of bioaccessible Cd in soils.

Section: The Effect Of Ageing On Bioaccessibility In Soilsmentioning

confidence: 99%

The effect of ageing on the bioaccessibility and fractionation of cadmium in some typical soils of China

Environment International

Zhu

Cui

et al. 2006

149

“…However, the extent of minimization of Pb bioaccessibility in the small intestinal phase is substantially larger than that in the gastric phase. Given the fact that the absorption of lead mainly takes place in the small intestine (Mushak, 1991), the addition of P amendments has great potential for reducing its bioaccessibility of Pb from the contaminated soil effectively.…”

Section: Soluble Pb Concentration In Simulated Gastrointestinal Tractmentioning

confidence: 99%

Assessment of the effectiveness of different phosphorus fertilizers to remediate Pb-contaminated soil using in vitro test

Environment International

Zhu

Chen

et al. 2004

The addition of P-containing amendments was found to effectively reduce the bioaccessibility of Pb in soils to the human, using an in vitro test. For all treatments with P additions, the removal of soluble Pb in the small intestinal phase was observed. The effectiveness of various P treatments in the small intestinal phase generally followed this order at the equivalent P addition level: hydroxyapatite (HA)>phosphate rock (PR)>HA + single super-phosphate (SSP)>SSP. The relatively low effectiveness of P amendments at the gastric phase may be explained by the high solubility of pyromorphite at relatively low pH of 1.7, compared with that at the neutral small intestinal pH. Single super-phosphate showed the best performance in minimizing the bioaccessibility of Pb in the gastric phase, possibly due to its highest solubility at pH 1.7. Single super-phosphate showed the best performance in minimizing the bioaccessibility of Pb in gastric phase, possibly due its highest solubility at pH 1.7. However, in the small intestinal phase, SSP appears to be the least effective amendment, possibly due to its lowest Ca supply level to replace Pb form exchangeable sites, as reflected by its lowest molar Ca/P ratio of 1:2. The disagreement of the sequential extraction results with that of the in vitro test results indicated that the sequential extraction was not suitable for the assessment of the effect of P addition on minimizing the bioaccessibility of Pb to human due to the formation of pyromorphite during the extraction procedure. Results from this study also suggested that the time required for the in vitro test might be shortened for fast screening. D

“…Fendorf et al [28] reported that Pb bioaccessibility in the B horizon of soil from the Oak Ridge National Laboratory site declines rapidly to less than 20% within 30 days of soil incubation with a mixture of NaAsO 2 , CrCl 3 and PbCl 2 in a 0.001-M CaCl 2 matrix at pH 3 in a 1:10 (w:v) soil-to-solution ratio, whereas exchangeable Pb extracted by MgSO 4 is relatively constant with time; however, this study was conducted only in the gastric phase, without further evaluation in the small intestinal phase where the main adsorption process usually occurs [30].…”

Section: Introductionmentioning

confidence: 99%

Pilot study of temporal variations in lead bioaccessibility and chemical fractionation in some Chinese soils

Journal of Hazardous Materials

Cui

Duan

et al. 2008

a b s t r a c tThe effect of ageing, following the addition of ∼400 mg kg −1 lead (Pb) as Pb(NO 3 ) 2 , on Pb bioaccessibility was examined in five typical Chinese soils using a physiologically based extraction test. Sequential extraction was employed to identify the source fraction(s) of bioaccessible Pb in the soils. Pb bioaccessibility decreased exponentially to nearly steady levels in mildly acidic or alkali (pH 6.09-7.43) soils, for both gastric (69.91-71.75%) and small intestinal (7.53-9.63%) phases within the first 2-4 weeks and 1-2 months of incubation, respectively; however, it took only 1-2 weeks for strongly acidic (≈ pH 4.5) soils to reach nearly steady levels of Pb bioaccessibility (73.01-74.46% and 10.30-10.98% in the gastric and small intestinal phases, respectively). In addition to the water-soluble and exchangeable fractions, the carbonate fraction of mildly acidic or alkali soils appeared to be a third main source of bioaccessible Pb in the small intestinal phase; however, bioaccessible Pb was likely to derive principally from Pb in the water-soluble and exchangeable fractions of strongly acidic soils. Bioaccessible Pb in the gastric phase appeared to derive from all the fractions in all five studied soils, even the residual fraction.