Uptake of heavy metals by vegetable plants grown on contaminated soils, their bioavailability and speciation

This research aimed to investigate the bioavailability of 9 metals (Cr, Mn, Fe, Ni, Cu, Zn, Mo, Cd, and Pb) to vegetable crops (spinach, lettuce, carrot and radish) cultivated in compost soils at different levels of metal contamination. The uptake and accumulation of these metals by the plants were examined. The elemental speciation using SEC-UV-ICP-MS and Nanospray Mass Spectrometry had been performed to characterize the metal containing species induced in the plants exposed to metal stress. In order to evaluate potential health risks arising from ingestion of the metal contaminated plants, the oral bioaccessibility i.e. the use of an in vitro physiologically based extraction test (PBET) simulating the transition of the metal pollutants in the plants into the human gastrointestinal system was undertaken. It was found that, with the exception of Cr, metal concentrations (Mn, Fe, Ni, Cu, Zn, Mo and Cd) in lettuce, spinach, carrot and radish depended on the concentrations of the total metal in the soils in which the plants were grown. For Pb, the amounts accumulated in the leafy vegetables also depended on their levels of contamination in the soils while the root vegetables had rather low uptake and the uptake levels did not increase when higher levels of contamination were applied. Mn, Fe and Zn were relatively easily mobilised from soils to plants; they tended to accumulate in all plants studied at high concentrations. The elements which were more enriched in leaves included Mn and Zn (in all plant types), and Fe and Cd (only in the root vegetables). In contrast, Fe, Ni, Cu, Mo and Pb were accumulated more in roots of the leafy vegetables. Among all plants studied, it was observed that carrot had low uptake for all elements (Cr, Ni, Cu, Mo, Cd and Pb), except for Mn, Fe, Zn which were found in all plants. The metal mobilised from soil to plant as indicated by the metal contents accumulated in the plants decreased in the order Mn >> Zn > Fe > Cu > Mo > Ni > Cd > Pb Cr. The metal bioavailability to plants was assessed by measuring transfer factor (TF) values of the metals based on total metal contents in the soils. It was found that the order of TF values was Mn > Zn >> Cd > Ni > Cu > Mo Pb > Cr Fe. The mean TF values of each element irrespective of plant types were 1.93, 1.77, 0.485, 0.194, 0.111, 0.052, 0.045, 0.037 and 0.036 for Mn, Zn, Cd, Ni, Cu, Mo, Pb, Cr, and Fe, respectively. Hence, Mn and Zn were most bioavailable to plants i.e. they can be transferred from soils to plants more easily than Ni, Cu, Mo, Pb, Cr and Fe. Whereas, the bioavailability of Cd was relatively moderate. In addition, the results enabled the development of statistical regression models that are suited to predict metal uptake by plants. It indicated that the relationship between the TF values and the extractable soil metals followed the power regression curve. However, there were some cases in which it did not follow the power regression curve but a linear model, these are; Mn (for carrot leaves and radish roots), Mo (for spinach roots and carrot roots), and Cd (for lettuce leaves, spinach roots and leaves and carrot roots). In the multi-elemental speciation study, it was found that a common association of the metals (Cd, Cu, Mo, Pb, and Zn) to the high molecular weight (MW) fractions (8160 Da) was observed in all plant extracts. The lower MW fractions of approximately 1000 — 3000 Da of Cd, Cu, Mo, Ni, Pb, and Zn containing compounds were found to be present in all plant extracts. Iron was not detected in the roots of carrot and radish, but present as both high MW (8200 Da) and low MW (2500 Da) compounds in the leaves of spinach and lettuce. To characterize the individual metal containing species present in the plant samples, the Nanospray Mass Spectrometry was employed. Unfortunately, no evidence from this analysis can confirm that these compounds are related to the phytochelatin family. The PBET (Physiologically-Based Extraction Test) resul..

Bioaccessibility of heavy metals in the seaweed Caulerpa racemosa var. corynephora: Human health risk from consumption

This study reports the total and bioaccessible concentrations of heavy metals (Mn, Fe, Cu, Zn, Cd and Pb) in the seaweed Caulerpa racemosa var. corynephora collected from local markets along the Andaman coast of Krabi Province, Thailand. Microwave-assisted acid digestion (EPA Method 3052) was used for sample preparation prior to total metal analysis. The in vitro Unified Bioaccessibility Method (UBM) was applied to assess the bioaccessibility of the metals in the seaweed samples. The total, gastric phase, and residual fraction concentration were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The total amounts found in the seaweed samples, in ascending order were Cd < Pb < Cu < Zn < Mn < Fe with the mean concentrations of 0.89, 0.97, 17.4, 59.0, 63.4, and 450 mg/kg dry weight, respectively. High bioaccessibility percentages for Mn (71.8–85.3%) were observed alongside moderate bioaccessibility percentages for Cu (44.3–56.3%), Zn (37.7–47.4%), and Cd (41.8–46.7%), a low bioaccessibility percentage for Pb (22.3–32.0%), and a very low bioaccessibility percentage for Fe (11.5–16.5%). A quality control procedure was implemented which involved the analysis of a certified reference material (Seaweed NMIJ CRM 7405-a) for total metals and a mass-balance approach for the assessment of the in vitro bioaccessibility method

Heavy metal bioavailability and bioaccessibility in soil

This chapter considers the use of a variety of approaches to assess either the bioavailability or the bioaccessibility of metals in soil. The bioavailability of metals from soils is considered with respect to a series of single-extraction methods, including the use of ethylenediaminetetraacetic acid (EDTA), acetic acid, diethylenetriaminepentaacetic acid (DTPA), ammonium nitrate, calcium chloride and sodium nitrate. Then, a procedure for the recovery of metals using a three-stage sequential extraction protocol is described. Two alternate approaches for assessing the environmental health risk to humans by undertaking in vitro gastrointestinal extraction (also known as the physiologically based extraction test, PBET) are considered. Finally, two acid digestion protocols that allow the pseudo-total metal content of samples to be assessed are provided. In all cases details of how the different approaches can be performed are provided, including the specific reagents required (and their preparation), details of the different extraction and acid digestion protocols to be followed and suitable analytical details to allow the measurement of metals by inductively coupled plasma mass spectrometry (ICP-MS) with/without a collision/reaction cell. A detailed Notes section provides experimental details to guide the reader through some of the practical aspects of the procedures. Finally, some experimental results are provided as evidence of the suitability of the approaches described including single-extraction data, using EDTA and acetic acid, for metals in CRM BCR 700. In addition, in vitro gastrointestinal extraction data are provided for metals in CRM SRM 1570A (spinach leaves). The influence of time on the intestinal fluid phase on the recovery of metals in CRM SRM 1570A (spinach leaves) and CRM INCT-TL-1 (tea leaves) is investigated, as well as the repeatability in terms of recovery of metals from soil over a 3-week period by in vitro gastrointestinal extraction

Uptake of heavy metals by vegetable plants grown on contaminated soils, their bioavailability and speciation

This research aimed to investigate the bioavailability of 9 metals (Cr, Mn, Fe, Ni, Cu, Zn, Mo, Cd, and Pb) to vegetable crops (spinach, lettuce, carrot and radish) cultivated in compost soils at different levels of metal contamination. The uptake and accumulation of these metals by the plants were examined. The elemental speciation using SEC-UV-ICP-MS and Nanospray Mass Spectrometry had been performed to characterize the metal containing species induced in the plants exposed to metal stress. In order to evaluate potential health risks arising from ingestion of the metal contaminated plants, the oral bioaccessibility i.e. the use of an in vitro physiologically based extraction test (PBET) simulating the transition of the metal pollutants in the plants into the human gastrointestinal system was undertaken. It was found that, with the exception of Cr, metal concentrations (Mn, Fe, Ni, Cu, Zn, Mo and Cd) in lettuce, spinach, carrot and radish depended on the concentrations of the total metal in the soils in which the plants were grown. For Pb, the amounts accumulated in the leafy vegetables also depended on their levels of contamination in the soils while the root vegetables had rather low uptake and the uptake levels did not increase when higher levels of contamination were applied. Mn, Fe and Zn were relatively easily mobilised from soils to plants; they tended to accumulate in all plants studied at high concentrations. The elements which were more enriched in leaves included Mn and Zn (in all plant types), and Fe and Cd (only in the root vegetables). In contrast, Fe, Ni, Cu, Mo and Pb were accumulated more in roots of the leafy vegetables. Among all plants studied, it was observed that carrot had low uptake for all elements (Cr, Ni, Cu, Mo, Cd and Pb), except for Mn, Fe, Zn which were found in all plants. The metal mobilised from soil to plant as indicated by the metal contents accumulated in the plants decreased in the order Mn >> Zn > Fe > Cu > Mo > Ni > Cd > Pb Cr. The metal bioavailability to plants was assessed by measuring transfer factor (TF) values of the metals based on total metal contents in the soils. It was found that the order of TF values was Mn > Zn >> Cd > Ni > Cu > Mo Pb > Cr Fe. The mean TF values of each element irrespective of plant types were 1.93, 1.77, 0.485, 0.194, 0.111, 0.052, 0.045, 0.037 and 0.036 for Mn, Zn, Cd, Ni, Cu, Mo, Pb, Cr, and Fe, respectively. Hence, Mn and Zn were most bioavailable to plants i.e. they can be transferred from soils to plants more easily than Ni, Cu, Mo, Pb, Cr and Fe. Whereas, the bioavailability of Cd was relatively moderate. In addition, the results enabled the development of statistical regression models that are suited to predict metal uptake by plants. It indicated that the relationship between the TF values and the extractable soil metals followed the power regression curve. However, there were some cases in which it did not follow the power regression curve but a linear model, these are; Mn (for carrot leaves and radish roots), Mo (for spinach roots and carrot roots), and Cd (for lettuce leaves, spinach roots and leaves and carrot roots). In the multi-elemental speciation study, it was found that a common association of the metals (Cd, Cu, Mo, Pb, and Zn) to the high molecular weight (MW) fractions (8160 Da) was observed in all plant extracts. The lower MW fractions of approximately 1000 — 3000 Da of Cd, Cu, Mo, Ni, Pb, and Zn containing compounds were found to be present in all plant extracts. Iron was not detected in the roots of carrot and radish, but present as both high MW (8200 Da) and low MW (2500 Da) compounds in the leaves of spinach and lettuce. To characterize the individual metal containing species present in the plant samples, the Nanospray Mass Spectrometry was employed. Unfortunately, no evidence from this analysis can confirm that these compounds are related to the phytochelatin family.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Bioavailability of iodine in the UK-Peak District environment and its human bioaccessibility: an assessment of the causes of historical goitre in this area

Iodine is an essential micronutrient for human health. Its deficiency causes a number of functional and developmental abnormalities such as goitre. The limestone region of Derbyshire, UK was goitre-endemic until it declined from the 1930s and the reason for this has escaped a conclusive explanation. The present study investigates the cause(s) of goitre in the UK-Peak District area through an assessment of iodine in terms of its environmental mobility, bioavailability, uptake into the food chain and human bioaccessibility. The goitre-endemic limestone area is compared with the background millstone grit area of the UK-Peak District. The findings of this study show that ‘total’ environmental iodine is not linked to goitre in the limestone area, but the governing factors include iodine mobility, bioavailability and bioaccessibility. Compared with the millstone grit area, higher soil pH and calcium content of the limestone area restrict iodine mobility in this area, also soil organic carbon in the limestone area is influential in binding the iodine to the soil. Higher calcium content in the limestone area is an important factor in terms of strongly fixing the iodine to the soil. Higher iodine bioaccessibility in the millstone grit than the limestone area suggests that its oral bioaccessibility is restricted in the limestone area. Iodine taken up by plant roots is transported freely into the aerial plant parts in the millstone grit area unlike the limestone area, thus providing higher iodine into the human food chain in the millstone grit area through grazing animals unlike the goitre-prevalent limestone area

Uptake of heavy metals by vegetable plants grown on contaminated soil and their bioavailability in the human gastrointestinal tract

Lettuce, spinach, radish and carrot were grown on compost that had previously been contaminated at different concentrations of Cd, Cu, Mn, Pb and Zn. Control plants of each vegetable were also grown on unadulterated compost. The experiment was carried out under greenhouse conditions. Mature plants were harvested and their roots and leaves collected. Soil samples from each growing pot and plant materials were acid digested and analysed to determine total metal concentration. Flame-Atomic Absorption Spectroscopy (FAAS) was employed to determine metal concentrations in soil and plant samples (Mn and Zn), while Cd, Cu and Pb in plant materials were analysed by Differential Pulse Anodic Stripping Voltammetry (DP-ASV). Soil (BCR 146R and GBW 07310) and plant (tea leaves, INCT-TL-1) certified reference materials were used to assess accuracy and precision. The edible part of plants, i.e. the leaves of lettuce and spinach and the roots of radish and carrot, were also extracted using an in vitro gastrointestinal (GI) extraction to assess metal bioavailability. The results showed that the uptake of Cd, Cu, Mn and Zn by plants corresponded to the increasing level of soil contamination, while the uptake of Pb was low. Soil-to-plant transfer factor (TF) values decreased from Mn≫Zn>Cd>Cu>Pb. Moreover, it was observed from this investigation that individual plant types greatly differ in their metal uptake, e.g. spinach accumulated a high content of Mn and Zn, while relatively lower concentrations were found for Cu and Pb in their tissues. From the in vitro gastrointestinal (GI) study, results indicate that metal bioavailability varied widely from element to element and according to different plant types. The greatest extent of metal releasing was found in lettuce (Mn, 63.7%), radish (Cu, 62.5%), radish (Cd, 54.9%), radish (Mn, 45.8%) and in lettuce (Zn, 45.2%)

In-vitro testing for assessing oral bioaccessibility of trace metals in soil and food samples

In-vitro gastrointestinal extraction, also known as oral bioaccessibility, is important when assessing chemical risk to humans. In use, it purports to simulate the release of chemicals from sample matrices (e.g., food and soil) that may be consumed intentionally or unintentionally in the diet, so in-vitro conditions are created to simulate, principally, enzymatic action in the mouth, the stomach and the intestines. This article reviews the current status of oral bioaccessibility in terms of the release of metals or metalloids from food and soil samples. We place particular emphasis on the parameters that influence gastrointestinal extraction, including gastric and intestinal pH, food constituents, residence time and particle size. It is clear that future development is needed to validate and standardize the methods

Use of the physiologically-based extraction test to assess the oral bioaccessibility of metals in vegetable plants grown in contaminated soil

The oral bioaccessibility of metals in vegetable plants grown on contaminated soil was assessed. This was done using the physiologically-based extraction test (PBET) to simulate the human digestion of plant material. A range of vegetable plants, i.e. carrot, lettuce, radish and spinach, were grown on metal contaminated soil. After reaching maturity the plants were harvested and analysed for their total metal content (i.e. Cr, Cd, Cu, Fe, Mn, Mo, Ni, Pb and Zn) by inductively coupled plasma-mass spectrometry (ICP-MS). The plant samples were then subsequently extracted using an in vitro gastrointestinal approach or PBET to assess the likelihood of oral bioaccessibility if the material was consumed by humans

Estimation of bioaccessibility of heavy metals in oysters using the physiologically based extraction test

A physiologically based extraction test (PBET) was applied to estimate the oral bioaccessibility of cadmium, mercury, and lead from oyster tissues. The PBET measures the fraction of a metal that is solubilized from the sample under simulated gastric and intestinal conditions. Both gastric and intestinal extracted solutions as well as microwave digested residue were analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES). The bio accessibilities (relative to the total metal concentrations) of cadmium and lead in the oyster samples were 33.8–59.2% and 28.3–51.4%, respectively. The bioaccessibility of mercury was non detectable (<0.019 mg=kg wet weight) due to the relatively low levels of mercury in the oyster samples (<0.110 mg=kg wet weight)