Bioavailability metal contaminants

Pierzynski GM, Schwab AP. 1993. Bioavailability of zinc, cadmium, and lead in a metal contaminated alluvial soil. J Environ Qual 22 247-254. 

An approach similar to that in soils can be applied to metal-contaminated sediments, where sulfides, measured as acid-volatile sulfides (AVS), have been demonstrated as being the predominant factor controlling metal mobility and toxicity in anaerobic sediments. The difference or ratio between SEM (simultaneous extracted metals) and AVS (SEM-AVS) is used to predict toxicity. In cases where SEM does not exceed the AVS, this approach has been shown to consistently predict the absence of toxicity (Allen et al. 1993 Ankley et al. 1996 DiToro, Hansen et al. 2001b). When SEM exceeds the AVS, toxicity is predicted, but the appearance and extent of toxicity may be determined by other binding phases (e.g., organic carbon) in the pore water. Luoma and Fisher (1997) stated that the association of metal bioavailability with AVS in sediments is not, however, straightforward in all cases and should be treated with caution. 

The forensic aspect of differentiating natural and anthropogenic contaminants is significant, and the difference in terms of risk posed is sometimes irrelevant. However, it is also fair to say that (metal) contamination tends to be less bioavailable if it is naturally occurring. 

Element uptake from soil and transfer into the edible parts of plants have been addressed in several other studies. Soil-to-plant transfer factors in fruit and vegetables grown in various agricultural conditions have been determined for, for example, Pt [100], T1 [101], and various other metal contaminants [102], In a study on stable isotopes of fission product elements (Ce, Cs, Sr), an in vitro enzy-molysis method has been applied to investigate the solubilization of the analytes from fodder in a simulated ruminant digestion [103], The effect of inhibitors of fission product solubility was also considered and essential elements were determined simultaneously to evaluate potential nutrition problems for the animals from the use of such inhibitors. Selective leaching of individual classes of metal complexes with different ligands and sequential enzymolysis have been recently applied to estimate the potential bioavailability to humans of Cd and Pb in cocoa powder and related products [104]. 

O Day, P.A. et al., Metal speciation and bioavailability in contaminated estuary sediments, Alameda Naval Air Station, California, Environ. Sci. Technol., 34, 3665, 2000. 

Phytoextraction is the best approach to remove the contamination primarily from soil and isolate it, without substantially alternating the soil structure and fertility. It is also referred as phytoaccumulation. As the plant absorbs, concentrates, and accumulates toxic metals and radionuclides from contaminated soils and waters into plant tissues, it is best suited for the remediation of diffusely polluted areas, where pollutants occur only at relatively low concentrations and superficial distribution in soil (Rulkens et al., 1998). Several approaches have been studied to enhance the effectiveness of phytoextraction, including the use of chelators to increase the bioavailability and plant uptake of metal contaminants. In order to make this... 

Many toxicants are sequestered in sediments (such as sediments contaminated by wastewater) or they are naturally the source of the toxicant (such as for metal toxicity). In both of these examples the sediment would be termed the toxicant reservoir. Thus, an understanding of the processes affecting the bioavailability of contaminants in sediments is important for a comprehensive understanding of bioavailability in the aquatic environment. 

Hettiarichchi, G. M., Pierzynski, G. M., Zwonitzer, I., and Lambert, M. (1997). Phosphorus sources and rate effects on cadmium, lead and zinc bioavailability in a metal-contaminated soil. Proc. Mh International Conference on the Biogeochemistiy of Trace Elements, Berkley, CA, June 23-26, 1997, 463-472. 

Metal bioavailability is an important parameter in determining the effectiveness of metal-contaminated soils in remediation. Assessment of metal bioavailability varies from humans to plants to microbes, and as such, various methods have been developed for a specific purpose. In this section we provide an overview of various methods used to determine the effectiveness of P-induced Pb immobilization. Reduction of Pb bioavailability by PR was demonstrated by feeding-trial and plant-uptake studies (Laperche et al., 1996). Hydroxyapatite and PR effectively... 

Chaney RL Angle JS Agronomy University of Maryland College Park, Maryland Phytoavailability and bioavailability of heavy metals from heavy metal contaminated soil USDA... 

Prediction of bioavailable heavy metal concentration appears to be more complex, and appropriate normalizing factors still have to be evaluated. Until predictive methods for determining bioavailability of contaminants in sediments can be validated, empirical measurements of body burden and effects as determined by the toxicity test and field monitoring provide the most direct approach for evaluating the impact of contaminated sediment in the aquatic environment (Fava et al., 1987). 

Metals dissolved in pore water are the most mobile and bioavailable. Adsorbed (exchangeable) metals are also bioavailable due to equilibrium between exchangeable and dissolved metals. Both dissolved and exchangeable metals are readily mobilized and bioavailable. On the opposite extreme are metals bound with the crystalline lattice structures of clay and other residual minerals. Metals in this form are essentially permanently immobilized and thus unavailable. Only under long period of mineral weathering, residual metals would become mobile and bioavailable. Between these two extremes are potentially available metals. In metal-contaminated soils, excess metals become primarily associated with these potentially available forms rather than the readily available soluble and exchangeable forms (Feijtel et al., 1988). By contrast, in uncontaminated soils or sediments, only background levels of metals exist in these forms. 

The need to assess the speciation of trace metals and to estimate their bioavailability in the plant root environment is crucial in order to establish the extent of trace metal contamination in soils and to address their potential adverse effects. Although the bioavailability of metals is best predicted by their liquid phase speciation, the assessment of the trace metal fractionation in the solid phase is still essential because the replenishment rate of metals in the soil solution is controlled by solid phase metals (Minnich et al., 1987 Zhang et al., 2001 Krishnamurti et al, 2002). For instance, Zhang et al (2001) showed that Cu concentrations in plant parts correlated best with the effective Cu concentration, which was defined as the Cu concentration in the soil solution combined with a... 

The uptake of metals from agricultural soil by crops and vegetables is an important pathway through which metals in contaminated soils impose health threats to organisms. On the other hand, the capacity of plant roots to remove heavy metals from contaminated soils is an emerging environmental cleanup and remedial biotechnology. In order to evaluate the risks of metal contamination in the area, it is essential to understand metal bioavailability, which depends on a metal s chemical form in the soil, rather than on the total amount accumulated (Allen, 1997 Zemberyova etal, 1998). 

These Fe deficiency-induced processes are likely to operate ubiquitously in soils because of limited bioavailability of Fe, especially in neutral to alkaline soils. Iron deficiency in crops may thus affect metal speciation in soil, and ultimately enhance the uptake of metals by plants. In the present study, we examined this hypothesis in the case of copper (Cu) and zinc (Zn), which are micronutrients and also potential metal contaminants. 

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