Metals bioavailability

The interpretation of previous attempts at measuring the impact of metals on microbially mediated processes has been hindered by the use of a wide range of experimental conditions and measurements. Already, a shift from studies based on total metal concentration to those based on bioavailable metal concentrations has occurred. The next step will entail accurately predicting and measuring metal speciation patterns in order to identify microbial responses to metal speciation. Only then will it be possible to develop more effective methods to quantify and mitigate deleterious effects of metals on the myriad processes that microbes mediate in the environment. 

MacRae, R. K., Smith, D. E., Swoboda-Colberg, N., Meyer, J. S. and Bergman, H. (1999). Copper binding affinity of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) gills implications for assessing bioavailable metal, Environ. Toxicol. Chem., 6, 1180-1189. 

Bioavailable metals and metalloid species are either adsorbed or incorporated into the structure of proteins, lipids, nucleic acids, amino acids, sugars, vitamins and hormones to form complexes of varying degrees of thermodynamic stability and reactivity. These complexes could be classified as either metal-proteins or metalloproteins on the basis of their stability during isolation and purification (Vallee and Coleman, 1964). Whereas metal-proteins are relatively labile and the metal is easily lost during dialysis, metalloproteins are stable and inert. 

Bioavailable metal species Hours Analysis of a subsample from the acceptor solution 68... 

Sauerbeck, D. R., and Styperek, P. (1985). Evaluation of chemical methods for assessing the cadmium and zinc availability from different soils and sources. In Chemical Methods for Assessing Bioavailable Metals in Sludges and Soils (R. Leschber, R. D. Davis, and P. L Hemite, eds.), p. 49. Elsevier, Amsterdam. 

It is clear that if measured concentrations of a metal are close to or above the EQS and the speciation-based approach is not available, then special attention needs to be given to identification of the local background level (however it is defined). In all cases, it is the bioavailable metal concentration that is relevant, but this is often not well defined and not readily determined for data-poor metals. 

CH3COOH solution (bioavailable metals and metals bound to carbohydrates)... 

Natural organisms can provide information pertaining to the chemical state within an environment, not through their presence or absence, but through their ability to concentrate heavy metals within tissues. For example, sentinel organisms, which include bivalves, have been used to monitor the concentrations of bioavailable metals and toxicity in aquatic ecosystems (Lau et al., 1998 Hall et al., 2002 Byrne and O Halloran, 2001). Bivalves have been used to monitor heavy-metal pollutants from gold-mine operations in Sarawak Malaysia (Lau et al., 1998). 

Hooda SP, Davison B, Zhang H and Edwards T (2001) DGTfor assessing bioavailable metals in soils. Proceedings, 6fh International Conference on the Biogeochemistry of Trace Elements,... 

Bioavailable metals Dissolved and particulate metals that are accessible to organisms during normal metabolic activity. 

There is currently no consensus on whether rhizospheric processes augment or impoverish the bioavailable metal pool. The conceptual model developed by Gobran and Clegg (1996) to assess nutrient availability in the mineral soikroot... 

Contradictory findings have been reported in other studies, where the rhizosphere is depicted as an environment depleted of bioavailable metal pools. Cherrey et al. (1999) found the rhizosphere of ryegrass (L. perenne cv. Aubisque) to be impoverished of extractable Cu (EDTA, DTPA or CaCl2). Furthermore, Lorenz et al. (1997) reported lower concentrations of soluble Cd and Zn in the rhizosphere than in the bulk soil. In a comparison of the soil solution concentrations of Cd and Zn before and after the growth of the hyperaccumulator T. caerulescens, Knight et al. (1997) observed a decrease in the total Cd and Zn concentrations in the soil solution of the rhizosphere, as well as in the free Cd + and Zn + concentrations. 

Bind lead preferentially over other bioavailable metal ions (notably calcium, zinc, and iron) by a factor of >10. ... 

---