Natural Attenuation: Implications for Trace Metal/Metalloid Nutrition
As discussed in detail in previous chapters, natural attenuation of metals by soils decreases metal bioavailability. It can therefore be highly desirable to facilitate this process in soils in which metals are present at concentrations of ecotoxicological concern. However, many metals are also essential micronutrients. In fact, micronutrient metals are probably more frequently present at low concentrations in soils than at toxic concentrations, resulting in constraints to crop growth and deficiencies for animal and human health. For example, millions of hectares of arable land are thought to be micronutrient deficient, limiting crop production (Fageria et al. 2002), with crop recovery rates for applied micronutrient fertilizers as low as 5 to 10% because of adsorption and fixation reactions in soils (Mortvedt 1994). Moreover, it has been estimated that more than 40% of the world’s population suffers from some form of micronutrient malnutrition (Welch and Graham 2002) due to insufficient micronutrient uptake by crops.