The influence of humic acid quality on the sorption and mobility of heavy metals

Abstract

Mobile and potentially mobile forms of heavy metals are probably one of the most important toxic hazards in the environment. Besides pH, which is a factor influencing the mobility/availability of heavy metals to the greatest extent, the content and mainly the quality of soil organic matter play a very important role in the evaluation of heavy metal behaviour in the environment. The fraction of metals bound to organic compounds is exclusively associated with humic substances and particularly with humic acids (HA). A relationship between the parameters reflecting the actual structure of humic acids and mobile or potentially mobile fractions of heavy metals was studied in 12 soil localities representing different soil types. It can be stated on the basis of the acquired data that heavy metals tend to form complexes with soil organic matter that are different for each metal. The results suggest that copper is bound mainly in an unavailable form (significant correlations of fraction IV with HA parameters) and cadmium prefers exchangeable forms (significant correlations of fraction I with HA parameters) and is more available. It can be assumed on the basis Spearman's correlations that mobile fractions of cadmium are predominantly bound to the aliphatic part of humic substances, and copper prefers strong bonds to humic acids with a high degree of humification.

Using Stripping Voltammetry to Determine Heavy Metals in Cooking Spices Used in Iraq

“…Table 5 ) in uncontaminated soils [35]. The other important factor that reduces the bioavailability of copper is the strong tendency of copper to bind organic materials to form stable coordination complexes [40]. Excluding the data given by Ansari et al [22], all the surveyed studies gave copper levels within the range established in this study ( Table 7).…”

“…However, although spices are consumed in small quantities, Table 9 reveals that Cu, Zn, Fe, Mn, Cr, and Ni of these additives contribute significantly (21, 7-10, 27-61, 46-59, 26-36, and 3%, respectively) to the recommended dietary allowance. On the other hand, the average amounts of Cu, Zn, Fe, Mn, and Ni consumed daily by Iraqi adults from spices (Table 9) were still far below the specified tolerable upper level (TUL) of these metals (10,40,45,11, and 1.0 mg kg -1 , respectively). This means that any adverse health effects from the consumption of these elements cannot be expected under normal conditions.…”

Sorption of heavy metals in organic horizons of acid forest soils at low added concentrations

“…Comparing to lead, copper sorption is significantly lower in all samples. This result can be attributed to generally low affinity of copper to inorganic part of soils, as this metal is preferentially sorbed to organic fraction (Barančíková & Makovníková 2003;Gondar et al 2006). The sorption of copper seemed to be more limited, despite a relatively higher number of functional groups in these organic samples and the ability of copper to displace other heavy metals from their sorption sites (Trakal et al 2012).…”

“…The sorption of copper seemed to be more limited, despite a relatively higher number of functional groups in these organic samples and the ability of copper to displace other heavy metals from their sorption sites (Trakal et al 2012). With this respect, copper preferential sorption to HAs rather than to FAs can be considered as the factor influencing copper sorption to humic substances, as for copper sorption the linkage of functional groups to aromatic structures is important (Schnitzer & Skinner 1967;Adriano 2001;Barančíková & Makovníková 2003). Sorption of Zn by the studied samples is several times lower when compared to Cu and Pb.…”

“…Humic substances are mixtures of different acids, they have high variability and their composition often differs according to the location or soil horizon in which they are present. At low soil pH, humic substances are bound mainly in the form of organo-mineral complexes, which present a surface with different sorption characteristics than each of these components individually (Barančíková & Makovníková 2003;Karpukhin & Bushuev 2007). Humic substances retain heavy metals mainly by pH-dependent formation of inner-sphere and/ or outer-sphere complexes and cation exchange, doi: 10.17221/144/2014-SWR but the form and extent of binding is different for each metal (Christl et al 2001;Barančíková & Makovníková 2003;Gondar et al 2006).…”