Iron humic substances

Biogeochemical interactions among the arsenic, iron, humic substances, and bacterial activities in mud volcanoes in southern Taiwan. Journal of Environmental Sciences Health A, 46 (11), 1218-1230. 

Figure 1 Proposed role of humic substances on iron nutrition of plants possessing dif fereni strategies for iron acquisition. WEHS, water-extractable humic substances, as described in the text.

J. Gerke, Aluminium and iron (III) species in the soil solution including organic complexes with citrate and humic substances. Z. Pflanzenemarhr. Bodenk. 160 421 (1997). 

S. Cesco, V. Rdmheld, Z. Varanini, and R. Pinton, Solubilization of iron by a water extractable humic substances fraction. J. Plant Nutr. Soil Sci. 763 285 (2000). 

R. Pinton, S. Cesco, M. De Nobili, S. Santi, and Z. Varanini, Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-dettcient cucumber plants. Biol. Fert. Soils 26 23 (1998). 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

R. (2000) Solubilization of iron by water-extractable humic substances. J. Plant Nutr. SoilSd. 163 285-290 Chabaux, F. Cohen, A.S. O Nions, R.K. ... 

Tipping, E., The adsorption of aquatic humic substances by iron oxides , Geochim. Cosmochim Acta, 45,191-199 (1981). 

Chemical Formation. A potential chemically mediated source of H202 would be the presence of reduced metals in oxygenated waters (15, 21, 32-34, 36-38). This pathway has never been demonstrated in fresh waters, although Miles and Brezonik (35) showed that 02 concentrations varied over 24 h in humic waters with iron present. No measurements of H202 were made, but most likely H202 was formed as the 02 was consumed. The net impact of these processes on H202 concentration in fresh waters is not likely to be important in waters rich in humic substances. However, this assumption has not been verified experimentally. 

Cano-Aguilera, I., Haque, N., Morrison, G.M. et al. (2005) Use of hydride generation-atomic absorption spectrometry to determine the effects of hard ions, iron salts and humic substances on arsenic sorption to sorghum biomass. Microchemical Journal, 81(1), 57-60. 

Tipping (1981) showed that the adsorption of terrestrial humic substances could reverse the positive electrophoretic mobility of iron oxides. Thus, both terrestrial and marine organics are strong adsorbates, able to reverse zeta potential. 

Jones, R. I., P. J. Shaw, and H. De Haan. 1993. Effects of dissolved humic substances on the speciation of iron and phosphate at different pH and ionic strength. Environmental Science Technology 27 1052-1059. 

Shaw, P. J. 1994. The effect of pH, dissolved humic substances, and ionic composition on the transfer of iron and phosphate to particulate size fractions in epilimnetic lake water. Limnology and Oceanography 39 1734—1743. 

Voelker, B. M., F. M. M. Morel, and B. Sulzberger. 1997. Iron redox cycling in surface waters Effects of humic substances and light. Environmental Science Technology 31 1004-1011. 

---