Effect Of Organic Complexation Research Articles

Geochemical behaviour of dissolved trace elements in a monsoon-dominated tropical river basin, Southwestern India

The study presents a 3-year time series data on dissolved trace elements and rare earth elements (REEs) in a monsoon-dominated river basin, the Nethravati River in tropical Southwestern India. The river basin lies on the metamorphic transition boundary which separates the Peninsular Gneiss and Southern Granulitic province belonging to Archean and Tertiary-Quaternary period (Western Dharwar Craton). The basin lithology is mainly composed of granite gneiss, charnockite and metasediment. This study highlights the importance of time series data for better estimation of metal fluxes and to understand the geochemical behaviour of metals in a river basin. The dissolved trace elements show seasonality in the river water metal concentrations forming two distinct groups of metals. First group is composed of heavy metals and minor elements that show higher concentrations during dry season and lesser concentrations during the monsoon season. Second group is composed of metals belonging to lanthanides and actinides with higher concentration in the monsoon and lower concentrations during the dry season. Although the metal concentration of both the groups appears to be controlled by the discharge, there are important biogeochemical processes affecting their concentration. This includes redox reactions (for Fe, Mn, As, Mo, Ba and Ce) and pH-mediated adsorption/desorption reactions (for Ni, Co, Cr, Cu and REEs). The abundance of Fe and Mn oxyhydroxides as a result of redox processes could be driving the geochemical redistribution of metals in the river water. There is a Ce anomaly (Ce/Ce*) at different time periods, both negative and positive, in case of dissolved phase, whereas there is positive anomaly in the particulate and bed sediments. The Ce anomaly correlates with the variations in the dissolved oxygen indicating the redistribution of Ce between particulate and dissolved phase under acidic to neutral pH and lower concentrations of dissolved organic carbon. Unlike other tropical and major world rivers, the effect of organic complexation on metal variability is negligible in the Nethravati River water.

Effect of atmospheric organic complexation on iron-bearing dust solubility

Abstract. Recent studies reported that the effect of organic complexation may be a potentially important process to be considered by models estimating atmospheric iron flux to the ocean. In this study, we investigated this process effect by a series of dissolution experiments on iron-bearing dust in the presence or the absence of various organic compounds (acetate, formate, oxalate, malonate, succinate, glutarate, glycolate, lactate, tartrate and humic acid as an analogue of humic like substances, HULIS) typically found in atmospheric waters. Only 4 of tested organic ligands (oxalate, malonate, tartrate and humic acid) caused an enhancement of iron solubility which was associated with an increase of dissolved Fe(II) concentrations. For all of these organic ligands, a positive linear dependence of iron solubility to organic concentrations was observed and showed that the extent of organic complexation on iron solubility decreased in the following order: oxalate >malonate = tartrate > humic acid. This was attributed to the ability of electron donors of organic ligands and implies a reductive ligand-promoted dissolution. This study confirms that among the known atmospheric organic binding ligands of Fe, oxalate is the most effective ligand promoting dust iron solubility and showed, for the first time, the potential effect of HULIS on iron dissolution under atmospheric conditions.

Effect of organic complexation on the toxicity of Cu to the earthworm Eisenia fetida

The relationship between Cu speciation in solution and mortality and tissue Cu concentrations in Eisenia fetida was investigated. E. fetida were exposed to solutions containing 0.009, 0.049 and 0.125 mg Cu L −1and 0, 0.15, 0.35 and 50 mg EDTA L −1. Mortalities of 100, 60, 50 and 25% were recorded in the 0.125 mg Cu L −1 solutions containing 0, 0.15, 0.35 and 50 mg EDTA L −1, respectively. Similarly tissue body burden decreased with increasing EDTA concentration. Complexation capacity of the solution increased with EDTA concentration. In the 0.125 mg Cu L −1 solution labile Cu concentration decreased with increasing EDTA concentration. These trends are attributed to complexation of free Cu ions with EDTA molecules, and the non-bioavailable nature of the resultant Cu–EDTA complex.

Effect of organic complexation on the behaviour of dissolved Cd, Cu and Zn in the Scheldt estuary

Samples from the Scheldt estuary have been assayed for dissolved Cd, Cuand Zn using differential pulse anodic stripping voltammetry, either astotal (after UV irradiation) or labile concentrations. Under theseexperimental conditions, labile concentrations ranged between51–65% of total Cu, 16–66% of total Zn and53–91% of total Cd. The metal–organic interactions wereassessed by evaluating (a) the distribution coefficient Kd forthe distribution of the metals between the liquid phase (complexation) andtheir binding to particulate matter, and (b) the competitive effect exertedby inorganic complexing ligands using a multi–element interactionmodel. The proportion of organically bound metals (strong and labile) wasestimated, in this speciation scheme, to range from 86 to 99% for Cu,from 90 to 96% for Zn, and from 10 to 35% for Cd. From thedissolved organic carbon distribution in the Scheldt (≤ 10 mg Cl-1 and taking into account competition from major cations Caand Mg, free ligand concentrations available for heavy metal complexationwere estimated to be ≤ 0.15 mg C l-1. With these values,conditional stability constants for the chelation of Cu, Zn and Cd werecalculated assuming either a single-step or a two-step complexation in thedissolved phase. Given the assumptions made in these models, stabilityconstants in the range of 107.8–1010.6 forCu, 107.0–109.1 for Zn and106.9–108.9 for Cd were obtained. Therelevance of these data to previous in vitro and in situ studies isdiscussed taking into consideration current concepts of metal bindingaffinity for organic ligands.

Effect of complexation by organic ligands on the bioavailability of copper to the brine shrimp, Artemia sp.

The effect of organic complexation on the bioavailability of copper to the brine shrimp, Artemia, was studied. Attention was focused on the interrelations between copper accumulation, metal-complex lipid solubility and aqueous metal speciation. The lipid solubility of copper added to the sea water was determined by partitioning between sea water and olive oil. A computer model was used to calculate the sea-water equilibrium speciation. Uptake of copper by the brine shrimp was proportional to time with no evidence of saturation over the experimental period. EDTA and citrate decreased the copper accumulation rate, while acetate did not affect the uptake process. Lipid solubility and accumulation data were in good agreement with the copper speciation model. It is suggested that, next to carrier mediated absorption of ionic copper, the metal may be taken up by passive diffusion of lipid soluble inorganic metal complexes across the body barriers.