Effects of various competing ligands on the kinetics of trace metal complexes of Laurentian Fulvic Acid in model solutions and natural waters

Assessment of the treatment efficiency of an urban stormwater pond and its impact on the natural downstream watercourse

During the last few decades, stormwater ponds have become an alternative management practice in order to avoid flooding and to contain rainwater and runoff in urban areas where impervious land cover has increased. A second purpose of stormwater ponds is to improve the quality of runoff water that is usually contaminated with nitrogen, phosphorus, metals and organic micropollutants. Processes used are based on natural methods such as settlement and contribute to minimize the impact of these inputs to the natural aquatic system. This study aims to better understand the behavior of a wet stormwater pond, Heron Lake (33 ha) located in the city of Villeneuve d'Ascq in northern France through various indicators [trace metals, PAHs, PCBs, caffeine (CAF), carbamazepine (CBZ), nutrients and pathogens]. For that purpose, water quality was monitored for 1 year, mainly at the entrance and at the outlet of the lake. Sampling have also been done in the downstream aquatic environment, the Marque River. Sediments were sampled in the lake to evaluate the pollution trapped during sedimentation. Our results of both water and sediment sampling highlight: (i) the wastewater input into the Heron Lake is estimated to be equivalent to that of roughly 3800 inhabitants; (ii) the removal rates observed at the outlet, relative to concentrations at the entrance channel, vary as follows for these dissolved species: 24% for NO₃^- and PO₄^3-, 28% for CBZ, 35% for Cu, 63% for Pb, 78% for CAF, 84% for Zn and up to 93% for NH₄⁺; (iii) there are high levels of sediment contamination with metals, PAHs and PCBs at the entrance channel; (iv) the eutrophication of this pond is attributed to persistent high nutrient concentrations in both water and sediment, and has contributed to the development of an invasive macrophyte, the Elodea nuttallii; and (v) there appears to be only a negligible impact of the discharge from the lake to the natural watercourse, contributing annual loads of <2 up to 6% of the total amount of Cu, Pb, Zn, CAF, CBZ and nutrients measured in the Marque River, and having a slight diluting effect on concentrations in the Marque River.

Kinetics of Heavy Metal Dissociation from Natural Organic Matter: Roles of the Carboxylic and Phenolic Sites

We developed a unifying model for the kinetics of heavy metal dissociation from natural organic matter (NOM) in this study. The kinetics model, integrated with the equilibrium model WHAM 7, specifically considered metal ion reactions with various NOM sites formed by the carboxylic and phenolic sites. The association and dissociation rate coefficients for metal reactions with various NOM sites were constrained by WHAM predicted equilibrium distribution coefficients at specific reaction conditions. We developed the relationship for the dissociation rate coefficients among different binding sites for each metal, which was internally constrained by the metal binding constants. The model had only one fitting parameter, the dissociation rate coefficient for the metal complexes formed with two weak carboxylic sites, and all other parameters were derived from WHAM 7. The kinetic data for metal dissociation from NOM were collected from the literature, and the model was able to reproduce most of relevant data analyzed. The bidentate complexes appeared to be the predominated species controlling metal dissociation under most environmental conditions. The model can help to predict the reactivity and bioavailability of heavy metals under the impact of multiple competing ligands including NOM.

Kinetic studies of Ni organic complexes using diffusive gradients in thin films (DGT) with double binding layers and a dynamic numerical model

In situ deployments of diffusive gradients in thin films (DGT) can provide direct information on complex dissociation rates in natural waters. Recent advances in understanding the dynamics of the interactions of metal complexes within DGT devices have highlighted the characteristics of the binding layer, but there are few data to complement these theoretical developments. In this work the penetration into the Chelex binding layer of complexes of Ni with nitrilotriacetic (NTA) and Suwannee River fulvic and humic acids (FA and HA) in solution at pH 7 was investigated by deployment of DGT devices with two sequential binding layers, a "front" and a "back" layer. In Ni-NTA experiments, the masses of Ni bound by the front and back binding layers were similar, as predicted for slowly dissociating complexes. For Ni-FA/HA solutions, a higher mass of Ni was taken up by the front binding layer, consistent with fast dissociation from a high proportion of the binding sites. The ratio of Ni in the front to back binding layers was significantly lower (p < 0.05) for solutions of Ni-HA compared to those of Ni-FA, indicating that Ni-HA complexes are less labile than Ni-FA complexes in similar solutions (FA = 10 mg L(-1) and HA = 8 mg L(-1)). A dynamic numerical model of the complexes in a DGT system was used to estimate the dissociation rate constants that provided the best agreement with the experimental data. Values obtained of 2 ± 0.5 × 10(-4) s(-1) for Ni-NTA and 2.5 × 10(-3) s(-1) for Ni-FA when FA = 20 mg L(-1) and 3.42 × 10(-4) s(-1) for Ni-HA when HA = 8 mg L(-1), could be rationalized with current knowledge of the dynamics of these systems. This approach can improve kinetic information obtainable using DGT and widen the range of considered complex labilities.

Evaluation of copper speciation in model solutions of humic acid by mini-columns packed with Chelex-100 and new chelating agents: application to speciation of selected heavy metals in environmental water samples

A solid-phase extraction procedure using mini-columns packed with Chelex-100 and two new chelating agents based on poly(vinyl chloride) functionalized with 3-ferrocenyl-3-hydroxydithioacrylic acid and N,N'-[1,1'-dithiobis(ethylene)]-bis(salicylideneimine) (H(2)sales) loaded on microcrystalline naphthalene, is reported. The columns were used to separate labile copper fractions in model solutions and in real samples with subsequent determination using electrothermal atomic absorption spectrometry (ETAAS). Various model solutions containing 20 microg L(-1) of Cu(2+) and 0.0, 0.2, 2.0 and 20.0 mg L(-1) of humic acid, respectively, and buffered to pH 6.0, 7.0 and 8.0 were considered. Results showed a decrease in labile copper fraction with increase in humic acid concentration. Application of the procedure to speciation of Cu, Ni, Zn and Pb in various environmental water samples yielded labile fractions in the range of 1.67-55.75% against a total dissolved fraction of 44.08-69.77%. Comparison of the three chelating agents showed that H(2)sales had a weaker metal chelating strength than Chelex-100, but PVC-FSSH had comparable chelating strength to Chelex-100.