Interaction of arsenic species with tropical river aquatic humic substances enriched with aluminum and iron

Abstract

The mobility and bioavailability of arsenic (As) are strongly controlled by adsorption/precipitation processes involving metal oxides. However, the organic matter present in the environment, in combination with these oxides, can also play an important role in the cycle of arsenic. This work concerns the interaction between As and two samples of aquatic humic substances (AHS) from tropical rivers. The AHS were extracted as proposed by IHSS, and were characterized by (13)C NMR. The experiments were conducted with the AHS in natura and enriched with metal cations, with different concentrations of As, and complexation capacity was evaluated at three different pH levels (5.0, 7.0, and 9.0). The AHS samples showed similar chemical compositions. The results suggested that there was no interaction between As(III) and AHS in natura or enriched with Al. Low concentrations of As(V) were bound to AHS in natura. For As(III), the complexation capacity of the AHS enriched with Fe was approximately 48 μmol per g of C, while the values for As(V) were in the range 69-80 μmol per grams of C. Fluorescence spectra showed that changes in Eh affected the complexation reactions of As(V) species with AHS.

Toxicity assessment of arsenic and cobalt in the presence of aquatic humic substances of different molecular sizes

“…Gontijo et al (2016) studied the bioavailability of arsenic in Brazilian rivers, showing that a considerable part of As was inserted in the labile fraction, and can therefore be attributed to its bioavailability. In the same way, studies proposed by Oliveira et al (2015) reported no interaction between HS and As (III) in natura or enriched with aluminum, taking into account NOM environmental relevant. Jones and Huang (2003) showed an apparent non-linear toxicity response for organic pesticides composed of arsenic after interacting with humic substances at varying concentrations, suggesting a complex relationship where several mechanisms for toxicity reduction may be operative.…”

“…Heavy metals were predominantly bound to highmolecular-mass colloids bigger than 10 kDa (Burba et al, 1998). Oliveira et al (2015) states that environmental anionic or neutral species and more than one mechanisms can contribute to formation of As(III)-AHS complexes. The same authors, after studying AHS enriched with Fe and Al by fluorescence spectra, observed changes in structures of fulvic and humic acids.…”

Dissolved arsenic in the upper Paraguay River basin and Pantanal wetlands

“…7), which results in repulsion forces between As and negatively charged AHS at high pH. However, the presence of dissolved Fe and Al, as mentioned in Barbiero et al (2016), leads to the formation of ternary complexes (As-Fe/Al-AHS) (Oliveira et al, 2016). This behavior could be at the origin of the results of the ANCOVA, emphasizing that the evaporation, but also the DOC content and the origin of the samples coming from the organic horizons have a significant influence on dissolved As (Table 3) (Ghosh et al, 2015;Mariot et al, 2007) .…”

Zinc Binding to Fulvic acids: Assessing the Impact of pH, Metal Concentrations and Chemical Properties of Fulvic Acids on the Mechanism and Stability of Formed Soluble Complexes

“…The exemplary excitation-emission matrices (EEM) of FAs at different pH are shown in Figure 1. The maxima of fluorescence intensities (FI) for the A-peak were located at ex/em: ~320 nm/~440 nm and were attributed to the humic substances of higher molecular weight [41] and Vis fulvic-like systems [42]. Fluorescent regions, located at longer excitation wavelengths, can be also related to the greater number of conjugated aromatic π-electron structures with electron withdrawing functional groups such as C=O [43,44].…”

“…Fluorescent regions, located at longer excitation wavelengths, can be also related to the greater number of conjugated aromatic π-electron structures with electron withdrawing functional groups such as C=O [43,44]. The maximum of the A-peak was slightly shifted (5-10 nm) toward the The maxima of fluorescence intensities (FI) for the A-peak were located at ex/em:~320 nm/~440 nm and were attributed to the humic substances of higher molecular weight [41] and Vis fulvic-like systems [42]. Fluorescent regions, located at longer excitation wavelengths, can be also related to the greater number of conjugated aromatic π-electron structures with electron withdrawing functional groups such as C=O [43,44].…”