Nanoparticle stability in lake water shaped by natural organic matter properties and presence of particulate matter

Predicting nanoparticle (NP) fate in the environment continues to remain a challenge, especially for natural surface water systems, where NPs can hetero-aggregate with natural organic and mineral suspended matter. Here we present the interactions and aggregation behavior of TiO₂ NPs with natural organic matter (NOM) in a natural lake water. NP fate in a synthetic water of the same pH and ionic composition was also tested in the presence and absence of NOM analogs to gain insight into the different stabilizing effects of each NOM type. Several complementary analytical techniques were utilized to assess lake NOM composition, including pyrolysis-gas chromatography-mass spectrometry, gel permeation chromatography, the polarity rapid-assessment method, and Nanoparticle Tracking Analysis. In the natural lake water, the TiO₂ NPs preferentially interacted with mostly anionic NOM of high and medium molecular weight (~1200-1450 and 400-520 Da). Specifically, strong interactions with proteins and polyhydroxy aromatics were observed. NP fate and stability were determined in both raw lake water containing mineral particulate matter and total NOM (NOM_tot) and filtered lake water containing only NOM <0.8 μm (NOM_<0.8), with different aggregation profiles observed over time. Additionally, three times the number of TiO₂ NPs remained in suspension when only NOM_<0.8 was present compared to the unfiltered water containing mineral particulate matter and NOM_tot. These results demonstrate the contrasting NP fates in the aquatic environment according to the presence of NOM_tot vs. NOM_<0.8 and further suggest that the use of pure NOM analogs may not accurately represent NP interactions and fate in the natural system.

Environmental exposure to TiO2 nanomaterials incorporated in building material

Nanomaterials are increasingly being used to improve the properties and functions of common building materials. A new type of self-cleaning cement incorporating TiO₂ nanomaterials (TiO₂-NMs) with photocatalytic properties is now marketed. This promising cement might provide air pollution-reducing properties but its environmental impact must be validated. During cement use and aging, an altered surface layer is formed that exhibits increased porosity. The surface layer thickness alteration and porosity increase with the cement degradation rate. The hardened cement paste leaching behavior has been fully documented, but the fate of incorporated TiO₂-NMs and their state during/after potential release is currently unknown. In this study, photocatalytic cement pastes with increasing initial porosity were leached at a lab-scale to produce a range of degradation rates concerning the altered layer porosity and thickness. No dissolved Ti was released during leaching, only particulate TiO₂-NM release was detected. The extent of release from this batch test simulating accelerated worst-case scenario was limited and ranged from 18.7 ± 2.1 to 33.5 ± 5.1 mg of Ti/m² of cement after 168 h of leaching. TiO₂-NMs released into neutral aquatic media (simulate pH of surface water) were not associated or coated by cement minerals. The TiO₂-NM release mechanism is suspected to start from freeing of TiO₂-NMs in the altered layer pore network due to partial cement paste dissolution followed by diffusion into the bulk pore solution to the surface. The extent of TiO₂-NM release was not solely related to the cement degradation rate.

Effect of silicon on reducing cadmium toxicity in durum wheat (Triticum turgidum L. cv. Claudio W.) grown in a soil with aged contamination

Agricultural soil contamination and subsequently crops still require alternative solutions to reduce associated environmental risks. The effects of silica application on alleviating cadmium (Cd) phytotoxicity in wheat plants were investigated in a 71-day pot experiment conducted with a historically contaminated agricultural soil. We used amorphous silica (ASi) that had been extracted from a diatomite mine for Si distribution at 0, 1, 10 and 15 ton ASi ha(-1). ASi applications increased plant biomass and plant Si concentrations, reduced the available Cd in the soil and the Cd translocation to shoots, while Cd was more efficiently sequestrated in roots. But ASi is limiting for Si uptake by plants. We conclude that significant plant-available Si in soil contributes to decreased Cd concentrations in wheat shoots and could be implemented in a general scheme aiming at controlling Cd concentrations in wheat.

TiO₂-based nanoparticles released in water from commercialized sunscreens in a life-cycle perspective: structures and quantities

This work investigates the physical-chemical evolution during artificial aging in water of four commercialized sunscreens containing TiO₂-based nanocomposites. Sunscreens were analyzed in terms of mineralogy and TiO₂ concentration. The residues formed after aging were characterized in size, shape, chemistry and surface properties. The results showed that a significant fraction of nano-TiO₂ residues was released from all sunscreens, despite their heterogeneous behaviors. A stable dispersion of submicronic aggregates of nanoparticles was generated, representing up to 38 w/w% of the amount of sunscreen, and containing up to 30% of the total nano-TiO₂ initially present in the creams. The stability of the dispersion was tested as a function of salt concentration, revealing that in seawater conditions, a major part of these nano-TiO₂ residues will aggregate and sediment. These results were put in perspective with consumption and life cycle of sunscreens to estimate the amount of nano-TiO₂ potentially released into AQUATIC environment.

Copper(II) interaction with 3,5-diisopropylsalicylic acid (Dips): New insights on its role as a potential OH inactivating ligand

The purpose of this study was to identify the low molecular mass complexes formed between copper(II) and 3,5-diisopropylsalicylic acid (Dips) in physiological conditions. Copper(II)-Dips complex equilibria were determined using glass electrode potentiometry and their solution structures checked by UV-visible (UV-vis) spectrophotometry. Because of the low solubility of Dips in water, the equilibria were investigated in different water/ethanol mixtures. Formation constants were extrapolated to 100% water and then compared with the values obtained for the other anti-inflammatory drugs previously studied. Given the prime role of histidine as the copper(II) ligand in blood plasma, copper(II)-histidine-Dips ternary equilibria were studied under similar experimental conditions. Computer simulations of copper(II) distribution relative to different biofluids, gastrointestinal (g.i.) fluid and blood plasma, show that like salicylic and anthranilic acids, Dips favors g.i. copper absorption, but cannot exert any significant influence on plasma copper distribution. Moreover, Dips can mobilize increasing fractions of copper(II) as the pH decreases. In conclusion, Dips seems to correspond to the notion of *OH-inactivating ligand (OIL) as determined for anthranilic acid.

Site-directed mutagenesis and molecular modelling studies show the role of Asp82 and cysteines in rat acylase 1, a member of the M20 family

Acylase 1 from rat kidney catalyzes the hydrolysis of acyl-amino acids. Sequence alignment has shown that this enzyme belongs to the metalloprotein family M20. Site-directed mutagenesis experiments led to the identification of one functionally important amino acid residue located near one of the zinc coordinating residues, which play a critical role in the enzymatic activity. The D82N- and D82E-substituted forms showed no significant activity and very low activity, respectively, along with a loss of zinc coordination. Molecular modelling investigations indicated a putative role of D82 in ensuring a proper protonation of catalytic histidine. In addition, none of the five cysteine residues present in the rat kidney acylase 1 sequence seemed involved in the catalytic process: the loss of activity induced by the C294A substitution was probably due to a conformational change in the 3D structure.

Copper(II) interactions with nonsteroidal antiinflammatory agents. II. Anthranilic acid as a potential. OH-inactivating ligand

It has long been established that copper complexes of inactive substances exert antiinflammatory activity and that copper complexes of nonsteroidal antiinflammatory drugs (NSAIDs) are more active than these drugs by themselves. Based on these observations, it was proposed that copper complexes of NAIDs are their active metabolites. This hypothesis was not confirmed for salicylic acid, however, as computer-aided speciation studies have shown that no copper-salicylate complex can reach significant levels in blood plasma. In view of this result, it was of interest to test with the same technique the influence on copper metabolism of an inactive substance known to be activated by copper. Anthranilic acid was chosen for this test in the present work. First, copper(II)-anthranilate interactions have been investigated by glass electrode potentiometry under physiological conditions. Given the key role of histidine as copper(II) ligand in blood plasma, copper(II)-histidine-anthranilate ternary equilibra have also been determined. Computer simulations of copper distribution have then been run relative to the two main biofluids in respect of global metabolism, i.e., gastrointestinal (g.i.) fluid and blood plasma. Like salicylic acid, anthranilic acid is expected to favor copper g.i. absorption, but cannot either exert any significant influence on plasma copper distribution. Clearly, the fact that anthranilate becomes antiinflammatory when administered with copper cannot originate in any effect of anthranilate on copper global metabolism. Speciation investigations have then been extended to the synovial fluid. Whereas salicylate does not appear to be a better ligand of copper in this medium than in blood plasma at any pH between 7.4 and 5.5, anthranilate on the contrary can mobilize increasing fractions of copper as the pH decreases, i.e., the more inflammation, the more copper is bound to anthranilate. This is in line with the recent observation that salicylate inactivates copper-induced .OH radicals through its bulk scavenging properties whereas .OH inactivation by anthranilate under the same conditions is a direct function of the copper-anthranilate binding. Anthranilate thus seems to correspond to the recently defined notion of .OH-inactivating ligand (OIL). More generally, these results provide a beginning of rationale for the antiinflammatory properties of copper complexes with substances that are active or inactive against inflammation by themselves. The extra antiinflammatory activity induced by copper on NSAIDs appears to be independent of any Cu(II)-NSAID association in vivo. On the contrary, the binding of inactive substances with copper(II) at inflammatory sites seems to be essential to their activation by copper.