The photocatalytic reduction of NO3- to N2 with ilmenite (FeTiO3): Effects of groundwater matrix.

This work analyzes the role of natural groundwater, as well as the effect of HCO3-, Ca2+, Mg2+, K+, SO42- and Cl- concentrations, upon the photocatalytic nitrate reduction using ilmenite as catalyst and oxalic acid as hole scavenger. The nitrate removal and the selectivity towards N2 are significantly limited compared to previous experiments using ultrapure water matrix. Calcium (Ca2+), bicarbonate (HCO3-) as well as pH are claimed as the major controlling factors related to the process yield. Thus, Ca2+ promotes the formation of insoluble oxalate microcrystals, reducing the amount of hole scavenger available. The presence of HCO3- leads to a steeply increase in the pH value, favoring the adsorption onto the ilmenite surface of ions OH-instead of NO3-, NO2- and C2O42. The aforementioned issues are overcome by working with C2O42-/NO3- ratio well above the stoichiometric one, that also maintains the pH value in an acid range. A completed depletion of the starting NO3-, the no detection of either NO2- or NH4+ in the aqueous phase, and a selectivity towards N2 above 95% were achieved using two times the stoichiometric dose.

Cephalosporin antibiotics in the aquatic environment: A critical review of occurrence, fate, ecotoxicity and removal technologies.

Due to their widespread occurrence in the aquatic environment, human and veterinary cephalosporin antibiotics have been studied as water pollutants. In order to characterize environmental risks of this compound class, this review evaluates relevant data about physicochemical properties, occurrence, ecotoxicity and degradation of cephalosporins. Although application of cephalosporins is rather low compared to other antibiotics and their environmental life-time is believed to be short (i.e. days), the available data is insufficient to draw conclusions on their environmental relevance. Few studies concerning the fate of cephalosporins in soil are available, while hydrolysis and photo-degradation are suggested as the main attenuation processes in the aquatic environment. Cephalosporins have been detected in different aqueous matrices in concentrations ranging from 0.30 ng L-1 to 0.03 mg L-1, with sewage and wastewater being the main matrices with positive findings. For wastewater treatment purposes, several technologies have been tested for the abatement of cephalosporins, including photolysis and adsorption. In most cases, the technology employed led to complete or significant removal (>95%) of parental drugs but few authors reported on cephalosporins' metabolites and transformation products. Furthermore, the present ecotoxicological data are insufficient for comprehensive ecological risk quotient calculations. Considering the total of 53 cephalosporins, effective values (EC, LC, NOAEC, NOAEL, etc.) are only available for around 30% of parental drugs and are very scarce for cyanobacteria, which is considered to be the most sensitive group of organisms to antibiotics. Furthermore, it has been demonstrated that cephalosporins' transformation products can be more toxic and more persistent than the parental drugs. Few investigations considering this possibility are available. Consequently, more effort on ecotoxicological data generation and verification of biological inactivation of cephalosporins-related products is needed. Likewise, the lack of natural depletion rates and knowledge gaps on mixture effects for cephalosporins' degradation and toxicity have to be overcome.

Ecotoxicity of the two veterinarian antibiotics ceftiofur and cefapirin before and after photo-transformation.

The release of antibiotics into the environment may lead to deleterious effects in non-target organisms as well as pressure in antimicrobial resistance acquirement. Ceftiofur (CEF) and cefapirin (CEPA) are veterinary cephalosporins used for recurrent and economically relevant infections. Both antibiotics have been detected in aquatic environments and their fate during drinking water processing is still unknown. This work investigated the acute and chronic toxicities of CEF and CEPA towards aquatic organisms including stability tests. Complementary, the effects of water disinfection radiation (UV-C, 254nm) on ecotoxicological responses were studied. CEF and CEPA have significant decay during Daphnia magna tests, portraying half-lives (t1/2) of 49 and 53h, respectively. During tests with green algae (Scenedesmus spec.), CEPA was more instable (t1/2 88h) than CEF (t1/2 267h). CEF and its presumable hydrolysis products induced deleterious effects in Daphnia magna (48h EC50 139, LC50 179 in µM), which was not observed with Scenedesmus spec. (72h NOAEC 82.5±2.5µM). In the case of CEPA, no toxic effects were observed in either test (48h EC-LC50>510 and 72h NOAEC 57±6, in µM). Photolysis of CEPA resulted in toxic products, which were effective for the cladoceran but not for the green algae. On the other hand, the different radiation doses studied did not affect CEF ecotoxicity. This investigation illustrates the importance of cephalosporin hydrolysis during standard toxicity tests. Furthermore, the potential formation of species-specific toxic compounds during water processing is demonstrated, highlighting the need of further assessing toxicity of both cephalosporins and their transformation products.

Base-catalyzed hydrolysis and speciation-dependent photolysis of two cephalosporin antibiotics, ceftiofur and cefapirin.

Lately, special attention has been given to veterinary cephalosporin antibiotics due to their broad activity spectrum and significant consumption. Indeed, the determination of hydrolytic and photolytic kinetics provides a better comprehension of the undesired persistence of cephalosporins in aqueous matrices. In this work, the two widely used veterinary antibiotics ceftiofur (CEF) and cefapirin (CEPA) showed high instability under alkaline conditions, degrading in few minutes at pH > 11. In buffered solutions at neutral pH and natural temperature (T = 22 ±â€¯1 °C), both drugs presented moderate stability (t½â€¯= 3 d, CEPA and 1.4 d, CEF). Our study also demonstrated that CEPA and CEF speciation did not significantly influence the direct photolysis rates. Using a simulated water disinfection set-up (λ = 254 nm), all ionic species of CEF and CEPA presented fast and similar pseudo-first order degradation rates, kapp 0.0095 ±â€¯0.0004 and 0.0092 ±â€¯0.001 cm2 mJ-1, respectively. Furthermore, using surface water in hydrolysis experiments, CEF demonstrated significant matrix-dependent stability with a half-life (t½â€¯= 14.7 d) tenfold higher than in buffered solutions. In contrast, CEPA presented a very similar hydrolysis rate in river water (t½â€¯= 4.2 d) and a subtle faster photo-degradation rate in this same matrix (kapp 0.0128 ±â€¯0.001 cm2 mJ-1), highlighting the importance of disinfection radiation for cephalosporin depletion in aqueous environments.

Determination of acid dissociation constants (pKa) of cephalosporin antibiotics: Computational and experimental approaches.

Cefapirin (CEPA) and ceftiofur (CEF) are two examples of widely used veterinarian cephalosporins presenting multiple ionization centers. However, the acid dissociation constants (pKa) of CEF are missing and experimental data about CEPA are rare. The same is true for many cephalosporins, where available data are either incomplete or even wrong. Environmentally relevant biotic and abiotic processes depend primordially on the antibiotic pH-dependent speciation. Consequently, this physicochemical parameter should be reliable, including the correct ionization center identification. In this direction, two experimental techniques, potentiometry and spectrophotometry, along with two well-known pKa predictors, Marvin and ACD/Percepta, were used to study the macro dissociation constants of CEPA and CEF. Additionally, the experimental dissociation constants of 14 cephalosporins available in the literature were revised, compiled and compared with data obtained in silico. Only one value was determined experimentally for CEF (2.68 ± 0.05), which was associated to the carboxylic acid group deprotonation. For CEPA two values were obtained experimentally: 2.74 ± 0.01 for the carboxylic acid deprotonation and 5.13 ± 0.01 for the pyridinium ring deprotonation. In general, experimentally obtained values agree with the in silico predicted data (ACD/Percepta RMSE: 0.552 and Marvin RMSE: 0.706, n = 88). However, for cephalosporins having imine and aminothiazole groups structurally close, Marvin presented problems in pKa predictions. For the biological and environmental fate and effect discussion, it is important to recognize that CEPA and CEF, as well as many other cephalosporins, are present as anionic species in the biologic and environmentally relevant pH values of 6-7.5.