Green Remediation of Veterinary Antibiotics in Soil-Water Systems

Veterinary antibiotics (VAs) are considered emerging contaminants of concern. Considerable efforts have been made to understand the fate and transport of VAs in soil and water environment and very few have attempted to develop novel remediation strategies to overcome the problem of antibiotic resistance and potential toxicity to aquatic species. To our knowledge, the present study is a pioneer study in which it attempts to develop a low-cost, “green” remediation technique utilizing a waste byproduct of the drinking water treatment industry, namely, the Al-based water treatment residuals (Al-WTR), as a sorbent to stabilize tetracycline (TTC) and oxytetracycline (OTC) in aqueous medium, manure piles and manure-treated soil. The ultimate goal of the study was to evaluate the effectiveness of Al-WTR in treating manure, soils, and manure-amended soils to immobilize tetracyclines (TCs) to lower risk associated with TCs in environment. We conducted: i) laboratory batch sorption study followed by modeling and surface spectroscopic characterization to understand the extent and mechanism of TTC/OTC retention by Al-WTR, ii) short-term incubation study to evaluate the effectiveness of Al-WTR in immobilizing and stabilizing TTC and OTC in manure, soils, and manure-amended soils under static conditions, and iii) long -term greenhouse column study to evaluate the effectiveness of Al-WTR in immobilizing and stabilizing TTC and OTC in soils and manure amended soils under dynamic conditions in a controlled environment. Results from the batch sorption study showed that Al-WTR has high sorption capacity for TTC and OTC as a function of solution properties. This, along with the rapid sorption kinetics and low release potential make them excellent sorbents for TCs removal from aqueous medium. Results from modeling and spectroscopic studies suggest that TTC and OTC are adsorbed on Al-WTR surface via strong inner-sphere mechanism, indicating permanent retention. Short term incubation and long term greenhouse column studies showed immobilization of TTC and OTC in Al-WTR amended soils and manure amended soils. LC/MS/MS analysis did not reveal any known detectable degradates or metabolites of TCs other than very low concentration of daughter compounds. Greenhouse column studies also showed that Al-WTR application significantly reduces plant available and water soluble TCs from soils and manureamended soils. Overall, this research demonstrated the potential of Al-WTR to develop into an effective, low-cost, green remediation technology for TC-contaminated soil-water systems

Evidence for Exocellular Arsenic in Fronds of Pteris vittata

The arsenic (As) hyperaccumulating fern species Pteris vittata (PV) is capable of accumulating large quantities of As in its aboveground tissues. Transformation to AsIII and vacuolar sequestration is believed to be the As detoxification mechanism in PV. Here we present evidence for a preponderance of exocellular As in fronds of Pteris vittata despite numerous reports of a tolerance mechanism involving intracellular compartmentalization. Results of an extraction experiment show that 43–71% of the As extruded out of the fronds of PV grown in 0.67, 3.3 and 6.7mM AsV. SEM-EDX analysis showed that As was localized largely on the lower pinna surface, with smaller amounts on the upper surface, as crystalline deposits. X-ray fluorescence imaging of pinna cross-sections revealed preferential localization of As on the pinna surface in the proximity of veins, with the majority localized near the midrib. Majority of the As in the pinnae is contained in the apoplast rather than vacuoles. Our results provide evidence that exocellular sequestration is potentially a mechanism of As detoxification in PV, particularly at higher As concentrations, raising concern about its use for phytoremediation

Effect of solution properties, competing ligands, and complexing metal on sorption of tetracyclines on Al-based drinking water treatment residuals

In the current batch study, we investigated the effect of solution properties, competing ligands (phosphate (P(V)) and sulfate), and complexing metal (calcium (Ca2+)) on tetracycline (TTC) and oxytetracycline (OTC) sorption by Al-based drinking water treatment residuals (Al-WTR). The sorption behavior for both TTC and OTC on Al-WTR was pH dependent. The sorption in absence of competing ligands and complexing metal increased with increasing pH up to circum-neutral pH and then decreased at higher pH. The presence of P(V) when added simultaneously had a significant negative effect (p \u3c 0.001) on the sorption of TTC and OTC adsorbed by Al-WTR at higher TTC/OTC:P ratios. However, when P(V) was added after the equilibration of TTC and OTC by Al-WTR, the effect was minimal and insignificant (p \u3e 0.1). The presence of sulfate had a minimal/negligible effect on the sorption of TCs by Al-WTR. A significant negative effect (p \u3c 0.001) on the adsorption of TCs by Al-WTR was observed in the pH range below 5 and at higher TCs:Ca2+ ratios, probably due to TCs-Ca2+ complex formation. Fourier transform infrared (FTIR) analysis indicated the possibility of inner-sphere-type bonding by the functional groups of OTC/TTC on Al-WTR surface. Results from the batch sorption study indicate high affinity of Al-WTR for TCs in the pH range 4–8 (majorly encountered pH in the environment) in the presence of competing ligands and complexing metal

Effectiveness of aluminum-based drinking water treatment residuals as a novel sorbent to remove tetracyclines from aqueous medium

Low levels of various veterinary antibiotics (VAs) have been found in water resources across the United States as a result of nonpointsource pollution. As the first phase of developing a potential green sorbent for tetracycline (TTC) and oxytetracycline (OTC), we examined the effects of solution chemistry, pH, ionic strength (IS), sorbate:sorbent ratio (SSR), and reaction time on TTC and OTC sorption by a waste byproduct of the drinking-water treatment process, namely, Al-based drinking-water treatment residuals (Al- WTR). The sorption of TTC and OTC on Al-WTR increased with increasing pH up to pH 7 and decreased in the pH range of 8 to 11. A concentration of 20 g L-1 was deemed as optimum SSR, where more than 95% of the initially added TTC and OTC were sorbed and equilibrium was reached in 2 h. A pseudo-second-order model (R2 = 0.99) was used for Al-WTR sorption for TTC and OTC. The data best fit the linearized form of the Freundlich isotherm (R2 = 0.98). No significant effect (p \u3e 0.05) of IS on sorption of TTC and OTC was observed between 0.05 and 0.5 mmol L-1. However, at higher initial concentrations (\u3e1 mmol L-1), IS dependence on TTC and OTC sorption was observed. Surface complexation modeling and Fourier transform infrared spectroscopy analysis indicated the possibility of TTC and OTC forming a mononuclear monodentate surface complex through strong innersphere-type bonds on Al-WTR. The results show promising potential of Al- WTR for use as a green and cost-effective sorbent to immobilize and stabilize TTC in soils and waters

Drinking Water Treatment Residual Amendment Lowers Inorganic Arsenic Bioaccessibility in Contaminated soils: A Long-Term Study

Inorganic arsenical pesticides were used widely in agriculture for a long time, leaving large tracts of farmlands and orchards contaminated with high levels of arsenic. These contaminated soils pose a significant public health risk as residential developments encroach on these lands due to urban sprawl. Several studies have documented the effectiveness of iron and aluminum hydroxides in immobilizing arsenic in contaminated soils. Solid residues left from drinking water treatment (Drinking water treatment residuals, or WTRs) have been proposed as a low-cost and effective amendment, as they contain large amounts of aluminum (Al) and iron (Fe) oxides. By conducting in vitro tests after 1 year of equilibration, our group recently documented the effectiveness of two types of WTRs (Fe- and Al-based) in significantly (p∈ \u3c ∈0.01) lowering As bioaccessibility. However, long-term studies under realistic conditions are necessary to test the ability of WTRs in reducing soil arsenic bioaccessibility. In the current study, the effect of WTRs on inorganic arsenic bioaccessibility and distribution in two soils (Immokalee and Orelia) with variable properties was evaluated over a 3-year time period in a greenhouse setup. Results show that arsenic bioaccessibility decreased significantly (p∈ \u3c ∈0.001) from 100 to ∼25 % after 3 years of equilibration, compared to the unamended controls. There was a significant (p∈ \u3c ∈0.001) decline in water-soluble arsenic with time, accompanied by an increase in Fe/Al and Ca/Mg-bound fractions, suggesting that these phases control the mobility of arsenic. The negative correlation between arsenic bioaccessibility Fe/Al- and Ca/Mg-bound fractions can be attributed to the transformation of soluble arsenic to less soluble mineral phases

Fate of arsenic in swine waste from concentrated animal feeding operations

Swine diets are often supplemented by organoarsenicals, such as 3-nitro-4-hydroxyphenylarsonic acid (roxarsone) to treat animal diseases and promote growth. Recent work reported roxarsone degradation under anaerobic conditions in poultry litter, but no such data exist for swine wastes typically stored in lagoons nearby concentrated animal feeding operations (CAFOs). The objectives of this study were to: (i) characterize a suite of swine wastes collected from 19 randomly selected CAFOs for soluble arsenate [As(V)], arsenite [As(III)], dimethylarsenic acid (DMA), monomethylarsonic acid (MMA), 3-amino-4-hydroxyphenylarsonic acid (3-HPPA), p-arsanilic acid, and roxarsone, and (ii) determine the geochemical fate of roxarsone in storage lagoons nearby CAFOs. Swine waste suspensions were spiked with roxarsone and incubated under dark/light and aerobic/anaerobic conditions to monitor roxarsone degradation kinetics. Arsenic speciation analysis using liquid chromatography and inductively coupled plasma mass spectrometry (LC-ICPMS) illustrated the prevalence of As(V) in swine waste suspensions. Roxarsone underwent degradation to either organoarsenicals (3-HPPA) or As(V) and a number of unidentified metabolites. Roxarsone degradation occurred under anaerobic conditions for suspensions low in solids content, but suspensions higher in solids content facilitated roxarsone degradation under both anaerobic and aerobic conditions. Increased solids content enhanced roxarsone degradation kinetics under aerobic conditions. According to current waste storage and sampling practices, arsenic in swine wastes stored in lagoons has been overlooked as a possible environmental health issue

Antimony sorption at gibbsite-water interface

Antimony (Sb) is extensively used in flame retardants, lead-acid batteries, solder, cable coverings, ammunition, fireworks, ceramic and porcelain glazes and semiconductors. However, the geochemical fate of antimony (Sb) remained largely unexplored. Among the different Sb species, Sb (V) is the dominant form in the soil environment in a very wide redox range. Although earlier studies have examined the fate of Sb in the presence of iron oxides such as goethite and hematite, few studies till date reported the interaction of Sb (V) with gibbsite, a common soil Al-oxide mineral. The objective of this study was to understand the sorption behavior of Sb (V) on gibbsite as a function of various solution properties such as pH, ionic strength (I), and initial Sb concentrations, and to interpret the sorption-edge data using a surface complexation model. A batch sorption study with 20gL-1 gibbsite was conducted using initial Sb concentrations range of 2.03-16.43μM, pH values between 2 and 10, and ionic strengths (I) between 0.001 and 0.1M. The results suggest that Sb (V) sorbs strongly to the gibbsite surface, possibly via inner-sphere type mechanism with the formation of a binuclear monodentate surface complex. Weak I effect was noticed in sorption-edge data or in the isotherm data at a low surface coverage. Sorption of Sb (V) on gibbsite was highest in the pH range of 2-4, and negligible at pH 10. Our results suggest that gibbsite will likely play an important role in immobilizing Sb (V) in the soil environment. © 2011

Oxytetracycline Sorption Onto Iraqi Montmorillonite

This paper assesses the use of certified Iraqi montmorillonite clay as a potential sorbent for the removal of oxytetracycline (OTC) from aqueous solutions. The clay is characterized by a cation exchange capacity of 0.756 meq g-1 and a zero point charge at pH 8.7. Aqueous solutions of OTC were equilibrated with montmorillonite under various experimental conditions, such as OTC concentration, pH and clay content, for 24 h at fixed ionic strength. Two forms of montmorillonite were evaluated: regular and iron-modified form. The effect of pH was minor on OTC adsorption. Kinetic study revealed that the sorption follows a pseudo-second-order model. Sorption isotherm showed a good fit with the Freundlich model. OTC sorption onto Fe-saturated montmorillonite was analyzed statistically using a response surface design to study the effects of experimental conditions. The introduction of iron improved the adsorption characteristics of the clay due to the ability of ferric ions to make stable complexes with OTC. The most favorable operating conditions for the treatment were deemed as follows: clay content, 6.85 g L-1, oxytetracycline concentration, 1.0 mmol L-1 and pH, 5.5 for the iron-modified form

Novel colorimetric method overcoming phosphorus interference during trace arsenic analysis in soil solution

A sensitive (method detection limit, 2.0 μg As L-1) colorimetric determination of trace As(v) and As(iii) concentrations in the presence of soluble phosphorus (P) concentrations in soil/water extracts is presented. The proposed method modifies the malachite green method (MG) originally developed for P in soil and water. Our method relies upon the finding that As(iii) and As(v) do not develop the green color during P analysis using the MG method. When an optimum concentration of ascorbic acid (AA) is added to a sample containing up to 15 times P > As (μM) concentrations, the final sample absorbance due to P will be equal to that of As(v) molecules. The soluble As concentration can then be quantified by the concentration difference between the mixed oxyanion (As + P) absorbance (proposed method) and the MG method absorbance that measures only P. Our method is miniaturized using a 96-well microplate UV-VIS reader that utilizes minute reagent and sample volumes (120 and 200 μL sample-1, respectively), thus, minimizing waste and offering flexibility in the field. Our method was tested in a suite of As-contaminated soils that successfully measured both As and P in soil water extracts and total digests. Mean% As recoveries ranged between 84 and 117%, corroborating data obtained with high-resolution inductively-coupled plasma mass-spectrometry. The performance of the proposed colorimetric As method was unaffected by the presence of Cu, Zn, Pb, Ni, Fe, Al, Si, and Cr in both neutral and highly-acidic (ca. pH 2) soil extracts. Data from this study provide the proof of concept towards creating a field-deployable, portable As kit

Novel colorimetric method overcoming phosphorus interference during trace arsenic analysis in soil solution

A sensitive (method detection limit, 2.0 μg As L-1) colorimetric determination of trace As(v) and As(iii) concentrations in the presence of soluble phosphorus (P) concentrations in soil/water extracts is presented. The proposed method modifies the malachite green method (MG) originally developed for P in soil and water. Our method relies upon the finding that As(iii) and As(v) do not develop the green color during P analysis using the MG method. When an optimum concentration of ascorbic acid (AA) is added to a sample containing up to 15 times P > As (μM) concentrations, the final sample absorbance due to P will be equal to that of As(v) molecules. The soluble As concentration can then be quantified by the concentration difference between the mixed oxyanion (As + P) absorbance (proposed method) and the MG method absorbance that measures only P. Our method is miniaturized using a 96-well microplate UV-VIS reader that utilizes minute reagent and sample volumes (120 and 200 μL sample-1, respectively), thus, minimizing waste and offering flexibility in the field. Our method was tested in a suite of As-contaminated soils that successfully measured both As and P in soil water extracts and total digests. Mean% As recoveries ranged between 84 and 117%, corroborating data obtained with high-resolution inductively-coupled plasma mass-spectrometry. The performance of the proposed colorimetric As method was unaffected by the presence of Cu, Zn, Pb, Ni, Fe, Al, Si, and Cr in both neutral and highly-acidic (ca. pH 2) soil extracts. Data from this study provide the proof of concept towards creating a field-deployable, portable As kit