Reply to comment on“Long-term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation–A mechanistic approach” by C. Noubactep, Geoscience Frontiers 14(2023), 101582

We welcome the opportunity to address comments provided by Dr.Noubactep and to further emphasize the concepts developed in our article titled“Long–term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation–A mechanistic approach”(Lawrinenko et al.,2023).

Long-term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation-A mechanistic approach

Permeable reactive barriers(PRBs)are used for groundwater remediation at contaminated sites worldwide.This technology has been efficient at appropriate sites for treating organic and inorganic contaminants using zero-valent iron(ZVI)as a reductant and as a reactive material.Continued development of the technology over the years suggests that a robust understanding of PRB performance and the mechanisms involved is still lacking.Conflicting information in the scientific literature downplays the critical role of ZVI corrosion in the remediation of various organic and inorganic pollutants.Additionally,there is a lack of information on how different mechanisms act in tandem to affect ZVI-groundwater systems through time.In this review paper,we describe the underlying mechanisms of PRB performance and remove isolated misconceptions.We discuss the primary mechanisms of ZVI transformation and aging in PRBs and the role of iron corrosion products.We review numerous sites to reinforce our understanding of the interactions between groundwater contaminants and ZVI and the authigenic minerals that form within PRBs.Our findings show that ZVI corrosion products and mineral precipitates play critical roles in the long-term performance of PRBs by influencing the reactivity of ZVI.Pore occlusion by mineral precipitates occurs at the influent side of PRBs and is enhanced by dissolved oxygen and groundwater rich in dissolved solids and high alkalinity,which negatively impacts hydraulic conductivity,allowing contaminants to potentially bypass the treatment zone.Further development of site characterization tools and models is needed to support effective PRB designs for groundwater remediation.

Uptake and translocation of sulfamethazine by alfalfa grown under hydroponic conditions

Antibiotics are routinely used in intensive animal agriculture operations collectively known as Concentrated Animal Feed Operations （CAFO） which include dairy, poultry and swine farms. Wastewater generated by CAFOs often contains low levels of antibiotics and is typically managed in an anaerobic lagoon. The objective of this research is to investigate the uptake and fate of aqueous sulfamethazine （SMN） antibiotic by alfalfa （Medicago satiua） grass grown under hydroponic conditions. Uptake studies were conducted using hydroponically grown alfalfa in a commercially available nutrient solution supplemented with 10 mg/L of SMN antibiotic. Analysis of alfalfa sap, root zone, middle one-third, and top portion of the foliage showed varying uptake rate and translocation of SMN. The highest average amount of SMN （8.58 μg/kg） was detected in the root zone, followed by the top portion （1.89μg/kg）, middle one-third （1.30 μg/kg）, and sap （0.38 μg/kg） samples, indicating a clear distribution of SMN within the sampled regions. The ultraviolet （UV） spectra of parent SMN and translocated SMN identified in different parts of the plant present the possibility of metabolization during the uptake process. Uptake of SMN using alfalfa grown under hydroponic conditions has potential as a promising remediation technology for removal of similar antibiotics from wastewater lagoons.

Preliminary studies on occurrence of monensin antibiotic in Bosque River Watershed

Water quality impact due to excessive nutrients has been extensively studied. In recent years, however, micro-pollutants such as pharmaceuticals and hormonal products used in animal agriculture have added an additional impact to overall water quality. Pharmaceuticals used in the poultry, swine, beef, and dairy industries have been detected in various environmental matrices such as, soil, groundwater and surface water. In this study, 26 surface water samples were collected throughout the Bosque River Watershed （BRW） with samples representing a range of land use conditions and locations of major dairy operations. Samples were analyzed using commercially available Enzyme-Linked Immunosorbent Assay test. Of the 26 samples, three samples consistently tested positive for monensin antibiotic with concentration ranging from 0.30 to 3.41 μg/L. These three samples were collected from sites that received varying amount of agriculture wastes （11.7% to 31.3%） and located downstream from sites associated with moderate levels of animal agriculture. The preliminary results suggest that there is a potential for monensin occurrence in the BRW, although initial findings indicate only very low levels.