Transport of pharmaceuticals in columns of a wastewater-irrigated Mexican clay soil

Mobility of antipyretic drugs with different molecular structures in saturated soil porous media

In the post-COVID-19 era, extensive quantities of antipyretic drugs are being haphazardly released from households into the environment, which may pose potential risks to ecological systems and human health. Identification of the mobility behaviors of these compounds in the subsurface environment is crucial to understand the environmental fate of these common contaminants. The mobility properties of three broad-spectrum antipyretic drugs, including ibuprofen (IBF), indometacin (IMC), and acetaminophen (APAP), in porous soil media, were investigated in this study. The results showed that the mobility of the three drugs (the background electrolyte was Na+) through the soil column followed the order of APAP > IBF > IMC. The difference in the physicochemical characteristics of various antipyretic drugs (e.g., the molecular structure and hydrophobicity) could explain this trend. Unlike Na+, Ca2+ ions tended to serve as bridging agents by linking the soil grains and antipyretic molecules, leading to the relatively weak mobility behaviors of antipyretic drugs. Furthermore, for a given antipyretic drug, the antipyretic mobility was promoted when the background solution pH values were raised from 5.0 to 9.0. The phenomenon stemmed from the improved electrostatic repulsion between the dissociated species of antipyretic molecules and soil grains, as well as the weakened hydrophobic interactions between antipyretic drugs and soil organic matter. Furthermore, a two-site non-equilibrium transport model was used to estimate the mobility of antipyretic drugs. The results obtained from this work provide vital information illustrating the transport and retention of various antipyretic drugs in aquifers.

Transport of emerging contaminants: a column experimental study in granitic, gneissic, and quaternary alluvial soils from Porto Alegre, Southern Brazil

Emerging contaminants is a topic that has been in evidence, especially in the last decades. These compounds are pesticides, pharmaceuticals, and personal care products that are present in several locations, mainly in large urban centers. The aim of this work was to investigate the fate of seven compounds (atrazine, simazine, ametrine, tebuthiuron, 2,4-D, fipronil, and diclofenac) using leaching column experiments to evaluate accumulation and transfer in 5 different types of urban soils from Porto Alegre, Southern Brazil. Chemical analyses were carried out through liquid chromatography tandem mass spectrometry (LC-MS/MS). The results showed that the soil derived from quaternary sediments, with well-sorted sandy sediments, was the one in which the contaminants had higher mobility. This soil also has a pH above the average of the others in the city, a factor that may also be responsible for less retention of substances. Tebuthiuron is the substance with the greatest leaching potential overall. Column experiments are a relevant tool to understand the behavior of emerging contaminants in soils and implications on the population health.

Sorption and mobility of metformin and guanylurea in soils as affected by biosolid amendment: Batch and column tests

Recent classification of metformin as an emerging contaminant warrants assessment of its fate and behaviour in the natural environment especially with land-based application of potentially contaminated wastewaters and biosolids. The present study provided further insight into the sorption mechanisms of metformin and its transformation product guanylurea in soil and upon biosolid fortification. Decreased metformin sorption (12.4%) as measured by the effective distribution coefficient (K_d^eff) was observed with biosolids amendment while significant increase (2500%) in guanylurea sorption was calculated. Analysis of co-solute effects confirmed their contrasting sorption mechanisms with the absence of competitive effects in unamended soil. Results of the column tests were in good agreement with the batch sorption studies as the fitted values of retardation factors decreased and increased for metformin and guanylurea, respectively, upon addition of biosolids. The shapes of the breakthrough curves suggest slower desorption rates for both compounds in unamended soil resulting to non-equilibrium conditions and back-end tailings. However, in biosolid-amended soil columns, these tailings were less pronounced resembling equilibrium transport. Results also demonstrated enhanced mobility of both compounds upon biosolids fortification. The non-equilibrium chemical transport model fitted the measured data well (0.975 > r² > 0.988) especially for unamended soils which suggests the existence of non-equilibrium conditions and rate-limited sorption sites.

Adsorption and degradation of sulfadiazine and sulfamethoxazole in an agricultural soil system under an anaerobic condition: Kinetics and environmental risks

Sulfonamides, one of the commonest antibiotics, were widely used on humans and livestock to control pathema and bacterial infections resulting in further environmental risks. The present study evaluated the adsorption and degradation of sulfadiazine (SDZ) and sulfamethoxazole (SMX) in an agricultural soil system under an anaerobic condition. Low sorption coefficients (K_d, 1.22 L kg^-1 for SDZ and 1.23 L kg^-1 for SMX) obtained from Freundlich isotherms experiment indicated that poor sorption of both antibiotics may pose a high risk to environment due to their high mobility and possibility of entering surface and ground water. Degradation occurred at a lower rate under the anaerobic environment, where both two antibiotics had higher persistence in sterile and non-sterile soils with degradation ratio <75% and DT50 > 20 d. Additionally, the addition of manure slightly increased degradation rates of SDZ and SMX, but there were no significant differences between single and repeated manure application at a later stage (p > 0.05), which suggested that the degradation was affected by both biotic and abiotic factors. Degradation rates would be slower at a higher concentration, indicating that degradation kinetics of SDZ and SMX were dependent on initial concentrations. During the degradation period, the antibiotics removal may change temperature, pH, sulfate and nitrate in soil, which suggested that the variation of antibiotics concentrations was related to the changes of soil physicochemical properties. An equation was proposed to elucidate the link between adsorption and degradation under different conditions, and to predict potential environmental risks of antibiotics.

Towards the understanding of antibiotic occurrence and transport in groundwater: Findings from the Baix Fluvià alluvial aquifer (NE Catalonia, Spain)

Antibiotics are an increasing focus of interest due to their high detection frequency in the environment. However, their presence in water bodies is not regulated by environmental policies. This field study investigates, for the first time, the occurrence, behavior and fate of a selection of 53 antibiotics, including up to 10 chemical groups, in an alluvial aquifer originated from manure application in an agricultural region using hydrogeological, hydrochemical and isotopic approaches. Up to 11 antibiotics were found in groundwater corresponding to 4 different chemical groups: fluoroquinolones, macrolides, quinolones and sulfonamides. In surface water, only 5 different antibiotics from 2 chemical groups: fluoroquinolones and sulfonamides, were quantified. The most frequent antibiotics were sulfamethoxazole and ciprofloxacin. Concentrations of antibiotics were in the order of ng/L, with maximum concentrations of 300ng/L in groundwater. Hydrochemistry and isotopic data and geostatistics confirmed the spatial trend observed for nitrates, where nitrate concentrations tend to be higher in the margin areas of the study area, and lower concentrations are found nearby the river. On the other hand, no clear continuous spatial concentration trend of antibiotics was observed in the aquifer, supported by the short spatial correlation found in the variograms. This indicates that the physical-chemical properties and processes of each antibiotic (mainly, sorption and degradation), and other environmental issues, such as a patchy diffuse input and the manure antibiotic content itself, play an important role in their spatial distribution in groundwater. A discussion on the estimation of the antibiotic sorption parameter reveals the difficulties of describing such phenomena. Furthermore, retardation factors will extend over several orders of magnitude, which highly affects the movement of individual antibiotics within the aquifer. To summarize, this study points out the difficulties associated with antibiotic research in groundwater in order to define water resources quality management strategies and environmental regulations.

Degradation kinetics and mechanism of sulfadiazine and sulfamethoxazole in an agricultural soil system with manure application

Recently, under the application of waste-water, manure and biosolids, antibiotics have been used massively in agriculture resulted in antibiotic resistance and potential environmental risks. In the present study, the removal of sulfadiazine (SDZ) and sulfamethoxazole (SMX) in an agricultural soil system was explored. All the experiments were conducted under different incubation conditions for 49days. The experimental results indicated that all the degradation processes could effectively follow a first-order kinetic model. Based on the analyses of these two antibiotics, SDZ had a higher reaction rate and a shorter DT50 value. Additionally, there were no marked differences in DT50 values at varying initial concentrations under the same conditions (p>0.05). Compared with the non-sterile soil, the degradation rates of SMX and SDZ were slower (<70%), and the associated DT50 values (>21days) were higher in the sterile soil. Because the biodegradation played a major role, it may be effective for the removal of these contaminants from the soils. The processes of SDZ and SMX degradations were slightly accelerated by applying manure (<20%). There were different accelerating effects on the removal of SDZ and SMX in soils by manure Single- and Repeated-application, which may be related to the amount of manure during the degradation processes, and different methods of adding manure could only affect the degradation rate. The major intermediate products were derived from the hydroxylation, sulfonamide SN bond cleavage and aniline moiety oxidation. Therefore, the present study inferred that possible degradation pathways of SDZ and SMX were hydroxylation of the benzene ring, oxidation of the amine group at the benzene ring, ring open and SN bond cleavage. Results revealed that more attention should be paid to the transformation products because they could be more toxic than the parent compounds.

Investigating natural attenuation of pharmaceuticals through unsaturated column tests

The growing consumption of pharmaceuticals together with their incomplete removal in wastewater treatment plants (WWTPs) implies the occurrence of these compounds in natural water resources. To investigate the natural attenuation of selected pharmaceuticals (caffeine, acetaminophen, sulfamethoxazole, naproxen and carbamazepine) during vadose zone infiltration, unsaturated column (L 26.67 cm, Ø 7.62 cm) experiments, filled with a sandy-loamy soil, were performed using two input concentrations (100 and 1000 μg L^-1). The software Hydrus 1D was used to simulate experimental data. Caffeine and acetaminophen were never detected at the column outlet indicating a low environmental concern. On the other hand, attenuation of the detected pharmaceuticals could be reproduced by a combination of retardation and removal approaches. Carbamazepine is among the selected contaminants the most persistent. A dependence of removal rates on input concentrations was detected for sulfamethoxazole (μ_w from 2.78 d^-1 to 1.16 d^-1) and naproxen (μ_w from 1.16 d^-1 to 0.63 d^-1) attributed mainly to decreased metabolism of microorganisms when a higher input concentration is applied. Two transformation products (TPs) (N4-Acetylsulfamethoxazole and epoxycarbamazepine) derived from sulfamethoxazole and carbamazepine transformation, respectively, were detected during the experiment with the highest input concentration.

Antibiotics degradation in soil: A case of clindamycin, trimethoprim, sulfamethoxazole and their transformation products

Twelve different soil types that represent the soil compartments of the Czech Republic were fortified with three antibiotics (clindamycin (CLI), sulfamethoxazole (SUL), and trimethoprim (TRI)) to investigate their fate. Five metabolites (clindamycin sulfoxide (CSO), hydroxy clindamycin sulfoxide (HCSO), S-(SDC) and N-demethyl clindamycin (NDC), N₄-acetyl sulfamethoxazole (N₄AS), and hydroxy trimethoprim (HTR)) were detected and identified using HPLC/HRMS and HRPS in the soil matrix in this study. The identities of CSO and N₄AS were confirmed using commercially available reference standards. The parent compounds degraded in all soils. Almost all of the metabolites have been shown to be persistent in soils, with the exception of N₄AS, which was formed and degraded completely within 23 days of exposure. The rate of degradation mainly depended on the soil properties. The PCA results showed a high dependence between the soil type and behaviour of the pharmaceutical metabolites. The mentioned metabolites can be formed in soils, and the most persistent ones may be transported to the ground water and environmental water bodies. Because no information on the effects of those metabolites on living organism are available, more studies should be performed in the future to predict the risk to the environment.

Accumulation of pharmaceuticals in groundwater under arid climate conditions - Results from unsaturated column experiments

Intense reuse of treated wastewater in agriculture is practiced all over the world, especially in arid and water-scarce regions. In doing so, pharmaceutical residues in the water are irrigated to the soil and subsequently can percolate into the local aquifers. Since evaporation rates in these areas are typically high, persistent substances might enrich in the groundwater recharge of closed catchments like the Jordan Valley. Against this background, unsaturated column tests were conducted to investigate the potential for evaporative accumulation of the two pharmaceuticals bezafibrate and carbamazepine under simulated arid climate conditions. Parallel tests were conducted with inhibited microbiological activity where both substances showed an increase in the effluent concentrations proportional to the evaporation loss of the inflow solution. The mean accumulation factors of the pharmaceuticals correspond to the evaporated water loss. The experiments indicate the accumulation potential for pharmaceuticals with high persistence against biodegradation. For the first time, the overall potential for evaporative enrichment could be demonstrated for pharmaceuticals. Under the given experimental conditions, the two investigated pharmaceuticals did not enrich faster than chloride, which might result in soil salting prior to reaching harmful pharmaceutical concentrations in soil water. The findings are relevant to future assessments of environmental impacts of persistent trace substances, which need to take into account that concentrations in the aquatic cycle might increase further due to evaporative enrichment.

Occurrence and distribution of antibiotics in urban soil in Beijing and Shanghai, China

The recycling of reclaimed wastewater for irrigation and road cleaning is an important strategy to minimize water scarcity in megacities. However, little is known regarding the potential accumulation of antibiotics contained in reclaimed wastewater in urban soil. We investigated the occurrence and distribution of eight quinolones (QNs), nine sulfonamides (SAs), and five macrolides (MLs) antibiotics in urban surface soil in Beijing and Shanghai, China. QNs, especially norfloxacin (NOR), ofloxacin (OFL), and ciprofloxacin (CIP) were the predominant antibiotics in urban surface soil, and NOR revealed the highest average concentration of 94.6 μg kg(-1). The antibiotic concentrations in urban soil in our study were higher than those detected in agricultural soils after long-term wastewater irrigation and manure fertilization. The concentrations of antibiotics in Shanghai urban soil showed a significant negative correlation with soil pH and a positive correlation with total organic carbon (TOC), reflecting the effect of speciation and soil organic matter content on sorption and retention. In addition, antibiotic concentrations in the urban soil were positively correlated with heavy metal contents, likely due to their coexistence in reclaimed wastewater and the promoting effect of metals on the sorption of antibiotics. In several soil samples, NOR, OFL, CIP, enrofloxacin (ENR), and fleroxacin (FLE) showed higher concentrations than the trigger value of 100 μg kg(-1) in soil, indicating a potential risk for the environment.

Field-scale monitoring of pharmaceutical compounds applied to active golf courses by recycled water

The scarcity of potable water in arid and semiarid environments has led to the wider use of recycled water for irrigating agricultural fields, parks, golf courses, and other areas. One concern using recycled water as a source of irrigation has been the presence, fate, and transport of pharmaceutical compounds in water that percolates below the root zone of plants; however, very few multiyear field studies have been reported in the peer-reviewed literature. Here, we assessed compound mass flux of 13 pharmaceuticals in the fairways of four golf courses in the southwestern United States during a 2-yr field study. The sites varied by climate and soil type but were similar regarding turfgrass management. The results showed the presence of at least one pharmaceutical compound in nearly all samples collected, although concentrations were substantially lower after transport through the soil. Percent reduction in compound mass fluxes in drainage water was effectively 100% in 22 of 52 cases, 98 to 100% in 27 of 52 cases, and 73 to 94% in 3 of 52 cases (a case is defined as a specific compound measured at a specific site). Mass fluxes migrating below the root zone were calculated as <250 × 10 g ha for all compounds and >100 × 10 g ha in only two cases. For cases where the majority of the analyses were reportable, all fluxes were <8.80 × 10 g ha. Carbamazepine, meprobamate, and sulfamethoxazole were most commonly found in drainage water, representing nearly 80% of all reportable detections. This research demonstrates the potential of turfgrass/soil systems to reduce contaminant loading below the root zone and potentially toward groundwater.

Biodegradability of pharmaceutical compounds in agricultural soils irrigated with treated wastewater

Pharmaceutical compounds (PCs) are introduced into agricultural soils via irrigation with treated wastewater (TWW). Our data show that carbamazepine, lamotrigine, caffeine, metoprolol, sulfamethoxazole and sildenafil are persistent in soils when introduced via TWW. However, other PCs, namely diclofenac, ibuprofen, bezafibrate, gemfibrozil and naproxen were not detected in soils when introduced via TWW. This is likely due to rapid degradation as confirmed in our microcosm studies where they exhibited half-lives (t1/2) between 0.2-9.5 days when soils were spiked at 50 ng/g soil and between 3 and 68 days when soils were spiked at 5000 ng/g soil. The degradation rate and extent of PCs observed in microcosm studies were similar in soils that had been previously irrigated with TWW or fresh water. This suggests that pre-exposure of the soils to PCs via irrigation with TWW does not enhance their biodegradation. This suggests that PCs are probably degraded in soils via co-metabolism.

Combined effects of biosolids application and irrigation with reclaimed wastewater on transport of pharmaceutical compounds in arable soils

Pharmaceutical compounds (PCs) are introduced into the agricultural environment through irrigation with treated effluents and application of biosolids. Transport processes can determine the fate of PCs and the associated risks related to their exposure in the environment. The aim of this work was to evaluate the combined effects of biosolids application and irrigation with treated effluents on the mobility of PCs in soil and to elucidate the main mechanisms affecting their transport. Column-leaching experiments revealed that application of biosolids generally increased the retardation of PCs, whereas treated effluents increased the mobility of weakly acidic PCs in the biosolids-amended soils. Experiments conducted at environmentally relevant PC concentrations (≈ 1 μg/L) highlight the importance of irreversible sorption as a possible mechanism for low leachability. Data generated from this study suggest that (i) transport behavior of PCs can be affected by common biosolids application to arable land; (ii) treated effluents increase the mobility of weakly acidic PCs mainly by increasing of the soil solution pH and not due to complexation of the PCs with dissolved organic matter; and (iii) it is highly important to evaluate transport behavior at environmentally relevant concentrations and not to base modeling on data obtained from experiments conducted in high concentrations.

Contribution of microorganisms to non-extractable residue formation during biodegradation of ibuprofen in soil

Non-extractable residues (NER) formed during biodegradation of organic contaminants in soil are considered to be mainly composed of parent compounds or their primary metabolites with hazardous potential. However, in the case of biodegradable organic compounds, the soil NER may also contain microbial biomass components, for example fatty acids (FA) and amino acids (AA). After cell death, these biomolecules are subsequently incorporated into non-living soil organic matter (SOM) and are stabilised ultimately forming hardly extractable residues of biogenic origin. We investigated biodegradation of (13)C(6)-ibuprofen, in particular the metabolic incorporation of the (13)C-label into FA and AA and their fate in soil over 90 days. (13)C-FA and (13)C-AA amounts in the living microbial biomass fraction initially increased, then decreased over time and were continuously incorporated into the non-living SOM pool. The (13)C-FA in the non-living SOM remained stable from day 59 whereas the contents of (13)C-AA slightly increased until the end. After 90 days, nearly all NER were biogenic as they were made up almost completely by natural biomass compounds. The presented data demonstrated that the potential environmental risks related to the ibuprofen-derived NER are overestimated.

Accumulation of pharmaceuticals, Enterococcus, and resistance genes in soils irrigated with wastewater for zero to 100 years in central Mexico

Irrigation with wastewater releases pharmaceuticals, pathogenic bacteria, and resistance genes, but little is known about the accumulation of these contaminants in the environment when wastewater is applied for decades. We sampled a chronosequence of soils that were variously irrigated with wastewater from zero up to 100 years in the Mezquital Valley, Mexico, and investigated the accumulation of ciprofloxacin, enrofloxacin, sulfamethoxazole, trimethoprim, clarithromycin, carbamazepine, bezafibrate, naproxen, diclofenac, as well as the occurrence of Enterococcus spp., and sul and qnr resistance genes. Total concentrations of ciprofloxacin, sulfamethoxazole, and carbamazepine increased with irrigation duration reaching 95% of their upper limit of 1.4 µg/kg (ciprofloxacin), 4.3 µg/kg (sulfamethoxazole), and 5.4 µg/kg (carbamazepine) in soils irrigated for 19–28 years. Accumulation was soil-type-specific, with largest accumulation rates in Leptosols and no time-trend in Vertisols. Acidic pharmaceuticals (diclofenac, naproxen, bezafibrate) were not retained and thus did not accumulate in soils. We did not detect qnrA genes, but qnrS and qnrB genes were found in two of the irrigated soils. Relative concentrations of sul1 genes in irrigated soils were two orders of magnitude larger (3.15×10⁻³±0.22×10⁻³ copies/16S rDNA) than in non-irrigated soils (4.35×10⁻⁵±1.00×10⁻⁵ copies/16S rDNA), while those of sul2 exceeded the ones in non-irrigated soils still by a factor of 22 (6.61×10^–4±0.59×10⁻⁴ versus 2.99×10⁻⁵±0.26×10⁻⁵ copies/16S rDNA). Absolute numbers of sul genes continued to increase with prolonging irrigation together with Enterococcus spp. 23S rDNA and total 16S rDNA contents. Increasing total concentrations of antibiotics in soil are not accompanied by increasing relative abundances of resistance genes. Nevertheless, wastewater irrigation enlarges the absolute concentration of resistance genes in soils due to a long-term increase in total microbial biomass.

Organic micropollutants in rivers downstream of the megacity Beijing: sources and mass fluxes in a large-scale wastewater irrigation system

The Haihe River System (HRS) drains the Chinese megacities Beijing and Tianjin, forming a large-scale irrigation system severely impacted by wastewater-borne pollution. The origin, temporal magnitudes, and annual mass fluxes of a wide range of pharmaceuticals, household chemicals, and pesticides were investigated in the HRS, which drains 70% of the wastewater discharged by 20 million people living in Beijing. Based on Chinese consumption statistics and our initial screening for 268 micropollutants using high-resolution mass spectrometry, 62 compounds were examined in space and time (2009-2010). The median concentrations ranged from 3 ng/L for metolachlor to 1100 ng/L for benzotriazole and sucralose. Concentrations of carbendazim, clarithromycin, diclofenac, and diuron exceed levels of ecotoxicological concern. Mass-flux analyses revealed that pharmaceuticals (5930 kg/year) and most household chemicals (5660 kg/year) originated from urban wastewaters, while the corrosion inhibitor benzotriazole entered the rivers through other pathways. Total pesticide residues amounted to 1550 kg/year. Per capita loads of pharmaceuticals in wastewater were lower than those in Europe, but are expected to increase in the near future. As 95% of the river water is diverted to irrigate agricultural soil, the loads of polar organic micropollutants transported with the water might pose a serious threat to food safety and groundwater quality.

Leaching of pharmaceuticals and personal care products in turfgrass soils during recycled water irrigation

An important beneficial reuse of treated wastewater (recycled water) in arid and semiarid regions is landscape irrigation. However, the environmental fate, especially groundwater contamination potential, of trace contaminants such as pharmaceuticals and personal care products (PPCPs) is a significant concern that can hinder the acceptance and adoption of such reuses. In this study, we irrigated mature turfgrass plots with nonspiked tertiary treated wastewater for over 6 mo at 100 or 130% of the reference evapotranspiration rate (ETo) and collected leachate water at the 90-cm depth on a weekly basis. In the recycled water, all 14 target PPCPs were consistently found, and the mean levels of atenolol, gemfibrozil, meprobamate, carbamazepine, and sulfamethoxazole were above 100 ng L. However, only five compounds were detected in the leachate at trace levels. Trimethoprim and primidone were frequently found, whereas the detection of sulfamethoxazole, meprobamate and carbamazepine was less frequent (<50%). When detected, the overall mean concentration in the leachate was 10.2 ng L for trimethoprim, 7.1 ng L for primidone, and 2.9 to 12.4 ng L for carbamazepine, sulfamethoxazole, and meprobamate. The majority of the target PPCPs were completely removed. Given that the irrigation rates were higher than normal, this study clearly demonstrated the efficacy of turfgrass systems in attenuating PPCPs during recycled water irrigation. However, it is also apparent that some PPCPs are more susceptible to leaching than others, and these PPCPs thus merit further research attention.

Assessing the fate of antibiotic contaminants in metal contaminated soils four years after cessation of long-term waste water irrigation

Spreading of urban wastewater on agricultural land may lead to concomitant input of organic and inorganic pollutants. Such multiple pollution sites offer unique opportunities to study the fate of both heavy metals and pharmaceuticals. We examined the occurrence and fate of selected antibiotics in sandy-textured soils, sampled four years after cessation of 100 years irrigation with urban wastewater from the Paris agglomeration. Previous studies on heavy metal contamination of these soils guided our sampling strategy. Six antibiotics were studied, including quinolones, with a strong affinity for organic and mineral soil components, and sulfonamides, a group of more mobile molecules. Bulk samples were collected from surface horizons in different irrigation fields, but also in subsurface horizons in two selected profiles. In surface horizons, three quinolones (oxolinic acid, nalidixic acid, and flumequine) were present in eight samples out of nine. Their contents varied spatially, but were well-correlated one to another. Their distributions showed great similarities regarding spatial distribution of total organic carbon and heavy metal contents, consistent with a common origin by wastewater irrigation. Highest concentrations were observed for sampling sites close to irrigation water outlets, reaching 22 μg kg(-1) for nalidixic acid. Within soil profiles, the two antibiotic groups demonstrated an opposite behavior: quinolones, found only in surface horizons; sulfamethoxazole, detected in clay-rich subsurface horizons, concomitant with Zn accumulation. Such distribution patterns are consistent with chemical adsorption properties of the two antibiotic groups: immobilization of quinolones in the surface horizons ascribed to strong affinity for organic matter (OM), migration of sulfamethoxazole due to a lower affinity for OM and its interception and retention in electronegative charged clay-rich horizons. Our work suggests that antibiotics may represent a durable contamination of soils, and risks for groundwater contamination, depending on the physicochemical characteristics both of the organic molecules and of soil constituents.

Sources, interactions, and ecological impacts of organic contaminants in water, soil, and sediment: an introduction to the special series

Agricultural and urban activities result in the release of a large number of organic compounds that are suspected of impacting human health and ecosystems: herbicides, insecticides, human and veterinary pharmaceuticals, natural and synthetic hormones, personal care products, surfactants, plasticizers, fire retardants, and others. Sorbed reservoirs of these compounds in soil represent a potentially chronic source of water contamination. This article is an introduction to a series of technical papers stemming from a symposium at the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America 2008 Annual Meeting, which was held jointly with The Geological Society of America, The Gulf Coast Association of Geological Scientists, and the Houston Geological Society, under one of the Joint Meeting's overarching themes: Emerging Trace Contaminants in Surface and Ground Water Generated from Waste Water and Solid Waste Application. The symposium emphasized the role of soils as sources, sinks, and reaction catalysts for these contaminants and the occurrence and fate of these contaminants in surface and underground water supplies. Topics covered included novel advances in analytical techniques, transport of infectious agents, occurrence and fate of veterinary pharmaceuticals, characterization of sorption mechanism, biotic and abiotic transformation reactions, the role of soil components, occurrence and fate in wastewater treatment systems, transport of engineered nanoparticles, groundwater contamination resulting from urban runoff, and issues in water reuse. Overviews of the reports, trends, gaps in our knowledge, and topics for further research are presented in this special series of papers. The technical papers in this special series reflect current gains in knowledge and simultaneously underscore how poorly we are able to predict the fate and, hence, the associated risk to ecological and human receptors of these contaminants.