Organic Contaminants In Groundwater Research Articles

Assessment of a wide array of contaminants of emerging concern in a Mediterranean water basin (Guadalhorce river, Spain): Motivations for an improvement of water management and pollutants surveillance

This study investigates the occurrence and distribution of 185 organic contaminants (regulated pollutants and contaminants of emerging concern; CECs) in surface and groundwater of the Guadalhorce River basin (southern Spain) providing the most detailed dataset regarding organic pollution presented so far in this area. Up to 63 contaminants were detected in a monitoring campaign conducted in March 2016. Most contaminants were detected more frequently in surface water where they generally present higher concentrations suggesting the prevalence of wastewater discharges into streams as the main pollutant sources. In general, hydrophobic CECs presented the highest frequencies of detection and concentrations, which can be a consequence of several factors: (1) hydrophobic compounds show a higher retardation factor, which result, along with a continuous contaminant input, in a widespread and homogeneous distribution. In contrast, hydrophilic contaminants are more easily transported by water flows towards the lower basin and potentially accumulate as driven by groundwater flow and because of low renewal rates in the detrital aquifers caused by re-pumping and irrigation return flows in agricultural lands; (2) hydrophobic CECs studied in this research are mainly personal care products and organophosphate esters flame retardants and plasticizers, which are present in many different products and are used in large amounts; Also, (3) use of biosolids (reclaimed sewer sludge) as fertilizer for crops is potentially an additional diffuse source of organic pollutants in the study area contributing to a widespread distribution, especially for hydrophobic compounds. Obtained results highlight the need to better define the potential risk of non-regulated contaminants in water resources as well as the great impact of untreated wastewater discharges.

Emerging organic contaminants in shallow groundwater underlying two contrasting peri-urban areas in Uganda.

This study investigated the occurrence and seasonal variation in concentrations of emerging organic contaminants (EOCs) in shallow groundwater underlying two peri-urban areas of Bwaise (highly urbanised) and Wobulenzi (moderately urbanised) in Uganda. Twenty-six antibiotics, 20 hydrocarbons, including 16 polycyclic aromatic hydrocarbons (PAHs), and 59 pesticides were investigated. Ampicillin and benzylpenicillin were the most frequently detected antibiotics in both areas, although at low concentrations to cause direct harm to human health, but could lead to a proliferation of antibiotic resistance genes. The most frequently detected hydrocarbons in Bwaise were naphthalene and xylene while anthracene and fluoranthene were the most frequent in Wobulenzi, also at low concentrations for ecological impact at long-term exposure. Molecular diagnostic ratios indicated pyrogenic and pyrolytic sources of PAHs in both areas. Cypermethrin (for vermin control) was the most frequent pesticide in Bwaise while metalaxyl (attributed to agriculture) was the most frequent in Wobulenzi. Banned organochlorines (8) were also detected in both areas in low concentrations. The pesticide concentrations between the two areas significantly differed (Z = - 3.558; p < 0.01), attributed to contrasting land-use characteristics. In Wobulenzi (wet season), the total pesticide concentrations at all the locations exceeded the European Community parametric guideline value while 75% of the detected compounds exceeded the individual pesticide guideline value. Thus, the antibiotic and pesticide residues in shallow groundwater underlying both Bwaise and Wobulenzi pose potential adverse ecological effects at long-term exposure. Monitoring of EOCs in both highly and moderately urbanised catchments should be strengthened towards mitigating associated risks.

Magnitude of Diffusion- and Transverse Dispersion-Induced Isotope Fractionation of Organic Compounds in Aqueous Systems

Determining whether aqueous diffusion and dispersion lead to significant isotope fractionation is important for interpreting the isotope ratios of organic contaminants in groundwater. We performed diffusion experiments with modified Stokes diaphragm cells and transverse-dispersion experiments in quasi-two-dimensional flow-through sediment tank systems to explore isotope fractionation for benzene, toluene, ethylbenzene, 2,6-dichlorobenzamide, and metolachlor at natural isotopic abundance. We observed very small to negligible diffusion- and transverse-dispersion-induced isotope enrichment factors (ε < −0.4 ‰), with changes in carbon and nitrogen isotope values within ±0.5‰ and ±1‰, respectively. Isotope effects of diffusion did not show a clear correlation with isotopologue mass with calculated power-law exponents β close to zero (0.007 < β < 0.1). In comparison to ions, noble gases, and labeled compounds, three aspects stand out. (i) If a mass dependence is derived from collision theory, then isotopologue masses of polyatomic molecules would be affected by isotopes of multiple elements resulting in very small expected effects. (ii) However, collisions do not necessarily lead to translational movement but can excite molecular vibrations or rotations minimizing the mass dependence. (iii) Solute–solvent interactions like H-bonds can further minimize the effect of collisions. Modeling scenarios showed that an inadequate model choice, or erroneous choice of β, can greatly overestimate the isotope fractionation by diffusion and, consequently, transverse dispersion. In contrast, available data for chlorinated solvent and gasoline contaminants at natural isotopic abundance suggest that in field scenarios, a potential additional uncertainty from aqueous diffusion or dispersion would add to current instrumental uncertainties on carbon or nitrogen isotope values (±1‰) with an additional ±1‰ at most.

Effects of endogenous and exogenous dissolved organic matter on sorption behaviors of bisphenol A onto soils

The transport of organic contaminants in groundwater might be greatly affected by coexistence of dissolved organic matter (DOM) from different sources. In this study, the effects of endogenous and exogenous DOMs (referred to as DOMen and DOMex, respectively) on sorption behavior of bisphenol A (BPA) onto two reference soils were investigated by batch experiments and microscopic characterization. The results showed that BPA sorption onto soils was dominated by soil organic matter content and affected by DOM properties. The effect of DOMen on BPA sorption was also related to the inorganic components of the two soils. The decrease of organic matter content reduced the sorption capacity of fluvo-aquic soil. However, because the content of available inorganic components in black soil was high, after removing DOMen, more inorganic sites were exposed to increase the sorption capacity. In addition, DOMen could form complexes with BPA in solution, thus the removal of DOMen promoted BPA sorption onto black soil. Under the experimental conditions, contribution of DOMex to the total sorption of BPA onto both soils was not more than 30%. Results of dialysis experiments and soil sorption experiments indicated that effects of coexisting DOMex on BPA sorption was related to the affinity of DOMex to soils and complexation of BPA and DOMex. Since the affinity of DOMex to fluvo-aquic soil was relatively low, the complex of BPA and DOMex in solution was the main inhibition mechanism for BPA sorption. For black soil, higher complexation proportion of BPA with DOMex adsorbed onto soil which promoted BPA sorption onto soil. The findings are of significance for understanding the co-migration of DOM with BPA through soils.

Assessment of Pollutants in Soils and Groundwater from the Coastal Plain of Paraíba do Sul River Delta, RJ, Brazil

In developing countries, the quality of the available freshwater is deteriorating mainly due to pollution. Underground water bodies are important resources, taking into account that they are usually more isolated and also protected from anthropogenic influence. Within this context, the present study aimed to assess trace metals, nitrate and organic contaminants in groundwater and soils from 10 bore wells located at the coastal plain of the Paraíba do Sul river delta. Groundwater of the study area revealed elevated concentrations of arsenic, iron, manganese and barium, surpassing the limits established by Brazilian legislation as well as the limits established by other regulatory agencies. As, Fe and Ba reached concentrations as high as 242.70, 31 919 and 4.041 µg.l-1 in groundwater. Despite the elevated values, results suggested a reducing environment and the contaminants appear to have a natural geogenic origin, which is corroborated by past studies in the same area. Soils of the aquifer presented low levels of trace metals, corroborating the hypothesis of geogenic contamination in groundwater. No significant differences among the bore wells were observed regarding trace metals in soils, and concentrations found in the present study were much lower than the ones found in impacted aquifers around the world. No PCB's were detected in groundwater or soils. Nitrate concentrations in groundwater were within the limits recommended by Brazilian legislation.

Comparison of Manganese Dioxide and Permanganate as Amendments with Persulfate for Aqueous 1,4-Dioxane Oxidation

Persulfate (PS) is widely used to degrade emerging organic contaminants in groundwater and soil systems, and various PS activation methods (e.g., energy or chemical inputs) have been considered to increase oxidation strength. This study investigates PS activation through manganese amendment in the form of potassium permanganate (KMnO4) and manganese dioxide (MnO2) to subsequently degrade the emerging and recalcitrant groundwater contaminant 1,4-dioxane (1,4-D). The activation of PS by MnO2 was confirmed by radical trap and by product formation. The degradation kinetics of 1,4-D by PS was also compared with varying amendments of KMnO4 and MnO2. The results showed that MnO2 activated PS, which increased the degradation rate constant of 1,4-D. KMnO4 activation of PS was not observed even though the binary oxidant mixture did enhance the degradation of 1,4-D. These results have implications for applying in situ chemical oxidation in subsurface systems, especially for conditions wherein manganese exists naturally in groundwater or aquifer minerals to support possible PS activation.

Remediation of contaminated soil and groundwater using chemical reduction and solidification/stabilization method: a case study.

This study presents a systematic on-site remediation case involving both heavy metal and organic contaminants in soil and groundwater in a historically industrial-used site in Shanghai, China. Lab-scale experiments and field tests were conducted to determine the optimum parameters for the removal of contaminants in soil and groundwater. It has been found that the remediation goal of hexavalent chromium in soil could be achieved with the mass content of added sodium hydrosulfite and ferrous sulfate reaching 3% + 6%. The total chromium in the groundwater was effectively removed, when the mass ratio of sodium metabisulfite was not less than 3g/L, and the added quick lime made pH value not less than 9. The concentrations of arsenic and 1,2-dichloropropane in the groundwater decreased evidently after extraction and mixing of groundwater. The pH and calcium chloride dosage added should be larger than 9.5 and 5g/L, respectively, to remove phosphate in groundwater. The removal efficiency of those contaminants was examined and evaluated after the on-site remediation. The results demonstrated that it was feasible to use the chemical reduction and solidification/stabilization methods for the on-site ex situ remediation of this site, which could be referenced for the realistic remediation of similar sites.

Emerging organic contaminants in groundwater under a rapidly developing city (Patna) in northern India dominated by high concentrations of lifestyle chemicals.

Aquatic pollution from emerging organic contaminants (EOCs) is of key environmental importance in India and globally, particularly due to concerns of antimicrobial resistance, ecotoxicity and drinking water supply vulnerability. Here, using a broad screening approach, we characterize the composition and distribution of EOCs in groundwater in the Gangetic Plain around Patna (Bihar), as an exemplar of a rapidly developing urban area in northern India. A total of 73 EOCs were detected in 51 samples, typically at ng.L-1 to low μg.L-1 concentrations, relating to medical and veterinary, agrochemical, industrial and lifestyle usage. Concentrations were often dominated by the lifestyle chemical and artificial sweetener sucralose. Seventeen identified EOCs are flagged as priority compounds by the European Commission, World Health Organisation and/or World Organisation for Animal Health: namely, herbicides diuron and atrazine; insecticides imidacloprid, thiamethoxam, clothianidin and acetamiprid; the surfactant perfluorooctane sulfonate (and related perfluorobutane sulfonate, perfluorohexane sulfonate, perfluorooctanoic acid and perfluoropentane sulfonate); and medical/veterinary compounds sulfamethoxazole, sulfanilamide, dapson, sulfathiazole, sulfamethazine and diclofenac. The spatial distribution of EOCs varies widely, with concentrations declining with depth, consistent with a strong dominant vertical flow control. Groundwater EOC concentrations in Patna were found to peak within ∼10km distance from the River Ganges, indicating mainly urban inputs with some local pollution hotspots. A heterogeneous relationship between EOCs and population density likely reflects confounding factors including varying input types and controls (e.g. spatial, temporal), wastewater treatment infrastructure and groundwater abstraction. Strong seasonal agreement in EOC concentrations was observed. Co-existence of limited transformation products with associated parent compounds indicate active microbial degradation processes. This study characterizes key controls on the distribution of groundwater EOCs across the urban to rural transition near Patna, as a rapidly developing Indian city, and contributes to the wider understanding of the vulnerability of shallow groundwater to surface-derived contamination in similar environments.

Outcomes of the first combined national survey of pesticides and emerging organic contaminants (EOCs) in groundwater in New Zealand 2018

The first national survey of Emerging Organic Contaminants (EOCs) involved sampling 121 wells located throughout New Zealand and analysis for a suite of 29 EOCs. This survey was carried out in conjunction with the 2018 national survey of pesticides in groundwater, a survey that is conducted on a four-yearly basis which included the analysis of glyphosate for first time. A total of 227 EOCs were detected in the 85 wells (70%). There were 29 different EOCs in the analytical suite and 25 different EOCs were detected in at least one well. The highest concentration measured was 655 ng/L for sucralose, an artificial sweetener. These results indicate that EOCs, sourced from either animal or human effluents/activities, are making their way into shallow groundwater systems and can be detected at low concentrations. A total of 135 wells were analysed for glyphosate, glufosinate and their principal metabolites. There was only one detection of glyphosate at a concentration of 2.1 μg/L. This well showed evidence of poor wellhead protection and the contamination likely came from containers that were stored near the well. A total of 279 wells were sampled and analysed for pesticides and 68 wells (24.4%) contained detectable residues of pesticides, with 28 of these wells having two or more pesticides detected. The maximum number of pesticides detected in one well was six. None of the sampled wells exceeded the Maximum Acceptable Value (MAV) for drinking water in New Zealand and the concentrations of most of the detected pesticides were equivalent to less than 0.5% of the MAV. Comparisons with earlier National Surveys of pesticides in groundwater in New Zealand indicate the frequencies of pesticide detections have remained similar over the last 16 years, with higher detection frequencies occurring before that time.

An investigation of anticoccidial veterinary drugs as emerging organic contaminants in groundwater

Intensification of the food production system to meet increased global demand for food has led to veterinary pharmaceuticals becoming a critical component in animal husbandry. Anticoccidials are a group of veterinary products used to control coccidiosis in food-producing animals, with primary prophylactic use in poultry production. Excretion in manure and subsequent land-spreading provides a potential pathway to groundwater. Information on the fate and occurrence of these compounds in groundwater is scant, therefore these substances are potential emerging organic contaminants of concern. A study was carried out to investigate the occurrence of anticoccidial compounds in groundwater throughout the Republic of Ireland. Twenty-six anticoccidials (6 ionophores and 20 synthetic anticoccidials) were analysed at 109 sites (63 boreholes and 46 springs) during November and December 2018. Sites were categorised and selected based on the following source and pathway factors: (a) the presence/absence of poultry activity (b) predominant aquifer category and (c) predominant groundwater vulnerability, within the zone of contribution (ZOC) for each site. Seven anticoccidials, including four ionophores (lasalocid, monensin, narasin and salinomycin) and three synthetic anticoccidials (amprolium, diclazuril and nicarbazin), were detected at 24% of sites at concentrations ranging from 1 to 386 ng L−1. Monensin and amprolium were the two most frequently detected compounds, detected at 15% and 7% of sites, respectively. Multivariate statistical analysis has shown that source factors are the most significant drivers of the occurrence of anticoccidials, with no definitive relationships between occurrence and pathway factors. The study found that the detection of anticoccidial compounds is 6.5 times more likely when poultry activity is present within the ZOC of a sampling point, compared to the absence of poultry activity. This work presents the first detections of these contaminants in Irish groundwater and it contributes to broadening our understanding of the environmental occurrence and fate of anticoccidial veterinary products.

Mechanistic insights into adsorptive and oxidative removal of monochlorobenzene in biochar-supported nanoscale zero-valent iron/persulfate system

Nanoscale zero-valent iron (nZVI) supported on rice stalk (RS) derived biochar composite (nZVI/RS) was synthesized as persulfate (PS) activator, achieving efficient adsorptive and catalytically oxidative removal for monochlorobenzene (MCB). Development of porous structures and enhanced aromaticity of RS with increased pyrolysis temperatures promoted MCB adsorption, with removal efficiencies of MCB rising from 11.2% for nZVI/RS300 to 72.3% for nZVI/RS700 after the adsorption for 14 h. The best PS activation performance was achieved for nZVI/RS500, with MCB removal efficiency being further increased to 98.8% after the oxidation for 3 h and reaction stoichiometric efficiency (RSE) reaching a maximum of 4.1% under conditions of 0.2 g·L−1 nZVI/RS500, 50.0 μM MCB, 2.0 mM PS and pH0 6.5. The pre-adsorption of MCB was a rate-promoting step in the oxidative degradation processes within the nZVI/RS-PS systems under low RS pyrolysis temperatures (<500 °C). However, excessive adsorptive capacity of nZVI/RS600 and nZVI/RS700 induced blocking of the active sites and low PS activation efficiencies. In addition to transformation of nZVI and surface functional groups on RS500, electron transfer from sp2 hybridized carbon enhanced by internal electron migration of sp3-sp2 hybridized carbon was also responsible for PS activation, producing SO4•−, ·OH and 1O2 for MCB degradation through both radical and nonradical pathways. Six degradation intermediates were identified with possible degradation pathways of MCB in the nZVI/RS500-PS system being proposed. Additionally, 80.2% and 67.4% of MCB removal rates were achieved in tap water and groundwater contaminated by MCB respectively. These findings have significant implications for the synthesis and application of metal-carbon composite based multifunctional materials with strong adsorption and catalytic potential for activating PS to completely remove organic contaminants in groundwater.

Passive and grab sampling methods to assess pesticide residues in water. A review

There is actually health concern about the uncontrolled use of pesticides, as some banned pesticides continue to be used in many regions of the world, especially in Latin America. Advanced analytical methods are thus required to detect pesticides in water. Common pesticide analysis is done by grab sampling of water volumes ranging from milliliters to liters. Grab sampling is suitable for moderate to high pesticide concentrations, but fails to detect trace levels and shows only a single-time snapshot of pesticide levels. Alternatively, passive sampling extracts and collects water directly in situ, thus allowing time for pollutants to be accumulated into the sampler. Passive sampling has recently become a major tool for extraction of organic contaminants in surface water, groundwater and wastewater. Diverse pollutants have been studied, such as pesticides, illicit and prescription drugs, metals, polycyclic aromatic hydrocarbons and cyanobacterial microcystin toxins. This review describes the main devices of passive sampling, used for the extraction of pesticides in waters.

1,2,3‐Trichloropropane: California's Response to a Persistent Pollutant

Key Takeaways1,2,3‐Trichloropropane, or TCP, is considered one of the most persistent organic groundwater contaminants and is linked to cancers and numerous damaging human health effects.The US Environmental Protection Agency has issued guidance on TCP and since it's not federally regulated, some states have established their own maximum contaminant levels.California's stringent TCP regulations and guidelines could serve as a blueprint for other states.

Mechanisms on the impacts of humic acids on persulfate/Fe2+-based groundwater remediation

Persulfate (PS) has been increasingly applied for in situ chemical oxidation of organic contaminants in groundwater, while the impacts of humic acids (HAs) on the efficiency of persulfate/Fe2+-based remediation are not well understood. This study examined the effects of HAs originating from different places, including three commercial HAs and two soil HAs, on 2,4-dinitrotoluene (DNT) degraded by PS/Fe2+. DNT degradation by PS/Fe2+ was dependent on the types and concentrations of HAs and pH in solution. The positive correlation between the first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs and the conditional stability constant (KM) indicates that the complexation of HAs with Fe3+ was beneficial to the degradation of DNT. The first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs correlated well with their absorbance intensity of HAs at 465 or 665 nm. High positive correlation coefficients indicated that π-electrons of HAs strongly influenced DNT degradation, which was consistent with the results provided by solid-state 13C NMR spectra. Two-dimensional correlation spectroscopy (2DCOS) analysis confirmed that the fulvic-like fraction of HAs is prior to the humic-like fraction complexed with Fe3+.

Nitrobenzene contamination of groundwater in a petrochemical industry site

Organic contamination of groundwater is a major concern in China. However, remediation technology for groundwater contamination to address the potential harm and danger brought by the above-mentioned serious issue is still in the research stage. This study aims to improve the current research findings. In the research project, drilling, soil, and groundwater sampling and analysis were conducted in a contamination site of a petrochemical plant, migration of contaminants to the river was predicted using a numerical model, the sequence permeable reactive barrier (PRB) for treating nitrobenzene (NB) and benzene was proposed, and simulation was carried out. Research findings demonstrated that three leaking locations had been identified in the plant, the major pollutants were NB and benzene, and the groundwater contamination area was around 640000 m2. Computation results of the numerical model indicated that, in the worst case, the groundwater plume would reach the river after migration for nearly 9 years, which would endanger the safety of surface water supply. Furthermore, the two- PRB system with the filling of zero-valent iron (ZVI) and granular activated carbon attached with biofilm exerted strong remediation effects. Experimental results indicated that ZVI could transform NB to aniline effectively with a rate of approximately 93%. Meanwhile, aniline, benzene, and other organic pollutants could easily be biodegraded.

Reductive biotransformation as a pretreatment to enhance in situ chemical oxidation of nitroaromatic and nitroheterocyclic explosives

In Situ Chemical Oxidation (ISCO) is increasingly being used to remediate a variety of organic contaminants in soil and groundwater. Explosives, such as 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4-dintroanisole (DNAN), and 3-nitro-1,2,4-triazol-5-one (NTO), are not easily oxidized due to the presence of nitro groups in their structures. However, these nitro groups can be reduced to amino groups by soil microorganisms, making them more prone to oxidation. In this study, we propose bioreduction as a pretreatment to ISCO. The oxidation of DNAN, DNT, NTO, and their respective reduced transformation products, 2-methoxy-5-nitroaniline (MENA), 4-amino-2-nitrotoluene (NAT), and 3-amino-1,2,4-triazol-5-one (ATO), by potassium permanganate showed that lower permanganate concentrations and shorter time-scales are needed to oxidize the compounds once they are reduced. Significant fractions of the daughter products were mineralized to CO2 (30% and 22% for MENA and NAT, respectively, using 2.5 mM permanganate, and 48% for ATO using 1.0 mM permanganate). The bioreductive pretreatment was demonstrated by incubating 1.0 mM NTO anaerobically using soil as inoculum and pyruvate as electron donor. Once NTO was completely reduced to ATO, 1.0 mM permanganate was added, immediately oxidizing 86% of the compound. In controls without pretreatment, no oxidation was observed. NTO and ATO oxidation was tested in soils that differed in organic matter content. The results indicate that natural organic matter decreases the efficiency of NTO oxidation. However, ATO oxidation was not affected by the presence of soil. Our results suggest that the proposed reductive pretreatment followed by ISCO presents a safe and cost-effective alternative for explosives remediation.

The aqueous solubility of common organic groundwater contaminants as a function of temperature between 5 and 70 °C

High-temperature thermal energy storage in shallow aquifers can potentially increase ambient groundwater temperatures up to 70 °C or even more. Since an increase in temperature is expected to influence contaminant mass flux into groundwater monitoring the spreading of organic contaminants located in the subsurface is crucial. In numerous former studies, the NAPL solubility, one major parameter controlling mass flux on field scale, was measured at temperatures up to 70 °C for a broad spectrum of organic substances. However, quantitative calculations of solubilities as a function of temperature considering a compiled database are largely missing. Aiming to examine the reliability of existing solubility-temperature relationships, to describe them functionally and further to identify knowledge gaps, previously published data on solubilities of 42 different organic groundwater contaminants were evaluated in this study. By using a common temperature regression function, the calculated solubility curves from compiled solubility data for 5–70 °C show relative changes between a few percent (CHCs and BTEX) and up to 2000% (PAHs). As published temperature-dependent solubilities for chlorinated ethylenes are contradictory in parts, solubilities of tetrachloroethylene, trichloroethylene, 1,2-cis-dichloroethylene and 1,2-trans-dichloroethylene were additionally investigated in more detail using batch experiments between 5 and 70 °C. The results show distinctive solubility minima at medium temperatures (20–40 °C) with concentrations decreasing from 5 °C to the minimum by 10–20%. The measured and calculated temperature-dependent solubilities enable a more reliable assessment of thermal energy storage at contaminated sites, of existing thermal remediation approaches and of combinations of underground heat storage with groundwater remediation.

Impact of on-site wastewater infiltration systems on organic contaminants in groundwater and recipient waters

On-site sewage treatment facilities, particularly septic systems combined with soil infiltration, can be an important source of emerging organic contaminants in groundwater and surface water and thus represent a significant source of environmental and human exposure. Two infiltration systems in Åre municipality, Sweden, were examined to assess the occurrence of contaminants in groundwater and their fate and transport during infiltration. Groundwater samples, recipient surface water samples, and wastewater samples from septic tanks were collected from 2016 to 2017 covering all climatological seasons. These samples were analysed for a total of 103 contaminants, including pharmaceuticals, personal care products, organic phosphorus flame-retardants, plasticisers, perfluoroalkyl substances, and food additives. Fourteen of 103 contaminants showed 100% detection frequency in groundwater at concentrations in the low ng L−1 to low μg L−1 range. Of the compounds analysed, tris(2‑butoxyethyl) phosphate, sucralose, caffeine, and benzophenone showed high abundancy with maximum concentrations in the μg L−1 range. The data were normalised for dilution using chloride and sucralose as commonly applied tracers; however, the level of sucralose decreased significantly during infiltration and it is thus suboptimal as a sewage water tracer. Large differences between the two infiltration sites were observed in detection frequencies and concentrations in groundwater, which could be attributed to the system design and the contaminant's migration time from release to sampling point. Seasonal variation was observed for selected chemicals, and the more hydrophobic chemicals showed a higher tendency for attenuation, indicating sorption as a major retention mechanism. A moderate environmental risk to aquatic organisms was estimated in adjacent surface water for galaxolide, tris(1‑chloro‑2‑propyl) phosphate, and tris(2‑butoxyethyl) phosphate. Due to this site-dependency and potential environmental risks, further studies are needed on infiltration systems in different settings and on alternative treatment techniques to reduce the contaminant discharge from on-site sewage treatment facilities.

Fenton oxidation of organic contaminants with aquifer sediment activated by ascorbic acid

In this study, we report the desirable conversion of H2O2 to OH with aquifer sediment activated by ascorbic acid. Although aquifer sediment contained various iron minerals, such as goethite, hematite, montmorillonite, muscovite, chlorite and phlogopite, it could not efficiently activate H2O2 to produce OH. Interestingly, the presence of ascorbic acid dramatically promoted the OH conversion efficiency of H2O2 by aquifer sediment to remediate organic contaminants in groundwater, which was ascribed to the efficient iron cycle of aquifer sediment induced by ascorbic acid. Among these minerals in sediment, goethite and hematite were more reactive than other minerals to activate H2O2 in the presence of ascorbic acid. Although the initial pH could affect the OH conversion efficiency of H2O2, H2O2 could be decomposed by aquifer sediment at pH 3–11 after the introduction of ascorbic acid. Along with the complete degradation of organic contaminants, the final pH of solution increased to 8.3, which was close to the initial pH (8.9) of groundwater. Moreover, packed column of aquifer sediment could also catalyze the H2O2 conversion to OH for the removal of different organic contaminants with adding ascorbic acid, suggesting a new strategy for in situ chemical oxidation remediation of organic contaminated groundwater.

Transformation of antimicrobial agent sulfamethazine by peroxymonosulfate: Radical vs. nonradical mechanisms

Peroxymonosulfate (PMS) is increasingly used as an oxidant for in situ remediation of organic contaminants in soil and groundwater. In this study we demonstrated that sulfamethazine (SMZ) could be transformed by PMS in the absence of any activators. Such transformation was ascribed to the oxidation by PMS per se, rather than free radicals (SO4− or HO), superoxide (O2−), or singlet oxygen (1O2). The aniline moiety of SMZ molecule was the reactive site for PMS oxidation, leading to the formation of nitrated products. This nitration pathway in fact played a significant role in the removal of SMZ in activated PMS oxidation processes. For instance, it contributed 26% of the total SMZ transformation, while SO4− contributed the other 74% during the removal of SMZ, in Co(II)/PMS oxidation process with initial PMS and Co(II) concentrations of 1.0 mM and 0.1 μM, respectively. Similar nitration reaction also occurred to other sulfonamide antibiotics bearing an aniline moiety upon the reaction with PMS. Since nitrated sulfonamide antibiotics appear more persistent than the parent compounds and may cause other environmental problems, such a pathway should not be desired. Therefore, PMS might not be an ideal oxidant for the treatment of sulfonamide antibiotics and other compounds having aniline moieties, especially in subsurface remediation practices where efficient activation of PMS represents a major challenge.