Ozonation of Gabapentin in Water─Investigating Reaction Kinetics and Transformation Mechanisms of a Primary Amine Using Isotopically Labeled Ozone

Aliphatic amines are abundant micropollutants in wastewater treatment plant effluents. In order to mitigate such micropollutants, ozonation is one of the most commonly employed advanced treatment processes. Current research regarding ozone efficiency is heavily focusing on reaction mechanisms of different contaminant groups, including structures with amine moieties as reactive sites. This study analyzes pH-dependent reaction kinetics and pathways of gabapentin (GBP), an aliphatic primary amine with an additional carboxylic acid group. The transformation pathway was elucidated applying a novel approach using isotopically labeled ozone (18O) and quantum chemistry calculations. While the direct reaction of GBP with ozone is highly pH-dependent and slow at pH 7 (13.7 M-1 s-1), the rate constant of the deprotonated species (1.76 × 105 M-1 s-1) is comparable to those of other amine compounds. Pathway analysis based on LC-MS/MS measurements revealed that ozonation of GBP leads to the formation of a carboxylic acid group and simultaneous nitrate formation, which was also observed in the case of the aliphatic amino acid glycine. Nitrate was formed with a yield of approximately 100%. Experiments with 18O-labeled ozone demonstrated that the intermediate aldehyde does most likely not include any oxygen originating from ozone. Furthermore, quantum chemistry calculations did not provide an explanation for the C-N scission during GBP ozonation without ozone involvement, although this reaction was slightly more favorable than for respective glycine and ethylamine reactions. Overall, this study contributes to a deeper understanding of reaction mechanisms of aliphatic primary amines during wastewater ozonation.

Advanced oxidation processes for removal of monocyclic aromatic hydrocarbon from water: Effects of O3/H2O2 and UV/H2O2 treatment on product formation and biological post-treatment

Several oxidative treatment technologies, such as ozonation or Fenton reaction, have been studied and applied to remove monocyclic hydroaromatic carbon from water. Despite decades of application, little seems to be known about formation of transformation products while employing different ozone- or ^∙OH-based treatment methods and their fate in biodegradation. In this study, we demonstrate that O₃/H₂O₂ treatment of benzene, toluene, ethylbenzene (BTE), and benzoic acid (BA) leads to less hydroxylated aromatic transformation products compared to UV/H₂O₂ as reference system - this at a similar ^∙OH exposure and parent compound removal efficiency. Aerobic biodegradation tests after oxidation of 0.15 mM BA (12.6 mg C L^-1 theoretical DOC) revealed that a less biodegradable DOC fraction > 4 mg C L^-1 was formed in both oxidative treatments compared to the BA control. No advantage of ozonation over UV/H₂O₂ treatment was observed in terms of mineralization capabilities, however, we detected less transformation products after oxidation and biodegradation using high-resolution mass spectrometry. Biodegradation of BA that was not oxidized was more complete with minimal organic residual. Overall, the study provides new insights into the oxidation of monocyclic aromatics and raises questions regarding the biodegradability of oxidation products, which is relevant for several treatment applications.

Isotopically labeled ozone: A new approach to elucidate the formation of ozonation products

As ozonation becomes a widespread treatment for removal of chemicals of emerging concern from wastewater treatment plant effluents, there are increasing concerns regarding the formation of ozonation products (OPs), and their possible impacts on the aquatic environment and eventually human health. In this study, a novel method was developed that utilizes heavy oxygen (¹⁸O₂) for the production of heavy ozone ([¹⁸O₁]O₂, [¹⁸O₂]O₁, [¹⁸O₃]) to actively label OPs from oxygen transfer reactions. To establish and validate this new approach, venlafaxine with a well-described oxygen transfer reaction (tertiary amine -> N-oxide) was chosen as a model compound. Observed ¹⁸O/¹⁶O ratios in the major OP venlafaxine N-oxide (NOV) correlated with expected ¹⁸O purities based on tracer experiments. These results confirmed the successful labeling with heavy oxygen and furthermore demonstrate the potential to monitor NOV as an indicator of ¹⁸O/¹⁶O ratios during ozonation. As a next step, ¹⁸O/¹⁶O ratios were used to elucidate the formation mechanism of previously described OPs from sulfamethoxazole (SMX). Seven OPs were detected including the frequently described nitro-SMX, which was formed with a maximum yield of 3.2% (of initial SMX). With the successful labeling of six of the seven OPs from sulfamethoxazole, it was possible to confirm their previously proposed formation pathways, and to distinguish oxygen transfer from electron transfer reactions. ¹⁸O/¹⁶O ratios in OPs indicate that hydroxylation of the aromatic ring and formation of nitro-groups mostly follows oxygen transfer reactions, while electron transfer reactions initiate the formation of hydroxylamine and the abstraction of NH₂ leading to catechol.

Characterizing a novel in-situ oxygen delivery device for establishing controlled redox zonation within a high infiltration rate sequential biofilter

By applying favorable oxic and oligotrophic conditions through subsequent aeration and an additional infiltration step, the sequential managed aquifer recharge technology (SMART) was proven to better remove trace organic chemicals (TOrCs) than conventional MAR systems. To minimize the physical footprint, pumping costs and hydraulic retention times, as well as to overcome limitations of site-specific heterogeneities of such systems, the SMART concept was further upgraded by two main engineered technologies. This SMARTplus bioreactor is comprised of an infiltration trench and highly homogenous porous media to provide high infiltration rates and plug-flow conditions. Additionally, an in-situ oxygen delivery device, in particular a self-designed PDMS gas-liquid membrane contactor, was designed to establish favorable subsurface oxic conditions. This novel SMARTplus technology was investigated at pilot scale and is designed for advanced water treatment either in the context of water reuse or treatment of impaired surface water. To determine the design specifications and to construct a pilot-scale membrane contactor, the mass transfer coefficients of the PDMS membrane were investigated at lab-scale for varying Reynold numbers (0.2-2). With the help of the customized membrane contactor, homogenous, bubble-free and passive oxygen delivery could be successfully demonstrated at pilot-scale under laminar flow conditions and short contact times. Oxygen concentrations downstream of the membrane contactors met the design specifications (>1 mg/L) as long as the required feed water quality was provided. However, high NH₄⁺ concentrations in the secondary effluent resulted in higher and unsteady oxygen demand than the target oxygen transfer rates could meet and suboxic conditions prevailed. Although a 20-50% enhancement in the removal of certain compounds (4-FAA, antipyrine, sulfamethoxazole, and citalopram) was achieved, demonstration of the full potential of enhanced TOrC removal by SMARTplus was hindered due to unsteady feed water quality.

Alcohol use, drug use and alcohol-related problems among men who have sex with men: the Urban Men's Health Study

AIMS

To measure the prevalence and independent associations of heavy and problematic use of alcohol and recreational drugs among a household-based sample of urban MSM (men who have sex with men).

DESIGN

Cross-sectional survey.

PARTICIPANTS

Men who identified as being gay or bisexual or who reported sex with another man in the prior 5 years were included in this analysis (n = 2172).

SETTING

A probability telephone sample of MSM was taken within Zip Codes of four large American cities (Chicago, Los Angeles, New York and San Francisco) estimated to have total concentrations of at least 4% of all households with one resident MSM.

MEASUREMENTS

Standard measures of alcohol use, problems associated with alcohol use, and recreational drug use were administered by trained telephone interviewers.

FINDINGS

Both recreational drug (52%) and alcohol use (85%) were highly prevalent among urban MSM, while current levels of multiple drug use (18%), three or more alcohol-related problems (12%), frequent drug use (19%) and heavy-frequent alcohol use (8%) were not uncommon. The associations of heavy and/or problematic substance use are complex, with independent multivariate associations found at the levels of demographics, adverse early life circumstances, current mental health status, social and sexual practices and connection to gay male culture.

CONCLUSIONS

The complex pattern of associations with heavy and/or problematic substance use among urban MSM suggests that heavy and/or problematic substance use is grounded in multiple levels: the individual, the interpersonal and the socio-cultural.

The impact of homophobia, poverty, and racism on the mental health of gay and bisexual Latino men: findings from 3 US cities

OBJECTIVES

This study assessed the relation between experiences of social discrimination (homophobia, racism, and financial hardship) and symptoms of psychologic distress (anxiety, depression, and suicidal ideation) among self-identified gay and bisexual Latino men in the United States.

METHODS

Data were collected from a probability sample of 912 men (self-identified as both Latino and nonheterosexual) recruited from the venues and public social spaces identified as both Latino and gay in the cities of Miami, Los Angeles, and New York.

RESULTS

The study showed high prevalence rates of psychologic symptoms of distress in the population of gay Latino men during the 6 months before the interview, including suicidal ideation (17% prevalence), anxiety (44%), and depressed mood (80%). In both univariate and multivariate analyses, experiences of social discrimination were strong predictors of psychologic symptoms.

CONCLUSIONS

The mental health difficulties experienced by many gay and bisexual Latino men in the United States are directly related to a social context of oppression that leads to social alienation, low self-esteem, and symptoms of psychologic distress.

Relapse outcomes in a randomized trial of residential and day drug abuse treatment

Relapse outcomes at 6-, 12-, and 18-month intervals were compared between clients randomly assigned to day (n=114) versus residential (n=147) drug abuse treatment. Day clients were more likely than residential clients to relapse 6 months post-admission (OR=3.06, p<0.001); however, no setting differences at 12 or 18 months were found. Few baseline predictors were prospectively related to relapse at 12 and 18 months. These predictors were usual employment status (part-time OR=17.47, p<0.001; full-time OR=2.54, p<0.001), history of drug injecting (OR=5.39, p<0.01), multiple sex partners (OR=1.16, p<0.01), and not having a gay sexual partner (OR=0.05, p<0.03) during 6 months prior to admission. Still, these baseline predictors, together with the existing literature, could be used by drug treatment professionals to identify individuals who may be at high risk for relapse over time, and to offer specialized treatment and aftercare resources as intervention and prevention measures.

Correlates of heavy substance use among young gay and bisexual men: The San Francisco Young Men's Health Study

Correlates of heavy substance use among a household-based sample of young gay and bisexual men (n=428) were identified and the odds ratio (OR) was calculated. A total of 13.6% reported frequent, heavy alcohol use and 43% reported polydrug use. Compared with men employed in professional occupations, men in service positions (OR=3.77) and sales positions (OR=2.51) were more likely to be heavy alcohol consumers. Frequent gay bar attendance and multiple sex partners were related to heavy alcohol use, as well as to polydrug use. Polydrug users were more likely to be HIV seropositive (OR=2.05) or of unknown HIV serostatus (OR=2.78). HIV serostatus was similarly related to frequent drug use. These correlates of heavier substance use among young gay and bisexual men could be used to identify and intervene early with members of this population who are at risk of substance misuse, as well as HIV/AIDS risk.

An outcome evaluation to measure changes in sexual risk-taking among gay men undergoing substance use disorder treatment

OBJECTIVE

To evaluate the effects of safe sex intervention at a substance use disorder treatment agency designed to serve gay men.

METHOD

Of all eligible men, 456 (78%) were recruited as they entered treatment for a substance use disorder. This cohort was followed for five waves of data collection, each wave measuring the previous 90 days. Assigned to the experimental condition (treatment for substance use disorder plus a safe sex intervention) were 82 men; 65 were assigned to the regular substance use disorder treatment.

RESULTS

Although levels of risk within each wave were never significantly different between the two treatment groups, reductions in unprotected anal intercourse (UAI) with a nonmonogamous partner for both groups from the baseline Wave-1 levels were uniformly significant (all p's < .05). Such high-risk sex in the year-long follow-up period was correlated with UAI reported at intake, enjoyment of UAI, relative youth, heavier concurrent use of alcohol or amphetamines and greater numbers of sexual partners.

CONCLUSIONS

We conclude that: (1) substantial HIV risk reductions can occur after initiation of treatment for substance use disorder among gay men; (2) risk reductions begin soon after treatment begins; (3) lapses to unsafe sex are common during treatment; (4) continued UAI is most likely among those men who are riskier at intake, who continue to be more sexually active and who are more likely to combine substance use and sexual behavior; (5) AIDS prevention activities conducted at treatment agencies cannot reach all high-risk substance-using gay men.