Analytical performance of eight enzymatic assays for ethanol in serum evaluated by data from the Belgian external quality assessment scheme.

OBJECTIVES: Fast and reliable ethanol assays analysis are used in a clinical context for patients suspected of ethanol intoxication. Mostly, automated systems using an enzymatic reaction based on ethanol dehydrogenase are used. The manuscript focusses on the evaluation of the performance of these assays. METHODS: Data included 30 serum samples used in the Belgian EQA scheme from 2019 to 2021 and concentrations ranged from 0.13 to 3.70 g/L. A regression line between target concentrations and reported values was calculated to evaluate outliers, bias, variability and measurement uncertainty. RESULTS: A total of 1,611 results were taken into account. Bias was the highest for Alinity c over the whole concentration range and the lowest for Vitros for low concentrations and Cobas 8000 using the c702 module for high concentrations. The Architect and Cobas c501/c502 systems showed the lowest variability over the whole concentration range. Highest variability was observed for Cobas 8000 using the 702 module, Thermo Scientific and Alinity c. Cobas 8000 using the c702 module showed the highest measurement uncertainty for lower concentrations. For higher concentrations, Alinity c, Thermo Scientific and Vitros were the methods with the highest measurement uncertainty. CONCLUSIONS: The bias of the enzymatic techniques is nearly negligible for all methods except Alinity c. Variability differs strongly between measurement procedures. This study shows that the Alinity c has a worse measurement uncertainty than other systems for concentrations above 0.5 g/L. Overall, we found the differences in measurement uncertainty to be mainly influenced by the differences in variability.

Diagnostic Accuracy of Biomarkers of Alcohol Use in Patients With Liver Disease: A Systematic Review.

BACKGROUND AND AIMS: Alcohol-related liver disease is the most frequent cause of cirrhosis and a major indication for liver transplantation. Several alcohol use biomarkers have been developed in recent years and are already in use in several centers. However, in patients with liver disease their diagnostic performance might be influenced by altered biomarker formation by hepatic damage, altered excretion by kidney dysfunction and diuretics use, and altered deposition in hair and nails. We systematically reviewed studies on the diagnostic accuracy of biomarkers of alcohol use in patients with liver disease and performed a detailed study quality assessment. METHODS: A structured search in PubMed/Medline/Embase databases was performed for relevant studies, published until April 28, 2019. The risk of bias and applicability concerns was assessed according to the adapted quality assessment of diagnostic accuracy studies-2 (QUADAS-2) checklist. RESULTS: Twelve out of 6,449 studies met inclusion criteria. Urinary ethyl glucuronide and urinary ethyl sulfate showed high sensitivity (70 to 89 and 73 to 82%, respectively) and specificity (93 to 99 and 86 to 89%, respectively) for assessing any amount of alcohol use in the past days. Serum carbohydrate-deficient transferrin showed low sensitivity but higher specificity (40 to 79 and 57 to 99%, respectively) to detect excessive alcohol use in the past weeks. Whole blood phosphatidylethanol showed high sensitivity and specificity (73 to 100 and 90 to 96%, respectively) to detect any amount of alcohol use in the previous weeks. Scalp hair ethyl glucuronide showed high sensitivity (85 to 100%) and specificity (97 to 100%) for detecting chronic excessive alcohol use in the past 3 to 6 months. Main limitations of the current evidence are the lack of an absolute gold standard to assess alcohol use, heterogeneous study populations, and the paucity of studies. CONCLUSIONS: Urinary and scalp hair ethyl glucuronide are currently the most validated alcohol use biomarkers in patients with liver disease with good diagnostic accuracies. Phosphatidylethanol is a highly promising alcohol use biomarker, but so far less validated in liver patients. Alcohol use biomarkers can complement each other regarding diagnostic time window. More validation studies on alcohol use biomarkers in patients with liver disease are needed.

Suicide by vaping the synthetic cannabinoid 4F-MDMB-BINACA: cannabinoid receptors and fluoride at the crossroads of toxicity?

A 22-year-old man was hospitalized after stating he would 'commit suicide in a non-detectable way'. He was admitted with a severe necrotizing pancreatitis and acute kidney injury, evolving to multiple organ failure. His condition rapidly deteriorated, and he died 11 days after hospital admission. Postmortem histopathology confirmed fulminant necrotizing pancreatitis, acute tubular necrosis, cerebral edema, pericentral/midzonal hepatocellular necrosis and acute respiratory distress syndrome. Metabolites of 4F-MDMB-BINACA, a synthetic cannabinoid, were detected in urine and serum collected at hospital admission. The same drug was found in a vapor fluid found in the man's apartment. As cannabis use has been etiologically linked to acute pancreatitis, we hypothesize that the more afferent and potent 4F-MDMB-BINACA could induce acute pancreatitis via stimulation of cannabinoid (CB)1-receptors. Alternatively, terminal fluorination could have induced a dose-dependent toxic effect on a wide range of cellular processes, leading to cell dysfunction and death. This is the first clinicopathological description of a lethal intoxication with 4F-MDMB-BINACA, following extensive vaping. Toxic effects could either relate to CB-receptor binding or to direct fluoride toxicity.

How to Interpret Hair EtG Concentrations in Individuals with High Body Mass Index? Brief Commentary on: Influence of Body Mass Index on Hair Ethyl Glucuronide Concentrations.

Body mass index (BMI) is a variable that complicates the interpretation of the alcohol metabolite ethyl glucuronide (EtG) in hair. However, direction on how EtG should currently be interpreted within individuals consuming moderate and excessive daily amounts of alcohol related to their BMI is lacking. In light of interpretation of EtG in individuals with high BMI, we present post hoc analysis of earlier data regarding the effect of BMI on hair EtG concentrations.

Influence of Body Mass Index on Hair Ethyl Glucuronide Concentrations.

AIM: Analysis of ethyl glucuronide (EtG) concentrations in hair is increasingly used to estimate the consumption of alcohol of the prior months. Linear correlations between the amount of alcohol consumed and the concentration of EtG in hair have been reported, and several variables that may influence this correlation have been investigated: e.g. cosmetic hair treatments, gender influences or hair color. Here, we investigate the influence of body mass index (BMI) on this correlation. METHODS: A post hoc analysis on the influence of BMI on the relation between amounts of alcohol consumed and the measured EtG concentrations in hair in 199 participants. RESULTS: Our data show higher EtG concentrations in participants with high BMI (≥25) compared to participants with low BMI (<25) (P = 0.001) across a wide range of amounts of alcohol consumed. CONCLUSIONS: We conclude that BMI should be taken into account when interpreting hair EtG concentrations. SHORT SUMMARY: Ethyl glucuronide concentrations in hair (hEtG) can be used to estimate the consumption of alcohol of the prior months. Body mass index (BMI) influences this relation and BMI should be taken into account when interpreting hEtG concentrations in participants with high BMI (≥25) compared to participants with low BMI (<25).

Determination of Common Antipsychotics in Quantisal-Collected Oral Fluid by UHPLC-MS/MS: Method Validation and Applicability for Therapeutic Drug Monitoring.

BACKGROUND: Oral fluid (OF) is an interesting alternative for conventional blood testing in therapeutic drug monitoring. OF can be used for screening but its value for quantification has to be established. METHODS: To evaluate the value of OF for quantification of 11 commonly used antipsychotics (APs) and 5 metabolites, an ultra-high performance liquid chromatography-tandem mass spectrometric method was validated. OF was obtained from psychiatric patients using a Quantisal collection device. OF to serum concentration ratios were determined, taking into account the exact volume of collected OF. RESULTS: Linearity was evaluated at 7 or 8 calibration levels. Accuracy criteria were fulfilled, except for pipamperone (PIP) at quality control (QC) low. The intraday precision ranged 0.88%-14.73% and interday precision ranged 1.92%-16.17%. The mean recovery from the collection pad was 37.1% at QC low and 40.3% at QC high for 1 mL of collected OF; for 0.5 mL collected OF mean recovery was 35.0% at QC low and 37.3% at QC high. When 0.1 mL OF was collected, recovery data were unreliable. Mean absolute matrix effect was 101.1% (82.0%-120.0%). OF patient samples (n = 89) containing 269 APs and metabolites were acquired and the mean volume of collected OF was 0.562 mL (0.057-1.232 mL). The OF to serum ratios were above 1 for all APs (1.54-28.50), except for aripiprazole (0.21) and zuclopenthixol (0.66). A broad range of calculated ratios for all APs was obtained. CONCLUSIONS: This validated ultra-high performance liquid chromatography-tandem mass spectrometric method can be used to reliably quantify APs in OF, even when recovery is low. Because the correlation between OF and serum concentrations was low and in addition results were highly variable, it can only be concluded that OF is a potentially interesting matrix, particularly for screening for noncompliance.

Does Biotransformation of Aryl Phosphate Flame Retardants in Blood Cast a New Perspective on Their Debated Biomarkers?

Aryl phosphate flame retardants (aryl-PFRs), such as triphenyl phosphate (TPHP) and 2-ethylhexyl diphenyl phosphate (EHDPHP), are emerging contaminants that can exhibit toxic properties, including severe aquatic toxicity and endocrine disruptive effects. Monitoring exposure to aryl-PFRs through specific biomarkers is necessary to assess the health risk associated with chronic exposure. Hydrolytic serum enzymes could play an important role in the formation of the hydrolysis product diphenyl phosphate (DPHP), the seemingly most abundant in vivo biomarker of TPHP in urine. Here, we assess whether serum enzymes have an impact on the toxicokinetics of TPHP and EHDPHP and on the contribution of both aryl-PFRs to in vivo DPHP levels. TPHP and EHDPHP were incubated separately with pooled human serum to measure the formation of hydrolysis products DPHP and 2-ethylhexyl phenyl phosphate (EHPHP) by liquid chromatography-tandem mass spectrometry. Clearance of TPHP and EHDPHP was 70 and 8.6 mL/min/L serum (as measured by formation of DPHP and EHPHP, respectively). No discernible amount of DPHP was produced from EHDPHP by serum hydrolases. Our results suggest that serum hydrolases can significantly contribute to the in vivo levels of DPHP formed from TPHP and can play an important role in the toxicokinetics, toxicity, and selection of biomarkers for aryl-PFRs.

Comprehensive Study of Human External Exposure to Organophosphate Flame Retardants via Air, Dust, and Hand Wipes: The Importance of Sampling and Assessment Strategy.

We compared the human exposure to organophosphate flame retardants (PFRs) via inhalation, dust ingestion, and dermal absorption using different sampling and assessment strategies. Air (indoor stationary air and personal ambient air), dust (floor dust and surface dust), and hand wipes were sampled from 61 participants and their houses. We found that stationary air contains higher levels of ΣPFRs (median = 163 ng/m(3), IQR = 161 ng/m(3)) than personal air (median = 44 ng/m(3), IQR = 55 ng/m(3)), suggesting that the stationary air sample could generate a larger bias for inhalation exposure assessment. Tris(chloropropyl) phosphate isomers (ΣTCPP) accounted for over 80% of ΣPFRs in both stationary and personal air. PFRs were frequently detected in both surface dust (ΣPFRs median = 33 100 ng/g, IQR = 62 300 ng/g) and floor dust (ΣPFRs median = 20 500 ng/g, IQR = 30 300 ng/g). Tris(2-butoxylethyl) phosphate (TBOEP) accounted for 40% and 60% of ΣPFRs in surface and floor dust, respectively, followed by ΣTCPP (30% and 20%, respectively). TBOEP (median = 46 ng, IQR = 69 ng) and ΣTCPP (median = 37 ng, IQR = 49 ng) were also frequently detected in hand wipe samples. For the first time, a comprehensive assessment of human exposure to PFRs via inhalation, dust ingestion, and dermal absorption was conducted with individual personal data rather than reference factors of the general population. Inhalation seems to be the major exposure pathway for ΣTCPP and tris(2-chloroethyl) phosphate (TCEP), while participants had higher exposure to TBOEP and triphenyl phosphate (TPHP) via dust ingestion. Estimated exposure to ΣPFRs was the highest with stationary air inhalation (median =34 ng·kg bw(-1)·day(-1), IQR = 38 ng·kg bw(-1)·day(-1)), followed by surface dust ingestion (median = 13 ng·kg bw(-1)·day(-1), IQR = 28 ng·kg bw(-1)·day(-1)), floor dust ingestion and personal air inhalation. The median dermal exposure on hand wipes was 0.32 ng·kg bw(-1)·day(-1) (IQR = 0.58 ng·kg bw(-1)·day(-1)) for ΣTCPP. The selection of sampling and assessment strategies could significantly affect the results of exposure assessment.

Ethyl glucuronide concentrations in hair: a controlled alcohol-dosing study in healthy volunteers.

Ethyl glucuronide (EtG) is a minor phase II metabolite of alcohol that accumulates in hair. It has been established as a sensitive marker to assess the retrospective consumption of alcohol over recent months using a cut-off of ≥7 pg/mg hair to assess repeated alcohol consumption. The primary aim was to assess whether amounts of alcohol consumed correlated with EtG concentrations in hair. Additionally, we investigated whether the current applied cut-off value of 7 pg/mg hair was adequate to assess the regular consumption of low-to-moderate amounts of alcohol. A prospective controlled alcohol-dosing study in 30 healthy individuals matched on age and gender. Individuals were instructed to drink no alcohol (N = 10), 100 g alcohol per week (N = 10) or 150 g alcohol per week (N = 10) for 12 consecutive weeks, before and after which hair was collected. Throughout the study, compliance to daily alcohol consumption was assessed by analyzing urine EtG three times weekly. Participants in the non-drinking group had median EtG concentrations of 0.5 pg/mg hair (interquartile range (IQR) 1.7 pg/mg; range < 0.21-4.5 pg/mg). Participants consuming 100 and 150 g alcohol per week showed median EtG concentrations of 5.6 pg/mg hair (IQR 4.7 pg/mg; range 2.0-9.8 pg/mg) and 11.3 pg/mg hair (IQR 5.0 pg/mg; range 7.7-38.9 pg/mg), respectively. Hair EtG concentrations between the three study groups differed significantly from one another (p < 0.001). Hair EtG concentrations can be used to differentiate between repeated (low-to-moderate) amounts of alcohol consumed over a long time period. For the assessment of repeated alcohol use, we propose that the current cut-off of 7 pg/mg could be re-evaluated.

Biotransformation of three phosphate flame retardants and plasticizers in primary human hepatocytes: untargeted metabolite screening and quantitative assessment.

Tris(2-butoxyethyl) phosphate (TBOEP), triphenyl phosphate (TPHP) and tris(1-chloro-2-propyl) phosphate (TCIPP) are current high-volume organophosphate flame retardants/plasticizers (PFRs) and are abundant in the indoor environment. While recent in vitro research has indicated potential toxic effects in the endocrine system, biotransformation of these compounds is still underexplored. In this study, we aimed to characterize the metabolite formation for three PFRs in primary human hepatocytes, an in vitro system that mimics in vivo liver metabolism more closely than hepatic subcellular fractions or cell lines. Cryopreserved human hepatocytes were thawed and suspended in media with 50 µm TBOEP or TCIPP, or 20 µm TPHP up to 2 h. Extracts were analyzed by liquid chromatography-quadrupole-time-of-flight-mass spectrometry. Quantification of biotransformation products in hepatocytes exposed for 2 h revealed that bis(1-chloro-2-propyl) phosphate and diphenyl phosphate corresponded to less than half of the depletion of TCIPP and TPHP, respectively, while bis(2-butoxyethyl) 2-hydroxyethyl phosphate compared to 40-66% of the depletion of TBOEP. Other metabolite structures of these PFRs were produced at 4- to 10-fold lower rates. These findings help interpret biological levels of the major metabolites and relate it to levels of their parent PFR. Percentage of substrate depletion was largest for TBOEP followed by comparable values for TPHP and TCIPP, indicating that hepatic clearance of TPHP and TCIPP would be slower than that of TBOEP. The resulting higher levels and longer presence of TPHP in the circulation after exposure, would allow TPHP a larger time window to exert its suspected adverse effects compared to TBOEP. Copyright © 2016 John Wiley & Sons, Ltd.

Application of the characteristic function to evaluate and compare analytical variability in an external quality assessment scheme for serum ethanol.

BACKGROUND: As a cornerstone of quality management in the laboratory, External Quality Assessment (EQA) schemes are used to assess laboratory and analytical method performance. The characteristic function is used to describe the relation between the target concentration and the EQA standard deviation, which is an essential part of the evaluation process. The characteristic function is also used to compare the variability of different analytical methods. METHODS: We fitted the characteristic function to data from the Belgian External Quality Assessment program for serum ethanol. Data included results from headspace gas chromatography and the enzymatic methods of Abbott, Roche, Siemens, and Ortho-Clinical Diagnostics. We estimated the characteristic function with weighted nonlinear regression. By introducing dummy variables, we rewrote the original formula of the characteristic function to assess statistical inference for comparing the variability of the different analytical methods. RESULTS: The characteristic function fitted the data precisely. Comparison between methods showed that there was little difference between the estimated variability for low concentrations, and that the increase in SD with increasing target concentration was slower for Abbott and Roche than for the other methods. CONCLUSIONS: The characteristic function can successfully be introduced in clinical schemes, although its applicability to fit the data should always be assessed. Because of its easy parameterization, it can be used to assess differences in performance between analytical methods and to assess laboratory performance. The characteristic function also offers an alternative framework for coefficients of variation to describe variability of analytical methods.

In vitro biotransformation of tris(2-butoxyethyl) phosphate (TBOEP) in human liver and serum.

Tris(2-butoxyethyl) phosphate (TBOEP) is a plasticizer present in indoor dust, reaching levels of several micrograms per gram. Such levels could lead to significant daily exposure of adults and children. Currently, no toxicokinetic data are available to estimate TBOEP clearance in humans after uptake and therefore, one objective of this study was to investigate intrinsic clearance of TBOEP by human liver microsome (HLM) and serum enzymes. Another objective was to generate information to identify and prioritize several metabolites of TBOEP for investigation of human exposure by biomonitoring. 1D and 2D-NMR methodologies were successfully applied on a mixture of the metabolites to confirm the structure of 3-HO-TBOEP (bis(2-butoxyethyl) 3-hydroxyl-2-butoxyethyl phosphate) and to tentatively assign structures to 1-HO-TBOEP and 2-HO-TBOEP. HO-TBOEP isomers and bis(2-butoxyethyl) phosphate (BBOEP), bis(2-butoxyethyl) hydroxyethyl phosphate (BBOEHEP) were further monitored by liquid chromatography-tandem mass spectrometry. Rates of formation of BBOEHEP and HO-TBOEP metabolites by liver enzymes were best described by the Michaelis-Menten model. Apparent Km values for BBOEHEP, 3-HO-TBOEP, and sum of 1- and 2-HO-TBOEP isomer formation were 152, 197 and 148µM, respectively. Apparent Vmax values for the formation of BBOEHEP, 3-HO-TBOEP, and the sum of 1- and 2-HO-TBOEP isomers were 2560, 643, and 254pmol/min/mg protein, respectively. No detectable formation of BBOEP occurred with liver or serum enzymes. Our findings indicate that intrinsic clearance of TBOEP is mainly catalyzed by oxidative enzymes in the liver and that its major in vitro metabolite is BBOEHEP. These findings can be applied in human biomonitoring studies and risk assessment.

In vitro Phase I and Phase II metabolism of α-pyrrolidinovalerophenone (α-PVP), methylenedioxypyrovalerone (MDPV) and methedrone by human liver microsomes and human liver cytosol.

The aim of the present study was to identify the in vitro Phase I and Phase II metabolites of three new psychoactive substances: α-pyrrolidinovalerophenone (α-PVP), methylenedioxypyrovalerone (MDPV), and methedrone, using human liver microsomes and human liver cytosol. Accurate-mass spectra of metabolites were obtained using liquid chromatography-quadrupole time-of-flight mass spectrometry. Six Phase I metabolites of α-PVP were identified, which were formed involving reduction, hydroxylation, and pyrrolidine ring opening reactions. The lactam compound was the major metabolite observed for α-PVP. Two glucuronidated metabolites of α-PVP, not reported in previous in vitro studies, were further identified. MDPV was transformed into 10 Phase I metabolites involving reduction, hydroxylation, and loss of the pyrrolidine ring. Also, six glucuronidated and two sulphated metabolites were detected. The major metabolite of MDPV was the catechol metabolite. Methedrone was transformed into five Phase I metabolites, involving N- and O-demethylation, hydroxylation, and reduction of the ketone group. Three metabolites of methedrone are reported for the first time. In addition, the contribution of individual human CYP enzymes in the formation of the detected metabolites was investigated.

Organophosphorus flame retardants in the European eel in Flanders, Belgium: Occurrence, fate and human health risk.

The present study investigated the levels, profiles and human health risk of organophosphorus flame retardants and plasticizers (PFRs) in wild European eels (Anguilla anguilla) from freshwater bodies in the highly populated and industrial Flanders region (Belgium). Yellow eels (n=170) were collected at 26 locations between 2000 and 2009 and for each site, muscle samples of 3-10 eels were pooled and analyzed (n=26). Muscle lipid percentages varied widely between 2.4% and 21%, with a median value of 10%. PFRs were detected in all pooled samples in the order of tris-2-chloroisopropyl phosphate (TCIPP)>triphenyl phosphate (TPHP)>2-ethylhexyl diphenyl phosphate (EHDPHP)>tris-2-butoxyethyl phosphate (TBOEP)>tris-2-chloroethyl phosphate (TCEP)>tris-1,3-dichloro-2-propyl phosphate (TDCIPP). The median sum PFR concentration for all 26 sites was 44 ng/g lw (8.4 ng/g ww), and levels ranged between 7.0 and 330 ng/g lw (3.5 and 45 ng/g ww). Levels and profiles of PFRs in eels showed that sampling locations and river basin catchments are possible drivers of spatial variation in the aquatic environment. Median PFR concentrations were lower than those of polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). No correlation was observed between the PFR concentrations and lipid contents, suggesting that the accumulation of PFRs is not primarily associated with lipids. Human exposure to PFRs, due to consumption of wild eels, seems to be of minor importance compared to other potential sources, such as inhalation and ingestion of indoor dust. Nevertheless, considering the very limited data available on PFRs in human dietary items and their expected increasing use after the phase out of PBDEs and HBCDs, further investigations on PFRs in biota and human food items are warranted.

The complementarity of phosphatidylethanol in whole blood and ethyl glucuronide in hair as biomarkers for the monitoring of alcohol use.

Monitoring long-term alcohol use and/or abstinence is essential in clinical and medico-legal cases. Analysis of ethyl glucuronide (EtG) in hair provides information on alcohol consumption over several months. However, there is a lag time between ethanol consumption, incorporation of EtG in the hair bulb and hair growing out of the scalp. Phosphatidylethanol (PEth) 16:0/18:1 analysis in whole blood has a detection window of 2-4 weeks, allowing for the detection of recent alcohol consumption. In this study, 2340 paired samples (of hair and venous whole blood from 1170 individuals) were analysed for EtG in hair (hEtG) and PEth 16:0/18:1 in venous whole blood. PEth 16:0/18:1 and hEtG results were subdivided into three categories according to the consensus of SoHT (hEtG) and PEth-NET (PEth): abstinence/low, moderate or excessive alcohol consumption. For hEtG analysis, 446 individuals presented abstinence/low alcohol consumption, of which 2% were classified as excessive alcohol users through PEth 16:0/18:1 analysis. This suggests excessive alcohol consumption in the weeks before sample collection. Out of 483 individuals classified as heavy alcohol users based on hEtG analysis, 14% showed abstinence/low alcohol consumption for PEth 16:0/18:1 analysis, implying that these subjects stopped drinking 2-4 weeks before sample collection. Our results show that the analysis of the two different biomarkers can lead to a more accurate categorisation of individuals. Therefore, we emphasize that for the retrospective investigation of alcohol use, it is necessary to include two alcohol use biomarkers with different detection windows.

Dynamics of organohalogenated contaminants in human serum from obese individuals during one year of weight loss treatment.

We investigated the dynamics of several organohalogenated contaminants (OHCs) and their metabolites in an obese population during weight loss. Serum samples from obese individuals were taken before patients lost weight and after three, six, and twelve months. Samples were also collected from a matched lean control population. Analyzed OHCs were polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (HO-PCBs), pentachlorophenol (PCP), polybrominated diphenyl ethers, and organochlorine pesticides (OCPs). Significantly lower concentrations of major PCBs, their metabolites, and PCP were measured in obese individuals at the initial moment of their enrolling in the project. While dilution differences might be responsible for the lower concentrations in the neutral OHCs, we suggest that a lower CYP-mediated metabolic activity can partially explain the data for the HO-PCBs. Additionally, lower chlorinated substituted PCBs had a higher percentage contribution to the sum PCBs in obese individuals, while higher chlorinated PCBs had a higher contribution for the controls. Increasing serum levels for all OHCs were observed during weight loss. The release from adipose tissue seemed dependent on the octanol-water partition coefficient, since OHCs with higher log Kow values displayed a higher release in serum. This also influenced the HO-PCBs profile after weight loss with lower chlorinated HO-PCBs increasingly gaining importance. Although weight loss is beneficial, it also influences the release of OHCs from adipose tissue and their metabolism. Therefore, the increase in the levels of compounds with endocrine effects might be of concern.