Transformation of phenylarsenic chemical warfare agents and their effect on bacterial communities in Baltic Sea sediment.

During the World Wars large quantities of phenylarsenic chemical warfare agents (CWAs) were dumped in the Baltic Sea. Many transformation products of these chemicals have been identified, but the pathways that produce the found chemicals has not been investigated. Here we studied the biotic and abiotic transformation of phenylarsenic CWAs under oxic and anoxic conditions and investigated how the sediment bacterial communities are affected by CWA exposure. By chemical analysis we were able to identify seventeen CWA-related phenylarsenicals, four of which (methylphenylarsinic acid (MPAA), phenylthioarsinic acid (PTAA), phenyldithioarsinic acid (PDTAA) and diphenyldithioarsinic acid (DPDTAA)) have not been reported for marine sediments before. For the first time PTAA was verified from environmental samples. We also observed equilibrium reactions between the found transformation products, which may explain the occurrence of the chemicals. 16S rRNA-analysis showed that bacterial communities in sediments are affected by exposure to phenylarsenic CWAs. We observed increases in the amounts of arsenic-resistant and sulphur-metabolising bacteria. Different transformation products were found in biotic and abiotic samples, which suggests that bacteria participate in the transformation of phenylarsenic CWAs. We propose that methylated phenylarsenicals are produced in microbial metabolism and that chemical reactions with microbially produced sulphur species form sulphur-containing transformation products.

Computational analysis of an electrostatic separator design for removal of volatile organic compounds from indoor air.

Concentrations of volatile organic compounds (VOCs) in air can be reduced in electrostatic separators where VOCs are ionized using ion-molecule reactions, extracted using electric fields, and eliminated in a waste flow. Embodiments for such separator technology have been explored in only a few studies, despite the possible advantage of purification without adsorbent filters. In one design, based on ionization of VOCs in positive polarity with hydrated protons as reactant ions, efficiencies for removal were measured as 30-40% . The results were fitted to a one-dimensional convective diffusion model requiring an unexpectedly high production rate of reactant ions to match both the model and data. A realistic rate of reactant ion production was used in finite element method simulations (COMSOL) and demonstrated that low removal efficiency could be attributed to non-uniform patterns of sample flow and to incomplete mixing of VOCs with reactant ions. In analysis of complex systems, such as this model, even limited computational modeling can outperform a pure analytical approach and bring insights into limiting factors or system bottlenecks.Implications: In this work, we applied modern computational methods to understand the performance of an air purifier based on electrostatics and ionized volatile organic compounds (VOCs). These were described in the publication early 2000s. The model presented was one-dimensional and did not account for the effects of flow. In our multiphysics finite element models, the efficiency and operation of the filter is better explained by the patterns of flow and flow influences on ion distributions in electric fields. In general, this work helps using and applying computational modelling to understand and improve the performance bottlenecks in air purification system designs.

Chlorinated organic compounds in concrete as specific markers for chlorine gas exposure.

The formation of chlorinated organic compounds in concrete debris exposed to reactive chlorine was studied to search for markers specific to chlorine gas exposure. Concrete materials of different origins were exposed to a range of species of reactive chlorine including bleach, humid and dry chlorine gas at different concentrations. Chlorinated organic compounds in concrete extracts were analysed by targeted gas and liquid chromatography-tandem mass spectrometry (GC-MS/MS and LC-MS/MS) and by non-targeted screening using the corresponding high-resolution techniques (GC-HRMS and LC-HRMS). Overall, different levels and species of chlorinated organic compounds namely chlorophenols, chlorobenzenes, chloromethoxyphenols, chloromethylbenzenes and chloral hydrate were identified in these chlorinated concrete extracts; two examples of diagnostic markers for neat chlorine exposure were trichloromethylbenzene and tetrachlorophenol. The old concrete samples from the 1930s and 1950s had the most chlorinated organic compounds after exposure to neat chlorine gas. Lignin or lignin degradation products were identified as probable candidates for phenolic precursor molecules in the concrete samples. Multivariate data analysis (OPLS-DA) shows distinct patterns for bleach and chlorine exposure. The chlorinated chemicals and specific markers for chlorine gas discovered in our research assist other laboratories in forensic investigations of chlorine gas attacks.

Quantitative Distributions of Product Ions and Reaction Times with a Binary Mixture of VOCs in Ambient Pressure Chemical Ionization.

A model to quantitatively predict ion abundances from atmospheric pressure chemical ionization (APCI) between hydrated protons and a volatile organic compound (VOC) was extended to binary mixtures of VOCs. The model includes differences in vapor concentrations, rate coefficients, and reaction times and is enhanced with cross reactions between neutral vapors and protonated monomers. In this model, two specific VOCs were considered, a ketone, 6-methyl-5-hepten-2-one (M, and an amine, 2,6-di-tert-butyl-pyridine (N), with measured "conditional rate coefficients" (in cm3·s-1) of kM = 1.11 × 10-9 and kN = 9.17 × 10-10, respectively. The cross reaction of MH+(H2O)x to NH+(H2O)y was measured as kcr = 1.31 × 10-12 at 60 °C. Cross reactions showed an impact on ion abundances at t > 30 ms for equal vapor concentrations of 100 ppb for M and N. In contrast, this impact was negligible for vapor concentrations of 1 ppb and did not exceed 5% change in product ion abundance up to 1000 ms reaction times. The model was validated with laboratory measurements to within ∼10% using an ion mobility spectrometer and effective reaction time obtained from computational fitting of experimental findings. This was necessitated by complex flow patterns in the ion source volume and was determined as ∼10.5 ms. The model has interpretative and predictive value for quantitative analysis of responses with ambient pressure ion sources for mass spectrometry and ion mobility spectrometry.

Glutathione conjugation of nitrogen mustards: In vitro study.

RATIONALE: This paper describes an in vitro study designed to identify metabolic biomarkers resulting from the conjugation of nitrogen mustards (NMs) with glutathione (GSH). The method developed is essential in providing evidence in the event of NM exposure in biomedical samples. METHODS: The mass spectral characterization of the proposed NMs-GSH conjugates was performed with liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). The final reaction mixtures were analysed in positive electrospray ionisation (ESI) at different incubation times. RESULTS: This study identified three types of conjugates in addition to ethanolamines, the hydrolysis products of NMs. Monoglutathionyl, diglutathionyl and phosphorylated conjugates were produced for each of the NMs, bis(2-chloroethyl)ethylamine (HN1), bis(2-chloroethyl)methylamine (HN2) and tris(2-chloroethyl)amine (HN3). The monoglutathionyl conjugates consisted of HN1-GSH, HN2-GSH and HN3-GSH. The spontaneous and primary conjugates of diglutathionyl were HN1-GSH2, HN2-GSH2 and HN3-GSH2. These included phosphorylated conjugates, namely HN1-GSH-PO4 , HN2-GSH-PO4 and HN3-GSH-PO4 , as might have formed due to hydrolysis in phosphate buffer. CONCLUSIONS: The mass spectral data of all conjugates formed in the presence of all NMs and GSH are reported in this study. These GSH metabolites can be used to confirm NMs toxicity in biological samples such as urine.

Osmolal and anion gaps after acute self-poisoning with agricultural formulations of the organophosphorus insecticides profenofos and diazinon: A pilot study.

Self-poisoning with organophosphorus (OP) insecticides is an important means of global self-harm. The insecticides are formulated with solvents that may also contribute to toxicity. We set up a study to detect changes in osmolal and anion gaps following ingestion of OP insecticides. We recruited consecutive patients admitted to a Teaching Hospital, Sri Lanka, with a history of OP self-poisoning. The osmolal and anion gaps were calculated on admission and at 4, 24 and 72 h post-ingestion together with ethanol concentration. Forty-nine patients were recruited (28 profenofos, 10 diazinon, one coumaphos, one chlorpyrifos, one phenthoate and eight unknown OP). Only modest increases in osmolal and anion gaps were noted. Small rises in osmolal gap above the upper limit of normal were noted in 16/49 (32.7%) of all cases, 9/28 (32.1%) profenofos cases and 4/10 (40.0%) diazinon cases. The anion gap was raised in 24/49 (49.0%) of all cases, 15/28 (53.6%) profenofos cases and 5/10 (50.0%) diazinon cases. We observed a trend for a fall in osmolal gap during the first 24 h, followed by an increase up to 72 h. There was no correlation between the anion gap and serum lactate concentration, indicating that a lactic acidosis was not responsible for the anion gap. Formate, which could have explained the increased gap, was not detected in any of the samples; ketoacids (beta-hydroxybutyrate and acetoacetate) were not measured. This pilot study found that profenofos and diazinon poisoning caused only modest increases in the osmolal and anion gaps in a minority of cases.

Advice on assistance and protection provided by the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons: Part 3. On medical care and treatment of injuries from sulfur mustard.

Blister agents damage the skin, eyes, mucous membranes and subcutaneous tissues. Other toxic effects may occur after absorption. The response of the Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) to a request from the OPCW Director-General in 2013 on the status of medical countermeasures and treatments to blister agents is updated through the incorporation of the latest information. The physical and toxicological properties of sulfur mustard and clinical effects and treatments are summarised. The information should assist medics and emergency responders who may be unfamiliar with the toxidrome of sulfur mustard and its treatment.

Metabolism and cytotoxicity of diphenylarsinic acid, a degradation product of sea-dumped chemical warfare agents, in a rainbow trout liver cell line RTL-W1.

Recent studies have found primary degradation products of phenylarsenic chemical warfare agents (CWAs) accumulating in fish tissues, while the potential effects of these dumped phenylarsenic CWAs, such as Clark I and II, in the Baltic Sea biota are poorly understood. In this study, the metabolism and cytotoxicity of diphenylarsinic acid (DPA), a primary degradation product of phenylarsenic CWA, was studied by incubating rainbow trout cell line RTL-W1 cells in media with 100 mg/L DPA. Previously undescribed metabolites were identified by ultra-high performance liquid chromatography-high resolution mass spectrometry (UPHLCHRMS). Moreover, the cytotoxicity of diphenylarsine glutathione conjugate (DPA-SG), the major metabolite of DPA, was studied. Cytotoxicity of the compounds was evaluated using the Neutral Red retention test (NRR), showing an IC50 value of 278 mg/L for DPA and 1.30 mg/L for DPA-SG, indicating that the glutathione (GSH) conjugate of DPA is more than two orders of magnitude toxic than DPA itself, suggesting that toxic properties of DPA are increased after conjugation with intracellular GSH leading enhanced toxicity after uptake. Results gained in this study give more detailed information for elucidating biological effects of dumped chemical munitions in marine environment. Moreover, the results help in assessing the environmental and health risks posed by marine munition continued presence and deterioration in the sea bottom.

Parametric Sensitivity in a Generalized Model for Atmospheric Pressure Chemical Ionization Reactions.

Gas phase reactions between hydrated protons H+(H2O)n and a substance M, as seen in atmospheric pressure chemical ionization (APCI) with mass spectrometry (MS) and ion mobility spectrometry (IMS), were modeled computationally using initial amounts of [M] and [H+(H2O)n], rate constants k1 to form protonated monomer (MH+(H2O)x) and k2 to form proton bound dimer (M2H+(H2O)z), and diffusion constants. At 1 × 1010 cm-3 (0.4 ppb) for [H+(H2O)n] and vapor concentrations for M from 10 ppb to 10 ppm, a maximum signal was reached at 4.5 µs to 4.6 ms for MH+(H2O)x and 7.8 µs to 46 ms for M2H+(H2O)z. Maximum yield for protonated monomer for a reaction time of 1 ms was ∼40% for k1 from 10-11 to 10-8 cm3·s-1, for k2/k1 = 0.8, and specific values of [M]. This model demonstrates that ion distributions could be shifted from [M2H+(H2O)z] to [MH+(H2O)x] using excessive levels of [H+(H2O)n], even for [M] > 10 ppb, as commonly found in APCI MS and IMS measurements. Ion losses by collisions on surfaces were insignificant with losses of <0.5% for protonated monomer and <0.1% for proton bound dimer of dimethyl methylphosphonate (DMMP) at 5 ms. In this model, ion production in an APCI environment is treated over ranges of parameters important in mass spectrometric measurements. The models establish a foundation for detailed computations on response with mixtures of neutral substances.

Optimized method for analysis of ethanolamines, hydrolysis products of nitrogen mustards, from urine samples using LC-MS/MS.

Highly polar ethanolamines (EAs), excreted in urine, are hydrolysis products of nitrogen mustards (NMs), which are prohibited by the Chemical Weapons Convention (CWC). The methods established for biological matrices are essential for verification analysis of the CWC related chemicals. This paper describes a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method developed for qualitative and quantitative analysis of EAs, N-ethyldiethanolamine (EDEA), N-methyldiethanolamine (MDEA) and triethanolamine (TEAOH) from urine samples. After optimization of sample preparation and chromatographic conditions, the method was fully validated. Silica solid-phase extraction (SPE) cartridges and a porous graphite carbon (PGC) column were selected for validation studies. The method is linear from 5 to 500, 0.5 to 250, and 0.5 to 500 ng/mL for TEAOH, EDEA, and MDEA, respectively. It is also precise and accurate. A minimum sample amount of 0.5 mL urine was used. The limit of quantification using this approach was 0.4, 5.5, and 6.3 ng/mL for MDEA, EDEA and TEAOH, respectively. The combination of the PGC column and high pH eluents in analysis retained and separated the studied EAs. Retention times were 2.11, 2.56 and 2.98 min for MDEA, EDEA and TEAOH, respectively. The method is applicable for verification analysis of the CWC.

Quantum mechanical reference spectrum simulation for precursors and degradation products of chemicals relevant to the Chemical Weapons Convention.

A selection of acidic, alkaline and neutral degradation products relevant to the Chemical Weapons Convention was studied in wide range of pH conditions to determine their spin systems as well as spectral parameters. The pH dependence of chemical shifts and J couplings was parameterized using Henderson-Hasselbalch-based functions using dichloromethane as additional shift reference in TSP-d4 referenced spectra. The resulting parameters allowed calculation of precise chemical shifts and J coupling constants in arbitrary pH conditions. The validity of the obtained spin system definitions and parameters as a source of quantum mechanically simulated reference data in chemical verification analysis is demonstrated.

Acute aquatic toxicity of arsenic-based chemical warfare agents to Daphnia magna.

Sea dumping of chemical warfare (CW) took place worldwide during the 20th century. Submerged CW included metal bombs and casings that have been exposed for 50-100 years of corrosion and are now known to be leaking. Therefore, the arsenic-based chemical warfare agents (CWAs), pose a potential threat to the marine ecosystems. The aim of this research was to support a need for real-data measurements for accurate risk assessments and categorization of threats originating from submerged CWAs. This has been achieved by providing a broad insight into arsenic-based CWAs acute toxicity in aquatic ecosystems. Standard tests were performed to provide a solid foundation for acute aquatic toxicity threshold estimations of CWA: Lewisite, Adamsite, Clark I, phenyldichloroarsine (PDCA), CWA-related compounds: TPA, arsenic trichloride and four arsenic-based CWA degradation products. Despite their low solubility, during the 48 h exposure, all CWA caused highly negative effects on Daphnia magna. PDCA was very toxic with 48 h D. magna LC50 at 0.36 µg × L-1 and Lewisite with EC50 at 3.2 µg × L-1. Concentrations at which no immobilization effects were observed were slightly above the analytical Limits of Detection (LOD) and Quantification (LOQ). More water-soluble CWA degradation products showed no effects at concentrations up to 100 mg × L-1.

Detection of chemical warfare agent related phenylarsenic compounds and multibiomarker responses in cod (Gadus morhua) from munition dumpsites.

Recently, sea-dumped chemical weapons (CWs) containing toxic chemical warfare agents (CWAs) have raised international attention. It is well known that CWAs are leaking from corroded munitions causing a risk to the surrounding marine environment, while the impact on marine biota is still unknown. In this study, cod (Gadus morhua) was used as a model species to study the possible bioaccumulation of phenylarsenic CWAs and their negative effects at multiple levels of biological organization on fish living in the vicinity of a major CWs dumpsite in the Bornholm Basin in the Baltic Sea. In total, 14% of the cod muscle samples collected close to the main dumpsite contained trace levels of phenylarsenic CWAs. However, most of the biomarkers measured did not show clear differences between this area compared with a lesser contaminated reference area. On the other hand, significant changes in some biomarkers were observed in individuals containing trace levels of CWA-related chemicals. The results gained in this study have significant importance for environmental risk assessment and for evaluating the risk of CWA contamination for human seafood consumers.

Fast, Miniaturized, Real-Time Unit for Sampling, Modulation, and Separation in Detection of Hazardous Chemicals.

A sampling, modulation, and separation (SMS) unit was tested for detection of hazardous chemicals. The SMS unit, designed and developed for on-site sampling and analysis, consists of a dynamic inlet system coupled with a fast, miniaturized gas chromatograph (GC). Feasibility of the SMS unit was evaluated together with a hazardous chemical vapor generator. The performance of the SMS unit was tested with automated thermal desorption after SMS to collect samples for GC-mass spectrometry (GC-MS) measurements. Detection of sarin nerve agent was verified. Additionally, the vapor generator was connected to the SMS unit, which was hyphenated with a photoionization detector (PID), thus creating a fast GC-PID system. This system gave a positive response for degradation products of sulfur mustard, thereby indicating suitability of the SMS-PID unit for field drone applications.

Derivatization and rapid GC-MS screening of chlorides relevant to the Chemical Weapons Convention in organic liquid samples.

A simple derivatization technique was developed for the analysis of seven Schedule 3 chemicals and one Schedule 2 chemical listed in the Chemical Weapons Convention (CWC). Phosgene, phosphorus oxychloride, phosphorus trichloride, phosphorus pentachloride, thionyl chloride, sulfur monochloride and sulfur dichloride (Schedule 3) as well as arsenic trichloride (Schedule 2) were derivatized using 1-propanol in 40% pyridine solution for analysis with gas chromatography-mass spectrometry (GC-MS). Derivatization temperature and concentration of the derivatization solution were optimized for maximum derivatization recovery. The stabilities of the target analytes and their derivatives in different solvents were studied. The derivatization yield showed a linear response within the analyte concentration range of 0.1-2 mM (10-200 µg ml-1) with correlation coefficients >0.99 (r2), except for AsCl3 which did not show a linear response after derivatization. Good reproducibility with relative standard deviations (RSDs) from 3 to 13% was achieved. The derivatization recovery was 66% for phosgene and 67-80% for the P-containing chemicals phosphorus oxychloride, phosphorus trichloride and phosphorus pentachloride. Recommendations to use the method for screening the presence of these chemicals in organic liquid samples are given. The method is used when CWC-related samples are screened at VERIFIN.

Exposure status of sea-dumped chemical warfare agents in the Baltic Sea.

About 50 000 tons of chemical weapons (CW) were dumped to the Baltic Sea after the Second World War. Munitions are located in the deep areas of the Baltic Sea, and there they act as a point source of contamination to the ecosystem. Corroded munitions release chemical warfare agents (CWAs) to nearby water and sediments. In this study we investigated known dumpsites (Bornholm, Gotland and Gdansk Deep) and dispersed chemical munitions, to evaluate the extent of contamination of nearby sediments, as well as to assess the degradation process of released CWA. It was found that CWA-related phenylarsenic chemicals (Clark I, Clark II and Adamsite) and sulfur mustard are released to the sediments and undergo environmental degradation to chemicals, of which some remain toxic. The extent of pollution of released CWAs and their corresponding degradation products reaches more than 250 m from the CW objects, and seem to follow a power curve decrease of concentration from the source. Bornholm Deep is characterised with the highest concentration of CWAs in sediments, but occasional concentration peaks are also observed in the Gdansk Deep and close to dispersed munitions. Detailed investigation of spreading pattern show that the range of pollution depends on bottom currents and topography.

Biological effects of dumped chemical weapons in the Baltic Sea: A multi-biomarker study using caged mussels at the Bornholm main dumping site.

After World War II, thousands of tons of highly toxic chemical warfare agents (CWA) were deposited in the Baltic Sea, the main dumping site locating in the Bornholm Basin. In the present study, Baltic mussels (Mytilus trossulus) were transplanted in the area in cages at two hotspot sites and a reference site at the depths of 35 and 65 m for 2.5 months to study bioaccumulation and biological effects of CWA possibly leaking from the corroding warfare materials. No traces of degradation products of the measured phenylarsenic CWA could be detected in the tissues of mussels. Nevertheless, several biochemical and histochemical biomarkers, geno- and cytotoxicity indicators, and bioenergetic parameters showed significant responses. The Integrated Biomarker Index calculated from the single biomarkers also showed a higher total response at the two hotspot areas compared to the reference site. Although no direct evidence could be obtained confirming the responses being caused specifically by exposure to CWA, the field exposure experiment showed unambiguously that organisms in this sea area are confronting environmental stress affecting negatively their health and this is likely related to chemical contamination, which is possibly connected to the sea-dumped CWA.

Identification of Degradation Products of Sea-Dumped Chemical Warfare Agent-Related Phenylarsenic Chemicals in Marine Sediment.

Previously unknown phenylarsenic chemicals that originated from chemical warfare agents (CWAs) have been detected and identified in sediment samples collected from the vicinity of chemical munition dumpsites. Nontargeted screening by ultrahigh-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) was used for detection of 14 unknown CWA-related phenylarsenic chemicals. Methylated forms of Clark I/II, Adamsite, and phenyldichloroarsine were detected in all analyzed sediment samples, and their identification was based on synthesized chemicals. In addition, other previously unknown CWA-related phenylarsenic chemicals were detected, and their structures were elucidated using MS/HRMS technique. On the basis of relative isotope ratios of protonated molecules and measures of exact masses of formed fragment ions, it could be concluded that some of these unknown chemicals contained a sulfur atom attached to an arsenic atom. In addition to that, some of the samples contained chemicals that had formed via addition of an OH group to the aromatic ring. However, it is not possible to say how these chemicals are formed, but the most plausible cause is activities of marine microbes in the sediment. To our knowledge, these chemicals have not been detected from sediment samples previously. Sensitive analytical methods are needed for these novel chemicals to assess the total CWA burden in marine sediments, and this information is essential for the risk assessment.

Studying the metabolism of toxic chemical warfare agent-related phenylarsenic chemicals in vitro in cod liver.

Large quantities of chemical warfare agents (CWAs), such as phenylarsenic chemicals, were disposed by sea-dumping after World War II. Nowadays, the release of these toxic chemicals from munitions poses a potential threat to living organisms. This study investigates the fate of these chemicals in fish by exposing selected CWA-related phenylarsenic chemicals and their oxidation products to cod (Gadus morhua) liver S9 fraction in vitro. Clark I (DA), Adamsite (DM) and their corresponding oxidation products as well as triphenylarsine oxide (TPA[ox]) and phenylarsonic acid (PDCA[ox]) were used as chemicals in in vitro experiments. Glutathione (GSH) conjugates of DA, DM and PDCA-related chemicals were found to be the most dominant metabolites, and methylated metabolites were detected as well, suggesting that these compounds are metabolised in the presence of cod liver enzymes. TPA[ox] was the only compound tested that did not form a GSH conjugate or methylated metabolite, indicating a different biotransformation pathway for this compound. Furthermore, hydroxylated metabolites were detected for each tested chemical. Due to their reactive nature, GSH conjugates may be difficult to detect in fish samples from CWA dumpsites. In contrast, both methylated and hydroxylated metabolites of phenylarsenic chemicals are promising target chemicals for the detection of CWA-related contamination in fish.

A pilot clinical study of the neuromuscular blocker rocuronium to reduce the duration of ventilation after organophosphorus insecticide poisoning.

Background: A common manifestation of organophosphorus insecticide self-poisoning is prolonged respiratory failure due to neuromuscular junction dysfunction and likely nicotinic receptor overstimulation. We aimed at collecting preliminary data on whether addition of the competitive nicotinic antagonist rocuronium to standard early therapy might be clinically feasible and associated with reduced duration of ventilation.Methods: A pilot three-arm dose-response phase II trial was set up to compare bolus doses of rocuronium bromide titrated to produce initial >95% or 50% inhibition of neuromuscular function, measured using acceleromyography, plus standard treatment, versus standard treatment alone. After attaining inhibition, patients receiving bolus rocuronium then received rocuronium infusions for a maximum of 120 h. Primary outcome was duration of intubation; secondary outcome was case fatality. Plasma butyrylcholinesterase activity was measured throughout the inpatient stay. Blood was analysed to confirm the organophosphorus insecticide ingested.Results: Forty-five patients were randomised to receive: rocuronium to initially attain 95% inhibition (Roc>95, n = 15), rocuronium to initially attain 50% inhibition (Roc50, n = 14), or no rocuronium (control, n = 16). The most commonly ingested pesticide was profenofos (29/45, 64.4%). Butyrylcholinesterase activity remained severely inhibited for the duration of the study for most patients. Case fatality was 9/45 (20%) and similar across study arms: control 3/16 (18.8%), Roc50 4/14 (28.6%) and Roc>95 2/15 (13.3%) (p = .5842). When excluding patients who died, median [IQR] duration of intubation was significantly longer in the Roc50 (259.5 [176-385] h) and Roc>95 (226.8 [186-355] h) groups compared to controls (88.5 [47-160] h, p = .0162 and p = .0016, respectively).Conclusions: In this pilot dose-response study, we found no evidence that rocuronium in addition to standard therapy reduced the duration of intubation. It is possible that it worsened neuromuscular junction function. Further clinical research, including testing of shorter duration regimens, needs to be performed before nicotinic antagonists can be used in the clinical management of OP poisoning.