Abstract  The production and use pattern of Diethylmalonate (DEM) and Dimethylmalonate (DMM) are comparable. The two chemicals have very similar physico-chemical properties and both esters are hydrolyzed via a two step reaction to malonic acid and the corresponding alcohol, methanol or ethanol. It is likely that unspecific esterases in the body catalyze the hydrolysis. The alcohols and malonic acid are physiological substances that are metabolized via physiological pathways. Ethanol (CAS No. 64-17-5) and methanol (CAS No. 67-56-1) were assessed at SIAM 19. For ethanol it was concluded that the chemical is currently of low priority for further work, because the hazardous properties of ethanol are manifest only at doses associated with consumption of alcoholic beverages. As it is impossible to reach these exposure levels as a consequence of the manufacture and use of malonates, it can be expected that malonic acid will be the metabolite that determines the toxicity of DEM. For methanol, SIAM 19 decided that this chemical is a candidate for further work. Methanol exhibits potential hazardous properties for human health (neurological effects, CNS depression, ocular effects, reproductive and developmental effects, and other organ toxicity). The effects of methanol on the CNS and retina in humans only occur at doses at which formate accumulates due to a rate-limiting conversion to carbon dioxide. In primates, formate accumulation was observed at methanol doses greater than 500 mg/kg bw (which would require a DMM dose of more than 1000 mg/kg bw). As there were no indications of a methanol associated toxicity from a well performed repeated dose toxicity study with DMM in rodents (which are, however, known to be less sensitive to methanol toxicity than humans), and because methanol toxicity would not be expected up to doses as high as 1000 mg DMM/kg bw/day, it was concluded that methanol does not make a relevant contribution to the toxicity profile of DMM. A possible mode of action for systemic toxicity of DMM and DEM can only be deduced from the repeated dose study with DMM, indicating a reversible liver hypertrophy at the cellular level at high doses of 1000 mg/kg bw/day. This effect can be an indication of an induction of metabolism in the liver rather than a clear systemic toxicity.

Abstract  A combination of in situ one-dimensional H-1 magnetic resonance profiling and two-dimensional imaging has been applied to study the shape and subsequent dynamic evaporation behaviour of a single liquid droplet after impact onto a porous surface. Diethyl-malonate (DEM) droplets are initially embedded in the porous substrate by impingement, and are then evaporated over a period of several hours; the surface of the substrate being ventilated by a controlled airflow. The configuration is intended to mimic the behaviour of droplets evaporating into atmospheric flows. In order to evaluate the influence of the airflow at the surface of the porous medium, different experimental configurations were tested by varying the speed of the airflow stream above the porous surface. The method produces several types of data, including images of impinged droplets inside the porous substrate and their development with time during the evaporation episode, one-dimensional concentration profiles through the substrates, and corresponding estimates of the mass fraction of liquid remaining, evaporation rate and mass flux per unit area. The results obtained show that although liquid droplets tend to evaporate faster and present larger evaporation rates when exposed to a more efficient removal of vapour from the surface, the limiting effects of the porous medium are even more evident. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract  The evaporation model of Roberts and Griffiths (1995 Atmospheric Environment 29, 1307-1317) has been subjected to an extensive validation exercise based on a major campaign of field experiments on evaporation from surfaces composed of sand and of concrete. This complements the previous validation which was limited to wind tunnel experiments on sand surfaces. Additionally, the validation using wind tunnel data has been extended to include concrete surfaces. The model describes the constant-rate and falling-rate periods that characterise evaporation from porous media. During the constant-rate period, the evaporation is solely determined by the vapour transport rate into the air. During the falling-rate period, the process in the porous medium is modelled as a receding evaporation front, the overall evaporation rate being determined by the combined effects of vapour transport through the pore network and subsequently into the air. The field trials programme was conducted at sites in the USA and the UK, and examined the evaporation of diethyl malonate droplets from sand and concrete surfaces. Vapour concentrations at several heights in the plume were measured at the centre of a 1 m radius annular source (of width 10 cm) contaminated by uniformly sized droplets (2.4 or 4.1 mm in diameter), key meteorological data being measured at the same time. The evaporation was quantified by coupling concentration and wind speed data. In all, 22 trials were performed on sand and concrete; a further 8 were performed an non-pore us surfaces (aluminium foil and slate) as references. The model performance was evaluated against the experimental data in terms of two quantities, the initial evaporation rate of the embedded droplets, and the mass-fraction remaining in the substrate at intervals over the evaporation episode. Overall, the model performance was best in the case of the field experiments for concrete, and the wind tunnel experiments for sand; the performance for wind tunnel experiments for concrete was reasonably good; in the case of the field experiments for sand there was significant underprediction of evaporation rates, though the trends with the determining variables were well predicted. (C) 1999 Elsevier Science Ltd. All rights reserved.

Abstract  Retention factors on a minimum of eight stationary phases at various temperatures by gas-liquid chromatography and in acetonitrile-water and methanol-water mobile phases by reversed-phase liquid chromatography on a Synergi Polar-RP column were combined with further values taken from the literature and liquid-liquid partition coefficients for up to eight totally organic biphasic systems to estimate descriptors for 24 esters (phthalate, oleate, stearate, arbietate, adipate, succinate, sebacate, and diethylmalonate) widely used as plasticizers and solvents in industry. The descriptors facilitated the estimation of several properties of environmental interest (octanol-water, air-octanol, and air-water partition coefficients, and soil-water distribution coefficients, vapor pressure, and water solubility). The descriptors are suitable for use in the solvation parameter model and facilitate the estimation of a wide range of physicochemical, chromatographic, biological, and environmental properties using existing models.

Abstract  To determine the potential environmental persistence and toxic effects of agent simulants Diethyl Malonate (DEM) and Methyl Salicylate (MS), plants, soils, earthworms, and oil microbial populations were exposed to projected aerosolized simulant concentrations of (approximately)100 (low) and (approximately)1000 (high) mg/m(sup 3). Both simulants exhibited biphasic residence times on foliar and soil surfaces following aerosol exposure. Half-times of DEM on soil and foliar surfaces were 1 to 3 h and 5 to 22 H, respectively, and 2 to 2 h and 5 to 31 h for the MS, respectively. Persistence was longer on the foliar surfaces than that of the soils. Both simulants proved phytotoxic to vegetation with a lower threshold of 1 to 2 (mu)m/cm(sup 2) for the MS versus that of 10 (mu)g/cm(sup 2) for the DEM. However, neither significantly affected chloroplast electron transport in vitro at concentrations of up to 100 (mu)g/mL. Results from in vitro testing of DEM indicated concentrations below 500 (mu)g/g dry soil generally did not adversely impact soil microbial activity, while the theshold was 100 (mu)g/g dry soil for MS. Earthworm bioassays indicated survival rates of 66% at soil doses of 204 (mu)g DEM/cm(sup 2) soil and 86% at soil doses of 331 (mu)g MS/cm(sup 2).

Abstract  The microbial capacity to degrade simple organic compounds with quaternary carbon atoms was demonstrated by enrichment and isolation of five denitrifying strains on dimethylmalonate as the sole electron donor and carbon source. Quantitative growth experiments showed a complete mineralization of dimethylmalonate. According to phylogenetic analysis of the complete 16S rRNA genes, two strains isolated from activated sewage sludge were related to the genus Paracoccus within the alpha-Proteobacteria (98.0 and 98.2% 16S rRNA gene similarity to Paracoccus denitrificans(T)), and three strains isolated from freshwater ditches were affiliated with the beta-Proteobacteria (97.4 and 98.3% 16S rRNA gene similarity to Herbaspirillum seropedicae(T) and Acidovorax facilis(T), respectively). Most-probable-number determinations for denitrifying populations in sewage sludge yielded 4.6 x 10(4) dimethylmalonate-utilizing cells ml(-1), representing up to 0.4% of the total culturable nitrate-reducing population.

Abstract  The uptake of dimethyl malonate and dimethyl succinate on aqueous surfaces was measured between 266 and 279 K, using the droplet train technique coupled with mass spectrometric detection. The uptake coefficients gamma were found to be independent of the aqueous phase composition and of the gas-liquid contact times. In addition, the uptake coefficients and the derived mass accommodation coefficients a show a negative temperature dependence in the temperature ranges studied. The mass accommodations decrease from 7.8 x 10(-2) to 5.0 x 10(-2) and from 4.5 x 10(-1) to 2.3 x 10(-2) for dimethyl malonate and succinate, respectively. These results are used to discuss the incorporation of oxygenated volatile organic compounds (VOCs) into the liquid using the nucleation theory. Henry's law constants of both compounds were directly measured between 283 and 298 K using a dynamic equilibrium system. Their values exponentially decrease when temperature increases, from (2.60 +/- 0.30) x 10(4) to (0.40 +/- 0.05) x 10(4) and from (1.20 +/- 0.10) x 10(4) to (0.30 +/- 0.03) x 10(4) for dimethyl malonate and succinate, respectively (in units of M atm(-1)). The partitioning of both dibasic esters between gas and aqueous phases and the corresponding atmospheric lifetimes have then been derived.

Abstract  Chemical warfare agent simulants are often used as an agent surrogate to perform environmental testing, mitigating exposure hazards. This work specifically addresses the assessment of downwind agent vapor concentration resulting from an evaporating simulant droplet. A previously developed methodology was used to estimate the mass diffusivities of the chemical warfare agent simulants methyl salicylate, 2-chloroethyl ethyl sulfide, di-ethyl malonate, and chloroethyl phenyl sulfide. Along with the diffusivity of the chemical warfare agent bis(2-chloroethyl) sulfide, the simulant diffusivities were used in an advection-diffusion model to predict the vapor concentrations downwind from an evaporating droplet of each chemical at various wind velocities and temperatures. The results demonstrate that the simulant-to-agent concentration ratio and the corresponding vapor pressure ratio are equivalent under certain conditions. Specifically, the relationship is valid within ranges of measurement locations relative to the evaporating droplet and observation times. The valid ranges depend on the relative transport properties of the agent and simulant, and whether vapor transport is diffusion or advection dominant.

Abstract  The purpose of the following chemical simulant studies is to assess the potential acute environmental effects and persistence of diethyl malonate (DEM). Deposition velocities for DEM to soil surfaces ranged from 0.04 to 0.2 cm/sec. For foliar surfaces, deposition velocities ranged from 0.0002 cm/sec at low air concentrations to 0.05 cm/sec for high dose levels. The residence times or half-lives of DEM deposited to soils was 2 h for the fast component and 5 to 16 h for the residual material. DEM deposited to foliar surfaces also exhibited biphasic depuration. The half-life of the short residence time component ranged from 1 to 3 h, while the longer time component had half-times of 16 to 242 h. Volatilization and other depuration mechanisms reduce surface contaminant levels in both soils and foliage to less than 1% of initial dose within 96 h. DEM is not phytotoxic at foliar mass loading levels of less than 10 (mu)m/cm(sup 2). However, severe damage is evident at mass loading levels in excess of 17 (mu)g/cm(sup 2). Tall fescue and sagebrush were more affected than was short-needle pine, however, mass loading levels were markedly different. Regrowth of tall fescue indicated that the effects of DEM are residual, and growth rates are affected only at higher mass loadings through the second harvest. Results from in vitro testing of DEM indicated concentrations below 500 (mu)g/g dry soil generally did not negatively impact soil microbial activity. Short-term effects of DEM were more profound on soil dehydrogenase activity than on soil phosphatase activity. No enzyme inhibition or enhancement was observed after 28 days in incubation. Results of the earthworm bioassay indicate survival to be 86 and 66% at soil doses of 107 and 204 (mu)g DEM/cm(sup 2), respectively. At higher dose level, activity or mobility was judged to be affected in over 50% of the individuals. 21 refs., 10 figs., 15 tabs.

Abstract  The rate coefficient for the gas-phase reaction of chlorine atoms with dimethyl malonate (DMM, CH3OC(O)CH2C(O)OCH3) was determined at 298 K using relative methods giving a value of (3.8 ± 0.4) × 10-12, cm3 molecule-1 s-1). The photo-oxidation mechanism of DMM was also investigated. The main products were identified by infrared spectroscopy, and computational calculations were performed in order to support the experimental data. The results reveal that the photo-oxidation occurs mainly by the abstraction of an H atom from the methyl groups. The CH3OC(O)CH2C(O)OCH2O• radical formed subsequently reacts according to three competitive paths: reaction with molecular oxygen to yield CH3OC(O)CH2C(O)OC(O)H, isomerization-unimolecular decomposition to lead finally to CH3OC(O)C(O)H, CO2, and HC(O)OH, and α-ester rearrangement to form monomethyl malonate and carbon monoxide. The yield of products as a function of oxygen pressure was also determined.