Thermal decomposition of captan and formation pathways of toxic air pollutants

Hazard identification posed by plant protection products during warehouse fires

In addition to fertilisers, plant protection products are essential in today's agricultural production. The increase in the human population leads to the need to optimise agricultural production, with an increasing demand for plant protection products. Historically, there have been serious fires at plant protection product storage facilities with devastating consequences for the environment. For this reason, it is worth investigating what risks arise for people and the environment during a fire at storage sites for these substances. In this article, tests were carried out for three plant protection products containing azoxystrobin as the active substance, in order to investigate the effects of the additives on combustion processes. Tests of combustion parameters were performed using a cone calorimeter. A tube furnace with asphyxiating and irritant gas analysers and gas chromatography with a mass spectrometer were used to analyse the resulting gas products. The Plant Protection Products tested achieved high values for combustion parameters. Analysis of the substances produced during their combustion showed that large amounts of asphyxiating and irritating gases (CO, N2O, NO, SO2, NH3, HCl, CH2O, HCN) were generated.

Thermal oxidation of dieldrin and concomitant formation of toxic products including polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F)

This paper examines the gas phase thermal decomposition of dieldrin and associated formation of toxic combustion products including polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F). Volatile Organic Carbon (VOC) analysis revealed the formation of pentachlorostyrene (PCS), hexachlorostyrene (HCS) and polychlorinated naphthalene as toxic combustion products generated during the combustion of dieldrin. The thermal pyrolysis of dieldrin resulted in the formation of chlorinated benzenes and chlorinated phenols, which are known PCDD/F precursors. The formation of PCDD/F commenced around 823 K @ 5s residence time and results indicate a preference for the formation of PCDF over PCDD under all experimental conditions studied. Subsequent experiments, to examine the yield of PCDD/F as a function of temperature, reveal the progressive chlorination of PCDD/F with temperatures up to 923 K. Octachlorodibenzofuran (OCDF) was the major dioxin congener detected in the oxidation of dieldrin. The highest toxicity factor for dioxin formation was recorded at 923 K with a 6% O₂ content in the feed gas and corresponds to 6.24 ng TEQ WHO 2005/mg of dieldrin and total PCDD/F concentration of 96.8 ng/mg of dieldrin.

Chromatographic determination of fungicides in biological and environmental matrices. New achievements

The newest results in the chromatographic analysis of synthetic and natural fungicides present in biological and environmental matrices are collected and critically evaluated. Examples of the employment of gas chromatography, liquid chromatographic technologies, such as thin-layer chromatography and high-performance liquid chromatographic methods as well as electrically driven systems are presented. The advantages and disasdvantages of the various chromatographic technologies are briefly discussed and the efficacies of the methodologies are compared.

Toxic pollutants emitted from thermal decomposition of phthalimide compounds

Phthalimide (PI) and tetrahydrophthalimide (THPI) are two structurally similar compounds extensively used as intermediates for the synthesis of variety of industrial chemicals. This paper investigates the thermal decomposition of PI and THPI under oxygen rich to oxygen lean conditions, quantifying the production of toxicants and explaining their formation pathways. The experiments involved a plug flow reactor followed by silica cartridges, activated charcoal trap and a condenser, with the decomposition products identified and quantified by Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS) and micro gas chromatography (μGC). The density functional theory (DFT) calculations served to obtain dissociation energies and reaction pathways, to elucidate the reaction mechanism. The oxidation of PI and THPI produced several toxic nitrogen-containing gases and volatile organic compounds, including hydrogen cyanide, isocyanic acid, nitrogen oxides, benzonitrile, maleimide and tentatively identified benzenemethanimine. The detection of dibenzo-p-dioxin (DD) and dibenzofuran (DF) suggests potential formation of the toxic persistent organic pollutants (POPs) in fires involving PI and THPI, in presence of a chlorine source. The oxidation of THPI produced 2-cyclohexen-1-one, a toxic unsaturated ketone. The results of the present study provide the data for quantitative risk assessments of emissions of toxicants in combustion processes involving PI and THPI.

Air pollutants formed in thermal decomposition of folpet fungicide under oxidative conditions

This contribution studies the decomposition of folpet fungicide under oxidative conditions and compares the product species with those of captan fungicide, which is structurally related to folpet. Toxic products arising from folpet comprised carbon disulfide (highest emission factor of 4.9 mg g(-1) folpet), thiophosgene (14.4), phosgene (34.1), hydrogen cyanide (2.6), tetrachloroethylene (111), hexachloroethane (167), and benzonitrile (4.5). Owing to their related molecular structures, folpet emitted similar products to captan but at different yields, under the same experimental conditions. It appears that the availability of easily abstractable H atoms, in the structure of captan but not in that of folpet, defines the product distribution. In conjunction with the quantum chemical calculations, these experimental measurements afford an enhanced explanation of the formation pathways of hazardous decomposition products of these two structurally related fungicides.

Bacterial degradation of fungicide captan

The phthalimide fungicide captan has been widely used to control plant pathogenic fungi. A strain of Bacillus circulans utilized the fungicide captan as sole source of carbon and energy. The organism degraded captan by a pathway involving its initial hydrolysis to yield cis-1,2,3,6-tetrahydrophthalimide, a compound without fungicidal activity. The formation of this compound was confirmed by HPLC, IR, NMR, and mass spectral analysis. The results also revealed that cis-1,2,3,6-tetrahydrophthalimide was further degraded to o-phthalic acid by a protocatechuate pathway. These findings indicated that there was a complete mineralization of fungicide captan by B. circulans.