Vorming van dioxinen in afvalverbrandingsinstallaties

Afgelopen zomer werd bekend dat de melk van koeien in het Lickebaert gebied (Zuid-Holland) 1,5 maal zoveel dioxine bevatte als toegestaan is. De afvalverbrandingsinstallatie van de Afvalverwerking Rijnmond (AvR) vormt in belangrijke mate de oorzaak van dit probleem. Uit onderzoek van TNO en de TU Delft blijkt dat de dioxinen niet tijdens de verbranding, maar erna ontstaan, via een ‘de novo synthese’ uit onvolledig verbrand organische stoffen en anorganische chloriden

Aqueous chlorination products: The Origin of Organochlorine Compounds in Drinking and Surface Waters

Applied Science

"De Novo"-synthesis of chlorinated biphenyls, dibenzofurans and dibenzo-p-dioxins in the fly ash catalyzed reaction of toluene with hydrochloric acid

Toluene is converted into benzaldehyde and halogenated aromatic oxidation products in an air atmosphere at 425 °C with fly ash from a municipal waste incineration plant as the catalyst. Several halogenated products such as chlorinated and brominated benzenes, biphenyls and traces of PCDDs/PCDFs could be detected under these conditions, resulting from the reaction of metal chlorides and hromides present on the surface of the fly ash. The addition of a “chlorine” source to the reaction gases in the form of trichloroethylene or hydrogen chloride dramatically increased the production of PCBs, PCDDs/PCDF5 and other chlorinated aromaticcompounds, giving evidence for a “de novo” synthesis of PCBs and PCDDs/PCDFs. A reaction pathway, based on the initial oxidation of toluene to benzaldehyde as the key intennediate, followed by chlorination and condensation reactions is proposed

Findings supporting the natural formation of trichloroacetic acid in soil.

The concentrations of trichloroacetic acid (TCAA) in soil and of chlorinated solvents in soil air from simultaneously taken samples from four sites are presented. The data show that there is a significant positive correlation between the concentrations of TCAA and chloroform - but not between TCAA and other chlorinated solvents - in soil. The calculated half-life of TCAA shows that the contribution of decarboxylation to the chloroform concentration in soil is negligible. Since TCCA and chloroform were found to be formed from humic acids in the chloroperoxidase (CPO)-mediated reaction and CPO activity has been detected in soil, the observed correlation between the concentrations of TCAA and chloroform provides novel support for the hypothesis that TCAA is formed naturally in soil

Mass balance of trichloroacetic acid in the soil top layer.

Since the ban on the use of trichloroacetic acid (TCAA) as a herbicide in several countries, TCAA is still found ubiquitously in the environment. The presence of TCAA nowadays is suggested to originate mainly from the atmospheric degradation of tetrachloroethene. Our mass balance calculations indicate that this may be true for the presence of TCAA in the atmosphere. However, our mass balance calculations also provide tentative evidence for the formation of TCAA in soil. If our calculated production fluxes are realistic estimates, a very large source of TCAA in soil has been identified

Balance of trichloroacetic acid in the soil top layer

Since the ban on the use of trichloroacetic acid (TCAA) as a herbicide in several countries, TCAA is still found ubiquitously in the environment. The presence of TCAA nowadays is suggested to originate mainly from the atmospheric degradation of tetrachloroethene. Our mass balance calculations indicate that this may be true for the presence of TCAA in the atmosphere. However, our mass balance calculations also provide tentative evidence for the formation of TCAA in soil. If our calculated production fluxes are realistic estimates, a very large source of TCAA in soil has been identified

Natural formation of chloroform and brominated trihalomethanes in soil.

We studied the occurrence of halogenated organic compounds in soil air of rural areas. Chloroform appeared to occur in elevated concentrations compared tO those in atmospheric air, while the concentrations of other chlorinated solvents were almost equal or lower than those in atmospheric air. We report conclusive evidence that chloroform is naturally produced from in situ N

Formation of aryl-chlorinated aromatic acids and precursors for chloroform in chlorination of humic acid

The formation of chloroform when humic substances are chlorinated is well known. Other chlorinated products that may be formed are chloral, di- and trichloroacetic acid, chlorinated C-4 diacids, and α-chlorinated aliphatic acids. Several of these compounds are formed in molar yields comparable to chloroform. The mechanism for the formation of these products is still largely unknown, due to the complex structure of humic material. Humic materials are geopolymers formed from lignin, carbohydrates, proteins, and fatty acids by microbial degradation and enzymatic or autooxidative coupling reactions. Although hummic materials are not well defined organic compounds, several structures have been proposed which contain moieties that may be converted into chloroform by chlorine in aqueous medium. For example, 1, 3-dihydroxybenzenes, 1, 3-diketo compounds, natural acids such as citric acid, and compounds with activated C-H bonds such as indoles or methylketones can form chloroform in high yield on chlorination in aqueaous medium. For humic substances 1 3-dihydroxybenzenes appear to be likely chloroform precursor candidates as suggested by the fact that 3, 5- dihydroxybenzoic acid is formed in the degradation of humic material with CuSO₄-NaOH at 175 to 180° C. However, the products of KOH fusion may be of no diagnostic value for the structure of humic substances. In recent KMnO₄ degradation studies of humic and fulvic acids no 1, 3- dihydroxybenzene structures were detected, probably because of complete oxidation of these structures. Although the possibility of l, 3-dihydroxybenzene structures as the precursor fragments for chloroform remains to be proven, Rook proposed a mechanism based on the chemistry of the reaction between chlorine and resorcinol. The identification of reaction intermediates is necessary to achieve a better understanding of this mechanism and to assist in the identification of the structural fragments in humic material that are converted into chloroform and chlorinated acids. In this study we describe (1) the identification and structural assignment of such intermediates in the reaction between terrestrial humic acid and chlorine in aqueous medium at pH 7.2, and (2) the attempts to demonstrate the presence of 1, 3-dihydroxybenzene structures in humic acids by means of Curiepoint pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS) and nuclear magnetic resonance (NMR) before and after the chlorination reaction

Natural Formation of Chlorinated Phenols, Dibenzo-P-Dioxins and Dibenzofurans in Soil of a Douglas Fir Forest.

Abstract not availableJRC.(EI)-Environment Institut