Han Wever

Octan-1-ol / water partition coefficients of polychlorinated dibenzo-p-dioxins and dibenzofurans : Experimental values determined with a stirring method

Abstract Octan-1-ol/water partition coefficients of a mixture of polychlorinated dibenzo-p-dioxins and dibenzofurans, originating from a fly-ash extract, were experimentally determined. A “(slow) stirring method” was used and values thus obtained were as high as 108.

The influence of the polymer matrix on the formation of polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs)

Abstract During micro-pyrolysis of polybrominated diphenylethers (PBDPOs), which are used as flame retardants in synthetic polymer blends, PBDDs and PBDFs are formed. The yield decreases from Br 5 DPO→Br 8 DPO→Br 10 DPO due to the energetically favourable elimination of HBr. The influence of the high impact polystyrene (HIPS) polymer matrix on the formation consists of a selectivity towards formation of PBDFs, a shift in the optimal PBDF formation temperature from T =600°C to the HIPS depolymerisation temperature T=350–400°C and an enhancement of the total yield of PBDFs with a factor 7. The key towards understanding of the low PBDF formation temperature lies in the fact that PBDPOs are incorporated in a polymer matrix. During radical depolymerisation of the HIPS polymer matrix PBDFs are formed by the exchange of hydrogen and bromine which is followed by a ring closure reaction. The thermal degradation processes of HIPS Br 10 DPO Sb 2 O 3 were studied dynamically with in-source temperature resolved Py-MS (negative ions). Several processes taking place during degradation of the HIPS Br 10 DPO Sb 2 O 3 polymer matrix, like debromination of the flame retardant Br 10 DPO to form less brominated diphenylethers, formation of PBDFs, bromination of polystyrene and formation of antimony (oxy)bromides, were elucidated with this technique.

Surface catalyzed formation of polychlorinated dibenzo-p-dioxins/dibenzofurans during municipal waste incineration

A series of reactions was carried out on different surfaces using carbon and CuCl2, and KCl or HCl as a Cl-source. The PCDD/PCDF congener distribution was seen to vary to a great extent but the isomer distribution remained fairly constant. It is concluded that thermodynamic properties are largely responsible for the PCDD/PCDF isomer distribution. With pentachlorobenzene Cl2 elimination, assisted by oxygen, appears to be the major pathway for PCDD/PCDF formation.

Influence of biotransformation on the accumulation of PCDDs from fly-ash in fish

Abstract An explanation is found for the lack of bioaccumulation of a great number of polychlorinated dibenzo-p-dioxin (PCDD) congeners. Two groups of goldfish were exposed to a fly-ash extract, which was dissolved in water with the aid of a generator column. The first group was exposed to piperonylbutoxide (PBO), which inhibits monooxygenase activity. Congeners which lack chlorine substitution on the lateral positions (2,3,7,8-positions) or which have one or more pairs of unsubstituted vicinal places are found in these fish. In the second group of fish, however, only 2,3,7,8-TCDD was found after 6 days. Therefore all other congeners are likely to be biotransformed rapidly in the fish which were not treated with PBO.

Formation and identification of azaarene transformation products from aquatic invertebrate and algal metabolism.

The metabolism of two azaarenes, viz. acridine and phenanthridine, by aquatic organisms was studied in short-term and chronic laboratory tests. The identity of metabolites observed in the test waters was investigated with different analytical methods, including HPLC, GC and hyphenated LC- or GC-MS. The Zebra mussel (Dreissena polymorpha), one green alga species (Selenastrum capricornutum) and periphyton or bacteria transformed acridine into 9[10H]-acridinone. Phenanthridine was transformed into 5[6H]-phenanthridinone by midge (Chironomus riparius) larvae. The findings indicate that closely related isomers may undergo species-specific biotransformation. It was concluded that keto-metabolites are major products in the aquatic fate of benzoquinolines, which may be overlooked in the risk assessment of parent compounds. This study illustrates the typical problems with, as well as the potency of, chromatographic methods in the elucidation of metabolic routes of organic contaminants.

Selective retention of toxic polychlorinated dibenzo-p-dioxins and dibenzofurans in the liver of the rat after intravenous administration of a mixture

A mixture of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), purified from fly ash from a municipal incinerator, was administered as a single intravenous dose to male rats. Livers were analyzed after 5 h, 1, 2, 4, 7 and 9 days for PCDD and PCDF content. Starting from t = 5 h 2,3,7,8-substituted congeners were the predominant PCDDs and PCDFs retained. 2,3,4,6,7-PnCDF was the only congener without 4 lateral chlorine atoms retained in the liver. For most of the 2,3,7,8-substituted congeners reliable half-lives could not be calculated due to the short experimental period. For only three 2,3,7,8-substituted congeners was a complete elimination from the liver found, within this time period. These congeners were 2,3,7,8-TCDF, 1,2,3,7,8- and 2,3,4,6,7-PnCDF with half-lives of less than 1, 2.1 and 1.6 days, respectively. The other PCDDs and PCDFs, without 4 lateral chlorine atoms, were not detected in the liver from 5 h to 9 days after i.v. administration. Based on the congeneric distribution patterns, it is suggested that besides metabolism, structural specific binding to the Ah-receptor and cytochrome P-450 complex might also be responsible for this selective liver retention.

Decomposition of octachlorodibenzofuran and formation of the hepta congeners during GLC analysis

Abstract For the identification and quantification of chlorinated dioxins and dibenzofurans a high resolution GLC coupled to a mass spectrometer is normally used. As a part of the clean-up procedure we use reversed phase HPLC. With the use of this method we isolated a fraction of pure OCDF. Injection of this fraction in the GLC resulted in peaks not only of OCDF but also of H 7 CDFs. At the longer retention time side of the latter peaks a higher background was found. This is probably caused by decomposition of OCDF at the beginning of the column and injection port. In this paper this problem is discussed and a method is suggested for overcoming the problem.

Vehicle-dependent bioavailability of polychlorinated dibenzo-p-dioxins (PCDDs) and -dibenzofurans (PCDFs) in the rat

Abstract PCDDs and PCDFs were administered as fly ash (500 mg) or fly ash extract to male Wistar rats. The extract was administered orally and intravenously by using arachidis oil and miglyol 812 as oily vehicles. Liver retentions were determined after 48 hours as a degree of bioavailability. In all experiments only the 2,3,7,8-substituted congeners, with the exception of 2,3,4,6,7-PnCDF, were detected in the liver. The dose was 10 to 40 ng for each congener. The lowest bioavailability was found in the experiments with crude or hydrochloric acid pretreated fly ash. Liver retentions were comparable for both experiments with fly ash (0.4 – 3.8%) and were approximately 10 times higher in the oral experiments with oily vehicles. Miglyol 812 produced slightly lower liver retentions compared with arachidis oil. Intravenous dosage with miglyol 812 resulted in liver retentions twice as high as oral administration with this vehicle.