Photocatalytic degradation of triazophos in aqueous titanium dioxide suspension: identification of intermediates and degradation pathways.

The photocatalytic degradation of triazophos in aqueous TiO2 suspension has been studied in a photoreactor operating with simulated solar radiation. The decrease in triazophos concentration followed first-order kinetics with a half-life of 4.76+/-0.42 h at a TiO2 suspension concentration of 10 mg/L. Seventeen degradation products were identified using HPLC-UV, HPLC/MS/MS, GC/MS/MS and IC, and by comparing retention times and spectra with commercially available authentic standards. On the basis of the observed transformation products, two routes were proposed, one based on the initial oxidative cleavage of PS bond to PO bond, and the other on initial cleavage of the ester P-O bonds. Photocatalysis holds promise for the solar treatment of pesticide-contaminated waters.

Evaluation of the oestrogen-receptor activating potency of environmental samples by means of yeast oestrogen assays.

A bioassay based on genetically modified yeast strains was applied to screen environmental samples for their oestrogen-like activity. The yeast system was selected from the vast number of "oestrogen bioassays" available because it permits rapid and easy handling at low costs. The test protocol developed allowed the examination of dimethyl sulfoxide-dissolved samples within one day, with an EC50 between 1.5 nM and 3.5 nM 17 beta-oestradiol and a detection limit between 0.3 nM and 0.5 nM 17 beta-oestradiol for yeast strain I. Advantages and disadvantages as well as future prospects of this kind of oestrogen bioassay will be considered by discussing selected results.

Applicability of a yeast oestrogen screen for the detection of oestrogen-like activities in environmental samples.

A (xeno)oestrogen bioassay was introduced, using a genetically modified yeast strain which produces a fusion protein encompassing the human oestrogen receptor hormone binding domain and the yeast GAL4-DNA binding domain. Upon binding of appropriate substances this fusion protein recognises the respective DNA sequence thereby enhancing the transcription of a beta-galactosidase reporter gene. The bioassay procedure was evaluated by screening 30 compounds, including some known or suspected (xeno)oestrogens and determining EC50-values for 17 beta-oestradiol, 1.5 nM, 4-tert.-octylphenol, 6.7 microM and bisphenol A, 104 microM. Toluene extracts from different environmental matrices were tested for their oestrogenic activity. The positive test results obtained with a sewage sludge extract indicated the applicability of this bioassay for environmental monitoring.

Pyrene degradation by Mycobacterium sp. strain KR2.

A Mycobacterium sp., strain KR2 which was able to utilise pyrene as sole source of carbon and energy was isolated from a polycyclic aromatic hydrocarbon (PAH) contaminated soil originating from the area of a former gaswork plant. The isolate metabolised up to 60% of the pyrene added (0.5 mg/mL) within 8 days at 20 degrees C. Cis-4,5-pyrene dihydrodiol, 4,5-phenanthrene dicarboxylic acid, 1-hydroxy-2-naphthoic acid, 2-carboxybenzaldehyde, phthalic acid, and protocatechuic acid were identified as degradation products. Based on these findings a degradation pathway for pyrene is suggested which is in good accordance with the data published so far on bacterial pyrene metabolism.

Bioconcentration of superlipophilic persistent chemicals : Octachlorodibenzo-p-dioxin (OCDD) in fish.

According to present understanding, persistent superlipophilic chemicals - such as octachlorodibenzo-p-dioxin, octachlorodibenzofuran, Mirex etc - with log Kow > 6 and cross sections > 9.5 Å, bioconcentrate in aquatic organisms only little from ambient water. The most convincing argument against it is that in bioconcentration experiments with superlipophilic chemicals amounts applied exceeded water solubility by several orders of magnitude. This paper describes various methods for determining bioconcentration factors (BCF) of superlipophilic compounds. As exemplified with octachlorodibenzo-p-dioxin, BCF values evaluated by these methods match well with those calculated by QSARs for fish and mussels based on log Kow and water solubility. As expected, these BCF values exceed previous values by several orders of magnitude. For BCF evaluation of superlipophilic chemicals in aquatic organisms we recommend: (i) flow-through systems, kinetic method (OECD guideline No. 305 E) (ii) ambient concentrations < water solubility (iii) during the uptake and especially during the elimination phase no toxic effects of the test organisms should occur.

Impact of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls on human and environmental health, with special emphasis on application of the toxic equivalency factor concept.

A scientific evaluation was made of the mechanisms of action of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls. Distinction is made between the aryl-hydrocarbon (Ah) receptor-mediated and non-Ah receptor-mediated toxic responses. Special attention is paid to the applicability of the toxic equivalency factor (TEF) concept.