DISCRISET: a battery of tests for fast waste classification--application of tests on waste extracts

The Hazardous Waste Directive (HWD, Council Directive 91/689/EC, 1991) provides a framework for classification of hazardous waste, based on 15 Hazard (H)-criteria. For complex wastes the HWD foresees the application of toxicity tests on the waste material itself to assess its toxic properties. However, these proposed test methods often involve mammalian testing, which is not acceptable from an ethical point of view, nor is it feasible economically. The DISCRISET project was initiated to investigate the use of alternative chemical and biological fast screening tests for waste hazard classification. In the first part of the project, different methods were reviewed and a testing strategy was proposed to minimize time and cost of analysis by a tiered approach. This includes as a first tier chemical analysis followed by a general acute toxicity screen as a second tier and as a third tier mechanistic toxicity tests to assess chronic toxicity (genotoxicity, hormone disturbance, teratogenic effects, immunologic activity). In this phase of the project, selected methods were applied to 16 different waste samples from various sources and industries. The first tier chemical tests are recommended for the full characterization of the leachate fraction (inorganics) but not for the organic fraction of samples. Here the chemical characterization is only useful if toxic content is known or suspected. As second tier the fast bacterial test Microtox is validated as a general toxicity screen for the organic fraction (worst case organic extract). Samples that are not classified in tier 1 or 2 are then further investigated in the third tier by the mechanistic toxicity tests and tested for their potential chronic toxicity: immune activity (TNF-α upregulation) is indicative for corrosive, irritating or sensitising effects (H4/H8/H15), reproductive effects (H10) are indicated by hormone disturbance and early life stage abnormalities in fish larvae when exposed to the extracts and mutagenicity and carcinogenicity (H7, H11) are indicated by SOS response induction and increased mutation frequency in the Ames test when exposed to the extracts. Results indicate that the combination of chemical tests and bioassays allows important hazardous properties to be addressed and the tiered approach ensures that the tests are performed quickly and economically. The suggested strategy provides a solid and ethical alternative to the methods described in the HWD and is a vast improvement on the current, arbitrary classification.

Potential of an in vitro toolbox combined with exposure data as a first step for the risk assessment of dietary chemical contaminants

In vitro risk assessment of dietary contaminants has become a priority in human food safety. This paper proposes an in vitro approach associating different complementary tools in an original toolbox and aims to improve the assessment of the toxicological impact of dietary contaminants at realistic human exposure levels, with a special focus on the intestinal compartment. The system is based on the use of four complementary cellular tools, namely stress gene induction in transgenic strains of Escherichia coli, modulation of the activity of key biotransformation enzymes (cytochrome P-450 (CYP) 1A1 and 3A4) in a human intestinal cell line, and activation of aryl hydrocarbon receptor (AhR) and oestrogenic receptor (ER)-dependent genes in agonistic and antagonistic assays with luciferase reporter cells. It was applied to four chosen model molecules: ochratoxin A (OTA) and deoxynivalenol (DON), two common food-borne mycotoxins, and imazalil (IMA) and benomyl (BEN), two fungicides widely occurring in foodstuffs. All these assays were performed at or around a realistic intestinal concentration, determined through a deterministic approach based on the calculation of a theoretical maximum daily intake (TMDI). Using the four model molecules, it is clearly highlighted that induction of CYP1A1 activity and inhibition of CYP3A4 activity occurred in Caco-2 cells at a realistic intestinal concentration of IMA. Furthermore, some bacterial stress genes were induced in a range of realistic concentrations, following exposure to DON and IMA. In addition, BEN clearly provoked an ER agonistic activity in a human oestrogen sensitive reporter cell line. All these results are in accordance with the literature, suggesting that the in vitro toolbox constitutes an interesting approach in order to obtain a first 'fingerprint' of dietary contaminants at realistic human exposure for further risk assessment.

Dose-response relationships and statistical performance of a battery of bacterial gene profiling assays

Because of increasing awareness and legislative demands, there is a demand for the development and use of biological assays for the assessment of the toxicity of chemicals, environmental samples. Recently, a growing number of bacterial reporter assays have been developed and implemented. Nevertheless, little data is published on the performance of these assays in terms of analytical parameters. We present results on a battery of 14 transgenic Escherichia coli strains carrying different promoter::reporter fusions. Growth characteristics and basal expression levels were modeled and fitted, data show that growth curves should be taken into account during test development. Our study shows that the induction profiles reflect the mode of action, e.g., paraquat clearly induces the soxRS operon. The sensitivity of the assay compares well to that of whole organism tests, e.g., fish and Daphnia for polar organics. Metal toxicity is detected less efficiently, e.g., cadmium is detected near the LC50 of carp, considered a relatively insensitive species towards cadmium. The assay variability ranges from 10 to 40% depending on the strain, comparable to that of other bioassays. The variability was shown to be determined by the intrinsic traits of the promoter-strain combination, not by operating conditions.