Summary

This study demonstrates that thenovel in vitro CALUX (chemical-activated luciferase expression) assay is a rapid, sensitive assay for assessing the toxic potencyof (mixtures of) aryl hydrocarbon receptor (AhR)-active compoundsin sediments and pore waters. A rat hepatoma (H4IIE) cell line,stably transfected with a construct containing the dioxin-responsiveelement (DRE) sequence and the luciferase reporter gene, was usedto determine the relative potency or the total activities of AhR-activecompounds in sediment and pore water extracts. This novel CALUXassay had a detection limit of 0.5 fmol of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD). The sensitivity and linear working range was slightlybetter than for the ethoxyresorufin O-deethylase (EROD) assay inH4IIE wild type cells. The primary improvement of the CALUX assaycompared to the EROD assay, however, is that the CALUX assay isinsensitive to substrate inhibition. The CALUX activity inducedby organic extracts from 450-mg aliquots of sediment or 250-microlaliquots of pore water corresponded with the instrumentallyanalyzed degree of pollution of the sediment. Using pore water,only a simple and rapid extraction procedure was needed, withoutadditional clean-up to prevent cell death. The response from porewater samples in an 8-day early life stage test with zebra fish (Branchydaniorerio) corresponded with the CALUX induction, although thecorrelation was sometimes disturbed by heavy metals. Twopolychlorinated terphenyl mixtures, the PCB-substitute Ugilec 141,polybrominated diphenylethers, and the PCB-mixture Clophen A50were tested in the CALUX assay and had induction potencies thatwere 10(-4)-10(-7) compared to TCDD.