Chronic toxicity and body residues of the nonpolar narcotic 1,2,3,4‐tetrachlorobenzene in Chironomus riparius

The use of internal concentrations as a dose parameter for baseline toxicity requires an understanding of the relationship between accumulation level and toxic effects, not only for acute but also for chronic exposure. In this study of chronic toxicity of the nonpolar narcotic 1,2,3,4-tetrachlorobenzene (TeCB) to Chironomus riparius, the chronic median lethal concentration (LC50) was determined to be 0.99 (0.54-1.82) muM, the median sublethal effect concentration (EC50) for growth was 0.76 (0.73-0.97) muM, and the chronic (sublethal) no-observed-effect concentration (NOEC) was 0.24 +/- 0.01 muM. An acute-to-chronic ratio of 9.8 was calculated from a previously determined acute LC50 value and this NOEC. The chronic critical body residue (CBR), 136 mmol/kg lipid, was the same as the acute CBR, previously determined. The similarity of the chronic and acute CBRs lends support to the exposure time independent aspect of baseline toxicity theory. An implication of this is that internal concentrations estimated by biomimetic sampling devices may be compared to acute CBR data to determine chronic baseline toxicity risk. Such sampling devices, solid-phase microextraction (SPME) fibers, were simultaneously exposed during the toxicity test. The results of this study suggest that body residues estimated with SPME may be used to predict baseline toxicity for various exposure durations.