A damage assessment model (DAM) was developed to describe and predict the toxicity time course for PAH in Hyalella azteca. The DAM assumes that death occurs when the cumulative damage reaches a critical point and was described by a combination of both first-order toxicokinetic and toxicodynamic models. In aqueous exposures, body residues increase in proportion to the water concentration. Damage is assumed to accumulate in proportion to the accumulated residue and damage recovery in proportion to the cumulative damage when damage is reversible. As a result, the toxicity time course, LC{sub}50(r), is determined by both a damage recovery rate and an elimination rate. The constant critical body residue (CBR) and the critical area under the curve (CAUC) models can be derived as two extreme cases from the DAM, and all three models were reanalyzed using a hazard modeling approach. As a result, the critical cumulative damage (DL) is the determinant of the concentration-time response relationship and not simply the CBR or the CAUC. Finally, from the DAM, two parameters, a damage recovery rate constant k{sub}r and the killing rate k{sub}t, were estimated and found to be relatively constant for selected PAH.
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