Lethal body residues for pentachlorophenol in zebra mussels (Dreissena polymorpha) under varying conditions of temperature and pH

Pentachlorophenol (PCP) toxicity was measured in the zebra mussel under var ying conditions of pH (6.5, 7.5, or 8.5) and temperature (10, 17, or 25 deg rees C). Toxicity decreased significantly with increasing pH at all tempera tures. At a given pH level, toxicity increased significantly with increasin g temperature. PCP was most toxic at pH 6.5, 25 degrees C and least toxic a t pH 8.5, 10 degrees C. Toxicokinetic parameters were determined at trace P CP concentrations under each combination of pH and temperature. Increasing temperature generally increased the PCP uptake clearance (k(u)) although el imination rate constants (k(d)) were unaffected. The effect of pH on toxico kinetic parameters was inconsistent but k(u) tended to decrease as pH and i onization of PCP increased. Lethal body residues (LR(50)s), estimated from kinetic parameters determined at trace PCP concentrations and the LC50 valu es, varied by a factor of 122 as a function of environmental conditions whi le LC(50)s varied by a factor of 381. LR(50)s were also estimated from the measured PCP tissue concentrations and varied by a factor of 8 across condi tions. Calculated LR(50)s were always higher than measured LR(50)s, determi ned under identical conditions, by at least a factor of five. However, when LR50, values were recalculated using k(u), values measured at the LC25 con centration, the resulting adjusted LR(50)s, varied only by a factor of 2.5 across the range of conditions studied and were more consistent with measur ed LR50 values. Thus, variance in the PCP concentration required to produce toxicity is reduced when LR(50)s are used in place of LC(50)s. Further, th e method by which lethal residues (LR50 values) are determined can signific antly affect the results and their interpretation. (C) 1999 Academic Press.