Compartmentalization and persistence of endothall in experimental pools

The compartmentalization and persistence of endothall, an aquatic herbicide, was studied using static greenhouse experimental pools. An overall aqueous pseudo-first-order decay rate coefficient of 0.173 day-1 and a half-life of 4.01 days were observed at endothall treatment levels of 0.03, 1.6, and 4.5 mg liter-1. Instantaneous sediment partition coefficients (Kp) were calculated at maximum endothall concentrations in sediments and ranged from 51.4 to 127.7. Bioconcentration factors (BCF) for the submerged aquatic macrophyte, Myriophyllum spicatum, ranged from 3.9 to 768.9. These instantaneous BCF values were calculated at the maximum M. spicatum endothall concentrations. The short aqueous half-life for endothall compares well with previous studies; however, both the Kp and BCF were one to three orders of magnitude higher than observed in a previous laboratory study and calculated from regression equations based on endothall solubility. Experimental pool studies can be important steps in translation of data from the laboratory to field and in the development of field sampling protocols that require understanding of expected behavior of a chemical in aquatic systems.