The pH dependent accumulation of PCP in aquatic microcosms with sediment

The fate of pentachlorophenol in aquatic microcosms, consisting of three trophic levels and held under varying conditions of pH and sediment type, was assessed. The pH was set at 4, 6, or 8, with an organic sediment (3% organic carbon) or an inorganic sediment (0% organic carbon) as a substrate. The distribution of PCP in the microcosm media and organisms varied significantly as environmental conditions changed. There was significantly more PCP (or phenate ion) in the water at pH 8 than pH 6 or 4 in both the organic and inorganic systems. However, accumulation of PCP in most of the microcosm organisms was significantly greater at pH 4, followed by 6 and then 8. Partitioning of PCP into organic sediment followed the same trend with the highest amounts of PCP appearing in sediment at pH 4. The organic carbon content of sediment was important in determining partitioning into sediment; the 3% organic carbon sediment sorbed significantly more PCP than the 0% organic carbon sediment. In addition, the organisms in the 3% organic carbon sediment microcosms accumulated significantly less PCP then did those in the 0% organic carbon systems. The 3% organic carbon sediment also appeared to facilitate the breakdown of PCP in sediment and water. Among others these data indicate that hazard assessments should not be based on aqueous levels of PCP unless pH is considered.