The magnitude of primary production may influence the degradation and bioavailability of contaminants in aquatic ecosystems. The rate at which these contaminants degrade is important in considering the toxicity and ultimate effect and fate of the chemicals. The degradation and fate of pentachlorophenol (PCP), a biocide and common contaminant, was studied in replicate pond ecosystems at three levels of primary production: (1) low-nutrient phytoplankton ecosystems (low primary production), (2) high-nutrient phytoplankton ecosystems (medium primary production), and (3) macrophyte-dominated ecosystems (high primary production). The PCP treatments were of two types: (1) a single heavy treatment (1 mg/L) applied early in the experiment and (2) multiple treatments of 0.2, 0.2, 0.4, and 0.4 mg/L applied at monthly intervals.

The concentrations of PCP in water and mud were consistently lower in the macrophyte pond group than in the phytoplankton pond groups. The difference between the amount of PCP in the phytoplankton ponds and that in the macrophyte ponds were not apparently due to sorption onto the macrophytes. Therefore, the macrophytes were either actively degrading the PCP or incorporating it into their structure in a form that was not extractable. PCP residues in fish also reflected the lower bioavailability of PCP in the macrophyte ponds. Both the total PCP and the concentration of PCP in fish from the macrophyte ponds were lower than those for either of the phytoplankton pond groups. High primary production rates appear to increase the degradation rate of PCP in pond ecosystems.