INFLUENCE OF NONIONIC SURFACTANTS ON BIOAVAILABILITY AND BIODEGRADATION OF POLYCYCLIC AROMATIC-HYDROCARBONS

The presence of the synthetic nonionic surfactants Triton X-100, Tergi tol NPX, Brij 35, and Igepal CA-720 resulted not only in increased app arent solubilities but also in increased maximal rates of dissolution of crystalline naphthalene and phenanthrene. A model based on the assu mption that surfactant micelles are formed and act as a separate phase underestimated the dissolution rates; this led to the conclusion that surfactants present at concentrations higher than the critical micell e concentration affect the dissolution process. This conclusion was co nfirmed by the results of batch growth experiments, which showed that the rates of biodegradation of naphthalene and phenanthrene in the dis solution-limited growth phase were increased by the addition of surfac tant, indicating that the dissolution rates were higher than the rates in the absence of surfactant. In activity and growth experiments, no toxic effects of the surfactants at concentrations up to 10 g liter(-1 ) were observed. Substrate present in the micellar phase was shown to be not readily available for degradation by the microorganisms. This f inding has important consequences for the application of (bio)surfacta nts in biological soil remediation.