Partition controlled delivery of hydrophobic substances in toxicity tests using poly(dimethylsiloxane) (PDMS) films

Interpretation of toxicity test results may be hampered when doubt exists a bout the actual exposure concentration. Processes that are responsible for differences between the nominal and the actual concentration in aqueous tes t systems may include sorption, precipitation, volatilization, chemical and biological degradation, and uptake into biological or test tissue. In this study, the use of a poly(dimethylsiloxane) (PDMS) film containing the test compound is introduced as a versatile technique for partition controlled d elivery of hydrophobic compounds to aqueous toxicity tests. Two methods dev eloped produced preloaded films, having toxicant added to the PDMS prepolym er solution before film deposition and curing, and postloaded films, which are created by the addition of toxicant in a solvent to an already-polymeri zed PDMS film. Preloaded films were generally more easily prepared, may bet ter accommodate larger molecules, and have a higher capacity than postloade d films. Postloaded films provided film-solution partition coefficients wit h higher precision and allowed for the use of films from stock and thus for a more portable technique. Chemical analysis showed that equilibrium betwe en films and the aqueous solution was established within 7-10 min and was m aintained for a suite of aromatic compounds (log K-ow ranging from 2.8 to 6 .1). The reliability of the film technique was demonstrated by application to the Microtox bacterial toxicity tests of solutions of polycyclic aromati c hydrocarbons (PAHs).