The porewater concentrations of pyrene were estimated by a negligible depletive solid-phase microextraction (SPME) method. The effects of organic matter (OM) and soil aging on the bioavailability of pyrene in soil were investigated by generation of reproductive effect concentrations (EC50) for the euedaphic springtail, Folsomia candida, under various test conditions. The soil used was a sandy loam soil with natural OM content of 2.6% (Askov soil). It was enriched with increasing organic matter concentrations of 5%, 10%, and 20% and was aged for 0, 56, and 112 days. The EC50 values of the springtails increased with increasing OM and aging of the soil. The increase of the OM content in the soil reduced the extractability of pyrene by SPME, as well as the toxicity of pyrene. An aging effect was demonstrated in Askov soil, EC50 values increased with increased contact time. The amounts of pyrene extracted by SPME were significantly affected by the soil concentration. Porewater concentrations determined by SPME decreased with increasing OM and aging. However, the pyrene EC50 porewater concentration remained largely constant at approximately 23 microg L(-1). The results demonstrated that the SPME method is a useful indicator for bioavailability to soil microarthropods.