A new bioassay for the ecotoxicological testing of VOCs on groundwater invertebrates and the effects of toluene on Niphargus inopinatus.

A protocol was developed for testing the ecotoxicological effects of volatile organic compounds (VOCs) on groundwater invertebrates. Test substance volatility was addressed in a "closed from start to analysis"-design. Since manifestation of toxic effects may be delayed in 'slower metabolizing' organisms such as groundwater fauna, a time-independent (TI-) approach was adopted. Toluene was used as a model substance and its toxicity to the groundwater amphipod Niphargus inopinatus was assessed as an example. The method evaluation process considered various methodological issues such as partitioning of the toxicant between the water and the gas phase (Henry equilibrium), the possible depletion of oxygen in closed test vials, as well as microbial biodegradation of the test substance. For N. inopinatus, an LC50,14 days of 46.6mgL(-1) toluene was obtained. The ultimate LC50 value was estimated at 23.3mgL(-1) toluene. No oxygen depletion occurred in the test vials and Henry equilibrium was found to be established after 6h. The new test system proposed now awaits broad practical application.