A chronic plant test for the assessment of contaminated soils part 1:: Method development

Background and Scope. As part of the efforts to improve the biological testing of contaminated soils, the German government sponsored the standardisation of a chronic plant bioassay. This new test is based on experiences with various acute plant tests (e.g. published by OECD or ISO) and existing North American Plant-Life-Cycle Bioassays. In this contribution, the characteristic properties of the test are described. Methods. The test can be performed either with Brassica rapa (turnip) or Avena sativa (oat). Its duration is 35 to 64 days with OECD artificial soil and a German standard field soil acting as controls. Water and nutrients are provided by an automatic wick irrigation system. Besides measuring biomass and shoot length, the number of pods, seeds and flowers are applied as chronic measurement endpoints. During the development of the test, TNT (2,4,6-trinitrotoluene) and Pyrene were used as model test substances. Results. Pyrene did not affect B. rapa (turnip) in concentrations of up to 10,000 mg/kg soil (due to the often low sensitivity of A. sativa (oat) no further test with this substance was performed). Depending on the endpoint, the results varied in the tests with TNT. With few exceptions, the NOEC (No Observed Effect Concentration) values were determined as 55.5 mg TNT/kg soil for B. rapa (turnip) and as 75 (unfertilised) and 150 (fertilised) mg TNT/kg soil for A. sativa (oat). The EC50-values varied between 96.3 and 207.2 mg TNT/kg soil for B. rapa (turnip) and 183.1-505.6 mg TNT/kg soil for A. sativa (oat), depending on the endpoints. Outlook. The results of this work have been used to prepare a draft test guideline, which has recently been standardised by the International Organisation for Standardisation (ISO). Practical experiences with this test system are described in Part 2 of this mini series.