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OECD 208: Terrestrial Plant Test - Seedling Emergence and Seedling Growth Test

Non-target plants, i.e. plants in natural and semi-natural habitats within the agricultural land such as hedgerows, field borders, meadows and other small biotopes, may unintentionally be exposed to plant protection products drifting from the agricultural fields, to veterinary medicinal products by fertilisation with manure from treated livestock, to biozides or chemicals.
The OECD guideline 208 assesses the potential effects of a test item on seedling emergence and early growth of seedlings following exposure to the test item in or on the soil.

Study Design

 

Plant species

The plant species selected for the test should derive from different plant families to consider the taxonomic diversity in the plant kingdom and should give reliable and reproducible results. Usually 6 to 10 plant species are chosen according to the specific properties of the test item and the intended use. Among them could be for example Allium cepa (onion), Zea mays (corn), Brassica napus (oilseed rape), Cucumis sativus (cucumber), Glycine max (soybean), Helianthus annuus (sunflower), Solanum lycopersicon (tomato) or Stellaria media (common chickweed).

 

Test concentrations / rates

Test concentrations / rates are usually determined in a range-finding pre-test. For plant protection products the rates for the pre-test are calculated based on the maximum application rate. For veterinary medicinal products concentrations for the pre-test can be calculated based on the expected PEC (Predicted Environmental Concentration) soil. Alternatively, it is possible to use 1000 mg/kg dry soil as maximum concentration in the pre-test.

 

Course of the test

Depending on the expected route of exposure, the test item is either incorporated into the soil (veterinary medicinal, chemicals) and seeds are planted in this treated soil or the test item is applied to the soil surface (plant protection products) after sowing. The test item concentration has to be confirmed analytically. After the application the plants are evaluated weekly for effects (phytotoxticity) in comparison to the water treated control plants for 14 to 21 days after 50 % emergence of the seedlings in the control group. At the test end the endpoints (e.g. fresh weight, dry weight, height) are measured and recorded.

Seedling Emergence and Seedling Growth Test with test item treated manure for veterinary medicinal products.

In the case of strong effects for a veterinary medicinal products in a OECD 208 test this test item can be applied to manure to have a more realistic approach (Concept development for an extended plant test in the environmental risk assessment of veterinary medicinal products). This manure is then incubated under anaerobic conditions. The incubation time depends on the type of manure (cattle, pig) and its normal storage time. The spiked manure is then incorporated into the soil. The further study design has to fullfill the requirements of OECD 208. The effects are evaluated in comparison to a manure treated control.

Endpoints

  • Endpoints are germination, mortality and fresh weight. If the test is conducted as multiple rate test effects on fresh weight are reported as ERX (effective rate) for each species individually or if the test is conducted as limit test as NOER (no observed effect rate).
  • Additional parameters that can be assessed are height and dry weight. Effects on these parameters are reported as ERX for each species individually.
  • Phytotoxicity (e.g. chlorosis, necrosis, abnormal growth, growth reduction) and growth stages (BBCH code) are recorded.

 

Guidelines and literature

  • OECD Guidelines for Testing of Chemicals No. 208 “Terrestrial Plant Test: Seedling Emergence and Seedling Growth Test”, adopted July 19, 2006
  • OCSPP 850.4100 “Seedling Emergence and Seedling Growth”, EPA 712-C-012, January 2012
  • Concept development for an extended plant test in the environmental risk assessment of veterinary medicinal products, Texte 15/2015, Federal Enviroment Agency, April 2015
  • EPPO PP 1/207(2): Efficacy evaluation of plant protection products, Effects on succeeding crops, 2007.