OECD 208: Terrestrial plant test

Assessment of the effects of a test substance on seedling emergence and early growth of higher plants according to OECD Test Guideline 208. The substance is applied to the soil surface or incorporated into the soil, using water, acetone, or ethanol as a carrier where needed; crop protection products may be spray-applied to mimic field use, and poorly soluble materials can be incorporated as weighed additions to dry soil.

Seeds of at least six species from different plant families are sown in treated natural soil or artificial substrate and observed for 14 to 21 days after 50% emergence in the controls. Measured endpoints include:

  • Percent seedling emergence

  • Shoot dry or fresh weight

  • Shoot height (where required by the regulatory authority)

  • Visual phytotoxicity score on a uniform injury scale (chlorosis, necrosis, wilting, deformation, mortality)

Analytical verification of test substance concentrations is performed where soluble formulations allow; insoluble substances are confirmed by weighed additions and, where necessary, soil homogeneity analysis.

Single-rate studies report the observed level of effect or its absence. Multi-rate studies are modelled to derive ECx/ERx values (e.g., EC25/ER25, EC50/ER50) with confidence intervals and, where applicable, NOEC and LOEC. Emergence data are analysed as quantal responses using logit, probit, Weibull, or Spearman–Kärber models.

OECD TG 208 is accepted for non-target plant effect assessment in EU regulatory frameworks, including REACH (where ECHA has issued guidance on its use for terrestrial plant hazard characterization) and Regulation (EC) No. 1107/2009 on plant protection products (with test methods listed in Commission Communication (2023/C 344/02)). In the U.S., aligned EPA guidelines include OCSPP 850.4100 (Seedling Emergence and Seedling Growth) and OCSPP 850.4230 (Early Seedling Growth Toxicity Test).

Suitable sample matrices
Chemicals, biocides, crop protection products
Available quality systems
Accredited testing laboratory
Standard
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