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2,4-D—Its Distribution and Effects in a Ryegrass Ecosystem¹

ABSTRACT

The fate and effects of the ¹⁴C-labeled butyl ester of 2,4-D (2,4-dichlorophenoxyacetic acid) applied as a foliar spray (1 kg ha^–1) were examined in a simulated ryegrass (Lolium perenne) ecosystem. The ecosystem consisted of a sandy loam soil, annual ryegrass, numerous invertebrates, and a gray-tailed vole (Microtus canicaudus) housed in a terrestrial microcosm chamber (TMC-II). In addition to 2,4-D distribution, the study was designed to evaluate the reproducibility of data derived from TMC-II studies within and between experiments. One month after 2,4-D application, all of the ¹⁴C materials detected in the soil were present as unextractable residues in the top 1 cm; plant material contained an average of 8.9 mg kg^–1, identified primarily as 2,5-dichloro-4-hydroxyphenoxyacetic acid. Residue levels in the animals ranged from 0.6 mg kg^–1 for earthworms (Lumbricus spp.) to 5.3 mg kg^–1 in pillbugs (Armandillarium spp.) of unidentified ¹⁴C residues. In excess of 90% of the material collected in the air stream was recovered within 24 h of application, which was identified as the butyl ester with no acid metabolites evident. The only effect observed in the ecosystem was a weight loss in the voles exposed to 2,4-D, in comparison with the control.

Key Words: fate • terrestrial • model ecosystem • carbon-14

¹ Contribution of the USEPA, Corvallis Environmental Research Laboratory, Corvallis, OR 97333.

² Toxicologist, Corvallis Environ. Res. Lab., USEPA, Corvallis, OR 97333.