trace résiduelle

CONT: For example, if contamination with a relatively water-soluble and readily degraded pesticide ... is suspected then historical pollution may have left only residual traces in surface soils but ground water would likely be affected.

CONT: [...] ofrece servicios de detección, ensayo y análisis de trazas residuales de plaguicidas o pesticidas, fungicidas y herbicidas en productos alimentarios y agrarios.