translate English to French: During the first 20 days of the experiment, approximately one-third of the antibacterial agents disappeared from the sediments. During the next 165 days another 25% vanished.
Pendant les 20 premiers jours de l'expérience, environ le tiers des agents antimicrobiens a disparu des sédiments et 25% s'est dissipé pendant les 165 jours suivants.