Effects of Pentachlorophenol on Soil Microbes-Alfalfa (Medicago sativa) Interaction

Pentachlorophenol (PCP) is a legacy wood preservative that, despite its regulatory phase-out, remains present in treated structures and soils due to its long service life and persistence. This study evaluates the effects of PCP on soil microbial communities and alfalfa (Medicago sativa) growth under greenhouse conditions. Two concentrations of PCP (1.58% and 2.7%) were applied to soil, with and without alfalfa cultivation, to assess changes in microbial colony counts and plant development over 60 days. Results revealed a concentration-dependent decline in microbial populations and plant biomass, with the 2.7% PCP treatment causing severe reductions. However, soils planted with alfalfa exhibited improved microbial recovery, especially at the lower PCP concentration, indicating a rhizosphere-mediated resilience. These findings suggest that alfalfa may enhance microbial resilience through rhizosphere interactions, offering potential benefits for managing historically contaminated sites. Given that PCP degrades over time, these insights contribute to understanding plant–microbe dynamics in aged preservative-treated environments without overstating long-term risks.