Evaluating a bioremediation tool for atrazine contaminated soils in open soil microcosms: The effectiveness of bioaugmentation and biostimulation approaches

A previously developed potential cleanup tool for atrazine contaminated soils was evaluated in larger open soil microcosms for optimization under more realistic conditions, using a natural crop soil spiked with an atrazine commercial formulation (Atrazerba FL). The doses used were 20× or 200× higher than the recommended dose (RD) for an agricultural application, mimicking over-use or spill situations. Pseudomonas sp. strain ADP was used for bioaugmentation (around 107 or 108 viable cells g−1 of soil) and citrate for biostimulation (up to 4.8 mg g−1 of soil). Bioremediation treatments providing fastest and higher atrazine biodegradation proved to differ according to the initial level of soil contamination. For 20× RD of Atrazerba FL, a unique inoculation with Pseudomonas sp. ADP (9 ± 1 × 107 CFU g−1) resulted in rapid atrazine removal (99% of the initial 7.2 ± 1.6 μg g−1 after 8 d), independent of citrate. For 200× RD, an inoculation with the atrazine-degrading bacteria (8.5 ± 0.5 × 107 CFU g−1) supplemented with citrate amendment (2.4 mg g−1) resulted in improved biodegradation (87%) compared with bioaugmentation alone (79%), even though 7.8 ± 2.1 μg of atrazine g−1 still remained in the soil after 1 wk. However, the same amount of inoculum, distributed over three successive inoculations and combined with citrate, increased Pseudomonas sp. ADP survival and atrazine biodegradation (to 98%, in 1 wk). We suggest that this bioremediation tool may be valuable for efficient removal of atrazine from contaminated field soils thus minimizing atrazine and its chlorinated derivatives from reaching water compartments.