Atrazine mineralization by indigenous and introduced Pseudomonas sp. strain ADP in sand irrigated with municipal wastewater and amended with composted sludge

Indigenous soil bacteria significantly mineralized atrazine irrespective of sand depth or treatment type. After 32 d, the mineralization ranged from 0.3 to 75%, with a variable lag period before the initiation of mineralization, indicating the presence of genes for atrazine mineralization. Soil DNA extraction followed by magnetic capture hybridization-PCR revealed the presence of the genes atzA, atzB and atzC, indicating potential mineralization via the same pathway as in Pseudomonas sp. strain ADP (P.ADP). When P.ADP was inoculated into the sands, its atzA copy number declined after 1 d from the initial inoculation size (7.5×106 copies g−1 sand) by at least two orders of magnitude (<3.9×104 copies g−1 sand) with no significant recovery after 18 d. In spite of atzA low copy number in the sand, 40 and 75% atrazine mineralization occurred after 1 week when the sand was irrigated with tap water or wastewater, respectively. Amendment with composted sludge, resulted in a similar mineralization rate to that in the sands irrigated with wastewater alone, when the Kd value for atrazine was less than 1.17 l kg−1, regardless of the irrigation water quality. In two replicates of the 10–20-cm layer, with Kd values of 1.57 and 2.79 l kg−1, only 23 and 5%, respectively, of the applied atrazine was mineralized. These observations suggest that, even though sludge amendment or wastewater irrigation increased the competition between indigenous populations and introduced bacteria, P.ADP was able to continue mineralizing atrazine. The atzA copy numbers remain in the treated sand in low but stable (and active) concentrations. The high organic matter content of the sludge was the main factor affecting atrazine mineralization, because of its atrazine sorption ability.