Atrazine mineralization by indigenous and introduced Pseudomonas sp strainADP in sand irrigated with municipal wastewater and amended with compostedsludge

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 mineralizati on, indicating the presence of genes for atrazine mineralization. Soil DNA extraction followed by magnetic capture hybridization-PCR revealed the pres ence 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 w as inoculated into the sands, its atzA copy number declined after 1 d from the initial inoculation size (7.5 x 10(6) copies g(-1) sand) by at least tw o orders of magnitude (< 3.9 x 10(4) 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 irrigat ed with tap water or wastewater, respectively. Amendment with composted slu dge, resulted in a similar mineralization rate to that in the sands irrigat ed with wastewater alone, when the K-d value for atrazine was less than 1.1 7 l kg(-1), regardless of the irrigation water quality. In two replicates o f the 10-20-cm layer, with K-d values of 1.57 and 2.79 l kg(-1) only 23 and 5%, respectively, of the applied atrazine was mineralized. These observati ons suggest that, even though sludge amendment or wastewater irrigation inc reased the competition between indigenous populations and introduced bacter ia, 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. (C) 200 0 Published by Elsevier Science Ltd. All rights reserved.