Biodegradation of S-Triazine Herbicides at Low Concentrations in Surface Waters

Fourteen bacterial strains were isolated from industrial waste (SL) agricultural soil (S), surface water (B) or water treatment filter material (WT) following enrichment in a minimal salts medium (MSM) containing 5-10 mgl(-1) of both atrazine and simazine. Biodegradation by the isolates of 1 mu gl(-1) of atrazine and 1 mu gl(-1) simazine in 100 ml MSM or reservoir surface water was assessed by comparison with non-inoculated controls. Extraction with dichloromethane recovered 100 +/- 5% of both s-triazines in non-inoculated MSM and reservoir surface water. Recovery was not reduced by adsorption of the s-triazines to bacteria, and no abiotic degradation occurred over the incubation periods. Isolate 54 degraded 20 +/- 7% of the atrazine and isolates S7 and S8 degraded 40 +/- 12% of the simazine in MSM after 7d at 30 degrees C. Decreasing the NH4NO3-N in the MSM from 35 mgl(-1) to 1 mgl(-1) stimulated biodegradation of atrazine by a fourth isolate (SL3). At 10 degrees C isolates BI, SL2, S4 and S6 each biodegraded 20 +/- 1% of the atrazine and isolate SL2 biodegraded 30 +/- 7% of the simazine in surface water after 15 d. No biodegradation occurred in MSM at 10 degrees C. Granular activated carbon (GAC, 1 gl(-1))was added to surface water (10 mu gl(-1) atrazine and 10 mu gl(-1) simazine) which adsorbed 9.7 mu gg(-1) s-triazine and provided sites for bacterial attachment. Recovery of adsorbed s-triazines (1, 10 and 40 mu gl(-1)) by Soxhlet extraction of non-inoculated GAC was 97 +/- 1.5%. Inoculation of s-triazine-degraders into surface water containing GAC reduced the solution concentration (0.3 mu gl(-1) atrazine and 0.3 mu gl(-1) simazine) by up to 86 +/- 18% (S8) after incubation for 15 d at 10 degrees C. Biodegradation of 25 mu gl(-1) atrazine and 28 mu gl(-1) simazine in surface water amended with 0.5 gl(-1) GAC and inoculated with isolate WT1 was 50 +/- 4% (atrazine) and 38 +/- 4% (simazine) after 21 d at 10 degrees C. Biodegradation by WT1 attached to 0.5 g GAC in surface water (0.5 mu gl(-1) atrazine and 6 mu gl(-1) simazine) was increased from zero atrazine and 23 +/- 7.6% simazine to 40 +/- 5.3% atrazine and 71 +/- 5.6% simazine following transfer of bioaugmented GAC into fresh surface water. Inoculation of GAC filters with selected strains has potential as a biotreatment for surface water containing s-triazine herbicides.