Mineralization of aged atrazine, terbuthylazine, 2,4-D, and mecoprop in soil and aquifer sediment

The effect of aging of the herbicides atrazine, terbuthylazine, 2,4-D, and mecoprop on their bioavailability to degrading microorganisms was studied in soil and aquifer sediment. ¹⁴C-ring-labeled herbicide (2.5 mg/kg) was added to sterilized soil or aquifer sediment and stored at 10°C for up to 103 d before inoculation with either the atrazine and terbuthylazine-degrading Pseudomonas sp. strain ADP (atrazine-degrading Pseudomonas) or an enriched culture able to mineralize 2,4-D and mecoprop. The initial mineralization rate and recovery of ¹⁴CO ₂ after 62 to 113 d of incubation were used as measures of the availability of the compounds to the microorganisms. Aging in soil reduced the initial mineralization of atrazine. Thus, only 17% of the added ¹⁴C-atrazine had been mineralized after 21 h of incubation when aged for 88 d as compared with 33% when the atrazine had been aged for 1 d. ¹⁴CO ₂ recovery was only 58% after 88 d of aging as compared with 81% when aged for 1 d. A similar effect of aging was seen with terbuthylazine. With 2,4-D, the effect of aging in soil on mineralization by the enriched culture was much smaller. Aging had no effect on mineralization of mecoprop in soil or on mineralization of any of the herbicides in aquifer sediment.