Abstract
Caffeine (1,3,7-trimethylxanthine) could represent a useful marker of contamination of effluent from agricultural land receiving biosolids. The persistence characteristics of caffeine in three agricultural soils was investigated. In laboratory microcosms of moist soil incubated at 30°C, [8-ring-14C]-caffeine was rapidly and thoroughly mineralized to 14CO2 in a sandy loam and a loam soil, and less rapidly in a silt loam soil. Caffeine mineralization was very responsive to soil temperature and moisture. Mineralization of caffeine was hastened by the addition of liquid municipal biosolids (LMB) from three municipal sewage-treatment plants (MSTPs) that aerate this material. In contrast, LMB from three MSTPs that did not aerobically digest their LMB did not accelerate caffeine mineralization. Autoclaved LMB had no effect on caffeine dissipation. Abacterium, designated Pseudomonas sp. Strain TH1, was isolated from aerated LMB. The bacterium first demethylated caffeine to 3,7-dimethylxanthine, and then mineralized the molecule. Inoculation of Pseudomonas sp. Strain TH1 into soil hastened mineralization of [8-ring-14C]-caffeine. In summary, caffeine was more stable in a silt loam soil than a sandy loam or loam soil, but biodegradation in all three soils was quite uniform upon the addition of caffeine-degrading bacteria or aerated biosolids. We suggest that caffeine would likely not be a suitably conservative chemical marker for detecting chronic contamination of agricultural drainage water following fertilization wit hLMB. Aerobic digestion of LMB promotes the enrichment of caffeine-degrading microorganisms. Key words: Caffeine biodegradation, biosolids chemical marker, biosolids organic contaminant, water quality
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