Biotransformation of pyridine and hydroxypyridine in anoxic estuarine sediments

Biotransformation of pyridine (PYR), 3 isomers of hydroxypyridine (OHPYR) and 5 isomers of dihydroxypyridine (diOHPYR) were investigated in anoxic estuarine sediment slurries (salinity 1.3 %, SO4−2 13.5 mM, pH 7.48) collected from the Tansui River, Taiwan. Substrate depletion was monitored in serum bottle incubations by HPLC technique. In most cases, PYR (7.5 ppm) was persistent in the sediment slurries following incubation for 11 months. However, in one case, PYR (7.5 ppm) was removed frog sediment slurries in 12 days without a lag phase. No intermediate product of PYR transformation was detected. 2-OHPYR (6.8 ppm) was removed from the sediment slurries within 15 days after a lag phase of 135 days. No intermediate product of 2-OHPYR transformation was detected. 3-OHPYR (6.5 ppm) was removed from the sediment slurries in 16 days without a lag phase. Re-addition of 3-OHPYR into the sediment slurries also increased the removal rate of 3-OHPYR. Following two days of incubation after the re-addition of 3-OHPYR into the sediment slurries, one intermediate product was detected in the anoxic estuarine sediment slurries. From HPLC retention time and spectrophotometry spectra, it seems that 2,3-diOHPYR was the intermediate product of 3-OHPYR. 2,3-diOHPYR was further transformed to unidentified product(s). 4-OHPYR (6.5 ppm) was persistent in the sediment slurries following incubation for 6 months. Among the 5 isomers of diOHPYR (7.5–12 ppm) tested, 2,3-, 2,5-, and 3,4-diOHPYR were completely removed within 110 days while 2,4- and 2,6-diOHPYR were persistent in the nonadapted sediment slurries during 6 monthsʹ incubation. No transformation products were detected in the 2,3-, 2,5- or 3,4-diOHPYR amended sediment slurries.