Effect of Inoculum Origin on Marine Biodegradation Kinetics

The persistence of chemicals in the marine environment can be assessed based on simulation biodegradation tests. However, there is a lack of studies that systematically investigate how the origin of the inoculum in these tests affects biodegradation kinetics and discuss the implications for persistence assessment. This study aims to (1) quantify the effect of inoculum pre-exposure on biodegradation kinetics, (2) quantify the variation in biodegradation kinetics between marine locations across a salinity gradient, and (3) explain differences in biodegradation kinetics based on bacterial abundance and composition. Seawater samples collected in three harbors and open waters (6-8 km from shore) were spiked with 0.5% produced water from an offshore oil platform and incubated for 1-60 days at 10 °C. Primary biodegradation kinetics of 27 petrochemicals were determined by solid phase microextraction GC-MS. Biodegradation half-times were on average 2.9-3.6 times shorter in harbor compared to open water samples, and varied on average by a factor of 1.2-1.9 between open water samples. Higher pre-exposure in harbors had the strongest impact on biodegradation kinetics, whereas geographic sampling location and salinity had the strongest impact on bacterial composition. Faster biodegradation in harbors could not be explained by differences in the overall inoculum composition or bacterial diversity.