Biological and chemical monitoring of the transformation of recalcitrant organic compounds in river sediment
This thesis reports on the degradation of two different models of organic pollutants in two contrasting Scottish river sediments. The first type of sediment (sediment 1) was collected close to an urban area with high percentage of organic matter content (1.3%). The second type of sediment (sediment 2) was collected from a pristine area and was less organic (0.2%). As organic pollutant model, radiolabelled (14C) 2,4-Dichlorophenoxyacetic acid (Acid-ring-UL-14C) and Naphthalene (Naphthalene-1-14C) were amended to individual microcosms (50g of sediment and 50ml of river water) at different concentrations (0.5, 5.0 and 50 mg per microcosm). Degradation was assessed by emission of 14CO2 during a period of 40 and 124 days for 2,4-D and Naphthalene, respectively. 2,4-D was mostly degraded between 20-35 days, and degradation rates (5 to 750 mgd-1) were proportional to initial concentrations. Almost 25% of applied Naphthalene was degraded by 40 days, at different degradation rates (2.7 to 405 mgd-1) according to sediment type. Assessment of the impact of 2,4-D and Naphthalene on the sediment microbial community was made using Biolog, DGGE and PLFA analysis to provide for a comparative physiological, molecular and chemotaxonomic assessment, respectively. These analyses linked differences in the rates and extents of 2,4-D degradation to differences in composition of the microbial communities. To assess the impact of 2,4-D, DGGE-profiling was used and show genetic changes were more significant in sediment 2 microcosms than sediment 1. Biolog suggested differences in the microbial structure of both sediments, but PLFA demonstrates that sediment 1 treatments were more affected by 2,4-D amendments than sediment 2. The extent of Naphthalene biodegradation was restricted by bioavailability, sediment type and volatilisation.