Linking biodegradation kinetics, microbial composition and test temperature - Testing 40 petroleum hydrocarbons using inocula collected in winter and summer.

Many factors affect the biodegradation kinetics of chemicals in test systems and the environment. Empirical knowledge is needed on how much test temperature, inoculum, test substances and co-substrates influence the biodegradation kinetics and microbial composition in the test. Water was sampled from the Gudenaa river in winter (2.7 °C) and summer (17 °C) (microbial inoculum) and combined with an aqueous stock solution of >40 petroleum hydrocarbons prepared by passive dosing. This resulted in low-concentration test systems that were incubated for 30 days at 2.7, 12 and 20 °C. Primary biodegradation kinetics, based on substrate depletion relative to abiotic controls, were determined with automated Solid Phase Microextraction coupled to GC/MS. Biodegradation kinetics were remarkably similar for summer and winter inocula when tested at the same temperature, except when cooling summer inoculum to 2.7 °C which delayed degradation relative to winter inoculum. Amplicon sequencing was applied to determine shifts in the microbial composition between season and during incubations: (1) the microbial composition of summer and winter inocula were remarkably similar, (2) the incubation and the incubation temperature had both a clear impact on the microbial composition and (3) the effect of adding >40 petroleum hydrocarbons at low test concentrations was limited but resulted in some proliferation of the known petroleum hydrocarbon degraders Nevskia and Sulfuritalea. Overall, biodegradation kinetics and its temperature dependency were very similar for winter and summer inoculum, whereas the microbial composition was more affected by incubation and test temperature compared to the addition of test chemicals at low concentrations.

Biodegradation Kinetics of Fragrances, Plasticizers, UV Filters, and PAHs in a Mixture─Changing Test Concentrations over 5 Orders of Magnitude.

Biodegradation of organic chemicals emitted to the environment is carried out by mixed microbial communities growing on multiple natural and xenobiotic substrates at low concentrations. This study aims to (1) perform simulation type biodegradation tests at a wide range of mixture concentrations, (2) determine the concentration effect on the biodegradation kinetics of individual chemicals, and (3) link the mixture concentration and degradation to microbial community dynamics. Two hundred ninety-four parallel test systems were prepared using wastewater treatment plant effluent as inoculum and passive dosing to add a mixture of 19 chemicals at 6 initial concentration levels (ng/L to mg/L). After 1-30 days of incubation at 12 °C, abiotic and biotic test systems were analyzed using arrow solid phase microextraction and GC-MS/MS. Biodegradation kinetics at the highest test concentrations were delayed for several test substances but enhanced for the reference chemical naphthalene. Test concentration thus shifted the order in which chemicals were degraded. 16S rRNA gene amplicon sequencing indicated that the highest test concentration (17 mg C/L added) supported the growth of the genera Acidovorax, Novosphingobium, and Hydrogenophaga, whereas no such effect was observed at lower concentrations. The chemical and microbial results confirm that too high mixture concentrations should be avoided when aiming at determining environmentally relevant biodegradation data.

Biodegradation of an essential oil UVCB - Whole substance testing and constituent specific analytics yield biodegradation kinetics of mixture constituents.

Testing and assessing the persistency, bioaccumulative and toxic properties of UVCBs (substances of Unknown or Variable composition, Complex reaction products or Biological materials) pose major technical and analytical challenges. The main aim of this study was to combine whole substance biodegradation testing with constituent specific analytics for determining primary biodegradation kinetics of the main UVCB constituents. An additional aim was to link the primary biodegradation kinetics of the main constituents to the bioaccumulation potential and baseline toxicity potential of the UVCB. Two closed biodegradation experiments were conducted using similar test systems but different analyses. The model substance, cedarwood Virginia oil, was tested at a low concentration and wastewater treatment plant effluent served as inoculum. We used microvolume solvent spiking for a quantitative mass transfer of the UVCB, while avoiding that co-solvent degradation would lead to anaerobic conditions. The biodegradation of UVCB constituents was determined with automated solid-phase microextraction coupled to GC-MS/MS using targeted analysis for main constituents and non-targeted analysis for minor constituents and non-polar degradation products. Primary biodegradation kinetics of main constituents, accounting for 73% w/w of the mixture, were successfully determined with degradation rate constants ranging from 0.09 to 0.25 d-1. Minor constituents were also degraded and non-polar degradation products were not observed. Finally, the bioaccumulation potential and baseline toxicity potential of the mixture at test start were calculated and both parameters decreased then substantially. The strength of the new approach is the possibility of biodegradation testing of a whole UVCB at low concentration while generating constituent specific biodegradation kinetics.