Biodegradation of hydrocarbon mixtures in surface waters at environmentally relevant levels – Effect of inoculum origin on kinetics and sequence of degradation

Abstract

Biodegradation is a dominant removal process for many organic pollutants, and biodegradation tests serve as tools for assessing their environmental fate within regulatory risk assessment. In simulation tests, the inoculum is not standardized, varying in microbial quantity and quality, thereby potentially impacting the observed biodegradation kinetics. In this study we investigated the effect of inoculum origin on the biodegradation kinetics of hydrocarbons for five inocula from surface waters varying in urbanization and thus expected pre-exposure to petroleum hydrocarbons. A new biodegradation method for testing mixtures of hydrophobic chemicals at trace concentrations was demonstrated: Aqueous solutions containing 9 hydrocarbons were generated by passive dosing and diluted with surface water resulting in test systems containing native microorganisms exposed to test substances at ng-μg/L levels. Automated Headspace Solid Phase Microextraction coupled to GC-MS was applied directly to these test systems to determine substrate depletion relative to abiotic controls. Lag phases were generally less than 8 days. First order rate constants were within one order of magnitude for each hydrocarbon in four of the five waters but lower in water from a rural lake. The sequence of degradation between the 9 hydrocarbons showed similar patterns in the five waters indicating the potential for using selected hydrocarbons for benchmarking between biodegradation tests. Degradation half-times were shorter than or within one order of magnitude of BioHCwin predictions for 8 of 9 hydrocarbons. These results showed that location choice is important for biodegradation kinetics and can provide a relevant input to aquatic exposure and fate models.

Culturable hydrocarbonoclastic marine bacterial isolates from Indonesian seawater in the Lombok Strait and Indian Ocean

“…For instance, during the logarithmic phase (from day 2 to day 14), the rates of hydrocarbon removal followed first-order kinetics, and the maximum and minimum slopes of the line represent the first-order kinetic constant k (Table 3). Similar results were found in previous studies on the bioremediation of petroleum-contaminated sediment (Birsch et al., 2017; Thessen and North, 2017). The reaction rate can also be calculated integrally by using the actual reaction order, and this kinetics approach to determining the biodegradation rate of crude oil for each bacteria yielded significantly different values, with IO-25, IO-24, and LS-15 most likely able to degrade the crude oil faster than the others.…”

Determining the water solubility of difficult-to-test substances: A tutorial review

“…The system dimensions in the study by Stibany et al [42], were not optimized for very fast equilibration times, and 11 hours were needed to establish equilibrium with algal medium containing 20 % methanol. Equilibration times less than 10 minutes have been demonstrated for passive dosing of hydrocarbons to water in an optimized design [63,64]. The concentrations in this study were below solubility, but very similar equilibration times are expected also for equilibration at the solubility limit.…”

Improving our understanding of the environmental persistence of chemicals

“…The new platform was intended to be applicable for assessing nonlabeled substances (monitoring primary biodegradation), multiconstituent mixtures, and hydrophobic and volatile chemicals. This research has also been summarized in recent publications (Birch, Andersen, et al, 2017;Birch, Hammershøj, et al, 2017;Birch et al, 2018). The advantage of this system was that it enabled testing multiconstituent mixtures and yielded large sets of well-aligned data.…”