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

Abstract

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.

Increasing the Environmental Relevance of Biodegradation Testing by Focusing on Initial Biodegradation Kinetics and Employing Low-Level Spiking

“…It is used to measure biodegradation by spiking the test chemical (concentrations of ≤10 μg L –1 are preferred) into aerobic natural waters or water–sediment systems with low suspended sediment concentrations (≤1 g of solids L –1 ) . However, chemical spiking has been shown to influence the microbial community and chemical attenuation, which creates doubts about the environmental relevance of the biodegradation test. ,− As an alternative, a nonspiked test has been suggested as it provides a better representation of biodegradation in the environment. , However, this test is constrained by the requirement for background contamination of the test chemicals in the environment of interest at quantifiable concentrations.…”

Technical guidance on biodegradation testing of difficult substances and mixtures in surface water

“…In our biodegradation test set-up, passive dosing systems are primarily used to prepare a spike solution in pure water, which is then transferred to test systems using gas tight syringes. It is also possible to add inoculum directly to the passive dosing systems in order to produce water with higher test chemical concentrations [14] . When doing so, it is important to minimize the equilibrium time for the passive dosing, since biodegradation will then start during dosing.…”

“…The applicability of the method has been demonstrated for very volatile chemicals with high Henry´s constants [4] , mixtures of hydrocarbons that covered a wide chemical space in volatility and hydrophobicity [5] , and UVCBs [8] . It has also been used for determining the mixture effect, the temperature effect and the concentration effect on the biodegradation kinetics of a wide range of chemicals [9 , 13 , 14] .…”

“…The reference substances should be analyzable using the same analytical method as the test chemicals. In our latest project we have used naphthalene and phenanthrene as reference substances since they were included in many of our previous experiments and their degradation was seen to be sensitive towards the density of cultivable bacteria in the surface water used as inoculum [14] . Degradation half-times for naphthalene were in the previous experiments generally within 3–7 days for active surface waters, while degradation did not occur in water with low densities of cultivable bacteria [4 , 5 , 14 , 17] .…”

“…Quality assurance includes a careful integration of the analytical peaks and a determination of the analytical detection limit. The analytical carryover (e.g., from the SPME fiber) can be measured from a number of standards and subsequent blank samples, and the cutoff can be determined as mean plus 3 times standard deviation on these ratios [14] . When full degradation occurs, some of the ratios will be below either the detection limit or the carryover limit (i.e.…”