Application of passive dosing to study the biotransformation and biodegradation of hydrophobic

Kilian E. C. Smith, Arno Rein, MB Heringa, Philipp Mayer, Ulrich Bay Gosewinkel

Research output: Contribution to conferencePaperResearch


Achieving well-defined and constant dissolved concentrations of hydrophobic compounds is
challenging due to volatilization or sorptive losses. With passive dosing, continual partitioning
into the test medium of compound(s) loaded in a polymer compensates for losses, and provides
defined and constant dissolved concentrations. Passive dosing can be used for studying biotransformation/
degradation. Here, the polymer HOC reservoir also compensates for losses due
to the bio-transformation/degradation process itself. Furthermore, a large mass of test compound
is introduced so that compound turnover is significant even at low dissolved concentrations thus
facilitating measurement of the relevant endpoint (e.g., metabolic products in biotransformation
or growth in biodegradation). This study details two applications of passive dosing for studying
bio-transformation/degradation. A format has been developed to study the biodegradation of
phenanthrene and fluoranthene by the bacterial strain EPA 505, allowing degradation rates to be
quantified at defined freely dissolved concentrations from mg/L down to ng/L levels. Passive dosing
was also applied for quantifying the mutagenicity of benzo(a)pyrene metabolites produced
after activation by the liver S9 mix in the in vitro Ames II assay. Compared to the case with spiking,
responses from passive dosing were shifted by a factor 100-1000 to lower concentrations,
and were also more reproducible between repeated tests. This difference in apparent sensitivity
cannot solely be explained by partitioning, and is due to slow dissolution kinetics as well as massdepletion
of the spiked benzo(a)pyrene. Therefore, passive dosing is a useful tool for the study of
hydrophobic compound bio-transformation/degradation at well-defined dissolved concentrations
down to very low levels. Important advantages include studying process kinetics at precisely
defined dissolved concentrations and allowing increased compound turnover even at constant
and low concentrations.

Original languageEnglish
Publication date15 May 2011
Publication statusPublished - 15 May 2011
EventSETAC Europe 21st Annual Meeting: Ecosystem Protection in a Sustainable World: A Challenge for Science and Regulation - Milano Convention Centre, Milano, Italy
Duration: 15 May 201119 May 2011
Conference number: 21


ConferenceSETAC Europe 21st Annual Meeting
LocationMilano Convention Centre
Internet address

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