Dissolved organic matter modulating the uptake, biotransformation, and elimination rates of pyrene in Daphnia magna

Abstract

In the current study, the toxicokinetics of pyrene in Daphnia magna was determined in detail, and the role of dissolved organic matter (DOM) in these processes was investigated. Uptake, biotransformation, parent compound and metabolite elimination rates (k(u), k(m), k(ep), k(em)), depuration rates, bioconcentration factors (BCFs), and biological half-lives were studied in one natural humic water, in two waters made from DOM isolates, and in DOM-free artificial fresh water. The daphnids were exposed to pyrene for 24 h and depurated for another 24 h. To analyze the data, the two-compartment model was used to obtain toxicokinetic parameters, and the depuration data were analyzed by linear regression. Extensive biotransformation of pyrene resulted in high metabolite concentration in the organisms (83% of total radioactivity) after 24 h exposure. Depuration of the parent compound seemed to be biphasic: at first, depuration was rapid, but after 4 to 10 h in uncontaminated water, the disappearance rate came close to zero. After a 24-h depuration time, 7.8% of the pyrene accumulated remained in the organism. Overall, the elimination of parent compound was faster than the elimination of metabolites, which might imply inefficient excretion of water-soluble biotransformation products from daphnids. The effect of DOM on accumulation of pyrene was seen in a decreased uptake rate, indicating lower bioavailability of the compound in waters that contain high-aromaticity DOM. In the same waters, DOM significantly accelerated pyrene biotransformation and overall elimination. Altogether, DOM appears to be able to affect toxicokinetics through mechanisms that are connected to interaction with the contaminant but also directly through interaction with biotransformation systems.

Determination of In Vivo Biotransformation Kinetics Using Early‐Time Biota Concentrations

“…This often manifests as exceptionally large confidence intervals or even negative rate constants (Supporting Table S8c). Only very limited studies have satisfactory regression or modeling results where all fitted toxicokinetic parameters were meaningfully bound (Ruotsalainen et al, 2010; Schuler et al, 2003). These examples highlight the overall difficulties in deriving biotransformation toxicokinetic parameters through rigorous regression or modeling.…”

“…The approximate approach works when parent compound can be distinguished from metabolite. This can be achieved, for instance, by measuring the radioactivity of parent compound following chromatographic separation of its metabolic intermediates (Ruotsalainen et al, 2010; Sarrazin et al, 2009; Selck et al, 2003), where f PC ( t ) can be determined as follows: …”

“…The first‐order toxicokinetic model underlies the interpretation and modeling of experimental bioconcentration and bioaccumulation of chemicals in various organisms (Barber, 2003, 2008; Chen & Kuo, 2018; Kuo & Chen, 2021; Kuo & Di Toro, 2013a). It has also been adopted in most of the experimental biotransformation studies (Ashauer et al, 2012; Carrasco‐Navarro et al, 2015; Rösch et al, 2016; Ruotsalainen et al, 2010; Schuler et al, 2003) and biotransformation kinetic modeling studies (Arnot et al, 2008a; Kuo & Chen, 2016; Kuo & Di Toro, 2013b).…”

“…Conditions 1 and 2 were consistent with the typical toxicokinetic or bioaccumulation experimental protocols. Condition 3 has been adopted as the basis in published works on biotransformation toxicokinetics (Ashauer et al, 2012; Carrasco‐Navarro et al, 2015; Kuo & Chen, 2016; Ruotsalainen et al, 2010; Schuler et al, 2003; Weston et al, 2009). Mathematical details of the adopted initial conditions are documented in Supporting Information S3.…”

Toward refined environmental scenarios for ecological risk assessment of down-the-drain chemicals in freshwater environments

“…TK‐TD models can explicitly separate TK from TD processes (Ashauer et al ). Thus, it is possible to model the influence of physical‐chemical properties, some species traits (Buchwalter et al ; Rubach et al ; Poteat and Buchwalter ), and environmental factors (Ruotsalainen et al ) on TK, as well as the influence of toxicity pathways (Gunnarsson et al ; Lalone et al ), species traits (Rubach et al ), and environmental factors (Heugens et al ) on TD (Rubach et al ; Jager ; Ashauer et al ). A single parameter, such as temperature, can influence TK, by changing uptake, elimination, and biotransformation rates (Buchwalter et al ; Heugens et al ; Harwood et al ), as well as TD, by changing physiology and intrinsic sensitivity (Harwood et al ).…”