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A B S T R A C TIdentification of transformation products (TPs) of emerging pollutants is challenging, due to the vast number of compounds, mostly unknown, the complexity of the matrices and their often low concentrations, requiring highly selective, highly sensitive techniques. We compile background information on biotic and abiotic formation of TPs and analytical developments over the past five years. We present a database of biotic or abiotic TPs compiled from those identified in recent years. We discuss mass spectrometric (MS) techniques and workflows for target, suspect and non-target screening of TPs with emphasis on liquid chromatography coupled to MS (LC-MS). Both low-and high-resolution (HR) mass analyzers have been applied, but HR-MS is the technique of choice, due to its high confirmatory capabilities, derived from the high resolving power and the mass accuracy in MS and MS/MS modes, and the sophisticated software developed.

The influence of salinity and organic matter on the distribution coefficient (K(d)) for perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in a brackish water-clay system was studied. The distribution coefficients (K(d)) for PFAs onto inorganic clay surfaces increased with salinity, providing evidence for electrostatic interaction for the sorption of PFAs, whereas the relationship between K(d) and organic carbon content (f(oc)) suggested that hydrophobic interaction is the primary driving force for the sorption of PFAs onto organic matter. The organic carbon normalized adsorption coefficient (K(oc)) of PFAs can be slightly overestimated due to the electrostatic interaction within uncoated inorganic surfaces. In addition, the dissolved organic matter released from coated clay particles seemed to solvate PFA molecules in solution, which contributed to a decrease in K(d). A positive relationship between K(d) and salinity was apparent, but an empirical relationship for the 'salting-out' effect was not evident. The K(d) values of PFAs are relatively small compared with those reported for persistent organic pollutants. Thus, sorption may not be a significant route of mass transfer of PFAs from water columns in estuarine environments. However, enhancement of sorption of PFAs to particulate matter at high salinity values could evoke potential risks to benthic organisms in estuarine areas.

So far, there is limited information on biotransformation mechanisms and products of polar contaminants in freshwater crustaceans. In the present study, metabolites of biocides and pharmaceuticals formed in Gammarus pulex and Daphnia magna were identified using liquid chromatography-high resolution mass spectrometry. Different confidence levels were assigned to the identification of metabolites without reference standards using a framework based on the background evidence used for structure elucidation. Twenty-five metabolites were tentatively identified for irgarol, terbutryn, tramadol, and venlafaxine in G. pulex (21 via oxidation and 4 via conjugation reactions) and 11 metabolites in D. magna (7 via oxidation and 4 via conjugation reactions), while no evidence of metabolites for clarithromycin and valsartan was found. Of the 360 metabolites predicted for the four parent compounds using pathway prediction systems and expert knowledge, 23 products were true positives, while 2 identified metabolites were unexpected products. Observed oxidative reactions included N- and O-demethylation, hydroxylation, and N-oxidation. Glutathione conjugation of selected biocides followed by subsequent reactions forming cysteine conjugates was described for the first time in freshwater invertebrates.

Despite the reports of widespread occurrence of perfluorinated compounds (PFCs) in estuarine and coastal waters and open seas, little is known on the effect of salinity on bioaccumulation. In this study, effects of salinity on bioaccumulation of PFCs in Pacific oysters (Crassostrea gigas) were investigated. Furthermore, partitioning of PFCs between water and particles (oysters' food) was examined at different salinities. The distribution coefficients (K(d); partitioning between water and particles) for selected PFCs, that is, PFOS, PFOA, PFDA, and PFUnDA, increased by 2.1- to 2.7-fold with the increase in water salinity from 10 to 34 psu, suggesting "salting-out" effect, and the salting constant (delta) was estimated to range from 0.80 to 1.11. The nonlinear regression analysis of bioaccumulation suggested increase in aqueous and dietary uptake rates (K(w) and K(f)), with the increase in salinity, which resulted in elevated bioaccumulation, although the depuration rates (K(e)) also increased. The relative abundance of long carbon chain length PFCs (i.e., PFDA and PFUnDA) increased as salinity increased, while the proportion of PFOS and PFOA decreased, which is explained by the positive relationship between delta and carbon chain length. The contribution of diet to bioaccumulation in oysters ranged from 18 to 92%. Overall, salinity not only affected the chemistry of PFCs, but also the physiology of oysters, contributing to sorption and bioaccumulation of perfluorochemicals in oysters.

Exposure and depuration experiments for Gammarus pulex and Daphnia magna were conducted to quantitatively analyze biotransformation products (BTPs) of organic micropollutants (tramadol, irgarol, and terbutryn). Quantification for BTPs without available standards was performed using an estimation method based on physicochemical properties. Time-series of internal concentrations of micropollutants and BTPs were used to estimate the toxicokinetic rates describing uptake, elimination, and biotransformation processes. Bioaccumulation factors (BAF) for the parents and retention potential factors (RPF), representing the ratio of the internal amount of BTPs to the parent at steady state, were calculated. Nonlinear correlation of excretion rates with hydrophobicity indicates that BTPs with lower hydrophobicity are not always excreted faster than the parent compound. For irgarol, G.pulex showed comparable elimination, but greater uptake and BAF/RPF values than D.magna. Further, G. pulex had a whole set of secondary transformations that D. magna lacked. Tramadol was transformed more and faster than irgarol and there were large differences in toxicokinetic rates for the structurally similar compounds irgarol and terbutryn. Thus, predictability of toxicokinetics across species and compounds needs to consider biotransformation and may be more challenging than previously thought because we found large differences in closely related species and similar chemical structures.

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Bioconcentration of perfluorinated compounds (PFCs) was studied in a biphasic (uptake and elimination) study with blackrock fish, Sebastes schlegeli. The blackrock fish was acclimated to varying salinities over a two-week period before the present study. Among the four selected PFCs: perfluorooctane sulfonate (PFOS), perfluoro-octanoic acid (PFOA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUnDA), PFUnDA accumulated significantly in serum, followed by PFDA, PFOS, and PFOA, in that order, while the accumulation profile in liver was PFOS > PFUnDA > PFDA > PFOA. Total PFC levels in plasma were approximately four times greater than those found in liver. The uptake and elimination rate constants (K(u) and K(e)) of PFCs decreased as salinity decreased, suggesting delayed diffusion of PFCs between water and fish, possibly associated with the osmolality gradient. A significant correlation was found between bioconcentration factors (BCF) of PFCs and salinity, except for PFOA, possibly resulting from the effects of salinity on biological responses and chemical activity of PFCs. Even though salinity did not affect the kinetics of PFC accumulation in serum and liver, the results provide useful information on the toxicokinetics of PFCs for saltwater fish.