In this review, we consider the two prevailing hypotheses for the mechanisms that control the bioaccumulation of perfluorinated alkyl acids (PFAAs). The first assumes that partitioning to membrane ...phospholipids, which have a higher affinity for charged species than neutral storage lipids, can explain the high bioaccumulation potential of these compounds. The second assumes that interactions with proteinsincluding serum albumin, liver fatty acid binding proteins (L-FABP), and organic anion transportersdetermine the distribution, accumulation and half-lives of PFAAs. We consider three unique phenomena to evaluate the two models: (1) observed patterns of tissue distribution in the laboratory and field, (2) the relationship between perfluorinated chain length and bioaccumulation, and (3) species- and gender-specific variation in elimination half-lives. Through investigation of these three characteristics of PFAA bioaccumulation, we show the strengths and weaknesses of the two modeling approaches. We conclude that the models need not be mutually exclusive, but that protein interactions are needed to explain some important features of PFAA bioaccumulation. Although open questions remain, further research should include perfluorinated alkyl substances (PFASs) beyond the long-chain PFAAs, as these substances are being phased out and replaced by a wide variety of PFASs with largely unknown properties and bioaccumulation behavior.
For a proactive risk assessment of engineered nanoparticles (ENPs) it is imperative to derive predicted environmental concentration (PEC) values for ENPs in different environmental compartments; PECs ...can then be compared to effect thresholds. From the basis of established multimedia environmental fate models for organic pollutants, we develop a new concept of environmental fate modeling for ENPs with process descriptions based on the specific properties of ENPs. Our new fate modeling framework is highly flexible and can be adjusted to different ENPs and various environmental settings. As a first case study, the fate and transport of TiO2 NPs in the Rhine River is investigated. Predicted TiO2 NP concentrations lie in the ng/L range in the water compartment and mg/kg in the sediment, which represents the main reservoir for the nanoparticles. We also find that a significant downstream transport of ENPs is possible. A fundamental process, the heteroaggregation between TiO2 NPs and suspended particulate matter (SPM), is analyzed in more detail. Our modeling results demonstrate the importance of both the SPM properties (concentration, size, density) as well as the affinity of TiO2 NPs and SPM, characterized by the attachment efficiency, αhet‑agg, on the transport potential of ENPs in a surface water system.
Perfluorinated alkyl acids (PFAAs) are important global pollutants with unique pharmacokinetics. Evidence is accumulating that their behavior within organisms is affected by interaction with a number ...of proteins. In mammals, serum albumin, fatty acid binding proteins (FABPs) and organic anion transporters (OATs) have been identified as important to the tissue distribution, species-specific accumulation, and species- and gender-specific elimination rates of perfluoroalkyl carboxylates and perfluoroalkane sulfonates. Similar pharmacokinetics has been identified in fish. Yet, no mechanistic model exists for the bioaccumulation of PFAAs in fish that explicitly considers protein interactions. In this work, we present the first mechanistic protein-binding bioconcentration model for PFAAs in fish. Our model considers PFAA uptake via passive diffusion at the gills, association with serum albumin in the circulatory and extracellular spaces, association with FABP in the liver, and renal elimination and reabsorption facilitated by OAT proteins. The model is evaluated using measured bioconcentration and tissue distribution data collected in two previous studies of rainbow trout (Oncorhynchus mykiss) and common carp (Cyprinus carpio). Comparing our model with previous attempts to describe PFAA bioconcentration using a nonspecific (partitioning-type) approach shows that inclusion of protein interactions is key to accurately predicting tissue-specific PFAA distribution and bioconcentration.
Chlorinated paraffins are industrial chemicals that can be subdivided into short-chain (SCCP), medium-chain (MCCP), and long-chain (LCCP) chlorinated paraffins. The global production volumes of MCCPs ...are nowadays suspected to be much higher than those of S- and LCCPs, and the few available studies on the environmental occurrence of chlorinated paraffins report often higher MCCP concentrations than S- or LCCP concentrations in the environment. The present review focuses, therefore, on MCCPs specifically and provides a literature overview and a data analysis of the production volumes, PBT properties (persistence, bioaccumulation potential, and toxicity), and the worldwide measured concentrations of MCCP in environmental samples, biota, and humans. Furthermore, we include our own measurements of technical CP formulations from China, the major global producing country, to estimate the global production amounts of MCCPs. The key findings from this review are that (1) MCCPs are toxic to the aquatic environment, and the available data suggest that they are also persistent; (2) available time trends for MCCPs in soil, biota, and most of the sediment cores show increasing time trends over the last years to decades; and (3) MCCP concentrations in sediment close to local sources exceed toxicity thresholds (i.e., the PNEC). Our study shows that overall, MCCPs are of growing concern, and regulatory actions should be considered seriously.
The production of toxic plant secondary metabolites (phytotoxins) for defense is a widespread phenomenon in the plant kingdom and is even present in agricultural crops. These phytotoxins may have ...similar characteristics to anthropogenic micropollutants in terms of persistence and toxicity. However, they are only rarely included in environmental risk assessments, partly because a systematic overview of phytotoxins is missing. Here, we present a newly developed, freely available database, Toxic Plants–PhytoToxins (TPPT), containing 1586 phytotoxins of potential ecotoxicological relevance in Central Europe linked to 844 plant species. Our database summarizes phytotoxin patterns in plant species and provides detailed biological and chemical information as well as in silico estimated properties. Using the database, we evaluated phytotoxins regarding occurrence, approximated from the frequencies of Swiss plant species; environmental behavior based on aquatic persistence and mobility; and toxicity. The assessment showed that over 34% of all phytotoxins are potential aquatic micropollutants and should be included in environmental investigations.
Under the European chemicals legislation, REACH, industrial chemicals that are imported or manufactured at more than 10 t/yr need to be evaluated with respect to their persistence (P), ...bioaccumulation potential (B), and toxicity (T). This assessment has to be conducted for several 10 000 of chemicals but, at the same time, empirical data on degradability, bioaccumulation potential and toxicity of industrial chemicals are still scarce. Therefore, the identification of PBT chemicals among all chemicals on the market remains a challenge. We present a PBT screening of approximately 95 000 chemicals based on a comparison of estimated P, B, and T properties of each chemical with the P, B, and T thresholds defined under REACH. We also apply this screening procedure to a set of 2576 high production volume chemicals and a set of 2781 chemicals from the EU’s former list of “new chemicals” (ELINCS). In the set of 95 000 chemicals, the fraction of potential PBT chemicals is around 3%, but in the ELINCS chemicals it reaches 5%. We identify the most common structural elements among the potential PBT chemicals. Analysis of the P, B, and T data for all chemicals considered here shows that the uncertainty in persistence data contributes most to the uncertainty in the number of potential PBT chemicals.
We quantify global emissions of C4–C14 perfluoroalkyl carboxylic acid (PFCA) homologues during the life-cycle of products based on perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), ...perfluorooctane sulfonyl fluoride (POSF), and fluorotelomer compounds. We estimate emissions of 2610–21400 tonnes of C4–C14 PFCAs in the period from 1951 to 2015, and project 20–6420 tonnes to be emitted from 2016 to 2030. The global annual emissions steadily increased in the period 1951–2002, followed by a decrease and then another increase in the period 2002–2012. Releases from fluoropolymer production contributed most to historical PFCA emissions (e.g. 55–83% in 1951–2002). Since 2002, there has been a geographical shift of industrial sources (particularly fluoropolymer production sites) from North America, Europe and Japan to emerging Asian economies, especially China. Sources differ between PFCA homologues, sometimes considerably, and the relative contributions of each source change over time. For example, whereas 98–100% of historical (1951–2002) PFOA emissions are attributed to direct releases during the life-cycle of products containing PFOA as ingredients or impurities, a much higher historical contribution from PFCA precursor degradation is estimated for some other homologues (e.g. 9–78% for PFDA). We address the uncertainties of the PFCA emissions by defining a lower and a higher emission scenario, which differ by approximately a factor of eight.
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•A global emission inventory for individual C4–C14 PFCA homologues is developed.•Emissions from PFOA-, PFNA-, POSF- and fluorotelomer-based products are quantified.•The relative contribution of each source is homologue- and time-dependent.•The majority of industrial PFCA sources are now based in Asia, especially China.
Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants in textiles, polyurethane foams, and plastics. PBDEs exert toxic effects in various organisms, including humans, and ...are ubiquitous in the outdoor and indoor environment. Here we estimate total daily PBDE doses received by consumers in North America and Europe, along with the most important pathways and congeners, and derive PBDE elimination half-lives for chronic exposure. We estimate distributions for all parameters (PBDE concentrations in exposure media, food consumption rates, etc.) and conduct a probabilistic exposure assessment. We find that Americans are exposed the most, likely due to stricter fire regulations, followed by consumers from the UK and Continental Europe. In the central quantiles of the exposure distributions derived, food is the dominant pathway; in the upper quantiles either food or oral and dermal exposure to dust. This reflects the lipophilic and persistent nature of PBDEs and their use in products for indoor-use. Median elimination half-lives are in a range of 1−3 years except for BDE-153 with about seven years and BDE-209 with 4−7 days.
The heteroaggregation of engineered nanoparticles (ENPs) with natural colloids (NCs), which are ubiquitous in natural surface waters, is a crucial process affecting the environmental transport and ...fate of ENPs. Attachment efficiencies for heteroaggregation, αhetero, are required as input parameters in environmental fate models to predict ENP concentrations and contribute to ENP risk assessment. Here, we present a novel method for determining αhetero values by using a combination of laser diffraction measurements and aggregation modeling based on the Smoluchowski equation. Titanium dioxide nanoparticles (TiO2 NPs, 15 nm) were used to demonstrate this new approach together with larger silicon dioxide particles (SiO2, 0.5 μm) representing NCs. Heteroaggregation experiments were performed at different environmentally relevant solution conditions. At pH 5 the TiO2 NPs and the SiO2 particles are of opposite charge, resulting in αhetero values close to 1. At pH 8, where all particles are negatively charged, αhetero was strongly affected by the solution conditions, with αhetero ranging from <0.001 at low ionic strength to 1 at conditions with high NaCl or CaCl2 concentrations. The presence of humic acid stabilized the system against heteroaggregation.
Surface processes occurring at the catalytic chiral surface of a cinchona‐modified Pt catalyst during the asymmetric hydrogenation of activated ketones have been monitored for the first time using ...operando ATR‐IR spectroscopy. Fundamental information about this catalytic system could be gained, including the chiral modification process of the catalyst, the surface interaction of reactant ketone with preadsorbed chiral modifier, the role of hydrogen as well as the influence of the product enantiomers in the catalytic cycle. The formation of a diastereomeric transient surface complex between ketone and chiral modifier was found to be related to the ketone consumption. Among the studied activated ketones, a correlation between stereoselection and the strength of the intermolecular hydrogen bond was identified. Dissociated hydrogen from the catalytic surface is found to play a crucial role in the formation of the diastereomeric surface complex.
Watching the working catalyst: Surface processes occurring at the catalytic chiral surface of a cinchona‐modified Pt catalyst during the asymmetric hydrogenation of activated ketones have been monitored by attenuated total reflection IR spectroscopy (see picture). Fundamental information about this catalytic system could be gained.
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