Guidelines for ecotoxicity testing with Daphnia magna specify particular feeding protocols during the exposure, yet standardization for preexposure feeding remains ambiguous despite its recognized significance in affecting organismal metabolic capacity and tolerance. This ambiguity may contribute to disparate responses and heightened uncertainty in determining the effect concentrations of test chemicals, particularly those inducing metabolic effects through narcosis. Here, we address this gap through a three-step doseresponse experiment with neonates of D. magna subjected to two alternative feeding regimes in the preexposure phase: starved and moderately fed during the first 24 hr after birth. Following this treatment, the daphnids were exposed to narcosis-inducing substances (polycyclic aromatic hydrocarbons; PAHs) for 72 hr before being transferred to clean media with algal food ad libitum for a 48 hr recovery phase. Daphnid survivorship, individual protein content, and body size at the end of each experiment phase-pre-exposure, postexposure and postrecovery-were compared between the treatments. Significant treatment effects were observed, including lower and less variable protein content in the starved daphnids entering the PAH exposure phase, yet higher survivorship and greater recovery potential in these daphnids compared with the fed individuals. Our findings underscore the importance of early-life food access and advocate for mandatory reporting of pre-exposure feeding regimes, particularly when testing substances acting via nonpolar narcosis.

Hydrophobic organic contaminants (HOCs) are conventionally screened by matching electron ionization (EI) mass spectra acquired using gas chromatography-mass spectrometry (GC-MS) to reference spectra. However, extensive in-source fragmentation hampers de novo structure elucidation of novel substances that are absent from EI databases. To address this problem, a new method based on GC-atmospheric pressure chemical ionization (APCI) coupled to ion mobility-high resolution mass spectrometry (IM-HRMS) was developed for simultaneous target, suspect, and nontarget screening of HOCs. Of 102 target chemicals, 85.3% produced (quasi-)molecular ions as base peaks, while 71.6% displayed method detection limits lower than those of GC-EI-low resolution MS. The optimized method was applied to standard reference sediment and sediments from the Baltic Sea, an Arctic shelf, and a Norwegian lake. In total, we quantified 56 target chemicals with concentrations ranging from 4.86 pg g-1 to 124 ng g-1 dry weight. Further, using a combination of full scan mass spectrum, retention time, collision cross section (CCS), and fragmentation spectrum, a total of 54 suspects were identified at Confidence Level (CL) 2. Among the remaining features, 169 were prioritized using a halogen-selective CCS cutoff (100 Å2 + 20% mass), leading to annotation of 54 substances (CL ≤ 3). Notably, a suite of fluorotelomer thiols, disulfides, and alkyl sulfones were identified in sediment (CL 1-2) for the first time. Overall, this work demonstrates the potential of GC-APCI-IM-HRMS as a next-generation technique for resolving complex HOC mixtures in environmental samples through exploitation of molecular ions.

Suspect screening strives to rapidly monitor a large number of substances in a sample using mass spectral libraries. For hydrophobic organic contaminants (HOCs), these libraries are traditionally based on electron ionization mass spectra. However, with the growing use of state-of-the-art mass spectrometers, which often use alternative ionization approaches and separation techniques, new suspect screening workflows and libraries are urgently needed. This study established a new suspect screening library for 1,590 HOCs, including exact mass and a combination of measured and model-predicted values for retention time (RT) and collision cross section (CCS). The accuracy of in silico predictions was assessed using standards for 102 HOCs. Thereafter, using gas chromatography-atmospheric pressure chemical ionization-ion mobility-mass spectrometry, a suspect screening workflow constrained by the full scan mass spectrum of (quasi-)molecular ions (including isotope patterns), RT, CCS, and fragmentation mass spectra, together with a continuous scoring system, was established to reduce false positives and improve identification confidence. Application of the method to fortified and standard reference sediment samples demonstrated true positive rates of 79% and 64%, respectively, with all false positives attributed to suspect isomers. This study offers a new workflow for improved suspect screening of HOCs using multidimensional information and highlights the need to enrich mass spectral databases and extend the applicable chemical space of current in silico tools to hydrophobic substances.

Persistent organic pollutants (POPs) pose a risk in aquatic environments. In sediment, this risk is frequently evaluated using total or organic carbon-normalized concentrations. However, complex physicochemical sediment characteristics affect POP bioavailability in sediment, making its prediction a challenging task. This task can be addressed using chemical activity, which describes a compound's environmentally effective concentration and can generally be approximated by the degree of saturation for each POP in its matrix. We present a proof of concept to load artificial sediments with POPs to reach a target chemical activity. This approach is envisioned to make laboratory ecotoxicological bioassays more reproducible and reduce the impact of sediment characteristics on the risk assessment. The approach uses a constantly replenished, saturated, aqueous POP solution to equilibrate the organic carbon fraction (e.g., peat) of an artificial sediment, which can be further adjusted to target chemical activities by mixing with clean peat. We demonstrate the applicability of this approach using four polycyclic aromatic hydrocarbons (acenaphthene, fluorene, phenanthrene, and fluoranthene). Within 5 to 17 weeks, the peat slurry reached a chemical equilibrium with the saturated loading solution. We used two different peat batches (subsamples from the same source) to evaluate the approach. Variations in loading kinetics and eventual equilibrium concentrations were evident between the batches, which highlights the impact of even minor disparities in organic carbon properties within two samples of peat originating from the same source. This finding underlines the importance of moving away from sediment risk assessments based on total concentrations. The value of the chemical activity-based loading approach lies in its ability to anticipate similar environmental impacts, even with varying contaminant concentrations. 

Hydrophobic organic contaminants (HOCs) affect phytoplankton at cellular to population levels, ultimately impacting communities and ecosystems. Baseline toxicants, such as some HOCs, predominantly partition to biological membranes and storage lipids. Predicting their toxic effects on phytoplankton populations therefore requires consideration beyond cell uptake and diffusion. Functional traits like lipid content and profile can offer insights into the diverse responses of phytoplankton populations exposed to HOCs. Our study investigated the vulnerability of five phytoplankton species populations to varying chemical activities of a mixture of polycyclic aromatic hydrocarbons (PAHs). Population vulnerability was assessed based on intrinsic sensitivities (toxicokinetic and toxicodynamic), and demography. Despite similar chemical activities in biota within the exposed algae, effects varied significantly. According to the chemical activity causing 50% of the growth inhibition (Ea₅₀), we found that the diatom Phaeodactylum tricornutum (Ea₅₀ = 0.203) was the least affected by the chemical exposure and was also a species with low lipid content. In contrast, Prymnesium parvum (Ea₅₀ = 0.072) and Rhodomonas salina (Ea₅₀ = 0.08), both with high lipid content and high diversity of fatty acids in non-exposed samples, were more vulnerable to the chemical mixture. Moreover, the species P. parvum, P. tricornutum, and Nannochloris sp., displayed increased lipid production, evidenced as 5–10% increase in lipid fluorescence, after exposure to the chemical mixture. This lipid increase has the potential to alter the intrinsic sensitivity of the populations because storage lipids facilitate membrane repair, reconstitution and may, in the short-term, dilute contaminants within cells. Our study integrated principles of thermodynamics through the assessment of membrane saturation (i.e. chemical activity), and a lipid trait-based assessment to elucidate the differences in population vulnerability among phytoplankton species exposed to HOC mixtures.

Understanding how key-species respond to anthropogenic stress such as chemical pollution is critical for predicting ecosystem changes. Little is however known about the intra-specific variability in the physiological and biochemical traits involved in contaminant exposure responses. Here, we explored this idea by exposing the Baltic amphipod Monoporeia affinis from two sites, one moderately polluted and one more pristine, to a sediment spiked with PAHs and PCBs. We evaluated the amphipods responses related to feeding, growth, a stress biomarker (acetylcholinesterase [AChE] inhibition) and stable isotope (delta C-13 and delta N-15) composition including isotope niche analyses. More adverse responses were expected in animals from the low-pollution site than those from the high-pollution site due to tolerance development in the latter. Amphipods from both populations showed a similar to 30% AChE inhibition when exposed to the contaminant spiked sediment. However, both controls and exposed amphipods from the high-pollution site had higher survival, nutrient uptake and condition status than the amphipods from the low-pollution site, which did not feed on the added diatoms as indicated by their isotope values. We found no signs of population-specific responses in physiological adjustments to contaminants with regard to classic ecotoxicological biomarkers such as AChE inhibition and growth status. Instead, isotope niche analyses proved useful in assessing contaminant stress responses at the population level.

The environmental fate of hazardous hydrophobic pollutants in the marine environment is strongly influenced by organic carbon (OC) cycling. As an example, the seasonality in primary production impacts both water column OC quantity and quality, which may influence pollutant mass transport from the water column to the sediment. This study aims to better understand the role of water column OC variability for the fate of pollutants in a near-coastal area. We conducted an in situ sampling campaign in the coastal Baltic Proper during two seasons, summer and autumn. We used polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) as model compounds, as they represent a wide range in physicochemical properties and are ubiquitous in the environment. Freely dissolved, and OC-bound concentrations were studied in the water column and surface sediment. We found stronger sorption of pollutants to suspended particulate matter (SPM) during the summer compared to the autumn (average 0.6 and 0.9 log unit higher particle-water partition coefficients during summer for PAHs and PCBs). Our data suggest that stronger sorption mirrors a compositional change of the OC towards higher contribution of labile OC during the summer, characterized by two times higher fatty acid and 24% higher dicarboxylic acids in SPM during summer. High concentrations of OC in the water column during the autumn resulted in increased SPM-mediated sinking fluxes of pollutants. Our results suggest that future changes in primary production are prone to influence the bioavailability and mobility of pollutants in costal zones, potentially affecting the residence time of these hazardous substances in the circulating marine environment.

The production and release of chemicals from human activities are on the rise. Understanding how the aquatic environment is affected by the presence of an unknown number of chemicals is lacking. We employed the chemical activity concept to assess the combined effects of hydrophobic organic contaminants on the phyto-plankton species Rodomonas salina. Chemical activity is additive, and refers to the relative saturation of a chemical in the studied matrix. The growth of R. salina was affected by chemical activity, following a chemical activity-response curve, resulting in an Ea50 value of 0.078, which falls within the baseline toxicity range observed in earlier studies. The chlorophyll a content exhibited both increases and decreases with rising chemical activity, with the increase possibly linked to an antioxidant mechanism. Yet, growth inhibition provided more sensitive and robust responses compared to photosynthesis-related endpoints; all measured endpoints correlated with increased chemical activity. Growth inhibition is an ecologically relevant endpoint and integrates ther-modynamic principles such as membrane disruption. Our study utilized passive dosing, enabling us to control exposure and determine activities in both the medium and the algae. The concept of chemical activity and our results can be extended to other neutral chemical groups as effects of chemical activity remain independent of the mixture composition.

Burial of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) in deep-sea sediments contributes to 60% of their historical emissions. Yet, empirical data on their occurrence in the deep-ocean is scarce. Estimates of the deep-ocean POP sink are therefore uncertain. Hadal trenches, representing the deepest part of the ocean, are hotspots for organic carbon burial and decomposition. POPs favorably partition to organic carbon, making trenches likely significant sinks for contaminants. Here we show that PCBs occur in both hadal (7720–8085 m) and non-hadal (2560–4050 m) sediment in the Atacama Trench. PCB concentrations normalized to sediment dry weight were similar across sites while those normalized to sediment organic carbon increased exponentially as the inert organic carbon fraction of the sediment increased in degraded hadal sediments. We suggest that the unique deposition dynamics and elevated turnover of organic carbon in hadal trenches increase POP concentrations in the deepest places on Earth.

The climate in Europe is warming twice as fast as it is across the rest of the globe, and in Sweden annual mean tempera-tures are forecast to increase by up to 3-6 & DEG;C by 2100, with increasing frequency and magnitude of floods, heatwaves, and other extreme weather. These climate change-related environmental factors and the response of humans at the individual and collective level will affect the mobilization and transport of and human exposure to chemical pollutants in the envi-ronment. We conducted a literature review of possible future impacts of global change in response to a changing climate on chemical pollutants in the environment and human exposure, with a focus on drivers of change in exposure of the Swedish population to chemicals in the indoor and outdoor environment. Based on the literature review, we formulated three alternative exposure scenarios that are inspired by three of the shared socioeconomic pathways (SSPs). We then con-ducted scenario-based exposure modelling of the >3000 organic chemicals in the USEtox (R) 2.0 chemical library, and fur-ther selected three chemicals (terbuthylazine, benzo[a]pyrene, PCB-155) from the USEtox library that are archetypical pollutants of drinking water and food as illustrative examples. We focus our modelling on changes in the population intake fraction of chemicals, which is calculated as the fraction of a chemical emitted to the environment that is ingested via food uptake or inhaled by the Swedish population. Our results demonstrate that changes of intake fractions of chemicals are possible by up to twofold increases or decreases under different development scenarios. Changes in intake fraction in the most optimistic SSP1 scenario are mostly attributable to a shift by the population towards a more plant-based diet, while changes in the pessimistic SSP5 scenario are driven by environmental changes such as rain fall and runoff rates.