Pollutants

Aquatic integrative passive samplers are used to determine aqueous concentrations of polar organic pollutants, yet their uptake mechanisms are poorly understood. We introduce a one-dimensional model to simulate uptake by a passive sampler, Chemcatcher. The model considers the uptake as molecular diffusion through a series consisting of the aqueous boundary layer (ABL), the membrane filter (MF), and the sorbent disk with concurrent sorption by matrix of the MF and the disk. Uptake profiles of ∼20 polar chemicals measured over a week and a month were accurately modeled. Characteristic behaviors such as lag phases, linear and curved uptake, and equilibrating behavior were explained well by the model. As the model is mechanistically based, it was able to show the combined influences of the MF/water (K_MF/w) and disk/water (K_disk/w) partition coefficients, diffusion coefficients, and the ABL thickness on the sampling rates. On the basis of the model results, we offer three concrete recommendations for achieving the linear uptake needed for measuring time-weighted average concentrations: (i) use a MF that does not significantly sorb chemicals (e.g., log K_MF/w < 3) to avoid lag phases, (ii) use a sorbent with strong sorption properties (e.g., log K_disk/w > 6) for effective trapping of chemicals on the disk top layer, and (iii) make the ABL and/or the MF thicker so that the diffusion toward the disk slows.

Compound-specific isotope analysis (CSIA) can provide insights into the natural attenuation processes of hexachlorocyclohexanes (HCHs), an important class of persistent organic pollutants. However, the interpretation of HCH stable isotope fractionation is conceptually challenging. HCHs exist as different conformers that can be converted into each other, and the enzymes responsible for their transformation discriminate among those HCH conformers. Here, we investigated the enzyme specificity of apparent ¹³C- and ²H-kinetic isotope effects (AKIEs) associated with the dehydrochlorination of γ-HCH (lindane) by two variants of the lindane dehydrochlorinases LinA1 and LinA2. While LinA1 and LinA2 attack γ-HCH at different trans-1,2-diaxial H–C–C–Cl moieties, the observed C and H isotope fractionation was large, typical for bimolecular eliminations, and was not affected by conformational mobility. ¹³C-AKIEs for transformation by LinA1 and LinA2 were the same (1.024 ± 0.001 and 1.025 ± 0.001, respectively), whereas ²H-AKIEs showed minor differences (2.4 ± 0.1 and 2.6 ± 0.1). Variations of isotope effects between LinA1 and LinA2 are small and in the range reported for different degrees of C–H bond cleavage in transition states of dehydrochlorination reactions. The large C and H isotope fractionation reported here for experiments with pure enzymes contrasts with previous observations from whole cell experiments and suggests that specific uptake processes by HCH-degrading microorganisms might modulate the observable HCH isotope fractionation at contaminated sites.

We studied thallium (Tl) isotope fractionation in white mustard grown hydroponically at different Tl doses. Thallium isotope signatures in plants indicated preferential incorporation of the light ²⁰³Tl isotope during Tl uptake from the nutrient solution. Negative isotope fractionation was even more pronounced in dependence on how much the available Tl pool decreased. This finding corresponds to the concept of isotope overprinting related to a high contamination level in the growing media (solution or soil). Regarding Tl translocation in plants, we observed a large Tl isotope shift with an enrichment in the heavy ²⁰⁵Tl isotope in the shoots relative to the roots in treatments with low/moderate solution Tl concentrations (0.01/0.05 mg Tl/L), with the corresponding α^205/203Tl fractionation factors of ˜1.007 and 1.003, respectively. This finding is probably a consequence of specific (plant) reactions of Tl replacing K in its cycle. The formation of the S-coordinated Tl(I) complexes, potentially affecting both Tl accumulation and Tl isotope fractionation in plants, however, was not proven in our plants, since we did not have indication for that on the basis of X-ray absorption spectroscopy, suggesting that Tl was mainly present as free/hydrated Tl⁺ ion or chemically bound to O-containing functional groups.

Neonicotinoids are widely used insecticides that have frequently been found in freshwater with concentrations ranging from ng to μg/L. It is known that these compounds impact non-target invertebrates, such as bees and gammaridae, in terms of toxicity and behavior, but impacts and species differences on vertebrates such as fish are little explored. The aim of this study was to investigate and compare the effects of one widely used neonicotinoid, imidacloprid, on development and behavior of two fish model species: Zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). Fish were exposed for 5 (zebrafish) and 14 (medaka) days from 0.2 to 2000 μg/L imidacloprid by aqueous exposure. Survival, development, behavior and histological features were monitored and organism-internal concentrations and biotransformation products measured. Imidacloprid caused sublethal effects in both species but the effects were much stronger in medaka with deformities, lesions and reduced growth being the most prominent impacts. Due to the overall longer time of development, time-integrated exposure of medaka was about 2-fold higher compared to zebrafish, potentially accounting for parts of the sensitivity differences. Our results underline the importance of taking species sensitivity differences into account especially when considering that medaka responded at imidacloprid concentrations that have been measured in the environment.