Pollutants

Iron (oxyhydr-)oxide reduction has been extensivelystudied because of its importance in pollutant redoxdynamics and biogeochemical processes. Yet, experimentalstudies linking oxide reduction kinetics to thermodynamicsremain scarce. Here, we used mediated electrochemicalreduction (MER) to directly quantify the extents and rates offerrihydrite, goethite, and hematite reduction over a range ofnegative reaction free energies, Δ_rG, that were obtained bysystematically varying pH (5.0 to 8.0), applied reductionpotentials (−0.53 to −0.17 V vs SHE), and Fe²⁺ concentrations(up to 40 μM). Ferrihydrite reduction was complete and fast atall tested Δ_rG values, consistent with its comparatively lowthermodynamic stability. Reduction of the thermodynamicallymore stable goethite and hematite changed from complete and fast to incomplete and slow as Δ_rG values became less negative.Reductions at intermediate Δ_rG values showed negative linear correlations between the natural logarithm of the reduction rateconstants and Δ_rG. These correlations imply that thermodynamics controlled goethite and hematite reduction rates. Beyondallowing to study iron oxide reduction under defined thermodynamic conditions, MER can also be used to capture changes iniron oxide reducibility during phase transformations, as shown for Fe²⁺-facilitated transformation of ferrihydrite to goethite.

The risks associated with pesticides in small streams remain poorly characterized. The challenges reside in understanding the complexities of (1) the highly dynamic concentration profiles of (2) several hundred active substances with (3) differing seasonality. The present study addressed these three challenges simultaneously. Five small streams in catchments under intensive agricultural land use were sampled using half-day composite samples from March to August 2015. Of 213 active substances quantified using liquid chromatography–high resolution mass spectrometry, a total of 128 was detected at least at one of the sites. Ecotoxicological acute and/or chronic quality criteria were exceeded for a total of 32 different active substances. The evaluation of risks over time revealed the necessity to evaluate the sequences of different active substances that are imposed on aquatic organisms. In contrast, a substance-specific perspective provides only a very limited assessment. Scenarios for reduction of either temporal resolution, number of substances or seasonal coverage were defined. It could be shown that risks can be underestimated by more than a factor of 10 in vulnerable catchments and that an increased temporal resolution is essential to cover acute risks but that a focused selection of substances is a possibility to reduce expenditures.

Permanent fish cell lines constitute a promising complement or substitute for fish in the environmental risk assessment of chemicals. We demonstrate the potential of a set of cell lines originating from rainbow trout (Oncorhynchus mykiss) to aid in the prediction of chemical bioaccumulation in fish, using benzo[a]pyrene (BaP) as a model chemical. We selected three cell lines from different tissues to more fully account for whole-body biotransformation in vivo: the RTL-W1 cell line, representing the liver as major site of biotransformation, and the RTgill-W1 (gill) and RTgutGC (intestine) cell lines, as important environment-organism interfaces, which likely influence chemical uptake. All three cell lines were found to effectively biotransform BaP. However, rates of in vitro clearance differed, with the RTL-W1 cell line being most efficient, followed by RTgutGC. Co-exposures with α-naphthoflavone as potent inhibitor of biotransformation, assessment of CYP1A catalytic activity, and the progression of cellular toxicity upon prolonged BaP exposure revealed that BaP is handled differently in the RTgill-W1 compared to the other two cell lines. Application of the cell-line-derived in vitro clearance rates into a physiology-based toxicokinetic model predicted a BaP bioconcentration factor (BCF) of 909-1057 compared to 920 reported for rainbow trout in vivo.