Characterization of ecotoxicological risks from unintentional mixture exposures calculated from European freshwater monitoring data: Forwarding prospective chemical risk management.

Current regulatory chemical safety assessments do not acknowledge that ambient exposures are to multiple chemicals at the same time. As a result, potentially harmful exposures to unintentional mixtures may occur, leading to potential insufficient protection of the environment. The present study describes cumulative environmental risk assessment results for European fresh water ecosystems, based on the NORMAN chemical surface water monitoring database (1998-2016). It aims to characterize the magnitude of the mixture problem and the relative contribution of chemicals to the mixture risk, and evaluates how cumulative risks reduce when the acceptable risk per single chemical is fractionally lowered. Available monitoring data were curated and aggregated to 26,631 place-time combinations with at least two chemicals, of which 376 place-time combinations had at least 25 chemicals identified above the Limit of Detection. Various risk metrics were based on measured environmental concentrations (MECs). Mixture risk characterization ratio's (ΣRCRs) ≥ 1 were found for 39% of the place-time combinations, with few chemicals dominating the ΣRCR. Analyses of mixture toxic pressures, expressed as multi-substance Potentially Affected Fractions of species based on No Observed Effect Concentrations (msPAFNOEC), showed similar outcomes. Small fractional reductions of the ambient chemical concentrations give a steep increase of the percentage of sufficiently protected water bodies (i.e. ΣRCR < 1 and msPAFNOEC < 5%). Scientific and regulatory aspects of these results are discussed, especially with reference to the representativeness of the monitoring data for characterizing ambient mixtures, the robustness of the findings, and the possible regulatory implementation of the concept of a Mixture Allocation Factor (MAF) for prospective chemicals risk management. Although the monitoring data do not represent the full spectrum of ambient mixture exposures in Europe, results show the need for adapting policies to reach European Union goals for a toxic-free environment and underpin the utility and possible magnitude of a MAF.

Assessment of recent developmental immunotoxicity studies with bisphenol A in the context of the 2015 EFSA t-TDI.

Humans are exposed to bisphenol A (BPA) mainly through the diet, air, dust, skin contact and water. There are concerns about adverse health effects in humans due to exposure to bisphenol A (BPA). The European Food Safety Authority (EFSA) has extensively reviewed the available literature to establish a temporary Tolerable Daily Intake (t-TDI). This exposure level was based on all available literature published before the end of 2012. Since then, new experimental animal studies have emerged, including those that identified effects of BPA on the immune system after developmental exposure. These studies indicate that developmental immunotoxicity might occur at lower dose levels than previously observed and on which the current EFSA t-TDI is based. The Dutch National Institute for Public Health and the Environment (RIVM) organized an expert workshop in September 2015 to consider recently published studies on the developmental immunotoxicity of bisphenol A (BPA). Key studies were discussed in the context of other experimental studies. The workshop concluded that these new experimental studies provide credible evidence for adverse immune effects after developmental exposure to BPA at 5µg/kg BW/day from gestation day 15 to postnatal day 21. Supportive evidence for adverse immune effects in similar dose ranges was obtained from other publications that were discussed during the workshop. The dose level associated with adverse immune effects is considerably lower than the dose used by EFSA for deriving the t-TDI. The workshop unanimously concluded that the current EFSA t-TDI warrants reconsideration in the context of all currently available data.

Comparative studies of O2 and N2 in pure, mixed and layered CO ices.

We present laboratory data on pure, layered and mixed CO and O2 ices relevant for understanding the absence of gaseous O2 in space. Experiments have been performed on interstellar ice analogues under ultra high vacuum conditions by molecular deposition at 14 K on a gold surface. A combination of reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) is used to derive spectroscopic and thermodynamic properties of the ices. It is found that for pure ices the desorption energy of O2 is larger than that of CO and N2. TPD spectra reveal similar desorption processes for all examined CO-O2 ice morphologies. The different amorphous and crystalline components of pure 13CO RAIR spectra are analyzed. The RAIRS data of the 13CO stretching vibration show a significant difference between layered and mixed CO-O2 ices: layered CO-O2 ices resemble that of pure 13CO whereas the spectra of mixed ices are broadened. The experiments also show that the sticking probabilities of O2 on CO and O2 on O2 are close to unity. These new results are compared with recently analyzed data of CO-N2 ices. The differences in the TPD and RAIRS spectra of the CO-N2 and CO-O2 ice systems are explained by differences in quadrupole intermolecular interactions and by different crystallization processes of these ices.

The activation of the [NiFe]-hydrogenase from Allochromatium vinosum. An infrared spectro-electrochemical study.

The membrane-bound [NiFe]-hydrogenase from Allochromatium vinosum can occur in several inactive or active states. This study presents the first systematic infrared characterisation of the A. vinosum enzyme, with emphasis on the spectro-electrochemical properties of the inactive/active transition. This transition involves an energy barrier, which can be overcome at elevated temperatures. The reduced Ready enzyme can exist in two different inactive states, which are in an apparent acid-base equilibrium. It is proposed that a hydroxyl ligand in a bridging position in the Ni-Fe site is protonated and that the formed water molecule is subsequently removed. This enables the active site to bind hydrogen in a bridging position, allowing the formation of the fully active state of the enzyme. It is further shown that the active site in enzyme reduced by 1 bar H(2) can occur in three different electron paramagnetic resonance (EPR)-silent states with a different degree of protonation.