No abstract

Toxicants and other, non-chemical environmental stressors contribute to the global biodiversity crisis. Examples include the loss of bees and the reduction of aquatic biodiversity. Although non-compliance with regulations might be contributing, the widespread existence of these impacts suggests that for example the current approach of pesticide risk assessment fails to protect biodiversity when multiple stressors concurrently affect organisms. To quantify such multiple stress effects, we analysed all applicable aquatic studies and found that the presence of environmental stressors increases individual sensitivity to toxicants (pesticides, trace metals) by a factor of up to 100. To predict this dependence, we developed the “Stress Addition Model” (SAM). With the SAM, we assume that each individual has a general stress capacity towards all types of specific stress that should not be exhausted. Experimental stress levels are transferred into general stress levels of the SAM using the stress-related mortality as a common link. These general stress levels of independent stressors are additive, with the sum determining the total stress exerted on a population. With this approach, we provide a tool that quantitatively predicts the highly synergistic direct effects of independent stressor combinations.

Current/potential responses of small organic molecules show as a characteristic feature an increase in anodic current when changing the potential in the cathodic direction. In situ infrared data on the adsorption of methanol, formic acid, and water at Pt(111) are used to develop a new model explaining these well-known catalytic effects. Since the strength of water adsorption increases with increasing potentials above 0.4 V, the adsorption of organic molecules has to be considered as a water displacement reaction. The reaction rate is thus the result of the concurrence of two processes that are oppositely affected by the potential:  the rate of oxidation (charge transfer) and the rate of adsorption. In situ IR data and cyclic voltammograms for the oxidation of methanol and formic acid on a Pt(111) surface are presented and discussed. For comparison, data on CO oxidation are presented.

Spectral data for HCOOH oxidation at Pt(111), Pt(100), and Pt(110) are presented and discussed. Spectra were taken shortly after the surfaces were contacted with a 0.1 M HCOOH/0.1 M HClO4 solution at a controlled potential of 0.05 V vs RHE and give information on the adsorption and oxidation processes at the early stages. The formation of on top and bridging CO on Pt(111) and Pt(100) is followed as a function of potential. Conversion of bridging into on top CO is observed at the Pt(100) surface in the low-potential region, while the parallel formation of both forms of adsorbed CO occurs at Pt(111) in the 0.1−0.4 V potential range. Only terminal CO is formed at Pt(110), this surface being the one presenting the highest level of poisoning at the initial potential. Very high values of the initial slopes of ν−E plots are observed for Pt(111) and Pt(100), which are rationalized in terms of lateral coupling due to adsorption in patches giving rise to high local coverages.

The adsorption of dimethyl methylphosphonate (DMMP), a model molecule for sarin, on three different organic interfaces, prepared by solution self-assembly of alkanethiols on gold, was followed by a surface acoustic wave mass sensor and infrared reflection-absorption spectroscopy at room temperature. The surfaces, characterized by the following tail groups (-OH, -CH 3 , -COOH), show both quantitative and qualitative differences concerning the interaction with DMMP, the acid surface giving rise to the strongest adsorption. Results obtained in UHV, at low temperatures using infrared spectroscopy and temperature-programmed desorption, support this observation and give complementary information about the nature of the interaction. The hydrogen-bond-accepting properties of the PdO part of DMMP and its impact on the design of sensing interfaces based on hydrogen bonding, as well as the use of self-assembled monolayers to study molecular interactions, are discussed.