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Selenium (Se) deficiency affects many millions of people worldwide, and the volatilization of methylated Se species to the atmosphere may prevent Se from entering the food chain. Despite the extent of Se deficiency, little is known about fluxes in volatile Se species and their temporal and spatial variation in the environment, giving rise to uncertainty in atmospheric transport models. To systematically determine fluxes, one can rely on laboratory microcosm experiments to quantify Se volatilization in different conditions. Here, it is demonstrated that the sulfur (S) status of bacteria crucially determines the amount of Se volatilized. Solid-phase microextraction gas chromatography mass spectrometry showed that Pseudomonas tolaasii efficiently and rapidly (92% in 18 h) volatilized Se to dimethyl diselenide and dimethyl selenyl sulfide through promiscuous enzymatic reactions with the S metabolism. However, when the cells were supplemented with cystine (but not methionine), a major proportion of the Se (;48%) was channeled to thus-far-unknown, nonvolatile Se compounds at the expense of the previously formed dimethyl diselenide and dimethyl selenyl sulfide (accounting for <4% of total Se). Ion chromatography and solid-phase extraction were used to isolate unknowns, and electrospray ionization ion trap mass spectrometry, electrospray ionization quadrupole time-of-flight mass spectrometry, and microprobe nuclear magnetic resonance spectrometry were used to identify the major unknown as a novel Se metabolite, 2-hydroxy-3-(methylselanyl)propanoic acid. Environmental S concentrations often exceed Se concentrations by orders of magnitude. This suggests that in fact S status may be a major control of selenium fluxes to the atmosphere. IMPORTANCE Volatilization from soil to the atmosphere is a major driver for Se deficiency. “Bottom-up” models for atmospheric Se transport are based on laboratory experiments quantifying volatile Se compounds. The high Se and low S concentration

Many countries and regional political unions have regulatory and policy frameworks for managing chemicals and waste associated with human activities to minimize harms to human health and the environment. These frameworks are complemented and expanded by joint international action, particularly related to pollutants that undergo long-range transport via air, water, and biota; move across national borders through international trade of resources, products, and waste; or are present in many countries (1). Some progress has been made, but the Global Chemicals Outlook (GCO-II) from the United Nations Environment Programme (UNEP) (1) has called for “strengthen[ing] the science-policy interface and the use of science in monitoring progress, priority-setting, and policy-making throughout the life cycle of chemicals and waste.” With the UN Environment Assembly (UNEA) soon meeting to discuss how to strengthen the science-policy interface on chemicals and waste (2), we analyze the landscape and outline recommendations for establishing an overarching body on chemicals and waste. The world has seen a tremendous increase in the amount and variety of chemicals in use, with continuous growth expected; global chemical sales reached over US$5.6 trillion in 2017 and are projected to almost double by 2030 (1). Similar trends are also true for waste generation; for example, global plastic waste entering the ocean is estimated to increase from 4.8 to 12.7 million tonnes in 2010 to some 100 to 250 million tonnes by 2025 (1). When chemicals and waste are poorly managed, not only are valuable resources lost, but chemical pollution can cause a wide range of adverse effects on human and ecosystem health at local, regional, and global levels. The latest Global Burden of Disease study estimated that exposure to lead and occupational exposure to 12 chemicals or groups of chemicals (a tiny fraction of the more than 100,000 chemicals in use) contributed to over 1.3 million premature human deaths i

In the current study, improved exposure control and measurements were applied for the aquatic toxicity testing of a highly hydrophobic organic compound. The aim was to reliably determine the ecotoxicity of the model compound dodecylbenzene (DDB, Log KOW = 8.65) by applying passive dosing for aquatic toxicity testing exactly at the solubility limit. Methodologically, silicone O-rings were saturated by immersion in pure liquid DDB (i.e., “loading by swelling”) and then used as passive dosing donors. Daphnia immobilization and fish embryo toxicity tests were successfully conducted and provide, together with recently reported algal growth inhibition data, a full base-set of ecotoxicological data according to REACH. All tests were conducted in closed test systems to avoid evaporative losses, and exposure concentrations were measured throughout test durations. The Daphnia test was optimized by placing the O-rings in cages to prevent direct contact between daphnids and the passive dosing donor. Toxicologically, Daphnia magna immobilization was 19.3 ± 8% (mean ± 95% CI; 6 tests) within 72 h, whereas Danio rerio fish embryos did not show any significant lethal or sublethal toxic responses within 96 h. Growth rate inhibition for the algae Raphidocelis subcapitata was previously reported to be 13 ± 5% in a first and 8 ± 3% in a repeated test. These results for aquatic organisms, spanning three trophic levels, demonstrate toxicity of a highly hydrophobic compound and suggest that improvements of the current ecotoxicological standard tests are needed for these “difficult-to-test” chemicals. Furthermore, the obtained toxicity results significantly question the existence of a generic Log KOW cut-off in baseline toxicity.