Environmental context. Understanding mercury transformations in the aquatic environment is of utmost importance for the improvement of mercury biogeochemical modelling and sound environmental risk assessment. In such a context, we discuss critically the advancement in the knowledge on the role of the phytoplankton (algae and cyanobacteria) in mercury cycling and transformations in the aquatic environment. Important research advances revealed that different microalgal species and cyanobacteria contribute to biotic reduction of inorganic mercury to elemental mercury, to demethylation of methylmercury and transformation of inorganic mercury into metacinnabar and to the production of different biomolecules which can contribute to abiotic mercury reduction.

Environmental context. The growth in demand for platinum has led to an increase in the presence of this metal in the environment but little is known about its toxicity to aquatic organisms. The presence of organic matter should contribute to decreasing metal bioavailability but the opposite was found for platinum. How ubiquitous natural organic matter can alter the accumulation and effects of platinum group elements remains to be fully elucidated.

Environmental context. Thiosulfate is present in natural waters, especially those influenced by sulfide oxidation, and it has a marked affinity for metals such as cadmium. Normally the binding of cadmium by thiosulfate would be expected to reduce the metal’s bioavailability. However, here we demonstrate that algal uptake of cadmium is enhanced in the presence of thiosulfate, indicating that Cd can enter the alga via a novel route as an intact Cd-thiosulfate complex.

Environmental context. Arsenic is a globally distributed element, occurring in various chemical forms with toxicities ranging from harmless to highly toxic. We conducted 48-h cell culture experiments under batch and continuous conditions using the ubiquitous marine unicellular alga Dunaliella tertiolecta and evaluated the alga’s arsenic metabolome over time. We found that the alga first methylates the inorganic As taken up from the surrounding water, and then further metabolises the intermediate simultaneously into more complex organo-arsenic molecules like sugars and lipids. These time series experiments are valuable pieces in the puzzle of how algae bio-metabolise arsenic, and in our understanding of the global arsenic cycle.

Environmental context. The use of assessment factors applied to guideline values derived using species sensitivity distributions adds an unnecessary level of conservatism. Using an adequate toxicity dataset and applying the latest model-averaging software will yield values of greatest reliability.

Environmental context. Excessive amounts of retinoic acids (RAs), the main derivatives of vitamin A, cause developmental abnormalities in animals, yet information on their fate in the marine environment is limited. This study investigated the degradation of all-trans-RA in seawater and found that over 90% was degraded and transformed in unfiltered natural seawater within 24 h. The results provide essential insights on the fate and risks of RAs in marine environments.

Environmental context. Base Mine Lake (BML) is a demonstration pilot pit lake for long term oil sands tailings reclamation in Alberta, Canada. This study quantified BML water cap sulfur mass balance and speciation to help understand potential risks to oxygen levels during its early-stage development. Results provide important insights for the adaptive management of water-capped oil sands tailings reclamation.

Environmental context. Monitoring uranium concentrations and speciation in aquatic systems is important for pollution control and for environmental studies. Although an in situ speciation technique based on diffusion and uptake of uranium has been developed, known as DGT, there were uncertainties over some parameters affecting the accuracy of the measurements. This study resolved those uncertainties by investigating diffusion and binding properties of uranium in DGT and provided confidence in monitoring uranium in the environment.