Temperate Versus Arctic: Unraveling the Effects of Temperature on Oil Toxicity in Gammarids.

Shipping activities are increasing with sea ice receding in the Arctic, leading to higher risks of accidents and oil spills. Because Arctic toxicity data are limited, oil spill risk assessments for the Arctic are challenging to conduct. In the present study, we tested if acute oil toxicity metrics obtained at temperate conditions reflect those at Arctic conditions. The effects of temperature (4 °C, 12 °C, and 20 °C) on the median lethal concentration (LC50) and the critical body residue (CBR) of the temperate invertebrate Gammarus locusta exposed to water accommodated fractions of a fuel oil were determined. Both toxicity metrics decreased with increasing temperature. In addition, data for the temperate G. locusta were compared to data obtained for Arctic Gammarus species at 4 °C. The LC50 for the Arctic Gammarus sp. was a factor of 3 higher than that for the temperate G. locusta at 4 °C, but its CBR was similar, although both the exposure time and concentration were extended to reach lethality. Probably, this was a result of the larger size and higher weight and total lipid content of Arctic gammarids compared to the temperate gammarids. Taken together, the present data support the use of temperate acute oil toxicity data as a basis for assessing risks in the Arctic region, provided that the effects of temperature on oil fate and functional traits (e.g., body size and lipid content) of test species are considered. As such, using the CBR as a toxicity metric is beneficial because it is independent of functional traits, despite its temperature dependency. To the best of our knowledge, the present study is the first to report CBRs for oil. Environ Toxicol Chem 2024;43:1627-1637. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biofouling impacts on polyethylene density and sinking in coastal waters: A macro/micro tipping point?

Biofouling causing an increase in plastic density and sinking is one of the hypotheses to account for the unexpectedly low amount of buoyant plastic debris encountered at the ocean surface. Field surveys show that polyethylene and polypropylene, the two most abundant buoyant plastics, both occur below the surface and in sediments, and experimental studies confirm that biofouling can cause both of these plastics to sink. However, studies quantifying the actual density of fouled plastics are rare, despite the fact that density will determine the transport and eventual fate of plastic in the ocean. Here we investigated the role of microbial biofilms in sinking of polyethylene microplastic and quantified the density changes natural biofouling communities cause in the coastal waters of the North Sea. Molecular data confirmed the variety of bacteria and eukaryotes (including animals and other multicellular organisms) colonizing the plastic over time. Fouling communities increased the density of plastic and caused sinking, and the plastic remained negatively buoyant even during the winter with lower growth rates. Relative surface area alone, however, did not predict whether a plastic piece sank. Due to patchy colonization, fragmentation of sinking pieces may result in smaller pieces regaining buoyancy and returning to the surface. Our results suggest that primarily multicellular organisms cause sinking of plastic pieces with surface area to volume ratios (SA:V) below 100 (generally pieces above a couple hundred micrometers in size), and that this is a "tipping point" at which microbial biofilms become the key players causing sinking of smaller pieces with higher SA:V ratios, including most fibers that are too small for larger (multicellular) organisms to colonize.