Per-and poly-fluoroalkyl substances (PFAS) encompass a large, heterogenous group of chemicals of potential concern to human health and the environment. Based on information for a few relatively well understood PFAS such as perfluorooctane sulfonate and perfluorooctanoate, there is ample basis to suspect that at least a subset can be considered persistent, bioaccumulative, and/or toxic. However, data suitable for determining risks in either prospective or retrospective assessments are lacking for the majority of PFAS. In August 2019, the Society of Environmental Toxicology and Chemistry sponsored a workshop that focused on the state-of-the-science supporting risk assessment of PFAS. This paper summarizes discussions concerning ecotoxicology and ecological risks of PFAS. First, we summarize currently available information relevant to problem formulation/prioritization, exposure, and hazard/effects of PFAS in the context of regulatory and ecological risk assessment activities from around the world. We then describe critical gaps and uncertainties relative to ecological risk assessments for PFAS and propose approaches to address these needs. Recommendations include the development of more comprehensive monitoring programs to support exposure assessment, an emphasis on research to support the formulation of predictive models for bioaccumulation, and the development of in silico, in vitro, and in vivo methods to efficiently assess biological effects for potentially sensitive species/endpoints. Addressing needs associated with assessing the ecological risk of PFAS will require cross-disciplinary approaches that employ both conventional and new methods in an integrated, resource-effective manner.

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Continuous recirculation of two municipal solid waste (MSW) landfill leachates from Ontario, Canada, through a vegetated clay surface cover was field tested in 39 bottom‐draining lysimeters over two field seasons. The more concentrated of the two leachates had an osmotic potential of about −1 kJ kg−1, an electrical conductivity of 0.8 to 1.0 S m−1, a chemical oxygen demand of 9.9 to 18.7 g kg−1, and a pH of 6.5 to 7.0. Vegetation tested included reed canarygrass (Phalaris arundinacea L.), meadow foxtail (Alopecurus pratensis L.), weeping willow (Salix babylonica L.), and hybrid poplar (Populus sp. nigra × maximowiczii). Leachate recirculation stimulated height growth by 36 to 141% in the four species tested relative to the growth observed in the water‐irrigated control plants. Chlorosis of early season foliage and widespread necrosis and leaf desiccation were visible in leachate‐irrigated hybrid poplar and weeping willow saplings after a total leachate application over two seasons of 740 ram. Leaf senescence in the hybrid poplar saplings preceded the normal senescence date by 5 to 6 wk. By the second field season, stomatal conductance was reduced by 73%, photosynthesis rate by 63%, and transpiration rate by 68% in leachate‐irrigated hybrid poplar sapling leaves relative to the water‐irrigated controls. Vegetative stress was most likely a result of osmoregulation disruption arising from a depressed soil solution osmotic potential. In the reed canarygrass swards, total actual evapotranspiration over the second field season was increased by 50%, height growth by 87%, and foliar biomass production by 160% through recirculation with the more concentrated MSW leachate in comparison to the water‐irrigated reed canarygrass. No phytotoxic symptoms or excessive trace metal accumulations were observed in reed canarygrass leaf tissue. Reed canarygrass shows good potential as a cover vegetation species for leachate recirculation sites under northern temperate climatic conditions. The field‐saturated hydraulic conductivity of the silty clay surface covers irrigated with landfill leachate, measured to be in the order of 10−5 m s−1, was significantly higher than that measured on the water‐irrigated surface covers after a cumulative total irrigant application of 2.9 pore volume equivalents. No evidence existed of soil pore clogging with particulates. Volumetric shrinkage of the clay‐rich soil cover due to physicochemical incompatibility with applied leachates containing organic solvents and salts was thought to be the principal contributing factor.

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