The effects of a microplastic mixture on wood frogs (<i>Rana sylvatica</i>) across multiple life stages in an outdoor mesocosm experiment

Microplastics have been found across the globe in the habitats of many amphibians. To investigate how exposure to microplastics affects hatching success, survival, growth, and development of wood frogs (Rana sylvatica), as well as how these animals may act as vectors for microplastics, a 96-day outdoor mesocosm experiment was conducted at the Queen's University Biological Station (Ontario, Canada). Wood frogs were allocated to a negative control group or exposed to an additive-containing microplastic mixture (equal parts polypropylene, polystyrene, and polyethylene terephthalate) at nominal water concentrations of 0.069 g/L or 0.691 g/L. Whereas hatchling survival, hatching success, and hatchling size did not differ among experimental groups, exposure to microplastics caused increased larval growth at both microplastic concentrations and delayed larval development at the highest concentration. However, there was little evidence that survival, body size, or development of metamorphs were affected by exposure to microplastics. We found microplastics in the gastrointestinal tract and on the skin of wood frogs and also inside the liver and leg muscle. In addition, the presence of frogs enhanced the flux of positively buoyant microplastics between the aquatic and terrestrial environment. This study provides new insights into how microplastic pollution affects the growth and development of wood frogs and suggests that amphibians with a biphasic life cycle may act as biovectors of plastics across water-land interfaces.