Effects of microplastics on growth and development of Rana latastei tadpoles: A mesocosm study

Microplastics (MPs) and their chemical additives have been demonstrated to affect the digestive system of exposed animals and its functionality. Their feeding habits make anuran larvae particularly vulnerable to MPs. However, in laboratory tests the effects of MP contamination on tadpoles showed to be inconsistent. We used mesocosms to test the effects of a mixture of plastic polymers (3 PVC: 3 HDPE: 3 PES: 1 PS) on the behaviour, growth and development of Italian agile frog Rana latastei under controlled near-natural conditions. Tadpoles were exposed for four weeks to four different treatments (1, 7, 50 mg/L MP concentrations and uncontaminated water as control). The mean number (± SE) of fibres per tadpole ranged from 0.17 ± 0.17-3882.6 ± 411.8. No significant difference in tadpole behaviour, survival and development (Gosner stage at the end of the experiment) was recorded. The clearest effect on morphology was a significant increase in tadpole mass for the 50 mg/L group compared to controls, which was confirmed, through geometric morphometric analysis, by variation in centroid size. The recorded increase in tadpole growth rate may be imputed to the obesogenic effects of MPs, mainly polyester fibres, and their associated chemicals. As MPs are currently ubiquitous, the role played by MP exposure on larval growth needs to be carefully investigated to point out the potential long-term effects of the most widespread polymers.