Microplastic and Organic Fibres in Feeding, Growth and Mortality of Gammarus pulex

Microplastic fibres (MPFs) are a major source of microplastic pollution, most are released during domestic washing of synthetic clothing. Organic microfibres (OMF) are also released into the environment by the same means, with cotton and wool being the most common in the UK. There is little empirical evidence to demonstrate that plastic fibres are more harmful than organic fibres if ingested by freshwater animals such as Gammarus pulex. Using our method of feeding Gammarus MPFs embedded in algal wafers, we compared the ingestion, feeding behaviour and growth of Gammarus exposed to 70 µm sheep wool, 20 µm cotton, 30 µm acrylic wool, and 50 µm or 100 µm human hair, and 30 µm cat hair at a concentration of 3% fibre by mass. Gammarus would not ingest wafers containing human hair, or sheep wool fibres. Given the choice between control wafers and those contaminated with MPF, cat hair or cotton, Gammarus spent less time feeding on MPF but there was no difference in the time spent feeding on OMFs compared to the control. Given a choice between contaminated wafers, Gammarus preferred the OMF to the MPF. There were no significant differences in growth or mortality among any of the treatments. These results conclude that MPFs are less likely to be ingested by Gammarus if alternative food is available and are not more harmful than OMFs.