Effect of the incidental intake of polyethylene and polypropylene on the growth of Oreochromis sp. handled under laboratory conditions

Abstract

Currently, microplastics contamination (MP) in aquatic ecosystems has increased, damaging marine biota. Ecotoxicological tests are a useful tool to evaluate this impact. This study estimated the effect caused by the intake of MP polyethylene (PE) and polypropylene (PP), on the growth of Oreochromis sp. juveniles. Three concentrations were established (25% / 75%, 50% / 50% and 75% / 25%) for each type of MP, including a control treatment (without MP), with three randomly distributed replicates on experimental units of eight Oreochromis sp. juveniles (initial size 2 ± 0.5 cm). Two individuals were randomly removed after each exposure time (7, 14, 21 and 28 days). In total 154 fish digestive tracts were examined.  Results showed no significant differences in the length (p=0.3444) and weight (p=0.0818) of the individuals of Oreochromis sp. in used in the treatments. There were no significant differences (p=0.513) in the nutritional condition index, though a higher nutritional status trend in the PE treatments compared to the PP treatments was observed. Significant differences (p=0.6078) were found in the content of MP in the first sampling of the experimental treatments, showing a greater presence of PE compared to PP in the digestive tract, due probably to retention and accumulation, shape difference or polymer type. Although MP intake does not appear to cause immediate effects on Oreochromis sp. growth, they could be evidenced in long term studies.