Photodegradation of polyamide, polyester, and HDPE aquaculture cage nets: Implications for microplastic pollution

The increased demand in protein-based food has led to the expansion of aquaculture especially cage fish farming sector. The commonly adopted cage fish farming nets namely, polyamide polyester and HDPE based polymers are susceptible to physical and chemical disintegration. The present study evaluated the physical and chemical alterations imparted to these commercial cage nets when subjected to sunlight and UV irradiation under dry and wet conditions at different salinity, representing fresh and brackish water environments. The results suggest that there is a higher weight loss, surface changes and alterations in chemical bonding for the polyamide cage nets. An analysis using fuzzy AHP-TOPSIS identified polyester and HDPE as more preferable materials than polyamide for cage nets, as polyamide exhibited the highest levels of degradation. To examine the implication of cage farms on the microplastic distribution in estuarine waters, water samples from cage farm areas and open lake areas from the Ashtamudi Estuary India were analysed for microplastics. The upstream cage farmed areas exhibited a higher concentration of microplastics with polyamide fibres being predominant among the others. An evaluation of the ecological risk of cage farming nets was further undertaken on the cage farmed fish and open catch fish from the estuary. The edible tissue of cage fishes Etroplus Suratensis exhibited a higher fibre content and fibres were identified to be polyamide while the microplastic contamination in open catch fishes were to a lesser degree and was identified to be polyester. The study highlights the environmental impact and risk posed with plastic net cage farming practises.