Spatial distribution, abundance, and characterization of emerging plastic forms in binational coastal ecosystems

The persistence of plastic waste in marine environments drives the formation of novel plastic forms through prolonged exposure to environmental conditions and interactions with organic and inorganic materials. This study is the first binational assessment of the spatial distribution, abundance, and characterization of three emerging plastic forms-plasticoncrete, plastimetal and plastisessiles on beaches in India and Thailand. A total of 29 distinct plastic forms were identified, including 11 plasticoncretes, 8 plastimetals and 10 plastisessiles. Plasticoncretes composed of widespread polyethylene (PE), polypropylene (PP) and polyamide (PA) fibres and a polyvinyl chloride (PVC) fragment hardened in concrete. Plastimetals consisted of metal rods rusted with PE, PP and polyester (PEST) fibres. Plastisessiles are formed by PA monofilament lines, PE fishing ropes and PP fibres attached to sessile invertebrates, including oysters and mussels. The plastic forms predominantly contained fibers (93.75%), which are mainly blue in colour, ranging from 2.3 cm to 43.5 cm in length, with PE and PP as the dominant polymers. Floating tests confirmed that all the plastic forms sank, suggesting their local formation, limited mobility and reduced longevity in the water column. This study provides insights into occurrence and characteristics of these plastic forms in coastal environments, highlighting the need for extensive research and monitoring in the Indian and Thailand coastal environment to understand plastic form distribution comprehensively.