Microplastics contamination in the fishes of selected sites in Pasig River and Marikina River in the Philippines

Microplastics (MPs), <5 mm in size, are a concerning pollutant in bodies of water because they can be ingested by biological organisms, posing risks to humans and the environment. This study assessed the extent of MPs contamination in various fish species (Oreochromis niloticus, Arius manillensis, and Pterygoplichthys spp.) in selected sites along two major river systems in the Philippines - Pasig and Marikina Rivers. An optimized Raman microspectroscopy technique was used for imaging and identification of MPs using a mean laser spot size of about 1 μm, which is advantageous in the identification of fibers which have small diameters (<50 μm). It also allowed the simultaneous identification of MPs and their pigment additives, which in turn enabled the tracing of possible sources of these MPs. This is important because the fate and accumulation of MPs in rivers systems, as well as its toxicity is dependent on various factors including polymer type and surface chemistry. Majority of the MPs identified from all the fish species were composed of polypropylene and polyethylene in the form of fragments, which reflects both the widespread use of these polymers for packaging and their environmental fate as riverine plastic debris. Moreover, the detection of MPs in the fish species may affect the food chain and eventually pose health risks for humans. The study could provide guidance on waste and environmental water management in the surrounding region.