Characteristics, abundance, distribution, and degradation dynamics of microplastics in the high Colca-Chilli water transfer systems: Tracing an emergent pollutant to Andean reservoirs

The presence, distribution, and degradation of microplastics (MPs) were evaluated in four high-altitude reservoirs of the Colca-Chilli water transfer system in Arequipa, Peru: El Pañe, Dique Los Españoles, Aguada Blanca, and El Frayle. In our study, the sampling points were classified into two groups according to their location within the Colca and Chilli River systems, which are separated by approximately 150 km. Climatological data from 2000 to 2023-including precipitation, wind speed, and solar irradiation-were analyzed to evaluate their influence on the presence, deposition, and degradation of microplastics (MPs). Wind patterns, particularly in arid zones such as Aguada Blanca and El Frayle, facilitated the airborne transport of MPs, whereas precipitation and temperature variability played a significant role in MPs distribution in wetter areas like El Pañe and Dique Los Españoles. MPs were detected in all reservoirs, with concentrations ranging from 2260 to 6440 MPs/m. The majority of MPs were smaller than 1 mm, indicating advanced fragmentation, likely caused by prolonged exposure to wind, water, or solar irradiation, as well as extended transport processes from larger plastic debris. Fibers were the most abundant form of MPs (≥70 %), followed by amorphous particles and films. These particles were analyzed using μRaman and μFTIR to determine their chemical composition and morphological characteristics. The predominant polymers identified were cellulose, polyethylene terephthalate (PET), cellophane, and semisynthetic fibers such as rayon. Spectral analysis of PET revealed significant degradation, evidenced by a reduction in CO and CH functional groups. The decrease in ester groups compared to the blank, together with the emergence of -COOH functional groups, suggests degradation processes driven by environmental factors. The loss of hydrocarbon functional groups increased particle hydrophilicity, thereby facilitating sedimentation and enhancing interactions with microorganisms. SEM/EDS analyses further confirmed degradation, showing variations in carbon and oxygen content consistent with oxidative and hydrolytic processes. Among the reservoirs, El Frayle exhibited the highest polymer volume (694.3034 mm/m), suggesting either lower degradation rates or higher levels of pollution. Conversely, "El Pañe-in" recorded the highest MP count but a lower total volume, reflecting the predominance of smaller particles. These findings emphasize the importance of evaluating both particle abundance and volume when assessing MPs pollution and its environmental implications. Overall, this study provides new insights into MPs dynamics in high-altitude reservoirs and highlights the need for further research to develop effective mitigation strategies for these critical water resources.