First evidence of microplastics in a freshwater river and their relationship to water quality

Microplastics are plastic fragments ranging from 0.1 to 5 mm, their presence in the environment is becoming increasingly evident because they do not degrade and they can enter the human body through inhalation or ingestion. Although their effects are not fully understood, they are a foreign material to the body that can have negative effects. Studies of microplastics in freshwater are scarce and even more so those that refer to bodies of water for recreational and tourist purposes. The objective of this study is to determine the relationship between the amount of microplastics and the physicochemical parameters that determine river water quality, in addition to detecting three organic compounds associated with the degradation of microplastics: naphthalene, phenanthrene, and pyrene. The results showed that the presence of microplastics increases in the sampling points where more than 4 million tourists per year and recreational activities are concentrated. With respect to the physicochemical parameters, it was found that the pH value, the amount of total dissolved solids (TDS), ammonia nitrogen, and color are within the permissible limits established by the official Mexican standard, but the number of fecal coliforms is higher than that established < 1 UFC/100 mL. Pearson's correlation coefficient showed that there are 6 physicochemical parameters that are positively correlated with microplastics, with high correlation for TDS and conductivity, moderate correlation for turbidity, nitrates, and fecal coliforms, and low correlation for dissolved oxygen. In addition, the three organic compounds naphthalene, phenanthrene, and pyrene were detected in the river freshwater samples.