Evidence of microplastics in water and commercial fish from a high-altitude mountain lake (Lake Titicaca)

Abstract

Microplastic pollution is a widespread environmental concern. Like other anthropogenic pollutants, microplastics can reach aquatic ecosystems through rivers and interact with the aquatic biota. For instance, Lake Titicaca (between Bolivia and Peru), one of the great ancient lakes in South America (3,809 m a.s.l.), shows a pollution problem, particularly in the southern shallow basin (Lago Menor) in Bolivia. Nevertheless, our knowledge of the presence of microplastics and their interaction with the biota of Lake Titicaca is limited. Therefore, this study evaluated the presence of microplastics in the stomach content of the four fish species targeted by local fisheries in Lago Menor of Lake Titicaca (Orestias luteus, Orestias agassizii, Trichomycterus dispar, and Odonthestes bonariensis; N = 1,283), and looked for relationships with trophic guilds or fishing areas. Additionally, surface water was analyzed to evaluate the presence of microplastics in the water. The evaluation of microplastics was carried out by visual observations. We observed that the frequency of microplastic ingestion was low in all species (<5%). Conversely, microplastic was present in the water, with the highest quantity at the southern part of Lago Menor (103 ± 20 particles per L), without differences in the microplastic number between sites. Most microplastics counted in stomach contents were fibers, whereas water samples mainly contained fragments. Our results point to microplastic pollution in Lago Menor of Lake Titicaca. However, we could not determine the pollution rate due to considerable methodological limitations. Further research will be needed to robustly detect microplastics in Lake Titicaca and their impact on the fish species in the lake.

Keywords: Fibers; Fishery impacts; Orestias; Plastic pollution.

Figure 1. Location map of sampling station in Lago Menor of Lake Titicaca.

Map the localization of the Lago Menor in the Lake Titicaca study area. Dark Blue circles show the water sampling replicates along the transect (blue dotted line). Red circles show the three landing zones in Lago Menor, and light blue show the fishing areas near the transect.

Figure 2. Examples of fibers of microplastics found in gut content.

Photograph of fibers found in stomach content of O. luteus and O. agassizii. (A) Microplastic fiber bun, (B) microplastic fiber with stomach content. The stereo microscope used has a magnification power of 6 X and 50 X (WILD M3, Heerbrugg).

Figure 3. Frequency of occurrence (FO) percentage of microplastics found in gut content of the fish studied in Lago Menor of Lake Titicaca.

Frequency of microplastics fibers found in the stomach content of four target species of Lago Menor artisanal fisheries. Bars indicate the SD.

Figure 4. Number of microplastics in water samples in Lago Menor of Lake Titicaca.

Box plot for the microplastic number found in the water samples in different sites in Lago Menor of Lake Titicaca. Visual examination was performed using an Olympus CX43 microscope, 4X and 10X objectives.

Figure 5. Size of microplastics found in the water samples in Lago Menor of the Lake Titicaca.

Bar plot of the size in length of microplastics found in the water samples in different sites in Lago Menor of Lake Titicaca. Bars indicate the SD. Visual examination was performed using an Olympus CX43 microscope, 4X, and 10X objectives, and photographed using an attached Olympus LC30 digital camera. No contrast, gain, and image saturation modification to the photographs were made.