Microplastic abundance in the Eastern Tropical Pacific 2008-2018

Results presented here are part of the paper by Bermudez et al. (2025) obtained by the re-analysis of zooplankton samples collected and stored by the Instituto Público de Investigación de Acuicultura y Pesca (IPIAP in Spanish) between the years 2008 and 2018. The four sampling stations were Station= Esmeraldas (1.161667,-80.433333) Puerto Lopez (-1.581667,-80.99) Salinas (-2.116667,-81.133333) Santa Clara (-3.356667,-80.731667), all of them located ~20 km offshore mainland Ecuador. Sample collection and analysis were conducted following the Standard Operating Procedure for Zooplankton Sample Collection (LG 402) (Environmental Protection Agency, 2013) and for Zooplankton Analysis (LG 403) (Environmental Protection Agency, 2016) from the United States Environmental Protection Agency. Microplastics were counted by microscopy in preserved (4% neutralized formaldehyde) zooplankton samples collected with a conical nylon (monofilament) plankton net with a PVC collection cup (0.3 m Ø, 200 µm mesh pore size) towed vertically through the water column from a depth of 50 m, with a volume of ~ 3530 L being sampled every time. The same, or the same type of net, was used for each sampling to have consistency through the sampling. A total of 36 samples were collected in Esmeraldas, 56 in Puerto Lopez, 42 in Salinas and 13 in Santa Clara, giving a total of 147 samples. The microplastic particles in the 147 analyzed samples were grouped into three classes as described by Eriksen et al., (2013): fragments (pieces derived from bottles, cups, food containers, etc.), fibers (derived from plastic rope and fishing net detritus) and film (fragments of plastic bags, zip bags, etc.); a fourth classification category, foam (sponge, foam, etc.), was not observed in our collected sample materials. MP were quantified by microscopy counting using an Olympus SZX10 microscope with a zoom range of 0.63x to 6.3x, and equipped with a Olympus DP cooled digital camera and image analysis software. Their abundance was expressed as number of particles per liter (MP L−1). A conservative approach was used where, if there was doubt if a particle was actual MP, it was not included in the analysis. MP were also measured using calibrated graticules and video software during counting. The samples were fractionated to fit a 20 ml Bogorov counting chamber. Homogeneity was assured using a Folsom wheel to obtain fractions of equal size. Additionally, the analysis time of each sample was ~1 hour, which significantly reduces the potential of additional laboratory contamination. Furthermore, all samples were analyzed at once using a random methodology approach and thus any chance of a procedural artifact would be minimized.