Using feces to indicate plastic pollution in terrestrial vertebrate species in western Thailand.

Plastic pollution is a widespread and growing concern due to its transformation into microplastics (MPs), which can harm organisms and ecosystems. This study, aimed to identify plastic pollution in the feces of terrestrial vertebrates using convenience sampling both inside and outside protected areas in Western Thailand. We hypothesized that MPs are likely to be detectable in the feces of all vertebrate species, primarily in the form of small black fragments. We predicted varying quantities of MPs in the feces of the same species across different protected areas. Furthermore, we expected that factors indicating human presence, landscape characteristics, scat weight, and the MP abundance in water, soils, and sediments would influence the presence of plastics in feces. Among 12 terrestrial species studied, potential MPs were found in 41.11% of 90 samples, totaling 83 pieces across eight species including the Asian elephant (Elephas maximus), Eld's deer (Rucervus eldii), Dhole (Cuon alpinus), Gaur (Bos gaurus), Sambar deer (Rusa unicolor), Wild boar (Sus scrofa), Northern red muntjac (Muntiacus vaginalis), and Butterfly lizard (Leiolepis belliana). Specifically, 3.61% of all potential MPs (three pieces) were macroplastics, and the remaining 96.39% were considered potential MPs with the abundance of 0.92 ± 1.89 items.scat-1 or 8.69 ± 32.56 items.100 g-1 dw. There was an association between the numbers of feces with and without potential plastics and species (χ2 = 20.88, p = 0.012). Most potential plastics were fibers (95.18%), predominantly black (56.63%) or blue (26.51%), with 74.70% smaller than two millimeters. Although there were no significant associations between species and plastic morphologies, colors, and sizes, the abundance classified by these characteristics varied significantly. FTIR identified 52.38% as natural fibers, 38.10% as synthetic fibers (rayon, polyurethane (PUR), polyethylene terephthalate (PET), polypropylene (PP), and PUR blended with cotton), and 9.52% as fragments of PET and Polyvinyl Chloride (PVC). Human-related factors were linked to the occurrence of potential plastics found in the feces of land-dwelling wildlife. This study enhances the understanding of plastic pollution in tropical protected areas, revealing the widespread of MPs even in small numbers from the areas distant from human settlements. Monitoring plastics in feces offers a non-invasive method for assessing plastic pollution in threatened species, as it allows for easy collection and taxonomic identification without harming live animals. However, stringent measures to assure the quality are necessitated to prevent exogenous MP contamination. These findings underscore the importance of raising awareness about plastic pollution in terrestrial ecosystems, especially regarding plastic products from clothing and plastic materials used in agriculture and irrigation systems.

Terrestrial wildlife as indicators of microplastic pollution in western Thailand.

Plastic pollution in terrestrial wildlife represents a new conservation challenge, with research in this area, especially within protected areas (PAs), being scant. This study documents the accumulation of microplastics (MPs) in terrestrial wildlife both inside and outside PAs in western Thailand. Carcasses of road-killed vertebrates in good condition, as well as live tadpoles, were collected to examine their exposure to plastic pollution. The digestive tracts of the vertebrate carcasses and the entire bodies of tadpoles were analyzed for MPs, which were identified if they measured over 50 µm. A total of 136 individuals from 48 vertebrate species were examined. The sample comprised snakes (44.12%), birds (11.03%), lizards (5.15%), tadpoles (32.25%), amphibians (5.88%), and mammals (1.47%). In total, 387 MPs were found in 44 species (91.67%), with an average occurrence of 3.25 ± 3.63 MPs per individual or 0.05 ± 0.08 MPs per gram of body weight. The quantities of MPs significantly varied among the animal groups, both in terms of number per individual (p < 0.05) and number per gram of body weight (p < 0.01). Furthermore, a significant difference in MP quantities was observed between specimens collected inside and outside PAs on an individual basis (p < 0.05), but not on a body weight basis (p = 0.07). Most MPs were fibers (77%), followed by fragments (22.22%), with only a minimal presence of film (0.52%) and foam (0.26%). Of all the MPs identified, 36.84% were confirmed as plastics or fibers made from natural materials, and 31.58% were plastics, including Polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), Polyvinylidene chloride (PVDC), and polyester (PES). Additionally, fibers made of cotton, and those containing polyurethane (PU), rayon, PES, and combinations of rayon and PU, were identified. The quantities of MPs were significantly influenced by animal body weight, factors associated with human settlement/activity, and land use types. Our findings highlight the prevalence of plastic pollution in terrestrial vertebrates within Thai PAs. Further toxicological studies are required to establish plastic pollution standards. It is proposed that snakes, obtained from road kills, could serve as a non-invasive method for monitoring plastic pollution, thus acting as an indicator of the pollution threat to species within terrestrial ecosystems. There is an urgent need for the standardization of solid waste management at garbage dump sites in remote areas, especially within PAs. Conservation education focusing on MP occurrence, potential sources, and impacts could enhance awareness, thereby influencing changes in behaviors and attitudes toward plastic waste management at the household level.