Pollution in the coastal wetlands of East Asia: Cascading effects from littoral macroinvertebrates to migrating shorebirds

Globally, coastal ecosystems are undergoing rapid changes with respect to habitat degradation and pollution, which is especially true along the East Asian coastline due to rapid industrial and urban development. This has led to effects on coastal wetlands in terms of biodiversity and also on the quality of the stopover sites for migrating birds, such as shorebirds. Shorebird populations are declining at an alarming rate along the East Asian Australasian flyway, the reasons for which are mostly unknown. Besides habitat degradation, pollution is suspected to play a role in these declines. One way that pollutants might decrease survival during migration may be through effects on the immune system that can affect the susceptibility to infectious diseases. Pollution has indeed been related to the outbreaks and increase in infectious disease as early as the 1960s in both animals, including birds, and humans. In this project, we have studied the impact of pollution in combination with food quality and infectious disease (i.e. avian influenza) on migrating shorebirds, with a specific focus on pollution picked up in Chinese coastal wetlands used as stop-over sites during migration. We have analysed benthic and sediment samples collected along the Chinese coast for both legacy and emerging organic pollutants and identified Bohai bay as a hot spot for pollutant exposure to the shorebirds during migration. We have also analysed pollutants in shorebirds from Australia and along the Chinese coast, including the so called "forever chemicals" (PFAS). We have found that there are many more PFAS present in shorebirds than can be found by normal targeted analysis, and especially high concentrations of PFAS precursors were found in the liver after TOPA (total oxidisable precursor assay) analysis, with up to 180 times higher concentrations of PFAS than could be detected before. We have also identified some potential biomarkers for effects in shorebirds and ducks (oxidative stress and specific micro RNAs). In addition, in an experimental egg injection study with PFAS in mallard ducks, we observed sex-specific effects on immune and metabolism gene expression, with changes most pronounced in males. This underscores the need for further research to understand the specific mechanisms induced by PFAS exposure. Our results also highlight the developmental risks of maternal PFAS transfer, potentially affecting the fitness of wild avian species. Lastly, we have identified mercury as a potential threat to several shorebird populations and found that well managed artificial wetlands could provide useful alternative habitats for shorebirds to rest and feed.

The impact of the project’s results for the scientific community and risk assessment are very important, as we identified several hot spot areas along the Chinese coast. In addition, our results indicated that there may be many more PFAS to consider than are currently included in routine monitoring. As a result, there is likely a much higher exposure (and associated health) risk to wildlife (and humans) due to PFAS. The following highlights and recommendations can be made as a result of this project: a) Current targeted PFAS analysis does not cover the exposure risk. TOPA or other types of analysis need to be employed to expand our measurement of PFAS exposure. b) The contamination with other pollutants such as chlorinated paraffins and pesticides and pharmaceuticals needs to be investigated. c) Contamination with legacy POPs, such as PCBs, organochlorine pesticides and PBDEs is relatively low in the foraging places (sediment), diet (shellfish) of the shorebirds and in the birds themselves, hence does not need to be prioritised in future research. d) miRNA research in wildlife has only recently started and many questions remain. Especially, the use of blood presents many challenges. Hence we are currently not ready to use miRNA profiling as biomarkers in wildlife. e) Population culling of the most contaminated birds may result in the birds being sampled representing the less contaminated ones. It may be preferable to investigate concentrations in dead birds along the flyway. f) The contamination of artificial wetlands should be monitored and managed to ensure the wetlands can provide alternative habitats for the shorebirds, in the face of widespread habitat loss in the flyway. These recommendations are significant and important for environmental agencies, risk assessors as well as the research community to design future research studies, to prioritize research and risk assessment/management efforts and to interpret the results of scientific studies. Our research published on PFAS by Zhang et al. in 2025 has already been covered in the international media because of its importance: PFAS: Found 180 times more ‘forever chemicals’ in birds, https://news.chemie.de/d?p00ltryq004k6u00i0000if000000000cd47ibhlyrtq7b5l7duw33ci000002000000b5yud3u (EN) PFAS: 180 Mal mehr "ewige Chemikalien" in Vögeln gefunden, https://news.chemie.de/d?p00ltrz0004k6u00i0000if000000000cd47ibhlyrtq7b5l7duw33ci000002000000nenpzvy (DE) PFAS : 180 fois plus de "produits chimiques éternels" chez les oiseaux, https://news.chemie.de/d?p00ltrzq004k6u00i0000if000000000cd47ibhlyrtq7b5l7duw33ci000002000000jm6gqp4 (FR) PFAS: halladas 180 veces más "sustancias químicas para siempre" en aves, https://news.chemie.de/d?p00ltr2i004k6u00i0000if000000000cd47ibhlyrtq7b5l7duw33ci000002000000f6504ye (ES)

Globally, coastal ecosystems are undergoing rapid changes with respect to habitat degradation and pollution, which is especially true along the East Asian coastline due to rapid industrial and urban development. This has led to effects on coastal wetlands in terms of biodiversity and also on the quality of the stopover sites for migrating birds, such as shorebirds. Shorebird populations are declining at an alarming rate along the East Asian Australasian flyway (EAAF), the reasons for which are currently unknown. The role of pollution in these declines, which is unknown, is suspected to play a role. One way that pollutants might decrease survival during migration may be via immunomodulative properties that can affect the susceptibility to disease. Pollution has indeed been related to the outbreaks of disease and increase in disease as early as the 1960s in animals, including birds, and humans. In this study, we aim to study the impact of pollution in coastal wetlands along the EEAF on the health and survival of shorebirds, in addition to potential effects on immunomodulation in shorebirds and other waterbirds. The potential combined impact of pollution and resultant disease on the fitness and decline of shorebirds has been neglected until now. The proposed project will pioneer investigations into the combined impact of pollution and disease on the decline of migratory shorebirds along the EAAF, with a specific focus on pollution picked up along the Chinese coastline during migration. As there is no information on the impact of pollution (in combination with other stressors e.g. lack of food, disease and high energetic demands during migration) on migratory shorebirds along the EAAF, nor in other flyways (e.g. the East-Atlantic Flyway), the results of the project will bring scientific renewal and will inform conservation and risk management measures for important stop-over ecosystems.