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Cadmium, Lead and Arsenic More Than Doubled in Grey Heron Droppings at a Saudi Urban Wetland

Wild grey heron eating fish near an urban park pond in Busan, South Korea
Research · Ecology

Concentrations of cadmium, lead and arsenic in droppings from grey herons (Ardea cinerea) more than doubled over four years at an urban wetland in the Eastern Province of Saudi Arabia. The study, published on 16 June 2026 in Urban Ecosystems, used repeated non-invasive sampling to track changes in metal and metalloid exposure between 2020 and 2023.

All three contaminants more than doubled by 2023

Researchers collected grey heron droppings at the wetland and measured cadmium, lead and arsenic using atomic absorption spectrophotometry. In this method, the concentration of an element is determined from how strongly its atoms absorb light at characteristic wavelengths. Mean concentrations increased consistently across the study period. Cadmium rose from 13.44 mg/kg in 2020 to 32.74 mg/kg in 2023, lead from 14.77 to 34.52 mg/kg and arsenic from 13.08 to 29.87 mg/kg.

Lead had the highest mean concentration throughout the period. The authors interpret the overall increase as evidence of growing contamination within the urban wetland food web and point to sustained inputs associated with industrial activity, traffic emissions and altered hydrology in the surrounding catchment as likely contributors.

Droppings track exposure without handling the birds

The study used droppings because they allow contaminant exposure to be monitored without capturing or handling the birds. The authors note that a single dropping primarily reflects recent exposure, but repeated sampling from the same wetland over several years can reveal temporal changes in the contaminants encountered by the local grey herons.

The researchers therefore propose grey herons as useful sentinel species for monitoring metal and metalloid contamination in urban wetlands. They argue that the rising concentrations recorded in eastern Saudi Arabia support continued environmental surveillance as urban development expands in coastal landscapes.

Sources and image credit

  1. Rubeena, K. A., Aarif, K. M., Alabdallah, N. M., Reshi, O., Mir, M. N., & Alhems, L. M. (2026). Locally migrant Grey Herons as urban sentinels: Non-invasive evidence of escalating metal(loid) contamination in a coastal urban wetland. Urban Ecosystems, 29(4), Article 179. https://doi.org/10.1007/s11252-026-02042-zPrimary peer-reviewed study, first published online 16 June 2026. Repeated Grey Heron droppings samples from an urban wetland in eastern Saudi Arabia showed consistent increases in cadmium, lead and arsenic from 2020 to 2023.
  2. King Fahd University of Petroleum & Minerals. (2026). Locally migrant Grey Herons as urban sentinels: Non-invasive evidence of escalating metal(loid) contamination in a coastal urban wetland [Publication record].Institutional research record reproducing the study summary and the authors’ interpretation of Grey Herons as non-invasive sentinels of metal and metalloid contamination in urban wetlands.

Image: Basile Morin / Wikimedia Commons — wild Grey Heron (Ardea cinerea) eating fish beside a pond in Busan Citizens Park, South Korea, 14 June 2024; representative urban-wetland food-web image, not a bird from the Saudi study; cropped to 16:9 from the original · CC BY-SA 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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