Pic: Dipper (Cinclus cinclus) courtsey, birdwatchireland.ie
From fishes to humans, effects of hormone disrupting pollutants has be recognized everywhere. A new research has shed light into effect of hormone disrupting pollutants in birds along the urban rivers of South Wales. An article published in the Environmental Toxicology and Chemistry journal revealed that the chicks of the Eurasian Dipper, a known river bird, found in upland stream, where found to be underweight as compared to their rural counterparts. These birds which are nesting near urban rivers were found to have altered levels of hormones, resulting in hatching of fewer female chicks as compared to the birds nesting near the rural rivers. This could have a direct impact on the population’s breeding and survival.
Researchers from Cardiff University along with University of Saskatchewan and Exeter and Natural Envrionment Research Council, state that urban contaminants such as PCB (polychlorinated biphenyls) and PBDR a flame retardant chemicals (polybrominated diphenyl ethers) are the key pollutants. The birds acquire them through their food. A strong correlation between these contaminants and depressed thyroid hormone levels in chicks has been found; one of these hormones where of 43% lower in chicks found around urban rivers as compared to that of rural rivers.
Table: Example of EDC’s hormone targets, and aquatic receptors (2)
Professor Steve Ormerod(1) stated: “Our findings are important in showing that pollutants are still a source of concern for the wildlife along Britain’s urban rivers despite very major recovery from the gross pollution problems of the past. Wild birds, such as dippers, are very important indicators of environmental well-being and food-web contamination, and we need to know if populations, other species – or even people – are also at risk”. Professor Steve Ormerod from Cardiff University School of Biosciences, has spent 35 years investigating rivers.
Study showed that urban dippers found along the heavily polluted rivers of South Wales, are exposed to complex mix of chemical contaminants, of which PCB and PBDE are dominant. Endocrine system is important and sensitive, since it controls thyroid and other hormones, alteration in thyroid hormone levels is an important predictor in pollution induced development effects. The effects of altered levels of thyroid hormone on birds are diverse. The primary effects include impaired growth; cognitive dysfunction; compromised immune function; changes in motor activity; and behavioural abnormalities which can persist into adulthood.
Dippers being top predators are important monitors for river pollution, helping in the assessment of urban contaminants which are influencing wildlife. Latest findings have led scientist to examine the effects of dippers sex ratio and thyroid hormone levels, as a consequence at an individual level, which could as a result alter the population dynamics. Locating the exact source of the pollution is one of the many solutions being considered.
RSPB’s Futurescape Officer John Clark said: “The return of Dippers to urban rivers is a fantastic outcome of pollution reduction in the UK. However, this study highlights the importance of birds as an indicator that some pollutants still persist in our rivers at harmful levels. We need to work in partnership with water companies, regulators, statutory agencies and communities at a catchment scale to address those practices that continue to introduce damaging chemicals to our rivers. The RSPB’s Futurescapes conservation work programme is doing exactly that – tackling environmental challenges at a truly large, landscape-scale, level.”
Problem with thyroid disruptors is emerging everywhere around the world. A joint effort is required in tackling these pollutants which throw environment off balance. WHO in their annual report on endocrine disrupting chemicals (EDC) state: The identification of chemicals with endocrine-disrupting potential, among all of the chemicals used and released worldwide, is a major challenge and it is likely that we are currently assessing only the tip of the iceberg. Adding greatly to the complexity of the issue, and to the number of chemicals in our environment, are the unknown or unintended byproducts that are formed during chemical manufacturing and combustion processes and via environmental transformations. In addition, many EDC sources are unknown because a large number of products, materials and goods, as well as waste products and e-waste, lack declarations indicating their chemical constituents (3)
1) Morrissey, C. A., Stanton, D. W.G., Tyler, C. R., Pereira, M. G., Newton, J., Durance, I. and Ormerod, S. J. (2014), Developmental impairment in eurasian dipper nestlings exposed to urban stream pollutants. Environmental Toxicology and Chemistry, 33: 1315–1323. doi: 10.1002/etc.2555
2) Doris S V. 2011. Background: Endocrine Disruption. [ONLINE] Available at: http://www.sccwrp.org/ResearchAreas/Contaminants/ContaminantsOfEmergingConcern/BackgroundEndocrineDisruption.aspx. [Accessed 20 June 14].
3) Europe, W.H.O, 2014. Identification of risks from exposure to endocrine-disrupting chemicals at the country level. 2nd ed. Europe: WHO Regional Office for Europe.