Exposure of birds to radionuclides and other contaminants in Special Protection Areas (SPAs) in North-West England

Abstract

There has been a decline in the population of some bird species at Morecambe Bay and the Solway Firth Special Protected Areas in North-West England during the last fifty years. It was suggested that the declines were caused, in part, by contaminants in the food and environment, primarily from the radioactive effluent discharge from the Sellafield Ltd nuclear fuel reprocessing plant in Cumbria. This study analysed bird feathers and tissues, vegetation and sediment for radionuclides, metals and persistent organic compounds. The non-radionuclide results were all low compared to relevant action limits. The ERICA model was used with field data to estimate the radiological dose to birds from exposure to ¹³⁷Cs and ²⁴¹Am with results between 1.26 to 3.83 μGy h^− 1, below the ERICA screening level of 10 μGy h^− 1 and within the IAEA 40 μGy h^− 1 guideline value below which potential adverse impacts on biota are unlikely. The study showed no link between bird population decline and anthropogenic discharges to the SPAs.

Introduction

Morecambe Bay and the Solway Firth, in the north-west of England (Fig. 1), are both designated as Special Protected Areas (SPAs) under the European Birds Directive (European Communities, 1979) based on the presence of internationally important populations of waterfowl, seabirds and regularly occurring migratory species.

The populations of some species of birds found in the SPAs have been counted every winter since 1947 as part of the UK-wide Wetland Bird Survey (WeBS). It became clear that for some species, annual population number declines occurred over part, or all of the period until the present (British Trust for Ornithology, 2008a, British Trust for Ornithology, 2008b). The causes were not fully understood but various theories were proposed including the potential threat from anthropogenic discharges along the west coast of Northern-England and Southern-Scotland leading to habitat contamination by radioactive and/or non-radioactive substances.

Both Morecambe Bay and the Solway Firth areas have received low levels of radionuclides via the authorised discharges from Sellafield Ltd, Cumbria, and other nuclear licensed sites, into the Irish Sea (Gray et al., 1995, Environment Agency et al., 2008). The most significant discharges of man-made radionuclides resulting in contamination of Morecambe Bay and Solway Firth arise from Sellafield Ltd.

In the Irish Sea, around 1% of radionuclides released from Sellafield Ltd are transferred into the aquatic food chain (RADMIL, 1999) a level thought not dangerous to either humans or wildlife. Studies carried out on wild bird populations along the east coast of the Irish Sea had not identified any link between falling bird numbers and radionuclide concentrations (Lowe, 1991) or observed any harm attributable to the radiation exposure (Lowe and Horrill, 1986). However, those studies were not carried out in SPA regions of Morecambe Bay and the Solway Firth. Annual environmental monitoring programmes around Sellafield Ltd and the north-west coast of England (and beyond), have monitored radionuclide specific activities in sediments and biota at locations in both Morecambe Bay and the Solway Firth for many years (MAFF, 1966–1998, Environment Agency et al., 2003–2007, Environment Agency et al., 2008). Another study considering radioactivity in birds, also discovered high levels of radioactive contamination in feral pigeons inhabiting buildings on the Sellafield Ltd site (Copeland Borough Council et al., 1999).

The implementation of the Habitats Directive in UK law (HMSO, 1994) required the protection of the SPA designated species from adverse impact due to anthropogenic activities. The main aim of the study presented here was to calculate the likely exposure of the bird populations in Morecambe Bay and the Solway Firth to ionising radiation arising from industrial discharges in the vicinity of the coast of North-West England. The dose to biota assessment tool, ERICA (2009), has been used to predict the radiation dose to the bird species of interest and the study also investigates the feasibility of using feather contamination to infer the internal activity concentration of radionuclides as an indirect sampling method.

However, to contextualise the potential radiological impacts on the bird species, this exposure route will be put in perspective with the presence of other contaminants (metals and persistent organic compounds (POC)) in the study areas introduced through the disposal of dredged sediments.