Critical loads of heavy metals: evaluation of effects-based approaches for mercury

The aim of this Defra-sponsored project is to combine new and existing data to develop, test and apply critical loads methods and dynamic models for mercury in UK soils. This will provide:

  • a critical assessment of the feasibility of using the Critical Loads approach for Hg, taking account of the unique properties and environmental behaviour of this metal
  • an assessment of the extent of the current risk of adverse ecological effects of mercury in soils in the UK

If the methodology is considered appropriate, the research will also provide:

  • an assessment of the timescale for recovery after emissions reductions
  • a scientific basis for assessing the benefits of emissions control

In addition, we will apply methods for freshwaters, developed in other countries, to representative water bodies to provide an initial assessment of the situation for the UK.

Collaboration

The project involves collaboration with York University (Professor Mike Ashmore), University College London (Dr Neil Rose) and the Agri-Food & Biosciences Institute, Belfast (Dr Crawford Jordan).

See Also

UK deposition modelling and mapping

Heavy metals

Critical loads - Dr Jane Hall

The specific objectives of the project are to:

  • Develop a pH-dependent Critical Limit Function (CLF) for mercury(II) ecotoxicity in soils, based on the free-ion concentrations
  • Calculate Critical Loads of mercury, using both the CLF and the Critical Limit expressed as soil Hg concentration
  • Map Critical Loads for mercury in the UK
  • Map current Critical Load exceedances for the UK, by comparing the Critical Loads with net Hg deposition
  • Compare the national maps of Critical Load exceedance for mercury with those developed by the CCE using default data and methods
  • Assess methods for measuring Hg in UK soils, estimate background levels, and calculate and map current Critical Limit exceedances
  • Develop and test a dynamic soil-water model for mercury, based on the CHUM-AM model already applied to nickel, copper, zinc, lead and cadmium
  • Apply the dynamic model with different scenarios to assess the response of terrestrial and aquatic pools of mercury to changes in deposition of mercury and other factors
  • Assess the dynamics of Hg at the national scale, using the Simple Dynamic Model for Metals
  • Calculate Critical Loads for representative freshwaters using empirical expressions developed for Sweden and the USA
  • Advise Defra on developments within the CLRTAP relating to application of critical loads of mercury and other toxic metals, and in particular on the environmental benefits of further measures to reduce emissions