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Development of an effect based approach for toxic metals in soils and surface waters - Phase II - AQ0812

The cumulative long-term deposition of metals from the atmosphere can have direct adverse impacts on soil and freshwater biota, and the long-term sustainability of soils, and indirect effects on human health through the food chain. Although UK emissions of metals such as lead, cadmium, copper and zinc have decreased significantly over the past two decades, concentrations of these and other metals still exceed critical limits in some parts of the country, while in others current rates of deposition of metals such as lead still exceed critical loads. To minimise the risk of these adverse effects, there are ongoing discussions, both nationally and within UN/ECE and EU, of the need for, and benefit of, further measures to reduce emissions of potentially toxic metals to the atmosphere. Within UN/ECE, agreement has been reached on new critical load methods to assess the long-term impacts of atmospheric deposition of toxic metals, in particular lead, cadmium and mercury.

The development of a critical load approach for metals within the UN/ECE Convention on Trans-boundary Air Pollution (CLRTAP) is of particular significance. The 1998 Protocol on Heavy Metals entered into force on 29 December 2003. A review of the Protocol is planned to formally start in November 2004, and is likely to continue through 2005 and 2006. A method for mapping of critical loads of cadmium, lead and mercury for both ecological and health impacts was recently approved within UN/ECE, and was incorporated in draft form into the Mapping Manual of ICP Mapping and Modelling. A call for data on national critical loads for lead, cadmium and mercury with a deadline of December 2004 has recently been issued. Further calls for maps of critical loads, including preliminary dynamic modelling, are expected in 2005 and 2006.

Nevertheless, there are important limitations to the current stage of development of effects-based approaches for metals that will significantly constrain the ability of the UK government to assess the extent of current ecological and health impacts of atmospheric deposition of toxic metals, to assess the benefits of future emissions reductions, and to respond to policy proposals within both the EU and UN/ECE. The most important of these are:-

• there are many significant uncertainties in the parameterisation of models used to map critical limits and critical loads of lead, cadmium, zinc and copper, which lead to uncertainties in the assessment of the degree of exceedance of critical limits and critical loads;

• the methods of critical load calculation adopted for use within UN/ECE are based on steady-state methods, despite the very long-timescales (decades or centuries) to steady-state for some metals, although any appraisal of the benefits of emission control must consider the dynamics of the system;

• historical deposition of metals in many parts of the U.K. has led to high concentrations of metals in soil and water pools, which mean that the rate of recovery in response to decreasing metal deposition is of major interest:

• although future emissions and deposition of S, N and acidity may significantly affect the future mobility and toxicity of metals, there has to date been no attempt to develop integrated risk assessments for these different emissions.

The work programme described in detail below aims to address these limitations.
1. To respond to the call for national data in the autumn of 2004 and to respond to one further call for national data in the period 2005-2007, with priority given to a response to a probable call for data on the time scales to reach critical limits that is expected in 2006, and to contribute to interpretation of the UK data in the context of the values submitted by National Focal Centres across Europe.

2. To contribute to work on critical loads of metals within UN/ECE CLRTAP, and in particular:- to contribute to the work of the Expert Panel on critical loads for heavy metals within the ICP on Mapping and Modelling; to contribute to the work of the UN/ECE Joint Expert Group on Dynamic Modelling; and to attend and contribute to international workshops within UN/ECE CLRTAP on critical loads of heavy metals.

3. To continue to provide advice to Defra on application of critical load methods for heavy metals, and in particular for lead and cadmium, in the UK.

Project Documents
• Final Report : Development of an effects-based approach for toxic metals   (559k)
Time-Scale and Cost
From: 2004

To: 2007

Cost: £377,648
Contractor / Funded Organisations
University - York
Air Pollution              
Environmental Protection              
Fields of Study
Air Quality