Heavy Metals Network

Previously the Urban/Industrial Heavy Metals Network and Rural Heavy Metals Network

The Heavy Metals (HM) Network is currently managed and operated by the National Physical Laboratory (NPL) for the Environment Agency, on behalf of Department for Environment, Food & Rural Affairs (Defra) and the Devolved Administrations.  The deposition measurements are subcontracted to UK Centre for Ecology & Hydrology (UKCEH). In 2014, the Urban & Industrial Heavy Metals Network and Rural Heavy Metals Network were combined into a single network comprising 24 monitoring sites.

What is measured?

The HM Network monitors the concentrations in air, and the deposition rates of a range of metallic elements at urban, industrial and rural sites.

All 24 sites (except Lough Navar) measure Arsenic (As), Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Iron (Fe), Manganese (Mn), Nickel (Ni), Lead (Pb), Selenium (Se), Vanadium (V) and Zinc (Zn) in the PM10 fraction of air (particulate matter with aerodynamic diameter of 10 µm or less).

Additionally, heavy metals in deposition are measured at 5 rural sites with mercury in deposition additionally measured at 4 of these stations.

What is the purpose of the network?

The purpose of the network is to provide evidence of the concentrations of heavy metals in air near industrial sources and areas of population. The HM Network forms the basis of the compliance monitoring for UK's Air Quality Standards Regulations (AQSR) 2010, including associated amendments, which:

  • provides a Limit Value for Pb concentration in air of 0.5 µg/m3, expressed as an annual mean.
  • sets target values for As, Cd and Ni in the PM10 fraction of ambient air.
  • requires monitoring of metals in deposition, including mercury, although no limit or target values are set.

Measurements at rural sites are used to generate a rural concentration field for the mapping of concentrations of metals in the UK. Mapping is necessary to assess concentrations of metals across the UK at locations at which monitoring is not carried out. They also provide information on the processes which influence concentrations and deposition and enables assessment of any ecological risks which might arise from heavy metal deposition.

History of the network

Historically, this network grew out of several separate long-term monitoring programmes, funded by the UK Government and latterly responding to specific needs of European Commission (EC) Directives in relation to toxic and industrial metals.

The HM Network originally included: five urban multi-element monitoring sites providing measurements of nine important trace elements (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn, V), eight sites for the monitoring of ambient lead resulting from Pb in petrol (two rural, three urban and three kerbside) and eight sites operating in three industrial areas monitoring lead.

A short-term survey from 2000-2001 at 30 industrial site locations across the UK established the UK's position with respect to the requirements of the EC 4th Daughter Directive which was then being drafted. Five of these sites continued to operate (PDF 509KB) following the survey.

In 2003, all monitoring was rationalised into a single integrated network in order to unify methods and practices. In September 2004, the number of elements measured at the old Industrial Metals sites was increased to ensure consistency across the Network.

In early 2011, two sites in Bristol were closed and two new sites in the Swansea Valley opened.

In early 2014, the Urban & Industrial Heavy Metals Network and Rural Heavy Metals Network were combined into a single network comprising a total of 24 monitoring sites. As part of the merging of the two networks, 18 sites were closed, nine from each original network.  

In 2016, the site at Harwell was closed and relocated to Chilbolton. During 2019, both Walsall Bilston Lane and Runcorn Weston Point were closed. A new site at Walsall Pleck Park was opened in January 2021, to replace Walsall Bilston Road.

During 2021 and 2022, all the ambient air samplers across the network were replaced with Digitel DPA-14 samplers. In 2023, the Chadwell St Mary site was closed.

How is the network run?

Sampling of the PM10 fraction of particles is carried out using Digitel DPA-14 ambient air samplers over one-week periods at each site, in accordance with BS EN 12341:2009. These samples are analysed using an inductively coupled plasma - mass spectrometer (ICP-MS) analyser, in accordance with EN 14902:2005 at NPL's UKAS-accredited laboratory.

For metals in deposition, sampling is performed by UKCEH using bulk collectors (bottle and funnel types) in accordance with BS EN 15841:2009 and BS EN 15853:2010. Analysis of these samples takes place at UKCEH’s Centralised Analytical Chemistry Group at Lancaster. Analysis for metals in deposition is done by ICP-MS in accordance with BS EN 15841:2009, and analysis for mercury in deposition is done by atomic fluorescence spectrometry (AFS) in accordance with BS EN 15853:2010 and ISO 17852:2008.

How to view data

You can view data for sites within this network using the links below:

View data for sites for Heavy Metals network

Use the dropdown list below to view data for a particular monitoring site.