Inputs of Mercury, Cadmium and Lead via Water and Air to the Greater North Sea
D8 - Concentrations of Contaminants
D8.1 - Concentration of contaminants
Total inputs of the heavy metals mercury, cadmium and lead to the Greater North Sea have reduced, since 1990. However, improved analytical procedures for mercury and cadmium since 1990 make it difficult to be certain what proportion of observed changes are due to reduced discharges and emissions.
OSPAR’s strategic objective with regard to hazardous substances is to prevent pollution of the OSPAR Maritime Area by continuously reducing discharges, emissions and losses of hazardous substances, with the ultimate aim to achieve concentrations in the marine environment near background values for naturally occurring substances and close to zero for manmade synthetic substances. Heavy metals are hazardous because they can cause adverse biological effects on an organism’s activity, growth, metabolism, reproduction or survival. Three of the most toxic heavy metals – mercury, cadmium and lead – are on OSPAR’s List of Chemicals for Priority Action owing to their high toxicity and potential to cause harm to marine life.
Mercury, cadmium and lead are emitted through a range of natural, industrial and agricultural processes, for example fertiliser can be a source of cadmium (Figure 1a). Heavy metals are most often transported as, or tightly bound to, fine particles and the particles can be blown into the air from exposed soils and earth, and also from the surface of the sea. As a result, heavy metals are subsequently transported via the atmosphere. Unlike other heavy metals, mercury can also evaporate and be transported as a gas. In addition, mercury and cadmium can accumulate in the food chain (Figure 2), whereas lead does not.
Waterborne inputs of mercury, cadmium and lead are monitored by OSPAR countries. Atmospheric inputs are modelled by OSPAR countries (Figure 1b), based on annual emissions reported under European Union Emissions Directives and the United Nations Convention on Long-range Transboundary Air Pollution.
The effects of high levels of heavy metals on humans can include: decreased learning ability (lead, mercury); reduced bone strength (cadmium), and damage to the central nervous system (mercury). This has resulted in restrictions on most uses of heavy metals and strict bans on mercury use. Mercury and cadmium accumulate in the food chain and are considered the most toxic heavy metals.
In the Roman Empire, lead was used for water pipes, as a sweetener in wine (lead-acetate) and as colouring for skin-cream. In modern times, it has been used in car batteries and until 2000 in leaded petrol as an engine lubricant. This was the main source of lead pollution in air and water during the 1970s until its ban (Larsen et al., 2012). It has also been used as a softener in poly(vinyl chloride) (PVC) piping and as a liquid anode in electrolysis in the paper and chlor-alkali industry.
Mercury was used in medicine as an antibacterial agent, and as a liquid anode in electrolysis in the paper industry. It has also been used in dental fillings, in thermometers and other scientific instruments. The Minamata Convention is an international global legally binding instrument banning the use of mercury, which was agreed in 2013, and is on the way to ratification.
Cadmium is used in batteries and electronics, and previously in certain red paints and plastics. It is found in minerals mined for zinc, copper and lead and is a minor constituent of all products of these metals. As it is taken up from soil by plants, it is also concentrated in plants, especially tobacco leaves, sunflower and linseed.
Both mercury and cadmium are suspected carcinogens, either in some other chemical form or as particles in the lungs.
OSPAR’s Coordinated Environmental Monitoring Programme (CEMP, ) requires OSPAR countries to monitor heavy metals, including mercury, cadmium and lead. OSPAR has also produced guidelines for
One of the OSPAR North East Atlantic Strategy objectives is “a steady reduction in heavy metal inputs” with the ultimate aim that heavy metal inputs should be close to background values (OSPAR Agreement 2010-03). The magnitude of background inputs has yet to be determined.
OSPAR has a long history of coordinating and agreeing measures to reduce heavy metal inputs to the North East Atlantic. As early as 1980, Recommendations to limit heavy metal concentrations in sewage sludge and Decisions about mercury concentrations in organisms were agreed. Further recommendations to limit mercury pollution came in 1981, 1982, 1989, 1990, 1993 and 2003. Recommendations to limit cadmium emissions were adopted and implemented between 1985 and 2010.
Heavy metals concentrations are measured in the OSPAR RID) programme (OSPAR Agreement 2014-04). These measurements are combined with high frequency freshwater discharge observations to give the total riverine inputs at the river mouth. Inputs are attributed to the country where the water enters the sea, although catchment areas often extend across national borders. These inputs are then supplemented by national reports of waterborne discharges from industry (OSPAR Agreement 2015-04), which European Union Member States also report under the Industrial Emissions Directive (EU, . Losses from unmonitored areas, between monitored riverine discharge points, are determined by modelling.
Atmospheric input data have been modelled and produced by EMEP–MSC-E (European Monitoring and Evaluation Programme – Meteorological Synthesising Centre East) based on national reporting of emissions to the air under the UNECE Convention on Long-range Transboundary Air Pollution (UNECE, 1983). Emissions data are reported to EMEP, the resulting transport and deposition is then modelled using atmospheric chemistry and meteorological models, together with estimates of ‘background’ heavy metal emissions due to re-suspension from exposed soils and earth or in the case of mercury, emission from the sea surface. Source apportionment allows the relative contributions of OSPAR countries and ‘natural’ sources, as well as sources outside the OSPAR Maritime Area, to be assessed. EMEP model results are validated against EMEP (often including the OSPAR Comprehensive Atmospheric Monitoring Programme, CAMP) observations of heavy metal deposition. More detailed information about EMEP MSC-E modelling is available.
Although inputs of mercury, cadmium and lead to the Greater North Sea appear to have more than halved since the start of the 1990s (Figure 3), advances in analytical methods resulting in improved (lowered) detection limits mean that while there is a downward trend in inputs, the change is certainly overestimated. However, it is not possible to determine by how much. Overestimation occurred in the past because the limit of quantification for an analysis was higher than the actual concentration of the substance in the environment. Similarly, some countries have changed their metal analysis, for example from total metals to dissolved metals, since the introduction of the European Union Water Framework Directive in 2000. This has also resulted in an apparent input reduction. It is unclear whether similar issues affect the atmospheric deposition data, which are dependent on the quality of reported emissions, the accurate description of meteorological and chemical processes, and the quality of the validation data.
Mercury inputs via water have approximately halved between 1990–1995 and 2010–2014 and air inputs have reduced by approximately one-third, noting a proportion of this is likely to be due to improved analytical techniques. Cadmium inputs via air and water have both reduced by two-thirds. Waterborne lead inputs have more than halved while airborne lead deposition is less than a third of the level it was in 1990.
All OSPAR countries have made substantial reductions in waterborne mercury inputs between 1990–1995 and 2010–2014. The Netherlands and Germany have made the greatest reductions in waterborne lead inputs, accounting for half the total waterborne reduction between them.
Airborne inputs of all three heavy metals have reduced significantly between 1990–1995 and 2010–2014. Mercury inputs due to Contacting Parties’ emissions are now significantly lower than inputs from ‘non-OSPAR’ countries. These non-OSPAR inputs come from outside the OSPAR Maritime Area as well as from re-suspended material; such as from exposed soils, and urban, arable and marine surfaces both within and outside the OSPAR Maritime Area.
There is moderate confidence in the methods and low confidence in the data used for this assessment.
Changes and improvements in analytical methods make it difficult to determine the exact scale of the input reductions for mercury, cadmium and lead achieved across the Greater North Sea, Figures b, c and d suggest that inputs have decreased by two-thirds since the early 1990s. Atmospheric input calculations, based on reported emissions and atmospheric transport and chemistry models have decreased by a similar amount. These results appear to be reflected in the metal concentrations in sediment and biota indicator assessments, which describe concentrations in sediment as “decreasing or show no significant change in the majority of areas assessed” and concentrations in mussels and fish as “decreasing or show no significant change in all assessed areas”. Despite this, the relevant objective of the OSPAR North East Atlantic Strategy, that concentrations are at natural background levels, has not yet been met.
Atmospheric pathways remain important, despite progress made under the 1998 Aarhus Protocol and its 2012 amendment, which introduces the requirement for Best Available Techniques (UNECE, 2012). Re-suspended material and sources from outside the OSPAR Convention area are particularly significant sources of mercury and lead.
Although there have apparently been rapid improvements in reducing inputs of mercury (Figure b), cadmium (Figure c) and lead (Figure d) to the OSPAR Maritime Area since 1990, changes since about 2007 have been minor, suggesting that most cost-effective measures have probably now been implemented and achieving further reductions will be challenging.
Changing limits of quantification have a substantial effect on the time series, and can result in the generation of an apparent trend unconnected to the actual inputs to the marine environment. Figure e shows an example using Belgian data, where greatly improved quantification limits in 2004 give an apparent input reduction compared to the previous period. While inputs may have reduced during this period, any real improvements are masked due to the inputs being overestimated prior to 2002. Overestimation occurs when the limit of quantification for an analysis is higher than the actual concentration of the substance in the environment. In this case, the assumed concentration is taken to be the mid-point between the upper and lower concentration estimates, which is then multiplied by the flow to estimate the input.
A similar problem occurs where some countries have changed analysis matrix since the introduction of the European Union Water Framework Directive (EC, 2000). Environmental Quality Standards for metals under the Water Framework Directive were derived for the liquid fraction only. As a result, some countries have stopped measuring total metal concentrations and concentrate solely on the dissolved phase. This also has the effect of introducing an apparent reduction in inputs reduction in the results.
These issues highlight the importance, when changing analysis laboratory or method, to consider whether limits of determination and quantification are maintained, so as not to introduce false trends into time series.
There is low confidence in the data used for this assessment. Monitoring, analysis and reporting are well established throughout the Greater North Sea catchment area. Despite this, there remain issues with differences in laboratory procedures, insufficient spatial coverage and possible missing sources (especially for direct discharges). In addition, historical data analysed using poorer methods are extremely uncertain, particularly in the case of mercury and cadmium.
There is moderate confidence in the methodology, which is straightforward, and the same as that used for the nutrient inputs indicator assessment.
OSPAR countries have made significant efforts to reduce emissions and losses of mercury, cadmium and lead to both air and water. These results appear to show significant progress towards the OSPAR objective to ‘prevent pollution of the Maritime Area by continuously reducing discharges, emissions and losses of hazardous substances, with the ultimate aim of achieving concentrations in the marine environment near background values for naturally occurring substances’.
OSPAR countries have been most successful in reducing atmospheric lead inputs to the Greater North Sea. Secondary atmospheric pollution from re-suspended material and from sources outside the OSPAR Maritime Area are now the major sources of airborne pollution and there is a need for cooperation beyond OSPAR’s boundaries to manage these in addition to the waterborne inputs.
Heavy metal input estimates are very uncertain, particularly for mercury and cadmium. Quantification limits vary between laboratories within countries, and as laboratories or methods change. This causes substantial changes in the estimated inputs. These uncertainties were greater at the beginning of the analysis period. Despite the methodological issues for mercury and cadmium, with measurement techniques that are close to detection limits, the monitoring data for the suite of heavy metals shows substantial input reductions.
Atmospheric mercury inputs from background sources and from outside the OSPAR Maritime Area are now greater than the combined waterborne and atmospheric emissions of OSPAR countries around the Greater North Sea.
For cadmium, inputs today are substantially lower than in 1990, with similar reductions in both waterborne and atmospheric inputs.
Waterborne lead inputs to the North Sea have halved since 1990, while atmospheric inputs are a fifth of their 1990 value. Modelled estimates of atmospheric lead inputs from OSPAR countries around the Greater North Sea have reduced by more than 90% compared to 1990.
Strict quality controls are needed in laboratories analysing heavy metal samples. High detection limits can lead to an overestimation of inputs and an inability to detect changes. The effect on quantification limits should be assessed whenever a change in analysis laboratory is considered.
There is a mismatch between the requirements of the European Union Water Framework Directive to measure metal concentrations in the dissolved fraction and the OSPAR Agreement to quantify total heavy metal inputs.
Knowledge gaps remain concerning the retention and export of heavy metals in estuaries, limiting knowledge of the proportion of metals that reach the marine environment.
There is limited knowledge of losses of heavy metals from harbours, shipping, historical dumping and other potential sources.
Reference levels and targets need to be set to quantify the natural background inputs of mercury, cadmium and lead and to improve harmonisation with the European Union Water Framework Directive.
Data from the Riverine Inputs and Direct Discharges Monitoring (RID) programme (OSPAR Agreement 2014-04) need to be more widely used to ensure that any data problems or gaps are identified and addressed as quickly as possible.
Modelled atmospheric deposition is validated using daily deposition observations from the European Monitoring and Evaluation Programme (EMEP) chemical network. However, this network is land-based and therefore the quality of the model products is less well validated over the sea surface. Overlapping the EMEP observation network are the OSPAR Comprehensive Atmospheric Monitoring Programme (CAMP) monitoring stations. These are coastal stations, which can be considered to be more representative of marine deposition, but with a lower (often monthly) monitoring frequency.
Waterborne inputs are based on a combination of observed (monitoring at the river mouth), modelled (unmonitored areas) and point source inputs. Observations are based on 12 chemical analyses per substance and year combined with modelled or observed flow data. While monitoring and analysis follow OSPAR RID guidelines and can be considered to represent the ’best’ input estimate, uncertainties in the relation between chemical concentration and run-off, together with analytical and flow uncertainties mean that estimated uncertainty may be in the region of 100–200%.
European Council (EC) 2000. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy. Official Journal of the European Union. 2000, vol 327, p. 1–73.
European Commission (EC) 2010/75/EU. Industrial Emissions Directive 2010/75/EU on industrial emissions (integrated pollution prevention and control)
Larsen M.M., Blusztajn J.S., Andersen O., Dahllöf I. (2012). Lead isotopes in marine surface sediments reveal historical use of leaded fuel. Journal of Environmental Monitoring, 2012:14, 2893-2901. DOI: 10.1039/c2em30579h
OSPAR Agreement 1997-08. Guidelines for the sampling and analysis of mercury in air and precipitation
OSPAR Agreement 2010-03. The North-East Atlantic Environment Strategy; Strategy of the OSPAR Commission for the Protection of the Marine Environment of the North-East Atlantic 2010–2020
OSPAR Agreement 2014-04. Riverine Inputs and Direct Discharges Monitoring Programme (RID) applicable from 1 January 2015
OSPAR Agreement 2015-03. Coordinated Environmental Monitoring Programme (CEMP). Update 2015. This Programme is currently under review.
OSPAR Agreement 2015-04. Guidance for the Comprehensive Atmospheric Monitoring Programme (CAMP)
United Nations Economic Commission for Europe (UNECE) 1983. Convention on Long-Range Transboundary Air Pollution, CLRTAP.
United Nations Economic Commission for Europe (UNECE) 2012. 1998 Protocol on Heavy Metals, as amended on 13 December 2012. Executive Body for the Convention on Long-range Transboundary Air Pollution. 2012, http://www.unece.org/fileadmin/DAM/env/documents/2012/EB/ECE.EB.AIR.115_ENG.pdf.
OSPAR Agreement 1997-08 Guidelines for the sampling and analysis of mercury in air and precipitation;
D8 - Concentrations of Contaminants
D8.1 - Concentration of contaminants
|Point of contact||
Philip Axe, Swedish Agency for Marine and Water Management;
Inputs of Mercury, Cadmium and Lead via Water and Air to the Greater North Sea
Common indicator total inputs of mercury, cadmium and lead via water and air to the Greater North Sea.
|Indirect spatial reference||
BE, DE, DK, FR, NL, NO, SE, UK
|Date of publication||
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