Apports aquatiques et atmosphériques de mercure, de cadmium et de plomb dans la mer du Nord au sens large
D8 - Teneurs en contaminants
D8.1 - Teneurs en contaminants
Message clé:
Les apports totaux des métaux lourds - mercure, cadmium et plomb - dans la mer du Nord au sens large ont diminué depuis 1990. Il est cependant difficile d’apprécier quelle proportion des modifications relevées est due à des réductions des rejets et émissions de mercure et de cadmium depuis 1990, étant donné les meilleures procédures d’analyse utilisées.
Zone Évaluée
Récapitulatif Imprimable
Contexte
L’objectif stratégique d’OSPAR, en ce qui concerne les substances dangereuses, est de prévenir la pollution de la zone maritime OSPAR en réduisant sans relâche les rejets, émissions et pertes de substances dangereuses, dans le but, en dernier ressort, de parvenir à des teneurs, dans l’environnement marin, qui soient proches des teneurs ambiantes dans le cas des substances présentes à l'état naturel et proches de zéro dans celui des substances de synthèse. Les métaux lourds sont dangereux car ils peuvent avoir des effets biologiques négatifs sur l’activité, la croissance, le métabolisme, la reproduction ou la survie d’un organisme. Trois des métaux lourds les plus toxiques – le mercure, le cadmium et le plomb – figurent dans la Liste OSPAR des produits chimiques devant faire l’objet de mesures prioritaires à cause de leur haute toxicité et leur potentiel de nuire à la vie marine.
Une série de processus naturels, industriels et agricoles produisent des émissions de mercure, de cadmium et de plomb, les engrais par exemple peuvent être une source de cadmium (Figure 1a). La plupart du temps, les métaux lourds sont transportés sous forme, ou fixés à, de fines particules. Ces particules peuvent être transportées dans l’air à partir de sols ou de terres dénudés ainsi que de la surface de la mer. Les métaux lourds sont donc ensuite transportés dans l’atmosphère. Le mercure, contrairement aux autres métaux lourds, peut également s’évaporer ou être transporté sous forme de gaz. De plus, le mercure et le cadmium peuvent s’accumuler dans la chaîne trophique (Figure 2) tandis que le plomb ne s’y accumule pas.
Les apports aquatiques de mercure, de cadmium et de plomb font l’objet d’une surveillance par les pays OSPAR. Les apports atmosphériques sont modélisés par les pays OSPAR (Figure 1b), en se fondant sur les émissions annuelles notifiées dans le cadre des Directives sur les émissions de l’Union européenne et de la Convention sur la pollution atmosphérique transfrontière à longue distance des Nations Unies.
Figure 1a: Les engrais minéraux sont une source importante de cadmium dans de nombreuses parties de l’Europe
Figure 1b: Station de surveillance atmosphérique
Figure 2: Le mercure provenant des centrales électriques au charbon et d’autres sources est transporté dans l’atmosphère et l’eau.
Le mercure, sous forme de méthylmercure, peut se bioaccumuler par l‘intermédiaire des réseaux trophiques marins, atteignant des teneurs élevées dans les prédateurs supérieurs
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.
Figure a: Riverine catchment areas supplying mercury, cadmium and lead to the Greater North Sea
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.
Résultats
Les apports de mercure, de cadmium et de plomb dans la mer du Nord au sens large semblent avoir diminué de plus de 50%, depuis le début des années 1990 (Figure 3) mais les avancées des méthodes d’analyse, permettant d’obtenir de meilleures limites de détection (abaissées) signifient qu’une tendance à la baisse des apports a été relevée mais que cette modification est certainement surestimée. Il n’est cependant pas possible de la quantifier. Des surestimations se sont produites antérieurement car la limite de quantification pour une analyse était supérieure à la teneur réelle de la substance dans l’environnent. De même, certains pays ont changé leur analyse des métaux, par exemple passant des métaux totaux aux métaux dissous, depuis l’introduction de la Directive cadre sur l’eau de l’Union européenne en 2000. Ceci a également donné lieu à une réduction apparente des apports. Il est difficile d’apprécier si des problèmes similaires affectent les données sur les retombées atmosphériques qui dépendent de la qualité des données notifiées sur les émissions, de la précision de la description des processus météorologiques et chimiques et de la qualité des données de validation.
Les apports aquatiques de mercure ont pratiquement diminué de moitié entre la période de 1990 à 1995 et celle de 2010 à 2014 et les apports atmosphériques ont diminué d’environ un tiers, ce qui est probablement dû, en partie, à de meilleures techniques d’analyse. Les apports atmosphériques et aquatiques de cadmium ont chacun diminué de deux tiers. Les apports aquatiques de plomb ont diminué de plus de 50% alors que les retombées atmosphérique de plomb représentent moins d’un tiers de celles relevées en 1990.
Figure 3: Apports totaux estimés (fluviaux et atmosphériques) de mercure, cadmium et plomb dans la mer du Nord au sens large de 1990 à 1995 et de 2010 à 2014. Valeurs exprimées en tonnes, arrondies à 5 tonnes près (100 dans le cas du plomb)
Tous les pays OSPAR sont parvenus à des réductions importantes des apports aquatiques de mercure entre la période de 1990 et 1995 et celle de 2010 à 2014. Les Pays-Bas et l’Allemagne ont obtenu les plus grandes réductions des apports aquatiques de plomb, ce qui correspond à la moitié des réductions des apports aquatiques totales.
Les apports atmosphériques des trois métaux lourds ont nettement diminué entre la période de 1990 à 1995 et celle de 2010 à 2014. Les apports de mercure dus aux émissions des pays OSPAR sont désormais nettement inférieurs aux apports de pays « autres qu’OSPAR ». Ces apports autres qu’OSPAR proviennent de l’extérieur de la zone maritime OSPAR ainsi que de la matière remise en suspension, telle que provenant des sols dénudés et des surfaces urbaines, arables et marines aussi bien dans la zone maritime OSPAR qu’à l’extérieur.
La méthodologie utilisée pour cette évaluation inspire une confiance modérée et les données utilisées inspirent une confiance faible.
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.
Figure b: Total mercury inputs to the Greater North Sea
This comprises waterborne inputs from OSPAR countries and modelled estimates of atmospheric deposition to the Greater North Sea from OSPAR and non-OSPAR countries. *, estimated waterborne values. Atmospheric deposition 2015 (empty box) estimated based on 2014 data. Notes: French data do not show actual inputs because limits of quantification are too high; Belgian data include a change from measuring total mercury to dissolved mercury; only two years of Danish data were available, which were excluded at Denmark’s request
Figure c: Total cadmium inputs to the Greater North Sea
This comprises waterborne inputs from OSPAR countries and modelled estimates of atmospheric deposition to the Greater North Sea from OSPAR and non-OSPAR countries. *, estimated waterborne values. Atmospheric deposition 2015 (empty box) estimated based on 2014 data. Notes: French data do not show actual inputs because limits of quantification are too high; only two years of Danish data were available, which were excluded at Denmark’s request
Figure d: Total lead inputs to the Greater North Sea
This comprises waterborne inputs from OSPAR countries and modelled estimates of atmospheric deposition to the Greater North Sea from OSPAR and non-OSPAR countries. *, estimated waterborne values. Atmospheric deposition 2015 (empty box) estimated based on 2014 data. Notes: only two years of Danish data were available, which were excluded at Denmark’s request
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.
Figure e: Illustration of the effect of changes in limit of quantification on estimated total inputs
Estimated total cadmium inputs to the Greater North Sea 1990–2014 for Belgium (upper panel) based on riverine inputs (lower panel) with upper and lower estimates. The total inputs are calculated from the average of the upper and lower riverine input estimates (plus direct discharges). If the upper estimate is unreasonably high due to poor laboratory quantification limits, then the resulting input estimate is also over-estimated. In this case, this results in an (apparently statistically significant) downward trend that should only be attributed to improved laboratory practice rather than reduced inputs to the environment
Confidence assessment
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.
Conclusion
Les pays OSPAR ont fait des efforts importants pour réduire les émissions et pertes de mercure, de cadmium et de plomb dans l’air et dans l’eau. Ces résultats semblent révéler des progrès significatifs dans le sens de l’objectif d’OSPAR, à savoir « prévenir la pollution de la zone maritime OSPAR en réduisant sans relâche les rejets, émissions et pertes de substances dangereuses, dans le but, en dernier ressort, de parvenir à des teneurs, dans l’environnement qui soient proches des teneurs ambiantes dans le cas des substances présentes à l'état naturel ».
C’est dans le cas de la réduction des apports atmosphériques du plomb dans la mer du Nord au sens large que les pays OSPAR ont connu le plus grand succès. La pollution atmosphérique secondaire provenant de matière remise en suspension et de sources à l’extérieur de la zone maritime OSPAR sont désormais les sources principales de pollution atmosphérique et il y a lieu de coopérer au‑delà des limites d’OSPAR afin de gérer ces sources en plus des apports aquatiques.
Les estimations des apports de métaux lourds sont aléatoires, en particulier pour le mercure et le cadmium. Les limites de quantification varient d’un laboratoire à l’autre au sein des pays et lorsque les laboratoires et les méthodes changent. Ceci entraîne des modifications importantes des apports estimés. Ces incertitudes étaient plus sérieuses au début de la période d’analyse. Malgré des problèmes méthodologiques quant au mercure et au cadmium, à savoir que les techniques de mesure sont proches des limites de détection, les données de surveillance pour le groupe de métaux lourds révèlent des réductions importantes des apports.
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.
Lacunes des connaissances
Des contrôles de qualité strictes sont nécessaires dans les laboratoires chargés de l’analyse des échantillons de métaux lourds. Des limites de détection élevées peuvent entraîner une surestimation des apports et entraver la détection des modifications. Lorsque l’on envisage de changer de laboratoire d’analyse il faudra évaluer les effets sur les limites de quantification.
Il existe un décalage entre les exigences de la Directive cadre sur l’eau de l’Union européenne, s’agissant de mesurer les teneurs en métaux dans la fraction dissoute, et l’Accord OSPAR 2014-04 pour quantifier les apports totaux de métaux lourds.
Des lacunes des connaissances subsistent quant à la rétention et l’exportation de métaux lourds dans les estuaires, limitant les connaissances de la proportion de métaux parvenant dans le milieu marin.
Les connaissances sur les pertes de métaux lourds provenant de ports, de la navigation, d’immersions historiques et d’autres sources potentielles sont limitées.
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.