Tendances de l’étain organique dans les sédiments dans la mer du Nord méridionale

D8 - Teneurs en contaminants

D8.1 - Teneurs en contaminants

Message clé:

A la suite des interdictions portant sur le tributylétain, les teneurs moyennes dans les sédiments ont diminué notablement dans la mer du Nord méridionale, et sont très faibles ou indétectables ailleurs.

Zone Évaluée

Récapitulatif Imprimable

Background

Le tributyltétain (TBT) et autres composés organostanniques sont des contaminants présents dans le milieu marin a l’échelle planétaire. Les étains organiques ont de nombreuses applications, telles que les revêtements, les additifs antifongiques / anti-odeurs, les pesticides, les biocides dans les peintures antisalissures marines, les catalyseurs, les produits de traitement et de conservation du bois. L’utilisation extensive des peintures antisalissures sur les embarcations (Figure 1) entraîne la présence généralisée du TBT dans l’eau, les sédiments et le milieu vivant.

Figure 1: Du TBT a été utilisé en tant qu’agent antisalissure dans des peintures appliquées sur la coque des navires © US Navy

Figure 2: Des teneurs élevées en TBT dans les sédiments sont normalement liées aux ports de commerce, aux ports, aux chantiers navals, aux couloirs de navigation et aux ports de plaisance

Des teneurs élevées en TBT dans les sédiment sont liées aux ports de commerce, aux ports, aux chantiers navals, aux couloirs de navigation et aux ports de plaisance (Figure 2).

Les étains organiques sont toxiques pour de nombreux organismes marins, même à des teneurs très basses. Des teneurs élevées peuvent entraîner des difformités des coquilles des huîtres et affecter la reproduction. Certaines escargots de mer femelles développent par exemple des caractéristiques sexuelles mâles dues à des perturbations endocriniennes causées par le TBT. Ceci a entraîné un déclin généralisé de certaines populations d’escargot (évaluation de l’indicateur de l’imposex). Cependant, la situation s’améliore lentement à la suite de la législation interdisant l’utilisation du TBT dans les peintures antisalissures.

La Stratégie substances dangereuses OSPAR a pour but de parvenir à des teneurs dans le milieu marin, qui soient proches de zéro dans le cas des substances de synthèse. L’utilisation du TBT est interdite depuis les années 1980 pour les navires d’une longueur inferieure à 25 m et depuis 2008 pour tous les navires et installations offshore. Les apports de TBT dans le milieu aquatique risquent cependant de continuer, provenant de pays ne se conformant pas à l’interdiction et de navires ou installations désaffectés. Les apports de TBT risquent de se poursuivre par l’intermédiaire de la redistribution de sédiments déjà contaminés. Les usines de traitement des eaux usées et les décharges sont d’autres sources potentielles de TBT dans le milieu marin car des composés organostanniques sont quelquefois appliqués à des produits de consommation.

A large number of organometallic derivatives in commercial use are based on tin (Batt, 2006). This has given rise to an increase of the worldwide production of organotin compounds over the past 50 years. A major application of organotin derivatives is their use as additives in the manufacturing of plastics in order to prevent thermal and UV decomposition of polyvinyl chloride (PVC) (Kawamura et al., 2000; Mersiowsky et al., 2001). Organotin derivatives also have biocidal properties which led to their use in several fungicides, miticides, molluscicides, nematocides, ovicides, rodent repellents, wood preservatives and antifouling paints, primarily containing tributyltin (TBT), triphenyltin (TPT) and tricyclohexyltin as toxic additives (Batt, 2006).

Owing to the wide range of commercial applications for organotins, considerable amounts have entered the environment (Strand and Jacobsen, 2005). As a result, TBT and some other organotin derivatives can be found not only in water and sediments, but also in various aquatic organisms and the tissues of some birds and mammals (Iwata et al., 1995; Guruge et al., 1996; Elgethun et al., 2000). While tin in its inorganic form is considered non-toxic, the toxicology patterns of the organotin compounds are complex (Ema et al., 1995; Vos et al., 2000; Jenkins et al., 2004). Depending on the type and number of the organic groups bound to the tin cation, some organotins show specific toxic effects in particular organisms even at very low concentrations (Vos et al., 2000; Whalen et al., 2002).

The effects of TBT are not limited to marine gastropods such as dog whelks (Nucella lapillus). The fertility of crustaceans, such as crabs, lobsters, crayfish, shrimp, krill and barnacles, is also affected and other effects have been observed in a range of species including birds and mammals (Waldock and Thain, 1983; Thain and Waldock, 1986; Vos et al., 2000). In spite of legislation regulating useof organotins in numerous countries, these compounds still represent a risk for aquatic and terrestrial ecosystems.

Legislation to ban the use of organotins on small boats was first introduced in France in 1982 and followed by the United Kingdom in 1987. Similar legislation has been introduced worldwide, leading to a significant decrease in organotin concentrations to the environment. A United States federal law was introduced early in 1989, banning the use of organotins on small boats but still permitting the use of paints containing organotins to be used on commercial vessels, provided the paint complied with a limited rate of release of organotins. Japan followed with a similar approach in 1990 and banned all use in 1997. In 1990, the International Maritime Organisation (IMO) adopted a resolution which recommended that Governments adopt measures to control the impacts associated with organotins in antifouling paints. In 1999, the IMO adopted a resolution to develop a legally binding resolution throughout the world, to address the harmful effects of anti-fouling systems used on ships. The resolution called for a global prohibition on the application of organotin compounds which act as biocides in anti-fouling systems on ships by 1 January 2003, and a complete prohibition by 1 January 2008.

The European Union has banned the use of certain organotin compounds in consumer products. Within the European Union, organotins are regulated by Decision 2009/425/EC (European Commission, 2009). Usage of tri-substituted organotin compounds such as TBT and TPT, dibutyltin (DBT) and dioctyltin (DOT) compounds in consumer products are all regulated by this decision. Bis(tributyltin)oxide (TBTO) is regulated under the REACH Candidate list of Substances of Very High Concern.

For each organotin at each monitoring site, the time series of concentration measurements was assessed for trends and status using the methods described in the contaminants online assessment tool http://dome.ices.dk/osparmime2016/main.html. The results from these individual time series were synthesised at an assessment area scale in a series of meta-analyses.

For trend analysis, data were used only from monitoring sites considered representative of general conditions. Data from monitoring sites impacted by point sources and data from baseline monitoring sites where trends would not be expected, were excluded. The analysis was also restricted to assessment areas with at least three monitoring sites with trend information and where those monitoring sites had good geographic spread. Only one assessment area fulfilled these criteria: the Southern North Sea.

The trend in each compound at each monitoring site was represented by the estimated annual change in log concentration, with its associated standard error. The annual change in log concentration was then modelled by a linear mixed model with fixed effects:

          ~ organotin

and random effects:

          ~ monitoring site + organotin: monitoring site + within-series variation

The ‘fixed effects’ measure the trend in each organotin in the Southern North Sea, while the ‘random effects’ measure variation in trends:

  • between monitoring sites common across organotins (monitoring site); and
  • residual variation (organo-meta: monitoring site + within-series variation)

There are two residual terms. Within-series variation is the variation associated with the estimate of the trend from the individual time series and is assumed known (and given by the square of the standard error). Organotin: monitoring site allows for any additional residual variation.

Evidence of trends in organotin concentrations in the Southern North Sea was then assessed by plotting the estimated fixed effects with point-wise 95% confidence intervals.

There are no assessment criteria for organotins in sediment, so a meta-analysis of status was not possible. However, a similar analysis was used to explore concentration profiles across compounds in the Southern North Sea. The summary measure was the fitted log concentration in the last monitoring year. Baseline monitoring sites were included in this analysis of concentration profiles.

Many more data series were used to assess the status of organotin concentrations in the Southern North Sea, than the Celtic Seas (Table a). Time series to assess temporal trends were only available for the Southern North Sea (Table b)

Table a: Number of monitoring sites used to assess organotin concentration status in sediment, by OSPAR contaminants assessment area and organotin compound. TBT: tributyltin, DBT: dibutyltin, MBT: monobutyltin, TPT: triphenyltin
OSPAR contaminants assessment areasStationsTBTDBTMBTTPT
Irish Sea11000
Irish and Scottish West Coast11000
Southern North Sea301924271

The location of the monitoring sites in the Southern North Sea is shown in Figure a.

Figure a: Monitoring sites used to assess organotin concentrations in sediment in the Celtic Seas and Southern North Sea (white lines)

Differences in methodology used for the IA 2017 compared with the QSR 2010

For the IA 2017, a meta-analysis is used to synthesise the individual time series results and provide an assessment of status and trend at the assessment area level. Meta-analyses take into account both the estimate of status or temporal trend in each time series and the uncertainty in that estimate. They provide a more objective regional assessment than was possible in the QSR 2010, where a simple tabulation of the trend and status at each monitoring site was presented.

Résultats

La plupart des pays ont arrêté la surveillance des étains organiques dans les sédiments, en particulier dans des sites offshore car les teneurs sont souvent si faibles qu’elles sont inférieures au seuil de détection. Ceci signifie qu’une évaluation fiable de l’étain organique dans les sédiments ne pourrait être réalisée que dans la mer du Nord méridionale.

Aucune valeur environnementale n’a été créée pour les étains organiques dans les sédiments. Ceci signifie qu’il n’est pas possible d’évaluer l’importance environnementale des teneurs relevées.

Dans les mers Celtiques des données ne sont disponibles que pour un site de surveillance dans la mer d’Irlande et un site dans la zone d’évaluation des côtes ouest irlandaise et écossaise. Les teneurs en TBT sont très faibles dans les deux sites de surveillance.

La mer du Nord méridionale est la seule zone d’évaluation pour laquelle des informations sur les tendances sont disponibles pour trois composés organostanniques (Figure 3): monobutylétain, dibutylétain et tributylétain. Les tendances des teneurs moyennes dans les sédiments pour les trois composés sont à la baisse mais encore décelables dans la mer du Nord méridionale. La moyenne annuelle des réductions se situe entre 3,1% et 13,6%. Ces tendances à la baisse sont également reflétées dans la réduction des effets biologiques liés à l’exposition au TBT, qui a été relevée dans l’ensemble de la zone évaluée (évaluation de l’indicateur de l’imposex). Ceci indique que les interdictions de l’utilisation du tributylétain ont déjà des effets positifs sur le milieu marin.

Figure 3:Modification du pourcentage annuel des teneurs en étain organique dans les sédiments par composé (avec des limites de confiance de 95%) dans la mer du Nord méridionale.

Triangle inversé: nette diminution statistiquement de la teneur moyenne (p <0,05), MBTIN: monobutylétain, DBTIN: dibutylétain, TBTIN: tributylétain

La méthodologie d’évaluation et d’échantillonnage et les données utilisées inspirent une confiance élevée.

Overall, organotin concentrations in sediment are declining in those parts of the OSPAR Maritime Area where monitoring is still ongoing. Most countries have stopped monitoring organotins in sediment, especially at offshore locations, because previous monitoring has shown that concentrations were consistently below the limit of detection. Therefore, a reliable assessment of current organotin concentrations in sediment is only possible based on the monitoring sites in the Southern North Sea (Figure a), where reducing concentrations of organotins in sediment are observed.

Individual Time Series Results per Monitoring Site

A summary of individual time series results per monitoring site (across the OSPAR Maritime Area) for organotin concentrations in sediment is available here http://dome.ices.dk/osparmime2016/regional_assessment_sediment_organo-metals.html. In summary, none of the monitoring sites show an increase in organotin concentration in sediment over the assessment period. It should be noted that not all individual time series results are included in the regional assessments (Table aandTable b), due to the criteria set out in the assessment methods.

Confidence Assessment

There is high confidence in the quality of the data used for this assessment. The data were collected over many years using established sampling methodologies. The data were screened to ensure that only sites with sufficient spatial coverage and temporal data were included. Although synthesis of monitoring site data for the assessment area scale uses new methodology, this is based on established and internationally recognised protocols for monitoring and assessment per monitoring site, therefore there is also high confidence in the methodology.

Conclusion

Près d’une décennie après l’interdiction de l’utilisation des étains organiques dans les peintures antisalissures sur les navires, les teneurs relevées dans les sédiments marins ont diminué considérablement et sont souvent inférieures à la limite de détection. Seuls quelques pays poursuivent donc la surveillance de l’étain organique dans les sédiments.

La partie néerlandaise de la mer du Nord méridionale est la seule zone pour laquelle la quantité des données est suffisante pour pouvoir réaliser une évaluation. Les données pour cette zone révèlent une tendance à la baisse des teneurs en étain organique dans les sédiments.

Les effets écologiques de l’étain organique dans les sédiments n’ont cependant pas été déterminés car il n’existe pas de teneurs ambiantes ou de critères d’évaluation pour les teneurs en étain organique dans les sédiments. La plupart des pays ont opté pour la surveillance des effets biologiques de la pollution par l’étain organique plutôt que par le tributylétain (évaluation de l’indicateur de l’imposex).

Monobutyltin and dibutyltin compounds are usually present in the environment as a result of the degradation of tributyltin, as well as from non-pesticidal industrial uses such as polyvinyl chloride (PVC) stabilisation. In the past, tributyltin (TBT) probably entered the environment mostly through their pesticidal uses. However, TBT may also enter the environment owing to their presence in other products and from the environmental breakdown of tetrabutyltin.

Lacunes des connaissances 

Bien que les apports directs de TBT dans le milieu marin aient été interdits, l’utilisation, autre que pesticide, du TBT se poursuit dans certains pays et la surveillance des teneurs en TBT dans le milieu marin est donc justifiée.

Etant donné qu’il n’existe pas de teneurs ambiantes ou de critères d’évaluation pour les teneurs en étain organique dans les sédiments, les experts OSPAR devraient envisager d’en créer.

There are only a limited number of monitoring sites in the OSPAR Maritime Area for which monitoring for organotins in sediment is still ongoing. In recent years, monitoring at several monitoring sites showed concentrations were below the limit of detection and as a result monitoring was discontinued. This assessment is limited to the Dutch part of the Southern North Sea, the only area with sufficient data for a temporal trend assessment. Although the use of organotins in antifouling paint is reducing, it is not known how harmful are the alternative antifouling options currently being used.

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