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3.8.         Contamination from navigation

Ships, boats and the infrastructure to support them can cause a range of environmental problems, if poorly managed. For example, dredging channels can disturb buried, contaminated sediments. This section focuses on a contaminant directly introduced into water by shipping activities.

Table 3.1e: Contamination mainly from navigation

(b) defined as priority hazardous substances, for which all discharges, emissions and losses must be ceased.

(c) Substance is ubiquitous, persistent, bioaccumulative and toxic (uPBT) as defined in 2013/39/EU.

Biocide: Tributyltin

Sources and uses

Organisms such as algae and barnacles settle on wood, metal or plastic surfaces a short time after the material has been put in the water. This is a natural colonization process called “fouling” and can degrade the material. On vessels it also slows the boat down, leading to higher energy use. Biocides are therefore used to resist biofouling, which work by coating the vessel’s hull with an antifouling coating and continuously leaching the biocide. This also results in water contamination.

Owing to aquatic toxicity and persistence, use of organotin compounds in antifouling coatings has been banned since 2008.

TBT has also been used in wood preservatives, silicone sealants, roof sheeting, textiles and diverse other coatings. The remaining production and use of TBT continues to result in emissions from industry and UWWTPs.

Toxicity and EQS

TBT compounds affect the endocrine (hormone) system of certain marine as well as freshwater molluscs at very low concentrations. This results in malformation of the reproductive system, which can lead to impairment or eventually a complete loss of the ability to reproduce. Severity of malformation increases with higher TBT concentrations (CIRCABC, 2005). The EQS was derived to protect organisms in both freshwater and saltwater environments.

WFD status

TBT causes failure to achieve good chemical status in surface waters in over 650 water bodies. These are spread across Europe, mainly in western and southern countries. TBT is a uPBT under the WFD, owing to the difficulty in remediating contaminated areas.

Emissions

Figure 3.14 gives an overview of the different reported loads.

Figure 3.14 : Tributyltin !!!

Notes: !!! – CAUTION – low confidence in data, as limited reporting of this substance, see Table 3.2. Details on the emissions data are given in Annex A.

Few Member States reported loads from industry, UWWTPs and diffuse sources.

No overview of the total emissions to water in Europe can be made, because only a few Member States have reported emissions.

Summary/Outlook

Following the restriction on use of TBT in boat antifouling, concentrations of TBT in water and sediments have decreased. Nevertheless, there are still exceedances of the EQS, which may relate to both historic contamination and to uses other than for antifouling.

Other than removing TBT-contaminated sediments and finding safe ways to dispose of hazardous material, there is little that can be done to remediate water bodies failing for this substance. Rather, careful management is required to allow burial of the contaminated material and avoid re-disturbance.

Non-toxic ways to prevent biofouling would have many applications. Finding them would   deliver both increased sustainability and market advantage.