TBT and Imposex
This article describes the use of Tributyltin (TBT) in aquatic antifouling paints, its behaviour in the marine environment and one of its powerful negative effects in non-target species - the phenomenon of masculinization (imposex) in marine gastropods, which has led to the partial ban of this coumpound.
Contents
Introduction
Tributyltin (TBT) is a compound which integrates certain anti-fouling paints used on the hulls of vessels to prevent biological fouling - a phenomenon which has considerable economic costs and environmental risks. Although very efficient, TBT has been subject to restrictions due to its toxic effects in non-target species, detected at the end of the 1970s. One of this harmful effects is imposex – the masculinisation of prosobranch gastropod females in response to exposure of TBT concentration in the magnitude of ng.l-1. So far this phenomenon has been described for over 150 species. The sensitiveness and high correlation between the intensity of this phenomenon and the environmental concentrations of TBT allow the use of certain neogastropod species as indicators of the degree of contamination in coastal zones. Though the use of TBT has been forbidden in many countries for vessels smaller than 25 m, the contamination levels are still a concern, particularly close to areas of intense boating and associated activities, such as fishing and commercial ports, marinas and dry-docks.
The Problem of Fouling in Vessels
Any submersed rigid structure can work as substrate and be colonized by several marine organisms. It is estimated that there are over 4000 marine fouling species. In the case of vessels, the degree of fouling of the hull depends on the time of submersion, the time the vessel is immobilized or its speed, but mainly on the features of the marine environment. Without an antifouling protection, the fouling can reach 150 kg per square meter, in less than 6 months. This phenomenon leads to an increase in the weight of the vessel, the drag resistance of the hull surface and therefore a decrease in speed, a consequent increase in the fuel consumption (up to 40%) but also more frequent maintenance operations. Additionally, the hulls can work as vectors of translocation of organisms form one place to the other, which poses the risks of introducing non-native invasive species.
Antifouling strategies
The problem of fouling in vessels was recognised since the beginning of navigation. The ancient Phoenicians and Carthaginians were thought to have used copper sheathing and the Greeks and Romans both used lead sheathing on their ships’ hulls. More recent methods included the usage of organic compounds of lead, arsenic, mercury and halogens (e.g. DDT) and copper oxide. The later is still widely used nowadays. The first antifouling paints using organic compounds of tin started to appear in the second half of the XX century and quicky dominated the markets during the following decades. Even today, TBT is globaly considered the most effective solution developed so far to prevent fouling.
Effects in non-target species
The case of the Bay of Arcachon (France)
During the period when TBT was being widely used as antifouling, the production of oisters in the Bay of Arcachon (France) almost collapsed. This coastal area is sumultaneasly a place of production of this shellfish and an area of intense recreative boating. Although the knowledge of TBT was very limited at the time, the French Authorities restricted the use of the compound in antifouling paints in the region, as a rare example of adopting the precautionary principle. Later on, it became clear that TBT was responsible for the reproduction failures and abnormal shell development of the oisters.
Imposex
Molecular probes are short oligonucleotides (18-25 bases) that are complementary to specific sequences in the genomes of the target organism. Ribosomal RNA genes are widely used targets for the development of molecular probes. They appear in high numbers in target cells and have both conservative and highly variable regions, which make it possible to develop probes that are specific at different taxonomic levels (Groben et al., 2004.[1]).
(...)
The goal of ALGADEC was the automatic detection of the different toxic algae species in three different areas in Europe: Skagerrak in Norway, the Galician coast in Spain and the area of the Orkney Islands in Scotland. Thus, chip sets for different toxic algae have been developed and tested in the lab for specificity with cultures of known toxic and non-toxic varieties of the same species (Diercks et al., 2008.[2]). The applicability of the ALGADEC biosensor for the detection of toxic algae in the hands of lay persons was evalutated in a workshop with end users of the device. After an introduction of the end users to the handling manual, contaminated field samples from the Orkney Islands (UK) were successfully screened by the end users for the presence of cells from the genus Pseudonitzschia. Chip sets for the following toxic algae are currently available:
- Dinophysis sp.
- Pseudonitzschia sp.
- Lingolodinium polyedrum
- Chrysochromulina polylepis
Prospects
In the course of the ALGADEC-project it was possible to develop a semi-automatic nucleic acid biosensor for the detection of toxic algae. The functionality of the device, even in the hands of lay persons, was shown with laboratory algae cultures, field samples spiked with algae cultures and field samples with naturally occurring toxic algae. However, in the future, the system has to be calibrated and optimised in respect to sensitivity for the detection of the target organisms. The sensitivity of the device is a crucial issue and has to be adapted, to the reference values for toxic algae e.g. toxic Alexandrium sp. in sea water of around ~100 – 250 cells/liter. The original idea of the ALGADEC project was to develop a nucleic acid biosensor for the detection of toxic algae. But the technology suggests an adaptation e.g. to the monitoring of microalgae in general. Therefore, molecular probes will be developed for key species of the phytoplankton of the North Sea. Furthermore, we are currently working on the automation of all steps involved in the analysis of water samples. In the long term a fully automated nucleic acid biosensor will be available that could work on its own or be implemented to the FerryBox-System in order to monitor microalgae autonomously at species level.
See also
Internal Links
- Harmful algal bloom
- Real-time algae monitoring
- Eutrophication in coastal environments
- Ships of opportunity and ferries as instrument carriers
- Differentiation of major algal groups by optical absorption signatures
External Links
References
- ↑ Groben, R., John, U., Eller, G., Lange M. & Medlin L.K. (2004). Using fluorescently-labelled rRNA probes for hierarchical estimation of phytoplankton diversity – a mini-review, Nova Hedwigia, 79, 313-320.
- ↑ Diercks, S., Metfies, K. and Medlin, L.K (2008). Molecular probes for the detection of toxic algae for use in sandwich hybridization formats. Journal of Plankton Research, In press.
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Please note that others may also have edited the contents of this article.
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Please note that others may also have edited the contents of this article.
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