Nation-wide study of organotin concentrations in freshwater and saltwater fish: OT concentrations in freshwater fish are one-tenth of those in saltwater fish


<div>For the first time, a nation-wide project investigated organotin concentrations in freshwater fish. The study found out that the Vanhankaupunginlahti bay in Helsinki was the most polluted sea area, that the Varkaus industrial area was the most polluted freshwater area and that Naantali had the most polluted harbour.</div>

The participants in the OT-Fish Program coordinated by the Finnish Food Safety Authority Evira were the Finnish Game and Fisheries Research Institute, the National Public Health Institute and the Finnish Environment Institute.

Organotin compounds more persistent than expected
Interest in organotin compound concentrations in fish arose in connection with the construction of a new super-port in Helsinki in 2005. The study was intended to find answers to questions occupying the minds of consumers, such as the kind of health hazards caused by organotin compounds, whether fish was safe to eat, which fishing waters were polluted, and the distance from a polluted harbour or industrial area at which fish were uncontaminated.

Organotin compounds have not caused much worry because they were supposed to decompose and people were confident that they would simply disappear in nature. Studies have shown that the half-life of organotins is much longer than was ever imagined, that is, not a few years but even decades in certain circumstances. For that reason, the present study is of significance to environmental protection as well, for example, where decision making on harbour dredging and the heaping of dredging masses is involved.

The most significant organotin compound discharges to the environment are caused by antifouling ship paints. These biocides have also been used in the paper industry, in timber preservation, the plastics industry and in fish farms. Since the beginning of 2008, the use of organotin compounds in antifouling ship paints has been totally banned in EU.

OT concentrations in fish in saltwater and freshwater areas, in polluted and background areas, and OT studies of sediments in corresponding areas
OT concentrations in freshwater fish were one-tenth of OT concentrations in saltwater fish. Farmed fish were found to be very clean. The Vanhankaupunginlahti bay in Helsinki was clearly the most polluted area in the entire study material. The average for OT compounds measured in perch caught there was 181 μg (micrograms)/kg with a range of 37–528. High OT concentrations in perch were also measured near the city of Porvoo.

Inland waters
A separate project coordinated by the Finnish Environment Institute collected sediment and water samples from the study areas covered by the present study. Very high OT concentrations were measured in the sediments of the Varkaus industrial area: 1,000 μg/kg in top layers and 25,000 μg/kg deeper down. OT concentrations of even 200 μg/kg in sediments are considered high.

OT concentrations measured in perch caught in the industrial area of Varkaus were only 28 μg/kg. Similar concentrations, 19-25 μg/kg, were analysed in Lohja, Jyväskylä and Tampere. In other localities (Jämsä, Joutseno, Kuusankoski, Valkeakoski, Äänekoski, Pyhtää, Taipalsaari and Mänttä), OT concentrations in fish were under 10 μg/kg. The cleanest samples were taken from Lake Oulujärvi.

Port cities
Among the port cities included in the present study, Naantali was found to be the most polluted. The average OT concentration of two samples taken from fish there was 175 μg/kg (individual concentrations were 332 μg/kg and 18 μg/kg). OT concentrations exceeding 30,000 μg/kg have been recently measured in sediments off the Naantali shipyard (Lounais-Suomi Environment Centre). The other cities from the most polluted to the cleanest were Rauma, Helsinki, Porvoo, Kokkola, Kotka, Hamina, Vaasa, Uusikaupunki and Raahe. The average OT concentration in perch in the last-mentioned city was 22 μg/kg.

Major variations in concentrations among different fish species in the same area
OT concentrations in fish species found in the same area varied considerably. This may be due to differences in nutritional behaviour and/or metabolism. Baltic salmon, large herring and sprat, which are known to accumulate dioxins and PCBs, did not accumulate organotin compounds in a similar manner. On the other hand, they tended to accumulate more in fish such as perch, pike-perch and bream.

Health hazards of organotin compounds
A significant fact from the viewpoint of health effects is that OT compounds are cumulative and consequently the duration of their action in organs is long. In its risk assessment, the European safety authority EFSA has used immunotoxic effects as its research data and set for humans the tolerable daily intake of the various OT compounds (TBT, DBT, TPhT and DOT) as a total concentration of 0.25 μg per kg of body weight. This is the daily intake without adverse effects in human organs. At the least, besides immunotoxic effects, these compounds cause hormonal disruptions in marine creatures at very low OT concentrations in the water (1 ng/L of water).

What’s next
Later this year, Evira will organise a seminar on OT compounds and other contaminants in fish. The question of contaminants will be discussed more detail concerning different contaminated areas and different fish species.

Next, Evira’s research project will study imported fish and, next year, assessments will be made of the intake of organotin compounds. At that time, it will be possible to consider new risk management efforts, such as new dietary advice on fish consumption. Until then, the current dietary advice on fish consumption with specified exceptions will be in effect.

For additional information see Evira’s website (Report in Finnish):

Additional information:
Project leader, Research Professor Anja Hallikainen, Evira, tel. 050 3868 433
Chemical analyses, Senior Researcher Panu Rantakokko and Researcher Riikka Airaksinen, National Public Health Institute, tel. (017) 201 395
Sampling, Senior Researcher Pekka Vuorinen, Finnish Game and Fisheries Research Institute, tel. 0205 751 277
Sediments and water, Senior Researcher, Jaakko Mannio, Finnish Environment Institute, tel. 0400148604.

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