Fotodegradering af TBT i vand | Photodegradation of TBT in Water

Tributyltin (TBT) er et biocid, der blandt andet indgår i bundmaling til skibe. Fra bundmalingen bliver TBT udledt tilhavmiljøet, hvor det medfører skadevirkninger hos især bløddyr. Hos bløddyr kan TBT ved koncentrationer ned til 2ng/L fremkalde imposex, og hos pattedyr kan TBT svække immunforsvaret.Halveringstiden har stor betydning for TBT’s økotoksikologiske egenskaber. Rapporten fokuserer på organotin, deromfatter både TBT og andre toksiske forbindelser. I projektet undersøges det, hvilken rolle dagslys og UV-lys spillerfor nedbrydningshastigheden af TBT til uorganiske tinforbindelser i vand. I eksperimentet anvendes UV-lys medsamme bølgelængder som det UV-lys der når Jordens overflade fra Solen – 270 til 400 nm.Eksperimentet består i en undersøgelse af organotins halveringstid i vand i UV-lys, dagslys og mørke. Halveringstidenbliver undersøgt for organotin opløst i demineraliseret, ionbyttet vand og i havvand. Halveringstiden bliver undersøgtved løbende at analysere koncentrationen af tinatomer i vandprøverne. Den anvendte analysemetode eratomabsorptionsspektrofotometri.Eksperimentet viste, at organotin nedbrydes langsomst i mørke, hurtigere i UV-lys og hurtigst i daglys. Forventningenvar, at nedbrydningstiden var kortest i UV-lys, da det er mere energirigt end dagslys. Det anvendte UV-spektrum vistesig ikke at blive absorberet af organotin, hvorfor resultaterne af eksperimentet viste halveringstider der var længere iUV-lys end i dagslys. Organotin absorberer UV-lys i spektret 230-250 nm, hvorfor det forventes at lys med dissebølgelængder kan forkorte organotins halveringstid væsentligt.Halveringstiden forventedes at være kortere i havvand end i demineraliseret, ionbyttet vand, på grund aftilstedeværelsen af chloridioner. Denne forventning bekræftes i eksperimentet.<br><br>Tributyltin (TBT) is a biocide, which among other things is used in antifouling paint for ships. From the paint TBT isreleased to the marine environment where it results in the adverse health effect of molluscs. In molluscs aTBTconcentration as low as 2 ng/L can cause imposex, and in mammals TBT can weaken the immune system.The half-life period is of great importance to the ecotoxicological properties of TBT. This report focuses on organotin,which include both TBT and other toxic compounds. It is examined how UV-light and daylight affects the half-life oforganotin in water. The source of UV-light used in the experiment has the same wavelengths as the UV-light thatreaches the surface of EarthThe experiment is a study of organotin’s half-life in water exposed to UV-light, daylight and darkness. Researches aremade into the half-life of organotin dissolved in demineralized ion exchanged water and in seawater. The half-life isexamined by ongoing analysis of the concentration of tin atoms in the water samples. The method of analysis is atomicabsorption spectroscopy.The experiment demonstrated that organotin degrades slowest when not exposed to light at all, faster exposed to UVlightand fastest in daylight. UV-light has a higher level of energy than daylight, and it was expected that thedegradation time would be shortest in UV-light. This study showed otherwise, which is probably because the appliedUV-spectrum is not absorbed by organotin. Organotin absorbs UV-light in the spectrum 230-250 nm. Light of thesewavelengths can be expected to shorten organotin’s half-life significantly.The half-life period was expected to be shorter in seawater than the half-life period in demineralized ion exchangedwater, because of the chloride ions present. This expectation was confirmed by the results from the experiment.