Fotodegradering af TBT i vand

Abstract

Tributyltin (TBT) er et biocid, der blandt andet indgår i bundmaling til skibe. Fra bundmalingen bliver TBT udledt til havmiljøet, hvor det medfører skadevirkninger hos især bløddyr. Hos bløddyr kan TBT ved koncentrationer ned til 2 ng/L fremkalde imposex, og hos pattedyr kan TBT svække immunforsvaret. Halveringstiden har stor betydning for TBT’s økotoksikologiske egenskaber. Rapporten fokuserer på organotin, der omfatter både TBT og andre toksiske forbindelser. I projektet undersøges det, hvilken rolle dagslys og UV-lys spiller for nedbrydningshastigheden af TBT til uorganiske tinforbindelser i vand. I eksperimentet anvendes UV-lys med samme 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. Halveringstiden bliver undersøgt for organotin opløst i demineraliseret, ionbyttet vand og i havvand. Halveringstiden bliver undersøgt ved løbende at analysere koncentrationen af tinatomer i vandprøverne. Den anvendte analysemetode er atomabsorptionsspektrofotometri. Eksperimentet viste, at organotin nedbrydes langsomst i mørke, hurtigere i UV-lys og hurtigst i daglys. Forventningen var, at nedbrydningstiden var kortest i UV-lys, da det er mere energirigt end dagslys. Det anvendte UV-spektrum viste sig ikke at blive absorberet af organotin, hvorfor resultaterne af eksperimentet viste halveringstider der var længere i UV-lys end i dagslys. Organotin absorberer UV-lys i spektret 230-250 nm, hvorfor det forventes at lys med disse bølgelængder kan forkorte organotins halveringstid væsentligt. Halveringstiden forventedes at være kortere i havvand end i demineraliseret, ionbyttet vand, på grund af tilstedeværelsen 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 is released to the marine environment where it results in the adverse health effect of molluscs. In molluscs a TBTconcentration 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 of organotin in water. The source of UV-light used in the experiment has the same wavelengths as the UV-light that reaches the surface of Earth The experiment is a study of organotin’s half-life in water exposed to UV-light, daylight and darkness. Researches are made into the half-life of organotin dissolved in demineralized ion exchanged water and in seawater. The half-life is examined by ongoing analysis of the concentration of tin atoms in the water samples. The method of analysis is atomic absorption spectroscopy. The experiment demonstrated that organotin degrades slowest when not exposed to light at all, faster exposed to UVlight and fastest in daylight. UV-light has a higher level of energy than daylight, and it was expected that the degradation time would be shortest in UV-light. This study showed otherwise, which is probably because the applied UV-spectrum is not absorbed by organotin. Organotin absorbs UV-light in the spectrum 230-250 nm. Light of these wavelengths 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 exchanged water, because of the chloride ions present. This expectation was confirmed by the results from the experiment.