Persistence and Fate of Tributyltin in Aquatic Ecosystems

Abstract

21.1. Introduction 21.1.1. Theory and background of degradation processes 21.1.2. Review of existing work on tributyltin degradation 21.2. Methods and materials 21.2.1. Studies of degradation in marine and estuarine systems 21.2.1a. Water column: analysis and experimental design 21.2.1b. Sediment: analysis and experimental design 21.2.2. Studies of degradation in freshwater systems in Canada 21.2.2a. Water column: analysis and experimental design 21.2.2b. Sediment: analysis and experimental design 21.2.2c. Laboratory experiments 21.2.3. Radiolabeled 14C-TBTO degradation study in an enclosed marine ecosystem 21 ABSTRACT Studies into the fate and persistence of tributyltin (TBT) in marine, estuarine, and fresh water environments have been conducted in diverse geographic regions and under various experimental conditions to determine rates of degradation and loss. Microbial degradation in water was found to be the most important process limiting the persistence of TBT in aquatic environments. Photolysis and chemical degradation were not significant in the degradation of TBT. Degradation studies were conducted using unfiltered seawater and fresh water incu-bated under natural conditions with sterilized controls from several geographic regions in the United States and Canada. Degradation half-lives were found to be in the range of 4-19 d in seawater and from a few weeks to several months in Canadian fresh water. The principal degradation product of TBT was dibutyltin (DBT) with lesser amounts of monobutyltin (MBT) formed. The behavior of TBT and its degradation products was evaluated by introducing radio-labeled TBT into a mesocosm (13-m 3 enclosure) to simulate a marine ecosystem including benthic sediments. Tributyltin disappeared from the water in the mesocosm initially at 0.20 d-1 (20%) and slowed to ~0.10 d-1 after 15 d. Degradation accounted for the