| dc.description.abstract | In recent years, a darkening of aquatic environments has been observed and traced back to an increased input of terrestrial dissolved organic matter (tDOM). This is causing changes to light and nutrient dynamics, and shifts towards bacterial production that can impact coastal areas, leading to reduced food quality for coastal organisms. Due to the aromatic, sizeable, and higher biorefractory nature of the humic substances of terrestrial DOM compared to humic substances from aquatic DOM (aDOM), which are smaller and have fewer shading properties (lighter), terrestrial DOM has a substantial effect on the physicochemical conditions of the water column in marine environments. The presence of tDOM is hypothesized to cause higher adsorption of lipophilic contaminants than other types of DOM. If this bioaccumulates in the organism at a low trophic level, it can be transported up the food web and thus impact the whole system. Previously, the uptake of teflubenzuron in a filter feeder (blue mussel) has been shown to be affected by the DOM origin. Teflubenzuron (log Kow 5.4) is a pesticide commonly used in aquaculture along the coast against sea lice on salmon. Teflubenzuron is highly toxic to crustaceans, and nontarget species in the vicinity of the salmon farms may be exposed to this contaminant and potentially bioaccumulate it. The present study addresses how the source of dissolved organic matter, aquatic DOM vs. terrestrial DOM, impacts contaminant uptake in ascidians, specifically adult Ciona intestinalis, a common sessile filter feeder. The ascidians were randomly distributed into 24 aquaria for a 16-day exposure of tDOM, aDOM, a mixture of aDOM and tDOM, or seawater. Half of the aquaria were exposed to teflubenzuron, and the other half were controls administered the acetone vehicle only. One individual was sampled from each aquarium every three days. Teflubenzuron accumulated in C. intestinalis, where concentrations up to 2.4 µg g-1 were detected when exposed to teflubenzuron concentration of 20 µg L-1 in the water. The highest concentrations were detected in ascidians exposed to DOM derived from aquatic sources, followed by the mix of terrestrial and aquatic DOM, terrestrial DOM, and seawater. Bacterial abundance did not explain the differences in uptake of teflubenzuron. Additionally, the filtration rate was similar in all treatments, indicating no effect from the contaminant. Although the bioaccumulation factors were low (27-70), given the log Kow of 5.4, the study showed a relationship between the DOM source and uptake of teflubenzuron. Any type of DOM treatment resulted in higher accumulation of teflubenzuron than only seawater treatment. | eng |