Assessing interactions between nutrients and toxicity : influences of nitrogen and phosphorus on triclosan toxicity to the aquatic macrophyte "lemna gibba".

In the present study, influences of nutrient availability on triclosan toxicity to a model aquatic macrophyte Lemna gibba were explored. Triclosan effective concentrations varied by up to 6.5-fold depending on nutrient treatment and standardized endpoint. Mesocosm results validated these laboratory findings by also indicating greater triclosan-inhibition under higher P-availability. Ecologically relevant endpoints such as elemental stoichiometry and uptake were also differentially affected according to nutrient – triclosan treatments. In particular, tissue-N inhibition was more pronounced that tissue-P leading to N:P dose-response trends, which were most sensitive in P-limited exposure media. These stoichiometric endpoints were generally less sensitive compared to standardized growth endpoints, except under a P-limited scenario. Interactions between nutrients and contaminants were further highlighted by variable triclosan toxicity to N-uptake kinetics determined over an N-gradient. Significant inhibition to N-uptake kinetics was determined for plants co-exposed at high N concentrations while lower N-availability did not result in significant N-uptake inhibition.