Exploring Lemna gibba thresholds to nutrient and chemical stressors: Differential effects of triclosan on internal stoichiometry and nitrate uptake across a nitrogen:phosphorus gradient

Abstract

Nutrient enrichment often co-occurs with chemical stressors in aquatic ecosystems, but the impacts of these multiple stressors across nutrient gradients is poorly understood and not typically addressed in ecotoxicity studies of lower trophic level models. Moreover, laboratory assays performed to determine threshold responses of aquatic macrophytes to contaminants typically use growth and morphometric endpoints to establish threshold effects and seldom report other important functional responses of lower trophic levels. Using the aquatic macrophyte Lemna gibba, we examined influences of varying nitrogen (N) and phosphorus (P) levels in combination with triclosan, a widely used antimicrobial agent in consumer care products, on internal carbon (C):N:P and NO(3) (-) uptake kinetics. Triclosan modulated L. gibba tissue N and P content, and these stoichiometric responses for P-limited plants to triclosan exposure were more sensitive than growth endpoints employed in standardized phytotoxicity assays. Nitrate uptake capacities were also differentially inhibited by triclosan exposure according to external nutrient levels. Uptake rates for plants cultured and exposed under saturating N-levels were inhibited by more than threefold compared with N-limited plants. The results suggest that stoichiometric and nutrient uptake responses to chemical stressors provide useful information regarding adverse ecological thresholds not defined in standardized phytotoxicity assays with aquatic macrophytes. Our findings further indicate that site-specific impacts of chemicals associated with the wide ambient ranges of N and P typical of surface waters may be anticipated in lower trophic levels. Future studies should examine adverse effects of other stressors to these ecologically relevant endpoints, which may be useful in environmental assessment and management.

Pharmaceuticals suppress algal growth and microbial respiration and alter bacterial communities in stream biofilms

“…Similar to other stressors that disrupt ecological interactions (e.g., nutrients, land use change) the occurrence of pharmaceutical compounds may influence aquatic ecosystems in interesting and nonadditive ways and result in novel community structure, altered function and important higher trophic level responses (Davis et al 2010). In addition, pharmaceuticals likely interact with other stressors, such as nutrients (Fulton et al 2009(Fulton et al , 2010, and research that explores the interactions among nutrients and pharmaceuticals is warranted. The use of this method in a wider variety of habitats with other pharmaceuticals has the potential to expand our understanding of the effects of these ubiquitous compounds on stream ecosystem structure and function.…”

Does nitrate co-pollution affect biological responses of an aquatic plant to two common herbicides?

“…The N or P availability and the resulting N:P ratios in the media affected the toxicity of triclosan to Lemna gibba (Fulton et al, 2010(Fulton et al, , 2009, the toxicity of cadmium to Chlorella vulgaris (Chia et al, 2015), and the toxicity of ionic silver to Lemna gibba (Bian et al, 2013). Nitrogen enrichment resulting in molar TN:TP ratios of more than 150 had severe negative effects on submerged vegetation and overrode atrazine effects 6 (Dalton et al 2015).…”

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“…Several anthropogenic organic compounds have been detected in springs; however, the low levels observed did not elicit alarm (Phelps et al 2006;Phelps 2004). Recent increases in consumer use of compounds such as atrazine, a herbicidal fertilizer additive, (Ackerman 2007) and triclosan, an antimicrobial agent, (Fulton et al 2010) suggest these compounds may have deleterious effects on SAV (and/or grazer population dynamics).…”