Abstract
The vast majority of nanotoxicity studies measures the effect of exposure to a toxicant on an organism and ignores the potentially important effects of the organism on the toxicant. We investigated the effect of citrate-coated silver nanoparticles (AgNPs) on populations of the freshwater alga Chlamydomonas reinhardtii at different phases of batch culture growth and show that the AgNPs are most toxic to cultures in the early phases of growth. We offer strong evidence that reduced toxicity occurs because extracellular dissolved organic carbon (DOC) compounds produced by the algal cells themselves mitigate the toxicity of AgNPs. We analyzed this feedback with a dynamic model incorporating algal growth, nanoparticle dissolution, bioaccumulation of silver, DOC production and DOC-mediated inactivation of nanoparticles and ionic silver. Our findings demonstrate how the feedback between aquatic organisms and their environment may impact the toxicity and ecological effects of engineered nanoparticles.
Highlights
Natural populations exert feedbacks on their environment through consumption, production and excretion
We investigated the effect of citrate-coated AgNPs on the freshwater algae Chlamydomonas reinhardtii in different stages of growth in batch cultures
We found a nano-specific toxic effect of the AgNPs that cannot be explained by the presence of silver ions, a result that differs from past studies that have found that AgNP toxicity is mediated entirely through ionic silver (Ag+) [11,12,14]
Summary
Natural populations exert feedbacks on their environment through consumption, production and excretion. Organisms could significantly impact the fate and toxicity of nanomaterials. Studies have found considerable leaching of silver from consumer products containing AgNPs [3,4]. These particles are utilized for their well-studied antimicrobial properties [5,6,7] through mechanisms such as cell wall damage [7,8] and free radical production [9]. Studies have identified a toxic effect of AgNPs on marine and freshwater algal species[10,11,12,13,14], but these ignore the crucial feedback effect of algal species on the particles themselves
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