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.
Nanoscale zerovalent iron (nZVI) and its derivatives hold promise for remediation of several pollutants but their environmental implications are not completely clear. In this study, the physicochemical properties and aggregation kinetics of sulfide/silica-modified nZVI (FeSSi) were compared in algal media in which Chlamydomonas reinhardtii had been cultured for 1, 2, or 11 days in order to elicit the effects of organic matter produced by the freshwater algae. Furthermore, transformation of FeSSi particles were investigated in C. reinhardtii cultures in exponential (1-d) and slowing growth (11-d) phases while monitoring the response of algae. We found evidence for steric stabilization of FeSSi by algal organic matter, which led to a decrease in the particles' attachment efficiency. Transformation of FeSSi was slower in 11-d cultures as determined via inductively coupled plasma and X-ray analyses. High concentrations of FeSSi caused a lag in algal growth, and reduction in steady state population size, especially in cultures in exponential phase. The different outcomes are well described by a dynamic model describing algal growth, organic carbon production, and FeSSi transformations. This study shows that feedback from algae may play important roles in the environmental implications of engineered nanomaterials.
Phytoestrogens are plant compounds that can act as endocrine disruptors in vertebrates. Biologically active levels of phytoestrogens have been found in aquatic habitats near wood pulp and paper mills, biofuel manufacturing plants, sewage-treatment plants, and agricultural fields. Phytoestrogens are known to cause hormonal and gonadal changes in male fish, but few studies have connected these effects to outcomes relevant to reproductive success. In one experiment, we exposed sexually mature male fighting fish Betta splendens to environmentally relevant (1 μg L(-1)) and pharmacological concentrations (1000 μg L(-1)) of the phytoestrogen genistein as well as to a positive control of waterborne 17β-estradiol (E2; 1 μg L(-1)), and a negative control of untreated water. In a second experiment, we exposed male B. splendens to environmentally relevant concentrations (1 μg L(-1)) of genistein and β-sitosterol singly and in combination as well as to the positive and negative controls. All exposures were 21 days in duration. We measured sex-steroid hormone levels, gonadosomatic index (GSI), sperm concentration and motility, and fertilization success in these fish. We found that exposure to genistein did not affect circulating levels of the androgen 11-ketotestosterone or the estrogen E2 relative to negative-control fish. We also found that neither of the compounds nor their mixture affected GSI, sperm concentration or motility, or fertilization success in exposed fish relative to negative-control fish. However, fish exposed to phytoestrogens showed some evidence of fewer but more motile sperm than fish exposed to the positive control E2. We conclude that sexually mature male B. splendens are relatively immune to reproductive impairments from short-term exposure to waterborne phytoestrogens.
Phytoestrogens are produced by plants and may cause endocrine disruption in vertebrates. The present study hypothesizes that phytoestrogen exposure of female Siamese fighting fish (Betta splendens) may disrupt endogenous steroid levels, change agonistic behavior expression, and potentially also disrupt oocyte development. However, only the pharmacologic dose of β-sitosterol had a significant effect on opercular flaring behavior, while we did not find significant effects of β-sitosterol or genistein on steroids or gonads. These findings are in direct contrast with previous studies on the effects of phytoestrogens in female fish. Results of the current study support previous work showing that the effects of phytoestrogen exposure may be less acute in mature female B. splendens than in other fish.
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