Impact of Predator Cues on Responses to Silver Nanoparticles in Daphnia carinata

Abstract

The past decades have witnessed a boom in nanotechnology that has led to increasing production and application of silver nanoparticles (AgNPs) in the textile industry due to their antimicrobial properties. Increase in the manufacture and use of NPs inevitably has resulted in their increased release into aquatic environments resulting in the exposure of organisms living in these environments. Recently, the risk of exposure to NPs and the potential interaction with biological systems has received increasing attention. The present study investigated the potential effects of predator cues on the toxicity of environmentally relevant concentrations of AgNPs in Daphnia carinata at organismal and biochemical levels. The results of this study show that exposure to environmentally relevant concentrations of AgNPs can result in adverse effects on daphnids with 24- and 48-h LC50 values of 3.56 and 1.75 μg/L, respectively. Furthermore, significant inhibition of reproduction was observed at concentrations as low as 0.5 μg/L. Exposure to predator cues alone resulted in an increase in reproduction and inhibition of superoxide dismutase activity in daphnids. However, coexposure to predator cues interacted in an antagonistic manner with AgNPs with a 24-h LC50 value of 10.81 μg/L compared with 3.56 μg/L for AgNPs alone. In summary, AgNPs could pose risks to aquatic invertebrates at environmentally relevant concentrations. Interestingly, the presence of other factors, such as predator cues, moderated the effects of exposure to AgNPs. Therefore, there is a need to further investigate the potential interactions between NPs and biological factors that can modulate toxicity of NPs for application to the risk assessment of aquatic invertebrates.

Standardized toxicity testing may underestimate ecotoxicity: Environmentally relevant food rations increase the toxicity of silver nanoparticles to Daphnia

“…Many other studies have found that very low concentrations of silver (0.05–6 µg/L) decrease daphnid reproduction , and some of these studies report decreased reproduction at concentrations that do not cause significant mortality or have any observable effect on zooplankton growth , similar to the present results for the highest food rations studied.…”

“…Most studies have found that Ag ions (Agþ) are toxic at parts per billion concentrations to Daphnia [13][14][15][16][17][18][19][20][21][22]. Also, AgNPs are toxic at these low concentrations [15,21,[23][24][25][26][27], and there is agreement in the literature that Agþ is more toxic at equimolar Ag concentrations than AgNPs (see Ivask et al [28] for a review of the literature). Longer (chronic) experiments have observed reductions in growth and/or reproduction of Daphnia exposed to Ag, as both Agþ [29] and AgNPs [21,[30][31][32][33].…”

“…Most studies on the effects of Ag toxicity to Daphnia follow OECD guidelines [7] and feed Daphnia the recommended amount of carbon as algae [21,[31][32][33]. Even more studies feed the Daphnia a mix of algae and other additives such as trout chow, yeast, alfalfa, wheat grass, and/or Daphnia food pellets [10,11,16,25,29,30,35,36]. All of these studies reported the amount of food given as a volume (e.g., a defined volume of a "mixture of Chlorella autotrophica and Daphnia pellets" [16] or "a 3:5 mixture of yeast, wheat grass, and trout chow .…”

“…and algae" [11]), such that calculation of the amount of carbon fed is impossible, whereas another study simply did not report the amount of food given [37]. However, we can get an idea of the carbon load these Daphnia are receiving based on the average reproduction of control individuals-these individuals produced 2.3 to 45 neonates/brood [16,25,29,35] compared to an average summer clutch size of an adult daphnid in the natural environment of less than 1 egg per brood [4]. To our knowledge, the present study is the first to investigate the effect of any toxicant on Daphnia fed rations as low as we used in the present study, except for one set of experiments published in a doctoral thesis exposing Daphnia to an herbicide [38].…”

Toxicological evaluation of silver nanoparticles and silver nitrate in rats following 28 days of repeated oral exposure

“…It is estimated that the production and usage of AgNPs could be over 1, 000 tons in 2015 (Stensberg et al, 2011). The increasing application of AgNPs raises concerns about their potential adverse effects to human and the environment (Cañas-Carrell et al, 2013Tang et al, 2015).…”