Silver nanoparticles flow in an aquatic trophic chain

Silver nanoparticles (AgNP) have been produced and applied in a variety of products ranging from personal care products to food package containers, clothing and medicine utilities. The antimicrobial function of AgNP makes it very useful to be applied for such purposes. Silver (Ag) is a non-essential metal for organisms, and it has been historically present in the environment at low concentrations. Those concentrations of silver increased in the last century due to the use of Ag in the photographic industry and lately are expected to increase due to the use of AgNPs in consumer products. The presence of AgNP in the aquatic environment may pose a risk for aquatic species, and the effects can vary from lethal to sublethal effects. Moreover, the contact of aquatic organisms with AgNP may not cause immediately the death of individuals but it can be accumulated inside the animals and consequently transferred within the food chain. Considering this, the objective of this work was to study the transfer of silver nanoparticles in comparison to silver ions, which was used as silver nitrate, within an aquatic food chain model. To achieve this goal, this study was divided into four steps: the toxicity assessment of AgNP and AgNO3 to aquatic test-species, the bioaccumulation assessment of AgNP and AgNO3 by Pseudokirchneriella subcapitata and Daphnia magna under different exposure scenarios, and finally the evaluation of the trophic transfer of Ag through an experimental design that included the goldfish Carassius auratus in a model trophic chain in which all the species were exposed to the worse-case scenario. We observed that the bioconcentration of Ag by P. subcapitata is mainly driven by ionic silver, and that algae cannot internalize these AgNPs, but it does internalizes dissolved Ag. Daphnia magna was exposed to AgNP and AgNO3 through different exposure routes: water, food and both water and food. The worse-case scenario for Daphnia Ag bioaccumulation was by the joint exposure of contaminated water and food, showing that Ag body burdens were higher for AgNPs than for AgNO3. Finally, by exposing C. auratus for 10 days through contaminated water and food (supplied as D. magna), with another 7 days of depuration phase, it was concluded that the 10 days of exposure were not enough for fish to reach a plateau on Ag internal concentration, and neither the 7 days of elimination were sufficient to cause total depuration of the accumulated Ag. Moreover, a higher concentration of Ag was found in the intestine of fish when compared with other organs, and the elimination rate constant of AgNP in the intestine was very low. Although a potential for trophic transfer of AgNP cannot be suggested based in the data acquired in this study, there is still a potential environmental risk for aquatic species.

An evaluation of trace metal distribution, enrichment factors and risk in sediments of a coastal lagoon (Ria de Aveiro, Portugal)

This paper describes a sediment survey undertaken to unravel patterns of distribution and dispersion of trace metals in an Iberian Peninsula northwestern coastal lagoon (Ria de Aveiro). Cadmium, lead, chromium, copper and zinc were analyzed in bottom sediments. Geochemical normalization is performed and two different regression models for each metal versus aluminum are tested and compared using the respective enrichment factors (EF), an estimation of the relative importance of anthropogenic contributions to the studied sediments. Mean sediment quality guideline quotients (mSQGQ) are used to evaluate sediment quality and associated potential risk to biota with effects range low as empirical sediment quality guideline (SQG) in the basis for mSQGQ calculation. Additionally, the geoaccumulation index is calculated to compare studied sediment levels to global baseline levels. The application of SQGs revealed insufficient characterization capability, especially when contrasted to EF calculated from the regression methods. These pointed a mildly enriched system with localized “hot spot” areas. Therefore, it can be considered that bottom sediments in the Ria de Aveiro system are in their majority unpolluted, zinc being the only metal of concern, presenting enrichment in all four main channels. The major rivers outlets (Caster, Antuã, and Vouga) constitute point sources, thus presenting potential risk for biota. Yet, the strong tidal influence creates a damping effect by efficiently redistributing sediment bound metals.