Implications of nanoparticles in the aquatic environment
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|Wageningen : Wageningen University|
|253 pagina’s figuren, grafieken|
|Proefschrift Wageningen University ter verkrijging van de graad van doctor in het jaar 2014 toon alle annotatie(s)
Met literatuuropgave. - Met samenvatting in het Engels en Nederlands
|Koelmans, Prof. dr. A.A.|
|Samenvatting door auteur||
The production and use of engineered nanoparticles (ENPs) is growing, which causes extended emissions into the environment. This thesis focuses on the implications of ENPs in the aquatic environment, emphasising the sediment, because ENPs are primarily expected to end up in aquatic sediments. ENPs can have direct effects on species in the aquatic environment, indirect effects on the community level and/or food web and effects on the fate and risks of other chemicals. To identify the risks of ENPs, not only information about the hazard, i.e. the potential for an effect, but also about the potential for exposure is needed. In this thesis (a) fate processes of ENPs in natural waters, i.e. sedimentation and aggregation, (b) sorption of polychlorinated biphenyls (PCBs) and perfluorooctane sulfonate (PFOS) to ENPs and (c) effects of ENPs on single species and a benthic community were studied. This information was used for calculation of the retention of ENPs and associated contaminants in lakes and for an evaluation of the expected risks based on these insights.
To study fate processes of ENPs quiescent settling was measured in filtered and unfiltered water to determine sedimentation rates and heteroaggregation rates for ENPs with natural colloids (NC) (Chapter 2). These experiments were performed with 4 different ENPs (i.e. CeO2, PVP-Ag, SiO2-Ag and C) in 6 different natural waters including a coastal sea, tidal water, river, small stream, lake and a small acid pond. Sedimentation rates ranged from 0.0001 m d-1 for SiO2-Ag to 0.14 m d-1 for C60. The determination of heteroaggregation rates was based on a simplified Smoluchowski-Stokes equation and ranged from 0.007 to 0.6 L mg-1 d-1, with the highest values observed in seawater. Besides the quiescent settling experiments, also experiments under turbulent conditions in the presence of sediment were performed (Chapter 3). These experiments were performed with 3 different ENPs (i.e. CeO2, PVP-Ag and SiO2-Ag) in natural coastal seawater, brackish tidal water and fresh water from a river. Sedimentation rates ranged from 0.14 m d-1 to 0.50 m d-1 and were one to two orders of magnitude higher than in quiescent systems with NC. Heteroaggregation rates ranged between 0.151 and 0.547 L mg-1 d-1, which is up to 29 times higher than in quiescent systems with NC. The scavenging and settling of resuspended sediment was dominant for the settling of ENPs, resulting in minor variation in sedimentation rates among ENP type, salinity and aging time.
To study sorption behaviour of perfluorooctane sulfonate (PFOS), the effects of pH, Ca2+ concentration and aqueous PFOS concentration on the sorption of PFOS to sediment and to multiwalled carbon nanotubes (MWCNT) present in the sediment were determined (Chapter 4). Log Kd values for PFOS to MWCNTs were relatively low, i.e. 1.92 – 2.90 L kg-1, because sediment organic matter (OM) fouling affected the interactions between PFOS and MWCNTs.
The sorption of 17 polychlorinated biphenyls (PCBs) to 10-180 μm polyethylene (micro-PE), 70 nm polystyrene (nano-PS), MWCNTs, C60 and a natural sediment was studied (Chapter 5). Isotherms in fresh- and seawater with and without the presence of sediment were measured to assess the effects of salinity and sediment organic matter on sorption. PCB sorption to sediment OM and micro-PE was linear, whereas sorption to nano-PS and MWCNTs was non-linear. Sorption to the latter sorbents and to C60 was much stronger than to OM and micro-PE. Especially for MWCNTs, presence of sediment reduced sorption, because of fouling with dissolved organic matter (DOM). Sorption of PCBs to sediment and MWCNTs decreased with increasing salinity, whereas it increased for micro-PE and nano-PS, suggesting a different influence on smooth polymer-based particles compared to heterogeneous surfaces of sediment and MWCNT aggregates.
Several standard ecotoxicity tests were performed for 7 types of ENPs i.e. TiO2, ZrO2, Al2O3, CeO2, C60, single-walled carbon nanotubes (SWCNTs) and polymethylmethacrylate (PMMA) (Chapter 6). Nominal concentration of up to 100 mg L-1 did not show any considerable effect. The rapid aggregation resulted in low free ENP concentrations, which explained that no effects were observed. Because ENPs are colloids, it was suggested that approaches based on the concepts of colloid chemistry should be applied instead of the bioavailability concepts used for convention chemicals.
For better ecological realism, a long term field experiment was performed to study the effects of MWCNT contaminated sediment on the recolonization of natural benthic macroinvertebrate communities (Chapter 7 and 8). The results after 3 months of exposure, showed no adverse effects up to 2 g kg-1 MWCNTs in the sediment (Chapter 7). After longer exposure however (Chapter 8) significant effects were observed already at the lowest dose of 0.002 g kg-1, suggesting that in the long term MWCNTs can affect the composition of natural benthic communities at much lower concentrations than those detected using shorter term single species toxicity tests. A parallel experiment performed with activated carbon (AC) observed similar effects, but AC was applied at a 50 times higher maximum dose, suggesting that the benthic community was more sensitive to MWCNTs than to AC.
Several implications of ENPs for the aquatic environment were identified (Chapter 9). The sedimentation and heteroaggregation rates of ENPs in presence of NC and SS in different natural waters were used to estimate the retention of ENPs in lakes. Lakes with a high Inverse Areal Hydraulic Loading (IAHL; d m-1), i.e. tendency for sedimentation, showed a higher retention for ENP. The data for PCB and PFOS sorption to the carbon-based ENPs were used to estimate the retention of PCBs and PFOS due to ENPs. This contribution of ENPs on the retention of these chemicals was shown to be generally negligible and will most likely not contribute to an increased risk. A summary of effect thresholds (PNEC) from single species toxicity tests was provided, which were compared with model-prediction based exposure concentrations (PEC). The resulting PEC/PNEC ratio was roughly estimated for 2125 ranging from 6.7·10-6 for CNT to 3.2·10-3 for Ag. Although this suggests that an actual potential risk for these ENPs is not expected in the near future, these results should be interpreted with care because of the large uncertainties in these PEC/PNEC ratios. Furthermore, the community study observed effects at much lower concentrations, concentrations that can be considered environmentally relevant. It is recommended to further develop analytical methods, fate and exposure models and ecotoxicity tests for ENPs in the aquatic environment, with more emphasis on long term in situ effects on the community level.
|Trefwoorden (cab)||microplastics / polychloorbifenylen / nanotechnologie / adsorptie / ecotoxicologie / aquatisch milieu / verontreinigde sedimenten / aquatische ecologie|
|Toelichting||De productie en het gebruik van synthetische nanodeeltjes (ENPs) nemen toe en veroorzaken toenemende emissies naar het milieu. Dit proefschrift richt zich op de implicaties van ENPs in het aquatisch milieu, met de nadruk op het sediment, omdat er wordt verwacht dat ENPs hoofdzakelijk in het aquatisch sediment terecht zullen komen. ENPs kunnen directe effecten veroorzaken op organismen in het aquatisch milieu, indirecte effecten op het levensgemeenschap niveau en/of voedselweb en kunnen effecten op het gedrag en de risico’s van andere contaminanten hebben. Om de risico’s van ENPs vast te stellen, is niet alleen informatie nodig over het gevaar, oftewel de kans op een effect, maar ook over de kans op blootstelling.|
WUR, Leerstoelgroep Aquatische Ecologie en Waterkwaliteitsbeheer