Investigating the ENvironmental impacts of TRANSformed engineered nanomaterials released from wastewater treatment plants

As the production, diversity and use of engineered nanomaterials (ENM) is increasing, there are corresponding increases in ENM emissions to wastewater treatment plants (WWTP) from domestic and industrial sources. Due to their dynamic nature, ENM undergo significant physicochemical transformations during transport through WWTPs and further when emitted to the natural environment. This leads to altered ENM characteristics, which can impact their environmental fate, bioavailability and effects on organisms. ENTRANS addresses the research challenge of understanding the environmental impacts of transformed ENM released from WWTP on organisms hosted in different relevant environmental compartments (soils and sediments). ENTRANS provides (i) an improved understanding of the behaviour and transformation of ENM following release from WWTPs, (ii) effects assessment of transformed ENM, and (iii) integration of data for modelling fate, exposure and toxicity. Isotopically enriched ENM, encompassing 68ZnO, 46TiO2, and 109Ag were successfully synthesized using methods developed within the project. Protocols using Inductively coupled plasma mass spectrometry (ICP-MS) were developed for determination of isotope ratios in various complex environmental matrixes and biota The use of isotopically labelled ENM allows their fate to be traced at low, environmentally relevant exposure concentrations used in ENTRANS, in the presence of high backgrounds of similar natural particles. Their fate and transformation were studied using a pilot WWTP operating with real municipal wastewater and the resulting effluent and sludge were used for fate, uptake and toxicity assessment evaluations using aquatic and terrestrial organisms. Sewage sludge from the pilot WWTP was applied to soil microcosms with earthworms, to study the behaviour in soil and transfer to organisms of environmentally relevant chemical forms of ENM. The sludge application rate was similar to that used in agriculture and the experiment lasted for a month. For 109Ag ENM, the dissolved fraction (i.e. the most easily accumulated in organisms) in sludge-amended soil was extremely low and comparable to that of Ag naturally present in sludge and soil, and transfer factors to earthworms were similar to those of natural Ag. For 68ZnO ENM, the dissolved fraction was 3-5 times higher than for Zn forms naturally present in soil, and transfer factors twice those of natural Zn. The immune cells of the exposed organisms were isolated in order to assess the immune-related responses on a cellular level. The first results showed an alteration in immune cell population and corresponding decrease in metabolic activity upon organism exposure to 109Ag and 68ZnO ENM- containing sludge. The uptake, fate and accumulation of the isotopically enriched ENM transformed through the WWTP was studied in the benthic amphipod (Hyalella azteca). The results showed that the WWTP processes reduce the availability of ENM. The inclusion of Au ENM in the experiments indicates that this decrease in ENM availability is attributed to both chemical changes and biological processes such as eco-corona formation. A method to generate artificially aged ENM was developed to compare the fate and toxicological effects of pristine and transformed ENM. Filter feeding bivalves were exposed to low concentrations of pristine and transformed Ag and TiO2 ENM for 20 days. Results analyzed so far show no effects on mortality, condition index, nutritional status and hemocyte cell populations (cell types and cell viability). Changes in digestive gland index were observed following aged Ag ENM exposure. Next steps include the assessment of ENM uptake, translocation and sublethal chronic effects on sediment-dwelling organisms, as such organisms are considered most at risk from ENM exposure. Sewage sludge from the pilot WWTP will be applied to soil microcosms with plants, to study the influence of plant roots and their exudates on speciation and bioavailability of environmentally relevant forms of ENM. The uptake, translocation and effects of pristine versus transformed ENM will be studied in vitro using cells representing the gill and gut allowing an in depth understanding of the uptake mechanisms and effects. The project outcomes will support the development of modelling and risk assessment tools for the sustainable development and use of nanotechnologies and ENM.

ENTRANS will study the transformation of engineered nanomaterials (ENMs) in wastewater treatment plants (WWTPs) and following their release in wastewater and sludge effluents, and how these transformations subsequently impact ENM bioavailability and toxicity to organisms from the soil and sediment environments considered the final sinks for ENMs. Isotopically labelled ENMs of ZnO, TiO2, Ag will be synthesized and used to differentiate ENM from natural particles at the low, environmentally relevant concentrations expected. The labelled ENM will allow transformation in a pilot WWTP system and biosolids that are applied to agricultural land to be studied more clearly, while their application as tracers will enable the potential uptake, biodistribution, depuration and impacts of ENM in different organisms to be studied more effectively. During the project the ENM occurrence and environmental levels will be determined in samples collected from WWTPs in Trondheim and Oslo and from sludge-amended soils. State of the art analytical and microscopy techniques will be employed to provide occurrence, form and exposure levels in WWTP biosolids applied in agricultural land in Norway, receiving soils and sediments. The transformation processes, exposure and uptake, biodistribution and toxicity data will be carefully generated so that the obtained results can be integrated into computational fate and exposure models and a risk assessment can be performed. During the project we will address key topics and bridge knowledge gap on sediment, soil health, nanomaterial transformation and environmental occurrence levels. The data generated during this study will be presented to stakeholders and interested parties and suggestions towards waste management will be provided. Moreover, the project will provide recommendations for OECD guideline developments and waste regulation supporting a more sustainable development and use of nanotechnology.