Analysis of currently available data for characterising the risk of engineered nanomaterials to the environment and human health — Lessons learned from four case studies

Abstract

Production volumes and the use of engineered nanomaterials in many innovative products are continuously increasing, however little is known about their potential risk for the environment and human health.

We have reviewed publicly available hazard and exposure data for both, the environment and human health and attempted to carry out a basic risk assessment appraisal for four types of nanomaterials: fullerenes, carbon nanotubes, metals, and metal oxides (ENRHES project 2009¹). This paper presents a summary of the results of the basic environmental and human health risk assessments of these case studies, highlighting the cross cutting issues and conclusions about fate and behaviour, exposure, hazard and methodological considerations.

The risk assessment methodology being the basis for our case studies was that of a regulatory risk assessment under REACH (ECHA, 2008²), with modifications to adapt to the limited available data. If possible, environmental no-effect concentrations and human no-effect levels were established from relevant studies by applying assessment factors in line with the REACH guidance and compared to available exposure data to discuss possible risks. When the data did not allow a quantitative assessment, the risk was assessed qualitatively, e.g. for the environment by evaluating the information in the literature to describe the potential to enter the environment and to reach the potential ecological targets.

Results indicate that the main risk for the environment is expected from metals and metal oxides, especially for algae and Daphnia, due to exposure to both, particles and ions. The main risks for human health may arise from chronic occupational inhalation exposure, especially during the activities of high particle release and uncontrolled exposure. The information on consumer and environmental exposure of humans is too scarce to attempt a quantitative risk characterisation.

It is recognised that the currently available database for both, hazard and exposure is limited and there are high uncertainties in any conclusion on a possible risk. The results should therefore not be used for any regulatory decision making. Likewise, it is recognised that the REACH guidance was developed without considering the specific behaviour and the mode of action of nanomaterials and further work in the generation of data but also in the development of methodologies is required.

Introduction

Novel properties of materials that become evident within a size in the nanorange (at least one dimension less than 100 nm) make them attractive for exploitation in a wide spectrum of fields, including information technology, energy production, environmental protection, biomedical applications, food, agriculture and many more. The same distinctive chemical and physical properties of engineered nanomaterials (ENM) that make them so attractive for new product development have raised concern over their safety to health and environment.

The provisions of the current regulatory framework for chemical risk assessment and management in the European Union, the REACH regulation³ (Registration, Evaluation, Authorisation and Restriction of CHemicals) apply to engineered nanomaterials (EC (European Commission), 2008a, EC (European Commission), 2008b). However, the technical Guidance Document (ECHA, 2008) for preparing a chemical safety assessment (CSA REACH terminology for a risk assessment ultimately showing how risks can be controlled) currently include very little reference to substances in particulate and nano-forms.

Within the EU funded project ENRHES (Engineered Nanoparticles: Review of Health and Environmental Safety; Stone et al., 2009) a basic risk assessment appraisal was carried out for four different classes of nanomaterials, metals (with focus on nano-silver), metal oxides (with focus on nano-titanium dioxide (TiO₂) and nano-zinc oxide (ZnO; environment only)), fullerenes and carbon nanotubes (CNT), based on available information in the literature. Each type of substance, e.g. nano-silver, included different forms, e.g. differences in size and shape, crystalline form, functionalisation and purity, and these different forms can exhibit quite different properties.

The risk assessment appraisals were intended to follow the general approach specified in the REACH Guidance on Information Requirements and Chemicals Safety Assessment (ECHA, 2008) in a structure similar to the format for preparing a Chemical Safety Report under REACH, based on the four basic steps of a classical risk assessment: hazard identification, hazard characterisation, exposure assessment and risk characterisation. However, as the risk assessment for the four case studies was built on publicly available data and only limited information was available (specifically, a lack of knowledge on use, exposure and risk management measures in place, as well as data on inherent properties), the approach could not be followed in all details.

On basis of the identified information, the risk assessments for human health and environment have been carried out following a quantitative and/or a qualitative approach (see Fig. 1). The methodology for setting no-effect levels followed the relevant chapters of the REACH guidance (Chapter R.8 and R.10 in ECHA, 2008). For the environmental assessment, the quantitative approach requires the determination of the Predicted Environmental Concentration (PEC) and the Predicted No-Effect Concentration (PNEC) for each environmental compartment (air, water, and soil). For human health, the quantitative approach requires establishing exposure values for the various routes of exposure (inhalation, dermal and oral) for consumers and workers and the establishment of Derived No-Effect Levels (DNELs), typically based on the extrapolation of animal data to the human situation by using appropriate assessment factors.

To indicate the uncertainties associated with the derived values and that they consequently cannot and should not be used for any regulatory purposes we have decided to use the terms Indicative No-Effect Concentrations (INECs) instead of PNEC and Indicative No-Effect Levels (INELs) instead of DNELs. INECs have been compared to PECs of different compartments and INELs to human exposure estimates in order to identify potential risks. In case where no INEC or INEL and/or no exposure values were available or could be estimated, a qualitative risk assessment has been carried out. In addition to the quantitative risk assessment, we have proposed a qualitative ranking of the investigated ENM, based on exposure, use and hazard information.

This current paper presents a summary of the results of the environmental and human health risk assessment appraisals of the four case studies in the ENRHES project, highlighting the cross cutting issues and conclusions about fate and behaviour, exposure, hazard and some methodological considerations. The risk assessment appraisals were complemented with additional information, not yet considered in the ENRHES project. It should be noted, that the rapid increase in information of relevance for risk assessment of ENM may quickly alter conclusions. Details of the individual case studies can be found in the final report of the ENRHES project (Stone et al., 2009), in Aschberger et al., 2010a, Aschberger et al., 2010b and in Christensen et al., 2010a, Christensen et al., 2010b.