Including nanoparticle mixtures in human health risk assessment
Article first published online: 28 DEC 2013
© 2013 SETAC
Integrated Environmental Assessment and Management
Volume 10, Issue 1, page 144, January 2014
How to Cite
Khanna, I. and Kumar, A. (2014), Including nanoparticle mixtures in human health risk assessment. Integr Environ Assess Manag, 10: 144. doi: 10.1002/ieam.1498
- Issue published online: 28 DEC 2013
- Article first published online: 28 DEC 2013
This Learned Discourse comments on the assessment of carbon nanoparticles (NPs: fullerenes and carbon nanotubes) from air under current human health risk assessment (HHRA) procedures, and presents the case for considering simultaneous exposures of different NPs. A modification in the steps for conducting HHRA of NPs is suggested. Specifically, for both exposure and effects assessments, the possible co-occurrence of NPs and combined toxicity should be considered.
Nanoparticles (NPs), particles that have at least one dimension in the 1- to 100-nm range, can occur as mixtures in air. The possibility of human exposure by inhalation to mixtures of NPs needs to be considered in HHRA. However, it is not clear that the exposure and effects assessment stages of an HHRA adequately consider mixtures of NPs in air.
CNPs, such as carbon nanotubes (CNTs) and fullerenes, are emitted into the environment during combustion processes and co-exist in air (Murr and Garza 2009; Gottschalk et al. 2009). For example, Murr and Garza (2009) found that 40% of the outdoor fine particulate matter consisted of fullerene and multi-walled CNTs; concentrations were approximately 105 m−3 above natural gas burners in kitchens compared with ambient concentrations in the range of 102 to 103 m−3. Thus, a person working in such kitchens would be exposed to both types of CNPs simultaneously. Exposure and the possibility of effects would depend on factors such as CNP concentration in air, air inhalation rate, and toxicities of CNTs and fullerenes absorbed to lung tissue (Murr and Garza 2009; Aschberger et al. 2011).
Although studies have determined the toxicity of either only CNTs or only fullerene by using animal models (and thus giving information on CNP concentrations producing toxicity), the toxicity of a mixture of CNTs and fullerene remains to be determined. Given the possibility of exposures of different NPs simultaneously from the environment and exposures of new aggregates formed during interaction of these NPs in the environment, it is important to decide whether to include possible simultaneous exposures of different NPs in a HHRA.
Current risk assessments of NPs focus on the effects of a single NP (Aschberger et al. 2011), probably due to lack of data on the co-occurrence of different NPs in the environment and of the toxicity of such mixtures. Some studies have estimated risk to be negligible without considering possible mixture effects. For example, Gottschalk et al. (2009) reported a hazard quotient for individual exposures of CNTs or fullerene to be less than 1 (i.e., no hazard and thus no risk) but did not consider possible mixture effects.
The USEPA (2000) Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures recommended incorporation of toxicity data for chemical mixtures. Qualitative analysis of interactions among contaminants is recommended in the absence of quantitative data (Teuschler 2007).
Figure 1 presents a schematic of proposed modifications in the steps for conducting an HHRA of inhalation exposures of different NPs. At the initial exposure assessment (Step 2) and later in the assessment (Step 6), the possibility of mixture exposure and effects need to be considered. There is a pressing research need to assess potential mixture effects of NPs to humans by means of inhalation (and other) exposure.
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