Evaluation
of Exposure Concentrations Used in Assessing Manufactured Nanomaterial
Environmental Hazards: Are They Relevant?
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Abstract
Manufactured
nanomaterials (MNMs) are increasingly produced and used in consumer
goods, yet our knowledge regarding their environmental risks is limited.
Environmental risks are assessed by characterizing exposure levels
and biological receptor effects. As MNMs have rarely been quantified
in environmental samples, our understanding of exposure level is limited.
Absent direct measurements, environmental MNM concentrations are estimated
from exposure modeling. Hazard, the potential for effects on biological
receptors, is measured in the laboratory using a range of administered
MNM concentrations. Yet concerns have been raised regarding the “relevancy”
of hazard assessments, particularly when the administered MNM concentrations
exceed those predicted to occur in the environment. What MNM concentrations
are administered in hazard assessments and which are “environmentally
relevant”? This review regards MNM concentrations in hazard
assessments, from over 600 peer-reviewed articles published between
2008 and 2013. Some administered MNM concentrations overlap with,
but many diverge from, predicted environmental concentrations. Other
uncertainties influence the environmental relevance of current hazard
assessments and exposure models, including test conditions, bioavailable
concentrations, mode of action, MNM production volumes, and model
validation. Therefore, it may be premature for MNM risk research to
sanction information on the basis of concentration “environmental
relevance”