A review and perspective of existing research on the release of nanomaterials from solid nanocomposites.

Advances in adding nanomaterials to various matrices have occurred in tandem with the identification of potential hazards associated with exposure to pure forms of nanomaterials. We searched multiple research publication databases and found that, relative to data generated on potential nanomaterial hazards or exposures, very little attention has focused on understanding the potential and conditions for release of nanomaterials from nanocomposites. However, as a prerequisite to exposure studying release is necessary to inform risk assessments. We identified fifty-four studies that specifically investigated the release of nanomaterials, and review them in the following release scenario groupings: machining, weathering, washing, contact and incineration. While all of the identified studies provided useful information, only half were controlled experiments. Based on these data, the debris released from solid, non-food nanocomposites contains in varying frequencies, a mixture of four types of debris. Most frequently identified are (1) particles of matrix alone, and slightly less often, the (2) matrix particles exhibit the nanomaterial partially or fully embedded; far less frequently is (3) the added nanomaterial entirely dissociated from the matrix identified: and most rare are (4) dissolved ionic forms of the added nanomaterial. The occurrence of specific debris types appeared to be dependent on the specific release scenario and environment. These data highlight that release from nanocomposites can take multiple forms and that additional research and guidance would be beneficial, allowing for more consistent characterization of the release potential of nanomaterials. In addition, these data support calls for method validation and standardization, as well as understanding how laboratory release scenarios relate to real-world conditions. Importantly, as risk is considered to be a function of the inherent hazards of a substance and the actual potential for exposure, data on nanomaterial release dynamics and debris composition from commercially relevant nanocomposites are a valuable starting point for consideration in fate and transport modeling, exposure assessment, and risk assessment frameworks for nanomaterials.

The uncertainty of nanotoxicology: report of a Society for Risk Analysis Workshop.

A September 2008 workshop sponsored by the Society for Risk Analysis(() (1) ()) on risk assessment methods for nanoscale materials explored "nanotoxicology" in risk assessment. A general conclusion of the workshop was that, while research indicates that some nanoscale materials are toxic, the information presented at the workshop does not indicate the need for a conceptually different approach for risk assessment on nanoscale materials, compared to other materials. However, the toxicology discussions did identify areas of uncertainty that present a challenge for the assessment of nanoscale materials. These areas include novel metrics, characterizing multivariate dynamic mixtures, identification of toxicologically relevant properties and "impurities" for nanoscale characteristics, and characterizing persistence, toxicokinetics, and weight of evidence in consideration of the dynamic nature of the mixtures. The discussion also considered "nanomaterial uncertainty factors" for health risk values like the Environmental Protection Agency's reference dose (RfD). Similar to the general opinions for risk assessment, participants expressed that completing a data set regarding toxicity, or extrapolation between species, sensitive individuals, or durations of exposure, were not qualitatively different considerations for nanoscale materials in comparison to all chemicals, and therefore, a "nanomaterial uncertainty factor" for all nanomaterials does not seem appropriate. However, the quantitative challenges may require new methods and approaches to integrate the information and the uncertainty.

Blood mercury levels in US children and women of childbearing age, 1999-2000.

CONTEXT: Humans are exposed to methylmercury, a well-established neurotoxin, through fish consumption. The fetus is most sensitive to the adverse effects of exposure. The extent of exposure to methylmercury in US women of reproductive age is not known. OBJECTIVE: To describe the distribution of blood mercury levels in US children and women of childbearing age and the association with sociodemographic characteristics and fish consumption. DESIGN AND SETTING: The 1999-2000 data from the National Health and Nutrition Examination Survey, a cross-sectional survey of the noninstitutionalized US population. PARTICIPANTS: In 1999-2000, 1250 children aged 1 to 5 years and 2314 women aged 16 to 49 years were selected to participate in the survey. Household interviews, physical examinations, and blood mercury levels assessments were performed on 705 children (56% response rate) and 1709 women (74% response rate). MAIN OUTCOME MEASURE: Blood concentration of total mercury. RESULTS: Blood mercury levels were approximately 3-fold higher in women compared with children. The geometric mean concentration of total blood mercury was 0.34 micro g/L (95% confidence interval [CI], 0.30-0.39 microg/L) in children and 1.02 microg/L (95% CI, 0.85-1.20 microg/L) in women. Geometric mean mercury levels were almost 4-fold higher among women who ate 3 or more servings of fish in the past 30 days compared with women who ate no fish in that period (1.94 microg/L vs 0.51 microg/L; P<.001). CONCLUSIONS: Measures of mercury exposure in women of childbearing age and young children generally fall below levels of concern. However, approximately 8% of women had concentrations higher than the US Environmental Protection Agency's recommended reference dose (5.8 microg/L), below which exposures are considered to be without adverse effects. Women who are pregnant or who intend to become pregnant should follow federal and state advisories on consumption of fish.