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"Do occupational exposures to engineered nanoparticles pose an unintended risk of adverse health effects?" This is not an abstract or theoretical question that prac titioners have the luxury of debating for years before it becomes a reality. Nanotech nology is a reality, with potential for great growth in the 21st Century. Workers are already engaged in processes in which they may be exposed to materials that never existed before in nature. We do not fully know how these engineered nanoparticles may enter the body, where they may travel once inside, or what effects they may have on the body' s systems. We do not fully know whether or how effects may differ for chemically or structurally different particles at the nanoscale. Diverse stakeholders have agreed that research to address these questions is essential for the responsible development of nanotechnology.
As research progresses to answer those questions, the National Institute for Oc cupational Safety and Health (NIOSH) has recommended prudent precautionary interim measures for reducing work-related exposures and assessing potential risk. In the hierarchy of prevention, it is important to consider where it may be of value to provide medical screening of workers who may be exposed to a potential health hazard, but who may be asymptomatic-that is, who have no identifiable symptom of an occupational disease. On the frontiers of nanotechnology, where as yet little data exist for assessing risk with confidence, it is difficult to recommend specific screening tests. NIOSH has sought a wide range of opinions on the matter and along with its own review of the scientific literature presents this interim guidance for medical screening and hazard surveillance. The evidence base on the health effects of engineered nanoparticles is rapidly growing and NIOSH will continue to monitor and assess it and will update those recommendations as more definitive information becomes available.

# Executive Summary
Concerns have been raised about whether workers exposed to engineered nanopar ticles are at increased risk of adverse health effects. The current body of evidence about the possible health risks of occupational exposure to engineered nanopar ticles is quite small. While there is increasing evidence to indicate that exposure to some engineered nanoparticles can cause adverse health effects in laboratory animals, no health studies of workers exposed to the few engineered nanoparticles tested in animals have been published. The purpose of this document from the Na tional Institute for Occupational Safety and Health (NIOSH) is to provide interim guidance about whether specific medical screening, including performing medical tests on asymptomatic workers, is appropriate for these workers.
Medical screening is only one part of what should be considered a complete safety and health management program. An ideal safety and health management program follows a hierarchy of controls and involves various occupational health surveil lance measures. Since specific medical screening of asymptomatic workers exposed to engineered nanoparticles has not been extensively discussed in the scientific lit erature, this document makes recommendations based upon what is known until more rigorous research can be performed.
Currently there is insufficient scientific and m edical evidence to recom m end the specific m ed ical screening o f w orkers p o ten tially exposed to engineered nanopar ticles. Nonetheless, this lack of evidence does not preclude specific medical screen ing by employers interested in taking precautions beyond existing industrial hygiene measures. If nanoparticles are composed of a chemical or bulk material for which medical screening recommendations exist, these same screening recommendations would be applicable for workers exposed to engineered nanoparticles as well. As research into the hazards of engineered nanoparticles continues, vigilant reas sessment of available data is critical to determine whether specific medical screen ing is warranted for workers. In the in te rim , the fo llo w in g recom m end ations are p ro v id e d fo r w orkplaces w here w orkers m ay be exposed to engineered nan o p ar ticles in the course o f th e ir w ork:
- Take p ru d e n t measures to co n tro l exposures to engineered nanoparticles.

# C o n d u c t h aza rd surveillance as the basis fo r im p le m e n tin g controls.
- C o n tin u e use o f established m ed ical surveillance approaches. NIOSH will continue to collect and evaluate new research findings and update its recom mendations about medical screening programs for workers exposed to nanoparticles.

# Introduction
Nanotechnology is a system of innovative methods for controlling and manipulating matter at the near-atomic scale to produce engineered materials, structures, and devices. Engineered nanoparticles are generally con sidered to include a class or subset of these manufactured materials with at least one di mension of approximately 1 to 100 nanome ters (www.nano.gov/html/facts/whatIsNano. html). At these scales, materials often exhibit unique properties beyond those expected at the chemical or bulk level that affect their physical, chemical, and biological behavior. The term "ultrafine" is also frequently used in the litera ture to describe particles with dimensions less than 100 nanometers that have not been inten tionally produced (e.g., manufactured) but are the incidental products of processes involv ing combustion, welding, or diesel engines. It is currently unclear whether a distinction in particle terminology is justified from a safety and health perspective if the particles have the same physicochemical characteristics. The potential occupational health risks associ ated with the manufacture and use of nanoma terials are not yet clearly understood. Many en gineered nanomaterials and devices are formed from nanometer-scale particles (i.e., nanopar ticles) that are initially produced as aerosols or colloidal suspensions. Exposure to these mate rials during manufacturing and use may occur through inhalation, dermal contact, or inges tion; however, inhalation exposure is the main route of concern . There is very limited information available about dominant exposure routes, the potential for exposure, and material toxicity.
At this time, society in general and companies in particular are faced with the dilemma of bal ancing a desire to expand a potentially boun tiful technology against the potential hazards that may result. The real risks from the technol ogy are not known, and the perceived risks are undetermined. In this regard, nanotechnology is no different from any other emerging tech nology. One of the first areas where exposures to engineered nanoparticles will occur is in the workplace. In the face of uncertainty about the hazards of nanoparticles, a corporate or soci etal response (such as implementing appropri ate occupational health surveillance measures) may assure the public that appropriate efforts are being taken to identify and control poten tial hazards in a timely fashion.
Concerned individuals from government, in dustry, labor, and academia, together with oc cupational health professionals and medical personnel, have raised questions about whether workers exposed to engineered nanoparticles should be provided some type of medical sur veillance. The purpose of this document is to 1 provide interim guidance concerning specific medical screening for these workers-that is, medical tests for asymptomatic workers-until additional research either supports or negates the need for this type of screening. The type and degree of screening recommended here is in addition to any medical surveillance taking place as part of existing occupational health surveillance efforts.

# Frequent Uses for Medical Surveillance
Medical examinations and tests are used in many workplaces to determine whether an employee is able to perform the essential NIOSH CIB 60 - Medical Screening of Workers functions of the job, with or without reason able accommodation, without posing a direct and imminent threat to the safety or health of the worker or others. Workplace medical ex aminations must be conducted in compliance with the Americans with Disabilities Act of 1990 (ADA) (Public Law No. 101-336). For example, this law prohibits making a job offer contingent upon the applicant' s submission to a medical examination. Still, medical examina tions and examinations conducted before plac ing a worker in a given job could potentially provide useful baseline information in a vari ety of ways. For example, even if there appears to be no reason for immediate concern about exposure to engineered nanoparticles in a par ticular workplace setting, this type of baseline data may benefit employers and workers alike if questions come up later regarding potential worker health problems associated with the specific engineered nanoparticle.
Medical surveillance of workers is also re quired by law when there is exposure to a spe cific workplace hazard. Although OSHA does not have a standard that specifically addresses occupational exposure to engineered nano particles, OSHA has a number of standards that require medical surveillance of workers. Workplaces with engineered nanoparticles comprised of chemicals addressed by current OSHA standards (Appendix B) are subject to the requirements of those standards, including the requirements for medical surveillance. In addition, medical surveillance of workers han dling engineered nanoparticles may also be triggered when workers are exposed to other hazardous substances (e.g., those listed in Ap pendix B) present in nanoparticle operations. NIOSH also recommends medical surveillance (including screening) of workers when there is exposure to certain occupational hazards (Ap pendix C). None of the hazards noted in Ap pendix C are identified as engineered nanopar ticles, but medical surveillance would apply to workers exposed to nanoparticles comprised of chemicals for which NIOSH has a recom mendation. The medical surveillance of these workers may provide useful information if questions arise in the future about the health effects of their exposure to nanoparticles.

# Hazard Surveillance and Risk Management
Hazard surveillance involves identifying poten tially hazardous practices or exposures in the workplace and assessing the extent to which they can be linked to workers, the effective The current body of evidence about the pos sible health risks of occupational exposures to engineered nanoparticles is not sufficient to support the determination of specific medical screening to identify preclinical changes asso ciated with exposure to engineered nanopar ticles. No substantial link has been established between occupational exposure to engineered nanoparticles and adverse health effects. In addition, the toxicological research to date is insufficient to recommend such monitoring, the appropriate triggers for it, or components of it. As the volume of research on the poten tial health effects from exposure to engineered nanoparticles increases, continual reassessment will be needed to determine whether medical screening is warranted for workers who are producing or using engineered nanoparticles. NIOSH will continue to examine new research findings and update its recommendations on medical screening programs for workers ex posed to nanoparticles. Appendix D provides a brief discussion concerning occupational health programs that include medical screening and might serve as a model for future reference for one or more engineered nanoparticles. Appen dix E provides discussion highlighting details of instances where sufficient evidence to support recommendations for specific medical screen ing for workers exposed to engineered nanopar ticles is lacking.

# Nanoscale Cadmium
Cadmium is a substance that has medical screen ing recommendations for workers exposed in or der to prevent or assess lung and kidney toxicity (see Appendices B and C). At a minimum, these recommendations should pertain to nanoscale cadmium (e.g., such as that used in the produc tion of quantum dots). Medical screening is typically triggered by the airborne concentra tion of the substance in the workplace (e.g., the "action level" concentration). An action level is some fraction, usually 50%, of an occupational exposure limit (OEL). Whether the action level concentration recommended for nonnanoscale cadmium particles is adequate for nanoscale cadmium is unknown. Workplaces with en gineered nanoparticles of materials addressed by current OSHA standards are subject to the requirements of those standards, including the requirements for medical surveillance.