Published 27 June 2026 • By Dr. Megan Tranter
Air monitoring quantifies the concentration of a contaminant in the worker’s breathing zone, but it cannot directly answer the question that matters most to health: how much of the agent has actually entered the body. Biological monitoring closes this gap by measuring the agent, its metabolites, or a biochemical effect in biological media such as blood, urine, or exhaled breath. In doing so, it integrates exposure across all routes, including inhalation, dermal, and ingestion, and accounts for individual differences in workload, respiratory rate, and the use of personal protective equipment. The ACGIH Biological Exposure Indices (BEIs) provide the interpretive framework that makes these measurements actionable.
What You’ll Learn
- Why biomonitoring measures internal dose rather than external exposure.
- What the ACGIH Biological Exposure Indices represent and how to interpret them.
- How biomarker selection and sampling time depend on toxicokinetics.
- How large harmonized programs have advanced guidance values for biomonitoring.
- How to run a defensible biomonitoring program under proper medical oversight.
Introduction
For agents that enter the body through the skin or through inadvertent ingestion or inhalation, an air sample tells only part of the story. Biological monitoring measures what the body has actually absorbed, making it uniquely suited to confirm whether a control program is working in practice. This article explains how biomonitoring moves from air concentration to absorbed dose, what the Biological Exposure Indices mean, how to choose and time biomarkers correctly, what population initiatives have contributed, and how to operate a biomonitoring program responsibly.
From Air Concentration to Absorbed Dose
The fundamental advantage of biomonitoring is that it measures internal dose rather than external exposure. Because a biomarker reflects what the body has absorbed, not merely what was present in the air, it captures contributions from the skin and inadvertent ingestion that air sampling cannot detect. This makes biomonitoring especially valuable for agents with significant dermal uptake, where airborne concentration may substantially understate total burden. The concept connects directly to dose, since the biomarker is, in effect, a measurement taken downstream of all recognized routes of entry. It also accounts for physiological variability between workers, because two people exposed to the same air concentration may absorb very different amounts depending on their breathing rate, workload, and use of protective equipment.
Biological Exposure Indices
The ACGIH BEIs are reference values representing the biomarker concentration expected in a healthy worker exposed by inhalation at the Threshold Limit Value. There are no sharp lines between safe and dangerous, but guidance values for interpreting results, accompanied by a specified biological medium and sampling time, whether end of shift, end of workweek, or prior to shift, reflecting the toxicokinetics of each agent. Classic examples include blood lead as a marker of inorganic lead exposure, urinary cadmium reflecting cumulative body burden, urinary mandelic acid for styrene exposure, and urinary methylhippuric acids for xylene exposure. Each pairing rests on an established quantitative relationship between exposure and biomarker. Because a BEI is a guidance value rather than a regulatory limit, results are interpreted in the context of the group and over time, not as a single pass-or-fail threshold for an individual.
Selecting and Timing Biomarkers
The validity of biomonitoring depends critically on choosing the right biomarker and sampling at the right time. Biomarkers may reflect recent exposure, such as a short-half-life metabolite sampled at the end of the shift, cumulative exposure, such as a substance sequestered in bone or kidney, or biological effect, such as inhibition of cholinesterase by organophosphates. Sampling time must align with the biomarker’s elimination kinetics; a metabolite cleared within hours yields meaningless data if collected days later. Pre-analytical factors, including creatinine correction for urine dilution, contamination control, and timing relative to non-occupational sources, must be rigorously managed. Diet, smoking, and environmental background can all contribute to a biomarker, so interpreting an elevated result requires distinguishing the occupational signal from these competing sources.
Population Initiatives and Guidance Values
Large-scale harmonized programs have advanced the science of biomonitoring beyond the individual workplace. The European Human Biomonitoring Initiative (HBM4EU) derived human biomonitoring guidance values for substances, including cadmium, and conducted occupational studies, such as biomonitoring of e-waste workers, measuring metals and organic compounds across exposed populations. These initiatives strengthen the toxicological basis for guidance values and demonstrate how biomonitoring informs both individual risk management and broader public health surveillance. By pooling data across countries and harmonizing laboratory methods, such programs also establish reference ranges for the general population, against which occupational cohorts can be compared.
What Industrial Hygienists Should Do
Industrial hygienists should deploy biomonitoring as a complement to, not a replacement for, air monitoring, particularly for lead, cadmium, mercury, solvents, and other agents with established BEIs or significant dermal uptake. Programs must specify the correct biomarker, biological medium, and sampling time, and must be conducted under medical oversight with informed worker consent and strict confidentiality. Results exceeding guidance values should trigger investigation of exposure pathways, including dermal contact and hygiene practices, rather than presumption of inhalation alone. This investigation often points back to the dermal route, and for lead in particular, it complements the medical surveillance described under lead exposure and biological monitoring. Trended over time, biomonitoring data provide a powerful, individualized confirmation that the overall control program is genuinely limiting absorbed dose.
Summary
Biological monitoring measures the absorbed dose that air sampling cannot detect, integrating exposure from inhalation, skin absorption, and ingestion. Interpreted through the ACGIH Biological Exposure Indices and supported by correct biomarker selection, careful sampling timing, and proper medical oversight, biomonitoring confirms whether a control program is genuinely protecting workers and flags the dermal and hygiene pathways that air data alone would miss.
Helpful Resources
- CDC: National Biomonitoring Program
- European Human Biomonitoring Initiative (HBM4EU)
- Related reading on this site: Dermal Exposure and Occupational Skin Disease and The Concept of Dose.
Bibliography
American Conference of Governmental Industrial Hygienists. (2026). 2026 TLVs and BEIs: Threshold limit values for chemical substances and physical agents and biological exposure indices. ACGIH.
Deutsche Forschungsgemeinschaft. (2023). List of MAK and BAT values. Wiley-VCH.
Lamkarkach, F., Ougier, E., Garnier, R., Viau, C., Kolossa-Gehring, M., Lewin, A., & Schoeters, G. (2021). Human biomonitoring initiative (HBM4EU): Human biomonitoring guidance values (HBM-GVs) derived for cadmium and its compounds. Environment International, 147, 106337. https://doi.org/10.1016/j.envint.2020.106337
Lauwerys, R. R., & Hoet, P. (2001). Industrial chemical exposure: Guidelines for biological monitoring (3rd ed.). CRC Press.
Manno, M., Viau, C., Cocker, J., Colosio, C., Lowry, L., Mutti, A., Nordberg, M., & Wang, S. (2010). Biomonitoring for occupational health risk assessment (BOHRA). Toxicology Letters, 192(1), 3-16. https://doi.org/10.1016/j.toxlet.2009.05.001
National Institute for Occupational Safety and Health. (2022). Adult Blood Lead Epidemiology and Surveillance (ABLES) program. NIOSH.
Occupational Safety and Health Administration. (n.d.). Lead standard, 29 CFR 1910.1025: Medical surveillance and blood lead monitoring. U.S. Department of Labor.
Snoj Tratnik, J., Kocman, D., Horvat, M., Andersson, A. M., Juul, A., Jacobsen, E., . . . Govarts, E. (2022). Cadmium exposure in adults across Europe: Results from the HBM4EU Aligned Studies survey 2014-2020. International Journal of Hygiene and Environmental Health, 246, 114050. https://doi.org/10.1016/j.ijheh.2022.114050
Plog, B. A., & Quinlan, P. J. (Eds.). (2012). Fundamentals of industrial hygiene (6th ed.). National Safety Council.
Scheepers, P. T. J., Duca, R. C., Galea, K. S., Godderis, L., Hardy, E., Knudsen, L. E., . . . Santonen, T. (2021). HBM4EU occupational biomonitoring study on e-waste: Study protocol. International Journal of Environmental Research and Public Health, 18(24), 12987. https://doi.org/10.3390/ijerph182412987
World Health Organization. (1996). Biological monitoring of chemical exposure in the workplace. WHO.