In this issue of Environmental Health Perspectives, Berky et al. admirably present important research on cord blood levels of select environmental agents and subsequent adverse reproductive health outcomes within the artisanal communities of Madre de Dios in Peru.1 Their work is timely and adds to the health effects literature for lead and mercury.
In Table 3 of their paper, Berky et al. report cord blood levels of nine minerals and toxic metals. Eight of the agents are reported in units of mass per liter. Only lead is reported in units per deciliter—an age-old convention based on reasons lost in the mists of history. This table illustrates one of two reasons we believe it is time to shift the reporting unit for blood lead from micrograms per deciliter to micrograms per liter.
First, is equal to 1 ppb; parts per billion is commonly used to report biomarkers of other environmental contaminants, such as chemicals measured in the National Health and Nutrition Examination Survey and the Biological Exposure Indices established by the American Conference of Governmental Industrial Hygienists.2 In addition, as Table 3 demonstrates, expressing blood lead in micrograms per liter would make it simpler to compare with other metals and chemicals in human studies.
However, the primary benefit of changing the reporting standard is perception and communication. In 2021 the U.S. Centers for Disease Control and Prevention lowered the reference value for lead in blood from to .3 This reference level is often misinterpreted as a “safe” level, especially by the general public. However, if it were expressed using our proposed metric—as instead of —this misinterpretation may be easier to counteract. That is because people find it easier to think and communicate in integers than in numbers followed by decimals. This change would address the “whole number bias” associated with decimals whereby individuals often concatenate decimal values to a single whole integer (i.e., 1.1, 3.3, and 6.5 are perceived as 1, 3 and 6, respectively).4
Recent advances in analytical measurements, namely, inductively coupled plasma mass spectrometry, are generating values down to a fraction of a microgram. As testing continues to improve, and with continued reductions in blood lead concentrations, “larger” numbers will be easier for policy makers and the general public to understand. For example, a blood lead concentration of (the median blood lead level of U.S. children 6–10 years of age) may seem low. However, when viewed as , it is more readily apparent that further reductions are necessary to reach the goal of zero lead in human blood, which has been universally adopted by the medical and public health communities.
Already, more and more scientific manuscripts are reporting lead in micrograms per liter, and the trend is accelerating. Universally shifting the unit of measurement for lead in blood to micrograms per liter would make it is simpler to compare with other metals and chemicals in human studies.
Refers to https://doi.org/10.1289/EHP10557
References
- 1.Berky AJ, Weinhouse C, Vissoci J, Rivera N, Ortiz EJ, Navio S, et al. 2023. In utero exposure to metals and birth outcomes in an artisanal and small-scale gold mining birth cohort in Madre de Dios, Peru. Environ Health Perspect 131(9):097008, 10.1289/EHP10557. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.ACGIH (American Conference of Governmental Industrial Hygienists). 2001. TLVs and BEIs: Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati, OH: ACGIH. [Google Scholar]
- 3.CDC (Centers for Disease Control and Prevention). 2022. Blood Lead Reference Value. [Website.] Reviewed 2 December 2022. https://www.cdc.gov/nceh/lead/data/blood-lead-reference-value.htm [accessed 17 July 2023].
- 4.DeWolf M, Vosniadou S. 2015. The representation of fraction magnitudes and the whole number bias reconsidered. Learn Instr 37:39–49, 10.1016/j.learninstruc.2014.07.002. [DOI] [Google Scholar]