Intake to Production Ratio: A Measure of Exposure Intimacy for Manufactured Chemicals

Abstract

Background: Limited data are available to assess human exposure to thousands of chemicals currently in commerce. Information that relates human intake of a chemical to its production and use can help inform understanding of mechanisms and pathways that control exposure and support efforts to protect public health.Objectives: We introduce the intake-to-production ratio (IPR) as an economy-wide quantitative indicator of the extent to which chemical production results in human exposure.Methods: The IPR was evaluated as the ratio of two terms: aggregate rate of chemical uptake in a human population (inferred from urinary excretion data) divided by the rate that chemical is produced in or imported into that population’s economy. We used biomonitoring data from the U.S. Centers for Disease Control and Prevention along with chemical manufacturing data reported by the U.S. Environmental Protection Agency, as well as other published data, to estimate the IPR for nine chemicals in the United States. Results are reported in units of parts per million, where 1 ppm indicates 1 g of chemical uptake for every million grams of economy-wide use.Results: Estimated IPR values for the studied compounds span many orders of magnitude from a low of 0.6 ppm for bisphenol A to a high of > 180,000 ppm for methyl paraben. Intermediate results were obtained for five phthalates and two chlorinated aromatic compounds: 120 ppm for butyl benzyl phthalate, 670 ppm for di(2-ethylhexyl) phthalate, 760 ppm for di(n-butyl) phthalate, 1,040 ppm for para-dichlorobenzene, 6,800 ppm for di(isobutyl) phthalate, 7,700 ppm for diethyl phthalate, and 8,000–24,000 ppm (range) for triclosan.Conclusion: The IPR is well suited as an aggregate metric of exposure intensity for characterizing population-level exposure to synthesized chemicals, particularly those that move fairly rapidly from manufacture to human intake and have relatively stable production and intake rates.

Model for Screening-Level Assessment of Near-Field Human Exposure to Neutral Organic Chemicals Released Indoors

“…20 Intake-to-production ratio, a semiempirical metric linking chemical intake inferred from biomonitoring data to manufactured chemical production volumes, has been proposed to screen for potential human population exposure. 23 Chemical properties and use patterns were found to influence human exposure indoors. 23 Models have been applied to assess exposure to select semivolatile organic chemicals (SVOCs) based on estimates of actual chemical use and release information.…”

“…23 Chemical properties and use patterns were found to influence human exposure indoors. 23 Models have been applied to assess exposure to select semivolatile organic chemicals (SVOCs) based on estimates of actual chemical use and release information. 21 Chemicals requiring evaluation display, however, a much greater range of properties than is represented by SVOCs.…”

Criteria pollutant impacts of volatile chemical products informed by near-field modelling

“…While most direct exposure to VCPs for people 28 will be in the indoor environment, ecosystem and other environmental exposure (e.g. secondary pollutants) resulting from VCPs will be dominated by the far-field environment 27 , 29 , 30 . Far-field exposure due to residential and commercial releases of VCPs and their resulting criteria pollutant formation are not considered in current chemical exposure estimates 28 .…”

Embracing microbes in exposure science

“…Triclosan presents a challenging case for exposure science. Its widespread incorporation into household and personal care products such as soaps and toothpastes have contributed to a high level of exposure intimacy [85]. Concerns have been raised about triclosan as a possible endocrine disrupting compound [86] and as a contributor to antibacterial resistance in environmental media, such as indoor dust [87].…”