Academic journal article Environmental Health Perspectives

Online Serum PFOA Calculator for Adults

Academic journal article Environmental Health Perspectives

Online Serum PFOA Calculator for Adults

Article excerpt

Introduction

Perfluorooctanoic acid (PFOA) is a synthetic hydrocarbon and a common environmental contaminant as a result of the long use of its ammonium salt in the manufacturing and processing of fluoropolymers used in cookware, waterproof fabrics, food packaging, and other applications (IARC 2016). Recent reviews of the toxicological and epidemiological literature have concluded that PFOA is known to be toxic to human reproduction and development (Lam et al. 2014) and a presumed immune hazard to humans (NTP 2016), possibly carcinogenic to humans (Benbrahim-Tallaa et al. 2014; IARC 2016), and probably linked to kidney cancer, testicular cancer, ulcerative colitis, thyroid disease, hypercholesterolemia, and pregnancy-induced hypertension in a highly exposed community in the eastern United States (C8 Science Panel 2012).

PFOA has been found in air samples and water supplies around the world (IARC 2016) and was detected in >95% of blood samples in the U.S. 2011-2012 National Health and Nutrition Examination Survey at a median concentration of 2.08ng/mL (CDC 2017). A national water testing program recently revealed (Hu et al. 2016) that the toxicant is present in >100 public water systems and that about 6 million U.S. residents are supplied with drinking water at concentrations exceeding the U.S. Environmental Protection Agency (EPA) health advisory limit of 70ng/L (U.S. EPA 2016) for the sum of PFOA and perfluorooctanesulfonic acid (PFOS).

By how much do we expect a person's serum PFOA concentration to increase from drinking PFOA-contaminated water, how quickly does it increase, and how long will it take to return to "normal" serum levels after switching to filtered or bottled water? A modified one-compartment exponential decay model with adjustment for background exposures adequately describes the relationship between PFOA intake and serum concentrations in adults (Olsen et al. 2007; Bartell et al. 2010; Bartell 2012). But this calculation may be unfamiliar or beyond the reach of some researchers, physicians, and journalists and the millions of people who have consumed PFOA-contaminated water.

This article describes an online Javascript serum PFOA calculator, available at http://www.ics.uci.edu/~sbartell/pfoacalc.html, that makes this pharmacokinetic model accessible and easy to use by anyone who wants to understand the relationship between consumption of contaminated drinking water and the resulting changes in blood serum concentration over time. In brief, users enter a water PFOA concentration and an initial serum PFOA concentration, and the web calculator returns results based on the modified one-compartment model for adults. Advanced users can select alternative estimates for the pharmacokinetic parameters and background contribution to serum PFOA.

Discussion

The mathematical solution for a one-compartment pharmacokinetic model with a constant exposure rate is well known (Thuresson et al. 2006; Bartell 2012):

[C.sub.t] = [C.sub.[infinity]] + ([C.sub.0] - [C.sub.[infinity]])[e.sup.-kt],

where [C.sub.t] is the serum toxicant concentration at time t, [C.sub.[infinity]] is the serum toxicant concentration at steady state (i.e., after enough time has passed for the serum concentration to stabilize after continuous exposure), [C.sub.0] is the initial serum toxicant concentration, and k is the elimination rate constant. k is related to the biological half-life through the expression k = ln(2)/[t.sub.1/2], where [t.sub.1/2] is the half-life. Although any consistent set of units can be applied, the web calculator uses units of nanograms per milliliter for serum PFOA concentrations, per year for the elimination rate constant, and years for time. For the web calculator, users enter [C.sub.0] in the first field, labeled "Starting serum PFOA concentration" (Figure 1). The other values are entered or calculated as described below.

Average biological half-lives for PFOA reported in previous human studies range from 2. …

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