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Page 6 of 15 Greene et al. J Environ Expo Assess 2024;3:12 https://dx.doi.org/10.20517/jeea.2024.09

[9]
of age [Table 1]. In the breastfed scenario, the infant transitions from breastfeeding to drinking water at
1 year of age, and the model transitioned from the body weights based on nursing infants to those calculated
from water intake, resulting in an abrupt body weight increase of 0.8 kg (9%) in the breastfed infant scenario
at 1 year of age. To address this, in the 2024 model, the gradual upward trend of breastfed infant body
weights at 1 year of age was extended linearly for six months, at which point it matched the water intake-
based body weight value for the 1- to 2-year-old age group (10.5 kg).

Parameter updates
Changes to model parameters are summarized in Table 1. Updated values included water intake rates and
chemical-specific toxicokinetic parameters (e.g., half-life, placental transfer, breastmilk transfer). MDH
utilizes a Reasonable Maximum Exposure (RME) scenario in the development of HBGVs, which consists of
selecting a mix of upper percentile values (e.g., fluid intake rate) and central tendency values (e.g., half-life).
This is consistent with our program mission to develop drinking water guidance values that are protective
of sensitive and/or highly exposed population groups. For more information, see the original model
[9]
publication .

Water intake rates
Water intake rates were updated to reflect the most recent revision of the EPA Exposure Factors
[20]
Handbook , which provided revised intake values for all ages, including intake rates specific to formula-
fed infants and lactating women, and some changes to the age groupings for individuals over 16 years of age
[Table 1]. The 95th percentile intake rates were used to ensure that the resulting guidance values would be
protective of individuals with high water intake. Breastmilk intakes, unchanged from the previous version of
the model, were sourced from the most current breastmilk consumption data from the EPA Exposure
Factors Handbook . Using these data, body weights for each age group and population were calculated by
[19]
dividing intake (mL/day) by weight-normalized intake (mL/kg/day).

A literature search for published studies regarding PFOA serum half-life, placental transfer, and breastmilk
transfer was conducted, incorporating publications up to July 31, 2023. This cutoff date was necessary for
MDH to develop revised guidance values in the second half of 2023 for public release in early 2024. A search
for studies between August 2023 and January 2024 found no additional studies that would affect the selected
parameter values. Empirical data published since the development of the original 2017 model were
incorporated into the calculation and selection of central tendency chemical-specific parameter values.

Human half-life
A mean PFOA serum elimination half-life value of 902 days (2.47 years) from Li et al. was selected as a
central tendency value for humans . This value is based on serial blood samples collected over the course
[21]
of 4 years in a community in Ronneby, Sweden (n = 114, age range 4 to 84 years) that was exposed to
contaminated drinking water.

Placental transfer
Studies of placental transfer published since 2017 were incorporated into calculating a central tendency
value for the ratio of cord to maternal serum concentrations. An overall mean of 0.83 was calculated from
[22]
[23]
25 studies, with mean values in individual studies ranging from 0.32 to 1.44 . This value is similar to
central tendency values of 0.82 and 0.79 reported in review papers by Appel et al. and Pizzurro et al. .
[24]
[25]
For more information, refer to Supplementary Table 1.