Figure 1. Approach #1: creating a meaningful health risk reduction zone using RHITotal (dimensionless) and occurrence (percent of the population exposed) as
separate parameters. The left side of the graph (left of the dotted line, without an x-axis label) are the alternate PFAS RHI values representing the varying proposed
regulatory limits for PFOA and PFOS and the corresponding RHITotal concentrations. Approach #2: calculating a threshold PopRHI value by multiplying health
impact and occurrence (percent population exposed * RHI). Both models include all contaminants with sufficient data that have regulatory determinations. The
PFOS and PFOA RHI calculations based on the concentrations currently set by EPA (70 ng/L each) are included as pending to assist in determining corresponding
regulatory zones.
22 SOURCE winter 2022
PFAS: HEALTH RISK REDUCTION?
Introduction
Every five years, USEPA prepares
a Contaminant Candidate List (CCL) of
all known contaminants that require
further evaluation. PFOA and PFOS,
the two most extensively studied per-
and polyfluoroalkyl substances, were
included in the fourth CCL (CCL4) and
were the only contaminants receiving
positive regulatory determinations as
part of CCL4. Research has shown that
elevated levels of exposure to these
compounds can lead to several adverse
health outcomes, including hepatic,
cardiovascular, endocrine, immune,
reproductive and developmental effects.
A positive regulatory determination
by the USEPA for a specified drinking wa-ter
contaminant must meet three criteria:
considerable contaminant toxicity; na-tional
contaminant occurrence; and pres-ent
a meaningful opportunity for health
risk reduction. This third criterion is sub-jective
and comes at the sole judgment of
the USEPA administrator, without a stan-dard
metric for assessing “meaningful
opportunities for health risk reduction.”
In this research, we attempt to calculate
historical levels of “meaningful” using
retrospective analyses of previously reg-ulated
contaminants and a comparative
Relative Health Impact (RHI) metric, and
contextualize the proposed regulatory
levels of PFOA and PFOS.
Relative Health Indicator
metric development
The Relative Health Indicator (RHI)
metric was developed as a simplistic tool
to assist water utilities and regulatory
policymakers contextualize current
regulated contaminants and prioritize
and communicate health risk reduction
strategies. The RHI metric consists of