www.ca-nv-awwa.org 23
both a non-cancer RHI and a cancer
RHI calculated separately based on
contaminant toxicity, severity outcomes
and population exposure estimates related
to contaminant concentrations. These
values are added to provide a total RHI
value. While certainly with limitations, the
RHI metric provides an accounting process
that normalizes all contaminant risk onto
a single, comparable scale — something
not currently done for estimating
drinking water contaminant risk in the
regulatory process. It is important to note
that the metric is not intended to replace
epidemiological studies or concerns, but
rather the intent is to create a normalized
scale to compare health risk reduction that
is possible from proposed and established
regulations. The RHI metric development
methodology details have been described
elsewhere (Seidel et al., 2014).
Occurrence and
toxicity analysis
To assess the national occurrence
of the contaminants included in this
study, we obtained estimates from a wide
variety of sources. Arsenic and uranium
provide context for current regulated
contaminants, establishing high and
low RHI metrics. Population-based
occurrence estimates of arsenic and
uranium before the enforcement date of
the revised regulations were calculated
using the data from USEPA’s second Six-
Year Review. In addition to arsenic and
uranium, we included all contaminants
with sufficient information that have
come under review as part of the USEPA
Regulatory Determination adjudication
process in our analysis. We used
occurrence estimates contained within
the USEPA Regulatory Determination
adjudication process for the unregulated
contaminants we included.
Toxicological data including RfD, UF
and critical effects were either obtained
from the USEPA Integrated Risk Infor-mation
System (IRIS) or collected from
the regulatory determination assess-ments
and individual health assessment
reports. Of the 37 contaminants included
in the four published regulatory determi-nations,
14 contaminants were included
in the analysis (arsenic, uranium, aldrin,
dieldrin, hexabhlorobutadiene, manga-nese,
naphthalene, boron, 1,3-dichloro-propene,
2,4-dinitrotoluene, 1,1,2,2-tetra-chloroethane,
perchlorate, nitrobenzene
and RDX), as well as PFOA and PFAS
calculated according to the EPA, ATSDR,
and CA toxicological values. The remain-ing
23 contaminants either contained no
occurrence data, no toxicological data
PFAS: HEALTH RISK REDUCTION?
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