Estimating Exposure Point Concentrations (EPCs)

The Olympic Mountains provide a backdrop to the historic pulp mill located along the waterfront of the city of Port Townsend.

Introduction

The online Public Health Assessment Training (PHAT) teaches you that an exposure point concentration, commonly referred to as an EPC, is a concentration of a contaminant that is representative of exposures for the population being evaluated. An EPC is calculated for each

Exposure unit or area,
Individual completed and potential exposure pathway, and
Exposure duration: acute (0-14 days), intermediate (15-364 days), or chronic (365 or more days).

You’ll need to know the detailed information in this primer when performing an exposure evaluation.

Let’s look at the public health evaluation process, and see where the topic in this primer—estimating EPCs—fits in. This flowchart highlights part of the process.

Public health evaluation process flowchart highlighting the step of estimating exposure point concentration

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Identify completed, potential and eliminated exposure pathways
Define exposure units to evaluate, as appropriate
Compile data for each contaminant in each completed and potential exposure pathway (by exposure unit, if appropriate)
Perform a screening analysis to identify potential contaminants of concern requiring further evaluation
Estimate exposure point concentration (EPC) for each potential contaminant of concern in each completed and potential exposure pathway
Calculate doses using the EPC or adjust air concentrations by duration
Calculate hazard quotients (HQs) for noncancer hazards and see if >1
Calculate cancer risks (CRs) for carcinogens and see if >1.0E-6
Perform tox evaluation for contaminants with HQ>1 or CR>1 E-6, no health guidelines, no cancer risk values for known or suspected carcinogens, community concern, or other factors that warrant it
Evaluate health outcome data, if available and appropriate for site
Summarize health effects evaluation findings, including discussing uncertainty

Note: As mentioned in the “Exposure Units Primer,” the sequences of steps laid out in the previous figure may differ slightly, depending on site factors.

The next section will provide an overview of the EPCs.