The following section provides a more detailed overview of the scientific methods that will be used to conduct the HHRA. This material is excerpted from the Terms of Reference for the study. To read the complete document, please click here.

The HHRA for the town of Flin Flon, Manitoba and Creighton, Saskatchewan, will be conducted

according to widely accepted HHRA methodologies and guidance published and endorsed by

such agencies as the Health Canada Guidance on Human Health Preliminary Quantitative Risk

Assessment (Health Canada, 2004), and the United States Environmental Protection Agency

Risk Assessment Guidance for Superfund (U.S. EPA, 1989) in addition to various HHRA

guidance updates published by U.S. EPA from the early 1990s to the present.

Given that there is evidence to warrant further assessment of risks to humans as a result of the

presence of certain metals in soil above CCME guidelines, and there is uncertainty regarding

the potential risks associated with other metals found to be elevated in soils, the objectives of

the HHRA are as follows:

Objective 1: To assess risks to human receptors residing in Flin Flon, Manitoba and

Creighton, Saskatchewan as a result of exposure to metals in soil and other environmental

media impacted by the activities of the HBMS complex. The HHRA will estimate the

contribution from individual exposure pathways and environmental media to assist in the

development of risk management objectives; and

Objective 2: Develop risk management objectives and/or mitigation plans if unacceptable

risk levels are identified in the HHRA. These risk management plans will be based on

scientific approaches in consultation with the Technical Advisory Committee and the community.

HHRA framework

The HHRA framework to be applied at this site will follow the standard HHRA framework that is

composed of the following steps:

i) Problem formulation

ii) Exposure assessment

iii) Hazard assessment

iv) Risk characterization

Problem Formulation Stage

This first step in the HHRA process is an information gathering and interpretation stage that

plans and focuses the study on critical areas of concern for the site or area being evaluated.

Problem Formulation defines the nature and scope of the work to be conducted, permits

practical boundaries to be placed on the overall scope of work and ensures that the assessment

is directed at the key areas and issues of concern.

The key tasks requiring evaluation within the problem formulation step include the following:

• Site Characterization – delineation of study area, and review of available site data to

identify factors affecting the availability of contaminants to potential receptors, such as

location and medium of contamination.

• Identification of Chemicals of Potential Concern (COPCs) - identification of the

chemicals of potential concern based on site environmental monitoring data.

• Receptor Characterization - identification of “receptors of concern”, which in this study

include those persons with the greatest probability of exposure to chemicals from the

site and those that have the greatest sensitivity to these chemicals.

• Identification of Exposure Pathways – consideration of various factors that influence the

means by which receptors come into contact with COPCs in environmental media

including: chemical-specific parameters, such as solubility and volatility; characteristics

of the site, such as physical geography, geology, and hydrogeology; as well as the

physiology and behaviour patterns of receptors.

Exposure Assessment

The exposure assessment evaluates data related to all chemicals, receptors and exposure

pathways identified during the problem formulation phase of the HHRA. The primary objective

of the exposure assessment is to predict, using site-specific data and a series of conservative

assumptions, the rate of exposure (i.e., the quantity of chemical and the rate at which that

quantity is received) of the selected receptors to the COPCs via the various exposure scenarios

and pathways identified in the problem formulation step.

Relevant environmental media include:

• Surface soil;

• Indoor dust;

• Outdoor/Indoor air

• Home grown produce (i.e., fruits, leafy vegetables, root crops);

• Market basket foods (from non-local sources);

• Locally caught fish;

• Locally harvested wild berries;

• Drinking water; and

• Surface water.

Hazard Assessment Stage

Toxicity is the potential for a chemical to produce any type of damage, permanent or temporary,

to the structure or functioning of any part of the body. The toxicity of a chemical depends on the

amount of chemical taken into the body (referred to as the “dose”) and the duration of exposure

(i.e., the length of time the person is exposed to the chemical). For every chemical, there is a

specific dose and duration of exposure necessary to produce a toxic effect in humans (this is

referred to as the “dose-response relationship” of a chemical). The toxic potency of a chemical

(i.e., its ability to produce any type of damage to the structure or function of any part of the

body), is dependent on the inherent properties of the chemical itself (i.e., its ability to cause a

biochemical or physiological response at the site of action), as well as the ability of the chemical

to reach the site of action (i.e., bioavailability). The dose-response principle is central to the

HHRA methodology.

Exposure limits for this project will be selected from reputable regulatory agencies, with

recognized experience and expertise in the derivation of exposure limits to protect human health

(e.g., Health Canada, U.S. EPA, ATSDR, WHO, Cal EPA OEHHA, OMOE, etc). The exposure

limits selected for this HHRA will be scientifically defensible and those routinely accepted and

used by government departments on HHRAs conducted in Canada and elsewhere. In selecting

the limits, the scientific basis and date of last major review will be among the considerations.

Risk Characterization Stage Calculation of Risk Levels

The risk characterization step integrates the exposure and hazard assessments to provide a

conservative estimate of human health risk for the receptors assessed in the various exposure

scenarios. Potential risk will be characterized through a comparison of the estimated or

predicted exposures from all pathways (from the Exposure Assessment) with the identified

exposure limits (from the Hazard Assessment) for all chemicals of potential concern.