Environmental & Occupational Health

Chapter 27: Risk Assessment in Environmental Health

Objectives
Identify risk as a probability of adverse effect occurring.

Evaluate risk assessment process of organizing scientific information about hazard in to understand population exposure and vulnerability and to characterize the probability of adverse health effects.

Identify risk management as a separate but a related process of deciding on policy options to reduce uncertainty.

Risk Assessment
Risk is the probability that some adverse event will occur (Rodricks, 2006).

In environmental health, measures of risk directly or indirectly guide many public services and private activities. For example, avoiding adverse health impacts, or risks, from pathogens and chemical contaminants in water is the rationale for regulation and monitoring of drinking water supplies.

There are many factors that contribute to population risk, from socioeconomic factors to individual environmental exposures (Figure 27.1).
These factors combine to determine the background or baseline risk of a population.
For example, the baseline lifetime risk of cancer in the U.S. population is about one in three (American Cancer Society, 2014). Globally, one in eight deaths annually is due to air pollution exposure (WHO, 2014).

History
There is evidence that as far back as ancient times, that humans carefully evaluated risk, whether for the purposes of anticipating poor agricultural harvests, inauspicious weather patterns, or other adversities.

The period from 1950 to 1970 was one of heightened awareness of environmental impacts on health, which catalyzed the development of what we now see as environmental and risk assessment milestones (Figure 27.2).

Rachel Carson’s 1962 book, Silent Spring, widely popularized concern about long-term, low-dose chemical exposures, in particular to DDT.

History
In 1983, the National Academy of Science (NAS) published Risk Assessment in the Federal Government: Managing the Process (commonly referred to as the Red Book).

A landmark report by the National Research Council (NRC) of the National Academy of Sciences that brought the principles of evaluating environmental chemical risks to human health together for the first time, presenting them in a framework that formalized the risk assessment process and outlined its four key steps (NRC, 1983).

In the United States, public and media pressure from such awareness raising as well as from high-profile chemical accidents stimulated government action and led to Congressional passage of new laws regulating air and water and the creation of the U.S. Environmental Protection Agency (U.S. EPA).

The Red Book also established as a separate phase a risk management (RM) process. In risk management, decision makers choose appropriate health-protective policy options based not only on the scientific analysis of the RA but also on key nonscience criteria, such as net economic cost, institutional feasibility, and political and other factors.

Risk Assessment (EPA)

https://www.epa.gov/risk/about-risk-assessment#tab-2https://www.epa.gov/risk/about-risk-assessment#tab-2

Risk Assessment
The Silver Book makes a number of technical refinements in each of the four Red Book analytical steps.

In addition, in a key modification, it includes an up-front problem formulation step, which places the specific risk analysis being undertaken within the context of available policy options for managing risk.

The recommended risk assessment process now has five steps: (1) problem formulation, (2) hazard identification, (3) dose-response assessment, (4) exposure assessment, and (5) risk characterization. This RA process is then followed by a separate RM phase (Figure 27.3).

The risk assessment of the environmental health issues began in the 1970s with the passing of the environmental health laws. It would be very costly and impossible to create a society completely free of pollutants. Thus risk assessment is used to determine acceptable limits of concentration of pollutants in air, water, soil, biota and in emission from vehicles and industry.
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Problem Formulation
Problem Formulation: Problem formulation is a systematic planning step linked to the regulatory and policy context. It identifies the major factors to be considered in RA, and results in a conceptual model identifying sources, environmental stressors, and exposed populations; the relationships among these elements; and a detailed plan for the RA.

Introduction: The first step in any RA is designing its goals, scope, and technical requirements. In this step, policymakers and decision makers interact with stakeholders and technical risk assessors.

The problem formulation step defines the environmental health problem within the policy context and decides on the specific technical and analytical approach needed to carry out the RA.

Problem Formulation
Goal: Problem formulation aims to identify the issues to be assessed and the goals, breadth, depth, and focus of the risk assessment, and it also aims to establish the roles of the decision maker, stakeholders and risk assessor (NRC, 2009).

Methods and tools used: The main products of problem formulation are a conceptual model and an analysis plan for the RA, along with the technical details of how the analysis will be carried out.
The conceptual model identifies the detailed environmental stressors, pathways, sources, populations at risk, and potential adverse health effects.
The analysis plan defines the analytical approach for the RA, identifying how data on pollution sources will be located, which chemicals are of concern, how their exposure pathways will be assessed, how exposure concentrations will be estimated or measured, and what risk metrics will be used.

Problem Formulation
Methods and tools used: The analytical approach also maps out technical requirements, including what epidemiological and toxicological data are available, what specific tools and methods (e.g., exposure and dose-response models) should be used, and what level of uncertainty analysis is needed (Text Box 27.1).

Issues and importance: the problem formulation step had not been formally part of RA until it was introduced with the Silver Book.

Problem formulation is likely to emerge as one of the most critical RA steps in that it can help to ensure greater commitment from both stakeholders and decision makers by fully involving them from the start of the process. This leads to a greater probability that an acceptable policy solution will be found.

Hazard Identification
Introduction: The second step in risk assessment is hazard identification, the process of examining the evidence for adverse health effects due to human exposures to an environmental contaminant. Traditionally, the principal sources of evidence have been observational human studies and experimental animal evidence.

Recent advances in technology have brought novel sources of evidence such as in vitro (cell-based) studies and in silicon (computer modeling) methods to contribute useful toxicity information. The hazard identification step produces a list of potential toxic effects, and a characterization of the nature and strength of established causal associations with adverse effects in human.

Goal: Hazard identification seeks to determine adverse health effects related to exposure to an environmental contaminant, and to evaluate the quality, nature, and strength of the scientific evidence supporting causation.

Hazard Identification
Methods and tools used: Hazard identification uses the available toxicological, epidemiological, and other sources of evidence to assess the contaminant, its degradation products, and metabolites.

This process also considers the determinants of toxicity, including the level, frequency, and duration of dose or exposure; what human (or nonhuman) populations are exposed; the exposure routes; the manner in which the contaminant is absorbed and metabolized; the physical form of the contaminant, and the presence of other contaminants that may have synergistic or additive effects.

Hazard Identification
Evaluation of the combined scientific evidence involves a characterization based on effects, target organs, and mode of action (or how the chemical affects a target cell or organ), and concludes with a judgment on the quality of the evidence (e.g., strengths or weaknesses of particularly studies) and the likelihood of health effects in humans via the given exposure

This is typically done using a weight of evidence analysis, a judgment regarding the adequacy of the entire body of available evidence to support a conclusion that the substance poses a hazard to humans.

Issues and importance: High-quality scientific studies, such as those that have been peer reviewed by qualified experts in the field and/or whose findings have been corroborated by other studies, provide the best evidence for hazard identification. However, such studies are not always available

Hazard Identification
The utility of observational studies in the general population may be limited by uncertainties about the amount and duration of exposure in the population or the presence of potential confounders, such as smoking or alcohol use.

Animal studies offer the advantage of being performed under controlled laboratory conditions that reduce some of the uncertainties associated with human studies.

They also present the challenge of determining whether an effect seen in animals is relevant to humans. These issues must be carefully weighed when interpreting studies.

Dose Response Relationship
A dose-response assessment characterizes the relationship between the dose of a chemical administered or received and the resulting incidence or severity of an adverse effect.

In other words, a substance may have no adverse effect at low levels, but increasing effects may be seen as the dose increases. This relationship is characterized through a mathematical model called the dose-response relationship.

Goal: The goal of dose-response assessment is to employ the information obtained in the hazard identification step to characterize the likelihood and severity of adverse health effects at different levels of exposures to a chemical.

Dose Response Relationship
Methods and tools: Traditionally, dose-response assessment has been performed differently for chemicals that cause cancer (carcinogens) and those that cause other health effects (noncarcinogens). The reason for this is that the mode of action of carcinogens has been assumed not to have a threshold; that is, for carcinogens it has been assumed that no level of exposure is without some risk of cancer.

In contrast, agents causing noncancer effects, such as asthma, nervous system dis s, birth defects, or cardiovascular disease, are typically assumed to act in relation to a threshold.

Dose Response Relationship
In simple terms, for carcinogens a dose-response model is fit to the available data to derive the slope of the dose-response curve. Based on this slope, a cancer slope factor (CSF), also called a unit cancer risk (UCR), is derived. (Combined with exposure data, the CSF is used to characterize risk in the final step of the RA.)

For noncarcinogens, a threshold dose is typically based on the no observed adverse effect level (NOAEL), or if that level is not identified, is based instead on the lowest observed adverse effect level (LOAEL).

These threshold estimates are used as the point of departure (POD) for extrapolating to a human dose that is without risk of substantial adverse effects if the chemical exposure occurs over a lifetime; this dose is called a reference dose (RfD), or a reference concentration (RfC).

An RfD is set by dividing the NOAEL by one or more uncertainty factors.

Dose Response Assessment
NOAEL and LOAEL

Non-Carcinogen Effect
RfD= NOAEL or LOAEL
UF1 x UF2…..Uf
Animal Dose Response Data
NOEL (No Observed Adverse Effect Levels)

Divided by 10
(account for inadequate animal data)

Divide by 10
(Animal to Human Extrapolation)

Divide by 10

(Human Variability or individual sensitivity)
Reference Dose (RfD) or Acceptable Daily Intake (ADI)

Dose Response Relationship
These are typically a value of 10 for interspecies extrapolation (if the NOAEL was derived from an animal study) and 10 for intraspecies extrapolation (to account for natural variability in response within the human population).

Additional uncertainty factors may be used: for instance in the case of sensitive populations such as children or if few relevant studies were available. (For noncarcinogens, the RfD is used with exposure data to characterize risk in the final step of the RA.)

Exposure Assessment
The next step in RA is exposure assessment, in which potential exposures in the population are calculated or estimated. Individuals can be exposed to chemicals in many ways—through the air they breathe, food they eat, or water they drink or through exposures in their workplace.

Environmental health RA typically involves evaluation of chronic exposures to low levels of chemicals in the environment.

Goals: exposure assessment describes the magnitude, duration, timing, and route of exposure to the chemical, along with the size, nature, and categories of the human population exposed.

Exposure Assessment
Methods and tools used:
4 categories of Risk Assessment:

characterizing the exposure setting.
identifying exposure pathways.
quantifying exposure within regard to magnitude, frequency, and duration.
quantifying potential human intakes (i.e., the mass or concentration of chemical in contact with the human body normalized to the unit by weight (BW) per unit time, typically expressed as mg/kg-BW/day).

Exposure Assessment
Several exposure characterization methods are used:

Direct or indirect measurements of actual frequency, intensity, and/or duration of exposure or dose through sampling air, water, soil, or food products.
Surveying people about their actual or hypothetical habits involving a particular exposure pathway.
Taking biological samples (biomonitoring) from those exposed (e.g., urine, blood, or hair) and identifying the concentrations of chemicals or chemical metabolites present in them.
Another approach is modeling, which uses mathematical equations to estimate hypothetical exposures resulting from the release of a chemical into the environment.

Exposure Assessment
Exposure assessment requires standard approaches to expressing dose

Average daily dose (ADD) is an estimate of the average daily dose level, used to characterize acute, subchronic, and chronic exposures for noncancer end points. Lifetime average daily dose.

(LADD) is an estimate of the average daily dose level over a person’s lifetime, used to characterize lifetime exposures for noncancer or cancer end points. These values, when used in dose-response calculations, support estimates of risk.

Exposure Assessment
Uncertainty and measurement error are common challenges in exposure assessment. It is for these reasons that assumptions about common exposure patterns must often be made.

One important category of assumptions is called exposure defaults. For example, two commonly used exposure defaults are that an average adult drinks 2 liters of water per day (and an average child 1 liter) and breathes 22 cubic meters per day of air (U.S. EPA, 2011).

FIGURE 27.6 Some Common Exposure Pathways

Risk Characterization
Once the risk assessment design, hazard identification, dose-response assessment and exposure assessment are completed, risk characterization provides a synthesis of the risk level for the particular health effect of a particular chemical contaminant in a particular population.

Risk characterization should respond to the original RA problem formulation statement by addressing the specific chemicals, pathways, adverse health effects, and populations identified at the outset.

Goal: The purpose of risk characterization is to make a judgment on the risk to the population evaluated, including characterizing uncertainty where it exists.

Risk Characterization
Methods and tool used:

For carcinogens, the population cancer risk is calculated by multiplying the cancer slope factor (CSF) determined in the dose-response assessment by the lifetime average daily dose (LADD) determined in the exposure assessment step. While a resulting risk lower than 1 in 1,000,000 (1 × 10−6) is ideal, a population lifetime cancer risk in the range of 1 in 10,000 to 1 in 100,000 (1 × 10−4 to 1 × 10−5) may typically be considered acceptable.

Risk Characterization
For noncarcinogens, the RfD calculated in dose-response assessment is commonly used as a “bright line” to guide environment risk management in public health.

Thus population exposures below the RfD are often considered acceptable risks in environmental health decisions. Specifically, this is calculated using a hazard index (HI), which is the relationship between an actual population exposure and an established RfD.

An HI lower than 1 (i.e., signifying exposure level below the RfD) suggests low risk whereas an HI greater than 1 is indicative of concern.

Risk characterization is the final step in formal risk assessment, however it is by no means an end point; it leads directly to risk management and risk communication.

Step 4: Risk Characterization
HQ = chemical intake (mg/kg-day)
RfD (mg/kg-day)

HI of greater than 1, implies risk to human health.

Risk Management and Communication
Risk management is the process of identifying, evaluating, prioritizing, and choosing among policy options. It is a decision-making step.

This guidance focused on identifying options, decisions, and actions based on the scientific findings of RA but also incorporating nonscience factors, such as economic costs and benefits, legal requirements and restrictions, administrative ease and implementability, the concerns of stakeholders, and political factors.

While risk assessors have an important role in providing technical input to the RM process, choices among policy options are made by decision makers in the light of multiple factors and in the context of consultation with stakeholders.

Risk Management and Communication
For each policy option the RM evaluation process will examine several factors, which may include

Acceptable level of risk, that is, the level of risk a society is willing to accept. While this may be based largely on science findings, different interpretations of those findings are possible (e.g., reference doses for a particular chemical may differ across countries).

Existing legislation, and whether the proposed policy fits within it or requires a new legal frame- work, which may involve constraints and political challenges.

Economic costs and benefits, Some policy options will be more costly than others, and some will address health risks more fully (have higher benefits) than others. Economic cost-benefit analysis and cost-effectiveness analysis are tools used to evaluate different policy options.

Risk Management and Communication
Administrative considerations, which may suggest that some policies are more complicated (and therefore more costly) to implement and administer, whereas others may be much easier.

A stakeholder is any person or group with an interest (or a “stake”) in a risk management situation.

If a policy is likely to be challenged or disregarded by the populations it seeks to protect from health harms, it is not likely to succeed. Therefore stakeholder consultation at every step of RA and RM is essential.

Risk Management and Communication
Risk communication, is an interactive process of exchange of information and opinion among individuals, groups, and institutions, involving multiple messages about the nature of risk.

Systematic stakeholder involvement throughout the RA and RM processes greatly facilitates effective risk communication; risk communication should, ideally, start at the beginning of RA. Populations are affected by many factors in their perception of risk, and these may color their understanding of risk communication.

“Good risk communication may not always improve a situation. However, poor risk communication will almost always make it worse” (NRC, 1989). Best-practice risk communication guidance recommends messages that raise the level of information and satisfy those involved that they are informed within the limits of available knowledge.

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