Risk In Perspective

"TRI chemicals vary widely in their ability to produce toxic effects. Some high-volume releases of less toxic chemicals may appear to be a more serious problem than lower-volume releases of highly-toxic chemicals, when just the opposite may be true."

"Release estimates alone are not sufficient to determine exposure or to calculate potential adverse effects on human health and the environment. Although additional information is necessary to assess exposure and risk, TRI data can be used to identify areas of potential concern."

"The determination of potential risk depends upon many factors, including the toxicity of the chemical, the fate of the chemical after it is released, the locality of the release, and the human or other populations that are exposed to the chemical after it’s release."

What is Risk?

Nothing is 100 percent risk free; consequently, each day we make many decisions based on personal evaluations of risk situations. Besides the personal risks that individuals must evaluate, many professionals also make assessments regarding risks to society (such as those related to air quality, waste disposal or nuclear power.)

1. Hazard identification
2. Dose/response assessment
3. Exposure assessment and
4. Risk characterization

Step 1 involves identifying a chemical, biological, or physical agent that presents a potential source of risk, or hazard, and possible negative consequences. This step qualitatively determines whether an agent of concern is likely to pose a risk to environmental or human health.

Step 2 quantitatively assesses the relationship between the degree of exposure (dose) and the extent and likelihood of an adverse response.

Step 3 identifies the potential exposure locations and receptor populations.

Step 4 incorporates information from the first three steps to formulate an estimate of the risk. Risk characterization should synthesize the results from hazard and exposure estimates, present a balanced representation of the available data, and identify key assumptions and areas of uncertainty. This step is critical because it is the link between the risk assessment and risk management processes.

Although risk assessment models aim to define a given risk as accurately as possible, there is always an element of uncertainty in the final risk characterization. Uncertainty arises because risk assessments are often based on limited information. In addition, the information available is influenced by the accuracy and precision of measurements and by the natural variability of systems and populations, all of which are potential and actual sources of error.

Assumptions, therefore, are made at each step of the assessment process. Because each assumption influences the final outcome and because most estimates communicate the risk estimate, risk analysts must explicitly state all the assumptions and uncertainties contained in the study.

What are the Key Steps in the Health and Ecological Risk Assessment of Chemicals (Including Metals and Metal Compounds)?

There are four major steps in risk assessment that is the determination of the relationship between predicted exposure and adverse effects. Indeed, a key to the effective risk management of chemicals contained in a product is the accurate assessment of the risks associated with the product's particular applications as well as with the other stages of the product life cycle.

The four steps are:

1. hazard identification
2. dose-response evaluation
3. exposure assessment
4. risk characterization

These steps constitute a general approach to risk assessment that has been endorsed by a number of national governments and international organizations such as: The International Programme on Chemical Safety (IPCS), the Organisation for Economic Cooperation and Development (OECD), the U.S. Environmental Protection Agency (US EPA), the European Union, among others.

Step 1: Hazard Identification

Hazard identification is defined as the identification of the adverse effects that a chemical has an inherent capacity or potential to cause. Examples of physical hazards include: combustion, explosivity, flammability, and corrosivity. Examples of health hazards are either acute (e.g., skin and eye irritation, lethal effects, asphyxiation) or chronic (e.g., carcinogenicity, sensitization, effect on reproductive system, effects on nervous system, effect on organs). Examples of ecological hazards include mortality (acute) or reduced growth and reproduction (chronic) to representatives species.

Hazard identification is only the first step in risk assessment and is not an appropriate basis upon which to make a risk management decision. However, hazard identification is a critical step often carried out before chemicals and products are introduced on the market. For human health and the environment, results of toxicity testing as well as epidemiology data are used to determine hazard.

Toxicity is the inherent potential or capacity of a chemical (generally established from a dose-response relationship) to cause adverse effects on a living organisms that seriously damages its structure or function or results in death. Usually toxicity testing (for human: toxicity or the environment: ecotoxicity) is performed through controlled studies on living organisms, isolated tissues, cells or cellular components. Toxicity is generally influenced by the unique physico-chemical properties of the chemical. Examples of toxicity tests that are pertinent to human health hazards relate to: skin and eye irritation, sensitization, carcinogenicity, and reproduction toxicity. Examples of ecotoxicity tests that are pertinent to ecological hazards relate to acute and chronic toxicity to fish and algae.

The term "toxic" is generally used in regulatory context to categorize chemicals based on certain criteria and tests results. Consequently, a chemical that may have a low level of toxicity (e.g., NaCl: table salt) may not be classified as toxic for regulatory purposes. In this context, all chemicals have a level of toxicity (i.e. inherent ability to cause some adverse effect under certain controlled conditions) but they are not necessarily classified as toxic.

Epidemiology is the study of the distribution and likely determinants of diseases and injuries in human populations. The incidence of disease is compared between people exposed and not exposed to the agent under study. Because epidemiology, as opposed to toxicology, evaluates human rather than animal and cellular data, it has the potential to be particularly informative for human hazard identification.

Step 2: Dose-response Evaluation

Dose-response evaluation is the determination of the relationship between the magnitude of an administered, applied or internal dose and a specific biological response. The dose is the total amount of a substance administered to, taken or absorbed by an organism under standardized laboratory conditions used for toxicology testing. The response can be expressed as the measured or observed incidence, the percent response in groups of subjects (or population), or the probability of occurrence of a response in a population.

"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy." Paracelsus, 1493-1541

Step 2: Exposure Assessment

Exposure Assessment is the process of measuring or estimating concentrations (or intensity), duration and frequency of exposures to a chemical present in the environment (either workplace or "outside environment"). Common routes of exposure are ingestion, injection (less likely), skin absorption and inhalation. Generally, estimates of exposure are obtained by determining the emissions, pathways and rates of movement of a chemical in the workplace or the general environment. There are a number of methods/ techniques available to estimate or measure level of exposure. Ecological Risk Assessment represents an extra challenge in the number of potential receptors/ species that may need to be considered when assessing risk.

Step 2: Risk Characterization

Risk is the probability that an adverse outcome will occur in a person, a group of persons or an ecological system that is exposed to a particular dose or concentration of a chemical. It is expressed as a probability in values ranging from zero (certainty that an effect will not occur) to one (100% certainty that an effect will occur).

Risk characterization is the final stage of risk assessment. It summarizes the information from hazard identification, dose-response evaluation and exposure assessment into an overall conclusion on risk. The result of a risk characterization is a qualitative and/or quantitative description under specific exposure conditions. Risk characterization is highly context-specific and cannot be automatically applied from one context or location to another. This is because risk should be determined for a chemical in a product in particular applications and through other stages of the product life cycle. Risk characterization should allow for the identification of the strengths and weaknesses of the tests used, the uncertainties in the database and the assumptions made within the methodology used to reach the overall conclusions.

Complete characterization of risk is very important to good risk management and risk communication. Full characterization can help distinguish between exposures that are likely to be associated with significant or socially unacceptable risks and those that are not.

Source: International Council on Metals and the Environment