Risk Assessment, Theory and Practices
Mohamed Tawfic Ahmed
Suez Canal University
Risk assessment, including ecological risk assessment, is an established discipline and has a significant potential for informing the decision process. It is an evaluation of the relative importance of an estimated risk with respect to other risks faced by the population, the benefits of the activity source of the risk, and the costs of managing the risk. For risks due to long-term exposure to chemicals, the risk assessment activity generally incorporates the estimation of the response of people to the exposure (that is, risk analysis is a part of risk assessment). The methods used include studies on animals, exposure of tissues, and epidemiology.
Finding thresholds and identifying the potential for irreversible change are important for the decision-making process. Although risk pervades modern society and is widely acknowledged, it continues to cause unending controversy and debate.
Risk assessments are conducted to estimate how much damage or injury can be expected from exposures to a given risk agent and to assist in judging whether these consequences are great enough to require increased management or regulation. Depending on the kind of hazard, the effects of primary concern might be workplace injuries; reproductive and genetic
abnormalities; diseases such as cancer or other debilitating illnesses; or ecological effects such as species extinction, loss of habitat, and other kinds of ecosystem damage.
It is widely acknowledged that risk assessment is a deeply embedded concept in every living organism as a main component for existence and survival. The daily challenges and threats that faced him throughout have sharpened his intuitive talents to weigh risks and to survive them. The state of the art of risk assessment has been linked in modern history with financial circles and monetary risks. Business men, dwelling in the dense array of risks and chances their assets are exposed to, had to establish some guidelines that may act as a defense mechanism not to risk their assets gliding into the despair of loss. Risk assessment was their vehicle to minimize losses and to give them a feeling of serenity, in the turbulent sphere of uncertainty.
The development of nuclear power stations, and space shuttle programmes launched last century, and with the need to combat uncertainties involved have, enriched risk assessment state of the art. Extensive funds were poured in to cope with the emerging new potential risks. Meanwhile, more asserted research and innovation clustered behind risk assessment giving it potential strides forward.
In the late 1960's of last century, the USA come up with the National Environmental Protection Act, better known as NEPA, as a milestone to maintain environmental integrity and safety. Environmental impact assessment was one of the first offspring of NEPA. The introduction of EIA was proven to be a momentous step in Man's endeavors to protect his environment. The USA legislation of EIA has become the most ever copied environmental practice at a global scale. Most of the nations have adopted EIA as a prerequisite step for project development worldwide.
- Environmental Assessment and Uncertainty
At its early stages, EIA made no reference to risk assessment. With the growing demand for EIA studies, uncertainty has emerged in environmental studies as a controversial issue, with no definite framework to contain. EIA studies extensively deal with parameters of relevant interest, formulated in terms of single figures, such as mean or worst - case value. For example the concentration of a particular contaminates in water or air could be expressed as average part per million. If uncertainties are large and important, such as oil spill or dam failure, a single figure cannot be used to indicate the probability of such serious incidents. A more structured and reliable approach is needed to assess the probability and / or the frequency of such incident, hence paving the way to risk assessment. It was quite evident soon after, that the need to assess risks associated with chemicals or gas emissions, failure of dams or other structure should be incorporated in the construct of EIA, and risk assessment was the answer to these question hence, became an integral part of EIA studies.
- Risk Assessment and Risk Management Processes
Risk assessment process, includes various steps that meant to identify and evaluate risks, risk impacts, and would also highlight risk-reducing and risk mitigation measures. Risk assessment culminates in risk management, a separate activity involving the process of evaluating alternative regulatory actions and selecting among them. Risk Management also includes prioritization of risks, categorization of recommended safeguards, their feasibility of implementation, and other risk mitigation processes and solutions within the management, operational and technical environment. Risk management is looked upon as an agency decision-making process that entails consideration of political, social, economic, and engineering information along with risk related information to develop, analyze, and compare regulatory options and to select the appropriate regulatory response to a potential health hazard. Using experience and judgment, the (risk) manager must determine a level of risk that is acceptable.
- Risk assessments have many uses, but a major one is to assist decision makers with the complex choices regarding the options in managing or reducing the potential human or ecological system risks associated with a substance or product.
- Risk Assessment, the Process
There is no general single definition of risk assessment. US, National Research Council defines risk assessment as the characterization of the potential adverse health effects of human exposure to environmental hazards. Risk assessment is also defined as the process of estimating the potential impact of a chemical, physical, microbiological or psychosocial hazard on a specified human population or ecological system under a specific set of conditions and for a certain timeframe.
- Scope of risk
The scope of risk assessment varies widely ( Paton, 1993). Risk assessment is used both as a predictive tool (to quantify impacts during project scoping) and as a management tool during the implementation and post implementation stages of a project to monitor actual impacts and to intervene in the management of impacts if necessary. In major projects, risk assessments are conducted to estimate how much damage or injury can be expected from exposures to a given risk agent and to assist in judging whether these consequences are great enough to require increased management or regulation. Depending on the kind of hazard, the effects of primary concern might be workplace injuries; reproductive and genetic abnormalities; diseases such as cancer or other debilitating illnesses; or ecological effects such as species extinction, loss of habitat, and other kinds of ecosystem damage.
- In the health, safety, and environmental fields, risk is usually identified as the likelihood that individuals (or a population) will incur an increased incidence of adverse effects such as disabling injury, disease, or death. Risk assessments range widely in scope and complexity, depending on the application from simple screening analyses to major analytical efforts that require years of effort and a substantial budget.
Contemporary risk assessments ordinarily rely on many branches of science such as toxicology, epidemiology, biochemistry, other health and environmental sciences, systems engineering, and related technical areas. The process of classic risk assessment involves scientific judgments/decisions made during a multi-step process.
Uncertainties and variability in the data available are identified and discussed as part of the risk assessment. The uncertainties are usually either due to questions about the available data or questions about the appropriateness of inferences made in the absence of sufficient data.
The hazard of a chemical or other substance is related to its potential harm or injury that may be associated with that chemical. The potential is intrinsic to that chemical or substance and cannot be altered. The nature of hazard differs depending on the substance in question. For a chemical substance, hazards may be described as physical or health hazards. Physical hazards of chemical substances may include the following :
Asphyxiant, combustible, explosive, pyrophoric, organic peroxide, oxidizer, water reactive, unstable / reactive.
Health hazards occur when a chemical reacts with living tissue. Appropriate hazards classes include: Carcinogen, Irritant, Mutagen, Poison, Toxic, Sensitizer, Teratogen.
Risk is the likelihood of an adverse effect that a substance can inflect on Man's health or on his environment. For a chemical substance, a risk is the release of that chemical on a target medium or organism. Risk as expressed in a variety of ways, depending on the receptor media, and whether it is human or an ecosystem. For humans, risk assessment is usually expressed in the statistical figure that represent the likelihood of inflecting a typical harm on exposed population.
Risk is frequently expressed in quantitative probability terms, such as some number of additional cancer deaths over a lifetime in a population of 1 million exposed people.
- Ecological risk assessment
In ecological risk assessment, risk is often expressed as the ratio of predicted environmental concentration (PEC) to predicted non - effect concentration (PNEC) for a particular chemical ( Rodreguez 1987) . A (PEC / PNEC ) of less than 1 implies that the risk arising from the hazard of toxicity is low or effectively zero.
The PEC values needed for the environmental risk assessment , i.e., the concentration of a substance that will reach the environment can be measured, using analytical instruments. PEC can also be predicted by applying mathematical models. The PEC values depend on physico- chemical properties of the substances, the production and emission process and the properties of the environmental compartments. Computer programmes are valuable tools for estimating the concentrations of substances in different environment compartments and to predict the chemical fate of a substance.
Risk Assessment Process
The process of risk assessment involves:
Hazard identification is the first stage of risk assessment process. This initial step of risk assessment is directed at determining if a substance (or other health-threatening risk agent) could cause particular adverse health effects in human populations. For example, will exposure to a particular substance cause cancer? Will it harm the nervous system or immune system? Will it give rise to reproductive defects or other serious health conditions or disabilities? The purpose of hazard identification is to develop an understanding of the key sources of impact resulting from chemical, substance, the receptors in the surrounding environment that might potentially be targeted by these sources of impact. It would also investigate the nature of the adverse effects that might result. For a newly established project, hazard identification is achieved through the following steps.
A systemic examination of the project to identify sources of impacts
A thorough knowledge of the project area to identify receptors of adverse impacts
A good understanding of the adverse impact
A variety of tools are used to assist in this area. For example, in the case of industrial facilities the use of qualitative checklist and regular sampling process of wastewater, emitted gases would be involved. Field survey will assist in the identification of sensitive ecological species.
- Dose-Response Assessment.
This step seeks to identify the quantitative relationship between a dose level and the resulting incidence of injury or disease. Most substances-even many of those used for beneficial purposes-cause harm when consumed in large enough quantity. For example, an anaesthetic may cause headaches at low doses, a medically advantageous sleep at higher doses, but is lethal at very high doses. Thus, the risk of a substance cannot be determined with confidence unless the dose-response relationship is quantified.
- Threshold levels
With noncarcinogens (or the noncarcinogenic effects of carcinogens), the normal working assumption (backed up by theory and empirical evidence) is that biological effects occur only after a threshold level of exposure has been exceeded.
- Various thresholds
Various thresholds have come to be established; they include a lowest observable effect level (LOEL), the smallest dose that causes any detectable effect; a no-observed-effect level (NOEL), the dose at or below which no biological effects of any type are detected; and a non observed- adverse-effect level (NOAEL), the dose at or below which no harmful effects are detected (WHO 1978). Toxicologists generally seek to identify (via animal testing, with progressively higher and lower exposure levels to a suspected toxic substance) several of these dose-response markers to help map thresholds.
With suspected carcinogens, however, the working assumption is usually that no threshold exists, (i.e., those exposures to carcinogenic substances pose some risk even at the smallest level of exposure). This concept has long been a mainstay of cancer risk assessment; the concept is based primarily on what is known about the health effects mechanisms associated with exposures to ionizing radiation and toxic substances. When a dose-response relationship derives from data on test animals, the need for an additional extrapolation arises: namely, translating the observed effects in animals to predicted risk in human populations. The usual approach is to introduce one or more inter-species extrapolation adjustments (usually termed scaling factors) to account for biological differences between the test animal and humans (such factors as lifespan, body size, genetic variability, and metabolic rate, among others) that may influence the response to exposures of a given substance.
In principle, the human response to the substance in question may be more or less sensitive than what is observed in the animal tested ( McColl 1990). Nonetheless, the working convention has been to assume greater sensitivity on the part of humans. Numerically speaking, the risk estimates from test animal dose-response data are substantially adjusted upward by 1 or more powers of 10. In a few cases, epidemiologic data are available to gauge the dose-response relationship. However, for most cases, the low level of most environmental exposures to suspected carcinogens combined with the lack of a threshold means that estimates of human cancer risk rely on the low-dose predictions from mathematical extrapolation models. The extrapolations are based on comparatively high dose levels given to laboratory animals.
For most types of toxic responses, there is a dose, called a threshold, below which there are no adverse effects from exposure to the chemical. The human body has defences against many toxic agents. Cells in human organs, especially in the liver and kidneys, break down chemicals into non-toxic substances that can be eliminated from the body in urine and faeces. In this way, the human body can take some toxic insult (at a dose that is below the threshold) and still remain healthy. The identification of the threshold beyond which the human body cannot remain healthy depends on the type of response that is measured and can vary depending on the individual being tested. Thresholds based on acute responses, such as death, are more easily determined, while thresholds for chemicals that cause cancer or other chronic responses are harder to determine. Even so, it is important for toxicologists to identify a level of exposure to a chemical at which there is no effect and to determine thresholds when possible.
- Exposure Assessment
This step attempts to identify the nature and size of
of the population(s) exposed to the risk agent, along with the magnitude, duration, and spatial extent of exposure. Depending on the purpose, the exposure assessment could concern past or current exposures or those anticipated in the future.
Case by case, the steps involved in an exposure assessment vary widely, because circumstances differ with respect to how much is known about existing exposures and what information is available. The most reliable picture comes from direct monitoring (personal, biological, and/or ambient) of the amounts of the substance to which people are actually exposed over time. This sort of information is, however, often not available. In fact, lack of knowledge about actual exposures is one of the weaker links in the knowledge chain supporting risk assessments. As a consequence, a good deal of what is done is derived from models and from generalized assumptions about relevant physical parameters and human behaviours. Numerous pathways exist through which exposures can occur (direct and indirect), and a large number of variables and moderating factors can be involved. For example, estimating the movement of a chemical in the environment depends on considerations such as how easily it evaporates, how easily it dissolves in different media (such as water or animal fat), how strongly it attaches to the soil, and how long it persists in the environment.
On the human behaviour side of the exposure equation, the issues include how much water or specific types of food people consume each day; whether or not people filter their water; how they prepare their food; what balance of time during the day is spent indoors versus outdoors, and so on.
Biomarkers are physiological or biochemicals measures, such as blood cholinesterase
concentration, that may be indicative of exposure to contaminants. They are seldom useful for estimating risks by themselves, but they can be used to support other lines of inference. If the biomarkers are characteristic of contaminant exposures, then the distribution and frequency of elevated levels must be compared to the distributions and concentrations of contaminants. Finally, to the extent that the biomarkers are known to be related to overt effects such as reductions in growth, fecundity, or mortality, the implications of the observed biomarker levels for populations or communities should be estimated.
Acute and Chronic Toxicity
The type of damage caused by sudden release of a chemical would include acute toxicity effects through dermal, contact and inhalation of fumes, burns from fires and explosives and damage to humans (Vermeire et al. 1993). On the other hand, chronic health effects are unlikely to happen from a single exposure to accidental releases to the atmosphere.
Chronic health effects on humans are caused by exposure to low level releases of chemicals during day - to - day operations. In this respect, chemicals can inflect a number of chronic health effects in humans, which would include
- Risk Characterization.
Risk characterization is looked at as the concluding task in a risk assessment, hence combining the principal findings of the hazard characterization, dose-response, and exposure phases of the risk assessment into an integrated picture of the nature and expected frequency of adverse health effects in exposed populations. It pulls together all the pieces of the previous steps of risk assessment in order to characterize and describe the risk. It is referred to by some as advice for decision-making. The tasks focus on the integration of the hazard characterization with the intake/exposure assessments for the general population of interest or vulnerable population subgroups (e.g., children).
Risk characterization could be best described as the interface between risk assessment and risk management. Available examples as to where risk assessment ends and risk management begins tend to offer different scenarios. In other words, the "bottom line" forthcoming from a risk characterization is a primary determinant of the risk management phase that follows risk assessment.
Ecological Risk Assessment
Even though there is a long history of evaluating environmental and ecosystem impacts, the concept of ecological risk has only recently emerged as a distinct field of risk assessment. Ecological risk is based on the understanding that healthy ecosystems can provide renewable resources and food, water storage and flood control, biodegradation and removal of contaminants from air and water. The objective of an ecological risk assessment is to estimate the possibility of adverse impacts on one or more of these ecosystem dimensions from exposures to ecosystem/environmental stressors such as technology (roads, buildings, and other types of development) and pollutants.
Methodologically, ecological risk assessment draws widely on the standard procedures of environmental impact analysis and monitoring. Tests of animal species (such as fish or insects) are commonly used tools as are computer-assisted geographic analysis and computerized ecosystem simulations. When we introduce a new chemical (such as a pesticide to a wheat field), accidentally import a new species (such as a foreign insect), or change a landscape (such as draining or filling a wetland), scientists often assess how much damage those actions may have on the plants or animals in the area. Although these procedures constitute a low cost, pragmatic means of ranking the toxicity of potentially hazardous chemicals, they do not directly evaluate the sublethal toxicity, or other adverse effects (e.g., disturbance of ecological relationships) on organisms exposed to complex mixtures of pollutants in the highly fluctuating conditions that prevail in the environment (Howard,1997; Kanzawa et al., 1997; Kortenkamp & Altenburger, 1998).
For estimation of risks, the distribution of observed concentrations should be used. These should be compared to the distributions of effective concentrations for plants, invertebrates, and microbial processes. The exposure distributions are interpreted as distributions over space since soil composition varies little over the period in which samples were collected, but samples and contaminants are distributed in space within areas. For plants, the effects distributions are distributions of species-soil combinations in soil toxicity tests. If we assume that site soils are drawn from the same distribution of soil properties as the tested soils and that test plants have the same sensitivity distribution as site plants, then the threshold concentrations for effects on site plants can be assumed to be drawn from the distributions of threshold concentrations for effects on plants in the toxicity tests. Therefore, overlap of the distributions indicates the proportion of locations in an area where concentrations of the chemical are expected to be toxic to a particular proportion of species in the site community. Assumptions for invertebrates are similar except that earthworms are assumed to be representative.
Additionally, expert judgments and opinions also play a substantial role because ecosystems are complex and do not lend themselves entirely to experiments or modelling.
Ecological risk assessments deal with human-caused changes that alter important features of ecological systems such as lakes, streams, forests, or watersheds. Ecological risks may be local-a hazardous waste site. The risks may be regional- the Mediterranean sea, the Nile river basin. The risks may be global-atmospheric transport of chemicals or global warming. Ecological risks may involve a specific type of plant or animal (a bass), a community of organisms (the fish in a lake), or an ecosystem (all of the biological and physical components of the lake).
For new substances, usually there is no exposure relevant measured data available. Therefore, concentrations of a substance in the environment must be estimated. Unlike for new substances, the exposure assessment of existing substances does not always depend upon modelling. Data on measured levels in various environmental compartments have been gathered for a number of substances. In many cases a range of concentrations from measured data or modelling is obtained. This range can reflect different conditions during manufacturing and use of the substance, or may be due to assumptions in or limitations of the modelling or measurement procedures. Measured concentrations can also have a considerable uncertainty associated with them, due to temporal and spatial variations.
For existing chemicals, it should always consider "reasonable worst case" exposure assessment based on modelling, to derive an environmental concentration. The subsequent step is to estimate the substance's release rate based upon its use pattern. All potential emission sources are analysed from production and formulation to use and disposal, and the receiving environmental compartment(s) is/are identified.
Risk characterization combines information concerning exposure to chemicals with information concerning effects of chemicals to estimate the magnitude of risks. Risk characterization for ecological risk assessments is performed by weight of evidence.That is, rather than simply modelling risks, ecological risk assessors examine all available data from chemical analyses, toxicity tests, biological surveys, and biomarkers to estimate the likelihood that significant effects are occurring or will occur and describe the nature, magnitude, and extent of effects on the designated assessment endpoints. The lines of evidence are integrated independently so that the implications of each are explicitly presented. This makes the logic of the assessment clear and allows independent weighing of the evidence by risk managers and stakeholders.
The most important task in risk management is implementing the management measures and allocating management resources. This should be followed by monitoring the effectiveness of these measures over time. Planning for implementation requires particular attention to resources required, management responsibilities and timing of tasks. Monitoring of risks and risk management effectiveness should be a routine and recognised activity. The frequency of monitoring, and the responsibility for it, should be specified in either the risk management plan or summary documentation.
- Risk management
For major projects risk management provides a structured way of identifying and analysing potential risks, and devising and implementing responses appropriate to their impact. These responses generally draw on strategies of risk prevention, risk transfer, impact mitigation or risk acceptance. Within a single project or proposal each of these strategies may have application for different individual risks.
The essential tasks of risk management are to
- (1) determine what hazards present more danger than the community with its full spectrum of stakeholders is willing to accept;
- (2) consider what control options are available; and
- (3) decide on appropriate actions to reduce (or eliminate) unacceptable risks. At the broadest level, risk management includes a range of management and policy-making activities: agenda setting, risk reduction decision making, program implementation, and outcome evaluation.
The management of risks builds on the results of risk assessment using a broader set of tools that include technical, economic assessments, societal approaches, and policy instruments to mitigate of health and environmental effects. The outcome of all risk management actions should be the reduction of risk. Prior to undertaking risk management, it is necessary to decide the priority in which risks must be managed and to maximize the reduction of risk for the available resources. This reduction in risks includes the consideration of the risk of alternative activities.
Risk communication covers a range of activities directed at increasing the public's knowledge of risk issues and participation in risk management. This includes, for example, warning labels that provide consumer education about existing hazards, development of publicly accessible databases characterizing hazardous circumstances, and public hearings on risk management issues.
Risk communication emerged as a recognized element of risk management early in the 1980s. At this time, it was realized that a large fraction of the public was not familiar with the nature of risk and that risk management decisions could not simply be made by technical experts and public officials and then imposed and justified to the public after the fact. Risk communication is now viewed as being a dialogue among interested parties, risk experts, policy makers, and affected segments of the public.
Limitation of Risk Assessment
Risk assessment is one method in a much broader field of risk management. Risk assessment is a process that does not result in a fixed final answer. It is impossible to determine the true magnitude and extent of any risk.
Research on the risks of chemicals on microbes, plants, animals and humans is confounded by factors such as:
- Variations in individual and species tolerances to the effects of contaminants;
- Environmental conditions and processes affecting the properties of the contaminant such as partitioning, transformation, degradation, temperature, pH, organic material, etc;
- Uncertainty in extrapolating study data between species (e.g. using the outcome of animal testing to predict the effect on people) and within species (e.g. using the effects on a specific group of workers such as miners to predict the effect on other groups of people such as children); and
- Large information gaps about the effects of contaminant mixtures that might have synergistic, magnifying or other effects.
- Large information gaps about the specific mechanisms and processes affecting functions and organs within the body, how these interact, and how they might be affected by a contaminant.
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