Aggregate risk assessment

Aggregate risk assessment The evaluation of risk from exposure to a given chemical from multiple routes of exposure. 

The need for aggregate and cumulative non-occupational exposure assessments, and lower reference doses for all assessments, means that some pesticides will fail lower-tier risk assessments and without more refined exposure data they might even fail higher-tiered assessments. For example, in North America many of the residential uses of the OPs have been discontinued as a result of the aggregate risk assessments. As a result, there has been increased emphasis on gathering better toxicology and exposure data to reduce the conservatisms that are contained in the current system. 

III. SINGLE-CHEMICAL, AGGREGATE RISK ASSESSMENTS FOR OPs AND A -METHYL CMs... 

Occupant vulnerabilities are one of the key factors in determining the levels of both individual and aggregate risks for building occupants. Occupant vulnerabilities are used in risk screening as discussed in Chapter 4 and are used in detailed risk assessments. 

Since the aggregate risks from Process Unit 2 are largely the result of single event—brittle fracture—the qualitative hazard assessment identified potential safeguards that could be put in place to prevent a brittle fracture occurrence. It was decided that the best option would be to install an emergency shutdown system in Process Unit 2 to prevent pressuring the nitrogen vapor vessel if a cold temperature situation was present. 

For companies to make risk-based decisions from risk screening or quantitative risk assessments, company-specific risk tolerance criteria or methodologies should be developed for both individual risk and aggregate risk. Chapter 4 provides a discussion of risk criteria and methodologies, and offers guidance for companies to consider in developing their own approaches to risk tolerability. 

The Food Quality Protection Act (FQPA) of 1996 mandated that the US EPA carry out risk assessments that consider the cumulative effects of exposure to pesticides having a common mechanism of toxicity, as well as consider exposure to each pesticide by various routes of exposure (e.g., dermal, dietary, inhalation) and sources (e.g., residues in food and water) in an aggregate manner [19]. To accomplish this, there needs to be sufficient evidence supporting a common adverse effect that is associated with a common mechanism of action in specific target tissues. To date, the required criteria necessary to establish a common mechanism of toxicity with a specific toxic effect for the pyrethroids are not available [1,8,98]. 

The MOE approach is often used to determine the acceptability of acute risks for single chemicals and MOEs of >100 or >10 are usually considered acceptable when derived from toxicological data from animal and human studies, respectively. The US-EPA favors this concept for performing aggregate and cumulative risk assessments (Whalan and Pettigrew 1997). 

Until very recently the risks associated with different types of chemicals such as food additives, pesticides, environmental contaminants and natural constituents of food were assessed and managed separately. However, a particular substance might fall into two or more of these categories and so the opportunity for simultaneous exposure might be overlooked. Furthermore, exposure to a chemical could occur through diet, drinking water, air pollution or dermal absorption. Aggregate exposure assessment aims to take all of the possible sources and routes of exposure into account in a realistic manner and thereby obtain a better overall estimate of risk. Initiatives have been set up in both the... 

Aggregate exposure assessment is naturally more complex than the methods used for dietary risk assessment. In the simplest analysis a worst case can be established for each source and exposure route and then summed to give a total exposure. If this were below any threshold of concern such as the PTWI then no further action would be required. However, if the total worst case exposure was above a PTWI then it is unlikely to reflect the real situation since the probability that any individual would be exposed to each source by each route at the maximum level is very remote. 

The methodology in the case study for chronic exposure, as well as several advances in probabilistic assessment methodology for acute exposure (e.g., a person s exposure on a single day), are being incorporated into the Cumulative and Aggregate Risk Evaluation System (CARES) begun in 2000 and being further developed with the International Life Sciences Institute (ILSI) in 2004. 

ILSI (1998). International Life Science Institute Risk Science Institute. Workshop on Aggregate Exposure Assessment. Washington, DC. 

USEPA (2000). General Principles for Performing Aggregate Exposure and Risk Assessments, Report No. 6040, Office of Pesticide Programs and Office of Prevention, Pesticides and Toxic Substances, (http //www.epa.gov/pesticides/trac/science/) Washington, DC, November 21. 

Cumulative risk assessments evaluate the health risk for aggregate exposures accumulated over time and for multiple contaminants or stressors. In some contexts (e.g. USEPA pesticide risk assessments), cumulative refers specifically to combined exposures to chemicals that share a common mechanism of toxicity (see http // www.epa.gov/oppsrrdl/cumulative/). Populations may be defined by their location relative to sources, their activities and customs, and their susceptibility to exposures. In this context, populations can include different ethnic groups, different communities, or different age groups. Cumulative risk is a very important concept in understanding environmental health risks to children in different settings, particularly in underdeveloped countries where children may be facing multiple stressors. 

LifeLine Group (2005) Aggregate and Cumulative Exposure and Risk Assessment Software, Version 4.3. Annandale, VA, The LifeLine Group, Inc. (http // www.thelifelinegroup.org/index.htm software accessed 5 May 2005). 

Multi-criterion analysis is a decision-making tool for qualitative weighting of aggregated impact assessment indicators. Further information is available in the OECD Technical Guidance Document on the use of Socio-economic Analysis in Chemical Risk Management Decision-Making [510]. 

EPA must estimate aggregate exposures to pesticides from food, drinking water, and nonfood (home, lawn, garden, etc.) uses when doing risk assessments. 

ASSESSMENT OF RISKS TO HUMANS EXPOSED TO PESTICIDES 2 The Four Steps in Risk Assessment 2 Hazard Identification 2 Dose-Response Assessment 3 Margin of Safety Approach 3 Quantitative Risk Assessment 3 Exposure Assessment 4 Risk Characterization 4 RISK MANAGEMENT 5 ADVANCES IN DATA INTERPRETATION 5 Probabilistic Approaches 5 Recognition of the Tier Approach 5 Aggregate Exposure 6 Cumulative Exposure 6 Impact of New Scientific Advances 7 Post-Registration Monitoring 7 HARMONIZATION OF REGULATORY APPROACHES SUMMARY 9... 

For classes of pesticides that cause their toxic effects through a common mechanism of toxicity, the non-occupational exposures to all members of the class have to be aggregated and used in a cumulative risk assessment. In 2003, the United States Environmental Protection Agency (USEPA) published a framework outlining how cumulative risk assessments should be conducted. There is no question that this approach has provided significant challenges to toxicologists, exposure assessors and risk assessors. Much of the developmental work on how to conduct... 

If the estimated level of exposure is less than the reference dose (RfD), the pesticide is considered to be safe to use. The aggregation (addition) of the amount of exposnre received from each source will increase the total exposure to a level which may then exceed the RfD. In addition to aggregation increasing the level of exposure, the reference dose is becoming smaller because of the use of extra safety factors to protect children. The trend towards lower reference doses impacts both residential and worker risk assessments. 

Probabilistic Approaches to Aggregate and Cumulative Risk Assessment... 

Probabilistic risk assessment methods are used to incorporate uncertainty and variability into both aggregate and cumulative risk assessments. Herein, uncertainty refers to lack of knowledge or the limitations in the current state of knowledge. For example, the dermal permeability of a pesticide may not be known with certainty. Variability, on the other hand, refers to a value that differs from one individual to another individual in a population or from one instance to another. For example, the number of apphcations of a residential pesticide in a year may vary from one individual to another. Probabilistic methods use probability distributions to incorporate uncertainty and variability into both aggregate and cumulative risk assessments. 

Until recently, most risk assessments focused on a single pesticide, considered each route separately, and evaluated each separately. Aggregate assessments consider a single pesticide but combine multiple routes and multiple sources of exposure. Cumulative assessments combine exposure assessments for chemicals that share a common mechanism of toxicity. 

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