This section explains how to develop hazard category conclusions during the PHA process, and how to assign a conclusion category to your findings.
Health assessors will develop a statement, based on available information, about the health hazards associated with the site. The statement will be for completed (and sometimes potential) exposure pathways and the time period(s) of concern. In you statement, you will determine whether conditions:
- are a health hazard,
- are not a health hazard, or
- cannot be fully evaluated because critical information is missing.
These statements align with each of ATSDR’s three overall health hazard conclusions – health hazard, no health hazard, or uncertain health hazard. Along with your overall health hazard conclusion, you will also assign a conclusion category to your findings. This conclusion category determination will also establish which public health documents you will develop and the follow-up actions you will take at the site (this diagram illustrates the process).
Only have one conclusion for each exposure pathway – do not include a separate conclusion for each contaminant in an exposure pathway. For instance, if drinking water has tetrachoroethylene and trichloroethylene contamination, this would be one conclusion, such as “ATSDR concludes that drinking tetrachloroethylene and trichloroethylene in water for a year or longer could harm people’s health.” Make sure your conclusion is not too broad, otherwise it could result in a misunderstanding of where there is and is not a hazard.
Depending on the site-specific circumstances and community needs, you might develop a public health assessment (PHA), a health consultation (HC), a letter health consultation (LHC), an exposure investigation (EI)-health consultation (EI-HC), a health advisory (HA), or a technical assist (TA) document. The conclusion categories are required in most site-specific products (PHAs, HCs, LHCs, and HAs) as you assess the public health implications of exposure pathways.
Selecting Conclusion Category
ATSDR has established five distinct descriptive public health hazard conclusion categories (see the Summary of Conclusion Categories table for the definitions, overarching hazard statements, and examples for each category). These categories help ensure a consistent approach in drawing your conclusions across sites:
- Category 1 (acute and intermediate) and Category 2 (chronic) fall under ATSDR’s health hazard conclusion. They indicate that there is a reasonable possibility that harmful health effects have occurred or are likely to occur because of exposure levels being high enough to potentially cause an effect in members of the exposed population.
- Category 3 falls under ATSDR’s uncertain health hazard conclusion and indicates that data are lacking to make a determination about harmful health effects.
- Category 4 falls under ATSDR’s no health hazard conclusion. It indicates that harmful health effects are not likely in the population; exposures might be possible, but the exposure is not sufficient to result in harmful health effects.
- Category 5 also falls under ATSDR’s no health hazard conclusion and indicates that no public health hazard exists because no exposure is occurring.
Overarching Hazard Category Statement
1: Short-term exposure, acute and/or intermediate hazard
|Physical hazards or short-term (less than 1 year) site-related exposure to contaminants 1) could result in harmful health effects and 2) require quick intervention to stop people from being exposed||Chemical Hazard:
ATSDR concludes that [SUBSTANCE/PATHWAY: Describe the pathway – drinking, breathing, eating, etc.] for [TIME PERIOD: List the time period – less than a year, less than 2 weeks, or 2 weeks or less] at/in [PLACE] could harm people’s health. This is an urgent public health hazard.
|ATSDR concludes that breathing mercury vapor for 2 weeks or less in the indoor air at XYZ School could harm people’s health. This is an urgent public health hazard.
Alternatively, adults and children at the XYZ School could breathe mercury in indoor air at levels that could cause harm. This is an urgent public health hazard.
2: Long-term exposure, chronic hazard
|Physical hazards or chronic (more than 1 year) site-related exposure to contaminants could result in harmful health effects||Chemical Hazard:
ATSDR concludes that [SUBSTANCE/PATHWAY: Describe the pathway – drinking, breathing, eating, etc.] for [TIME PERIOD: List the time period – a year or longer] at/in [PLACE] could harm people’s health. The following optional statement may be added for this category: “This is a public health hazard.”
|ATSDR concludes that touching, breathing, or accidentally eating lead and arsenic in soil or dust for a year or longer in Yakliske residential yards could harm people’s health. This is a public health hazard.|
|Uncertain Health Hazard
3: Lack of data
|Critical information is lacking to support a judgment about the level of public health hazard||ATSDR cannot currently conclude whether [SUBSTANCE/PATHWAY: Describe the pathway – drinking, breathing, eating, etc.] at/in [PLACE] could harm people’s health. The following optional statements may be added for this category: 1) “The reason for this is [add information why data will never be available]” or 2) “The information we need to make a decision is not available. We are working with [specify agencies] to gather the needed information.”||ATSDR cannot conclude whether sulfur dioxide air emissions from the XYZ plant could harm people’s health. The information we need to make a decision is not available. We are working with the State of Zarizona to gather the needed information.|
|No Health Hazard
4: Exposure, no harm expected
|Exposure to site-related contaminants might have occurred in the past or is still occurring, but not at levels likely to cause harmful health effects||ATSDR concludes that [SUBSTANCE/PATHWAY: Describe the pathway – drinking, breathing, eating, etc.] at/in [PLACE] is not expected to harm people’s health. The following optional phrase may be added to the end of the sentence for this category: “because [state reason].” Or, the following optional statement may be added for this category: “The reason for this is [state reason].”
Note: There are two options for Category 4 – exposure with further action or without further action.
|ATSDR concludes that touching, breathing, or accidentally eating zinc found in soil and dust at the XYZ site is not expected to harm people’s health as zinc levels in soil are below levels of health concern.|
|No Health Hazard
5: No exposure, no harm expected
|No exposure to site-related contaminants||ATSDR concludes that the [SUBSTANCE/PATHWAY] will not harm people’s health. The following optional phrase may be added to the end of the sentence for this category: “because people have not been [describe the pathway – drinking, breathing, eating, etc.]” Or, the following optional statement may be added for this category: “The reason for this is that people have not been [describe the pathway – drinking, breathing, eating etc.]”||ATSDR concludes that mercury vapors at the XYZ site will not harm people’s health because people have not been breathing the vapors.|
In your documents, the preferred approach is to order your conclusions from the most hazardous exposures to the least; however, it is OK to use a different order if it is more appropriate based on your specific site conclusions. To assign a conclusion category, consider and integrate all of the information available for the site, including the following:
- Presence of completed or potential exposure pathways
- On-site and off-site environmental contaminant concentrations
- Potential for multiple source exposures
- Potential for interactive effects (chemical mixtures) from multiple contaminant sources or exposure routes
- Contaminant interactions
- Presence of potentially exposed populations, including sensitive or highly susceptible populations
- Opportunities for acute, intermediate, or chronic exposures
- Nature of toxic effects associated with site contaminants and the exposure conditions associated with these toxic effects
- Community-specific health outcome data
- Community health concerns
- Presence of physical hazards
Remember: Every site is different, so determining the appropriate hazard category requires professional judgment.
Examples of instances where you do not need a conclusion category include:
- Presenting comments on a site-related document not developed by ATSDR (e.g., a remedial investigation/feasibility study, a work plan).
- Providing technical assistance in determining contaminants to test, detection limits, monitoring levels, or other similar assistance.
- Providing general information on hazardous substances, diseases, or issues that are not directly related to a specific site.
Not only is every site unique, but different levels of public health hazards might occur at different parts of the site. Conclusion categories should be assigned to exposure pathways that might cause a hazard to affected populations. If site conditions have varied over time, you might find it appropriate to assign a separate conclusion category for past, current, and future exposure conditions. When assigning separate conclusion categories for different time periods, put the highest hazard and associated time frame first, followed by a statement about the lesser hazard and its related time frame (see Changing Exposure Conditions Example).
Scenario: A community that formerly got drinking water from private wells now has municipal water.
Conclusion Category: Indicate that before the community had access to municipal water, the historical groundwater exposure pathway could harm the health of those persons drinking water for a year or longer from private wells within ½ mile south of the site. Note that current and future pathways are not expected to harm people’s health because the municipal water hook-up eliminated the potential for exposure to contaminants in groundwater by any means (e.g., drinking water, water used for gardening, showering).
You might also have cases where you identify actual or potential exposures but ultimately determine no health hazards exist (i.e., Category 4 — Exposure, No Harm Expected) (see Exposures Where No Harm Is Expected Example).
Scenario: An exposure dose associated with a metal gives a hazard quotient (HQ) above 1. Upon closer examination and integration of site-specific exposure and health effects data, you determine that harmful exposures are not occurring, based on the following:
- The temporal and spatial distribution of the data shows that assuming exposure at the exposure point concentration (EPC) used in the dose calculation overestimates likely exposures.
- Limited bioavailability of the metal greatly reduces exposure potential.
- Estimated doses are much lower than harmful effect levels reported in the relevant scientific literature.
A scenario such as this example might cause confusion. However, in cases where the U.S. Environmental Protection Agency (EPA) or another regulatory agency is proposing or taking measures to reduce exposures by cleaning up the site (e.g., soil removal or groundwater treatment), you can offer your perspective as to why. For instance, detected concentrations that exceed screening levels or regulatory action levels might not be a public health concern. Reiterate that media-specific screening levels (ATSDR-derived comparison values and health-based non-ATSDR screening levels), health guidelines, cancer risk values, and regulatory action levels are not indicators of harmful health effects but are generally used as levels considered thoroughly safe. Explain that while the evaluation does not indicate that exposure is high enough to indicate health hazards, prudent public health practice calls for reducing exposures if possible (see Follow-Up Actions Example).
Scenario: Based on available sampling, groundwater near a site contains elevated levels of some volatile organic contaminants. People have not been exposed to these contaminants at concentrations or for durations that would result in harmful health effects. However, exposure is still occurring. Also, contaminants could migrate or change to other volatile organic contaminants (i.e., degrade) over time.
Recommendation: To protect public health, recommend that EPA performs routine sampling of the groundwater. If future sampling indicates an issue, recommend that EPA take action to eliminate and reduce potential future exposures.