Ecological Risk Assessment Step 1
Sections of Step 1 - Problem Forumlation and Toxicity Evaluation:
The first step in the Ecological Risk Assessment process is Problem Formulation. This initial step of an Ecological Risk Assessment (ERA) is to decide which components of an ecosystem (the sum of all the living organisms, their interactions, and the physical factors in a particular area) should be protected, and therefore, which species should be the focus of the ERA. This is different from human health risk assessments in which the species is predetermined (human). The decisions of what to protect and how to measure it are made in the Problem Formulation step of the ERA.
At this stage, information about the chemicals that are contaminating the
site (including what and where they are) is most likely limited. Step 1
(Problem Formulation) is the first stage in determining what is the problem
at the site: a basic understanding of possible risk to the local environment/ecology.
This includes a visit to the site to help 1) determine what plants and animals
might be at risk to factors such as chemical contamination at the site,
2) gather information on the chemical contaminants present at the site,
and 3) determine how those chemicals might affect the plants and animals
at the site.
Screening Level Problem Formulation
Problem formulation includes the development of a conceptual model, which is a representation of how the particular contaminants at a site are expected to behave in the environment. The conceptual model is based on fate (e.g., does a contaminant break down in the environment or is it persistent?) and transport (how does a contaminant move through the environment and where does it end out?). The conceptual model is used to narrow attention to the animals and/or plants likely to be exposed to the contaminants at the site. In risk assessment language, the species that may be exposed to contaminants are called "receptors".
It is not possible to study every species that is potentially at risk at a site. For example, in the Great Lakes region there are some 75 species of amphibians and reptiles, 80 species of mammals, over 200 species of breeding birds (and a nearly equal number of nonbreeding and accidental species), hundreds of species of fish, several thousand species of terrestrial plants, 20,000 species of insects, and so forth. The purpose of the problem formulation is to focus attention on a few species or groups of species that are appropriate for answering the question of whether an ecological risk exists at the site.
For this step, the risk assessor gathers information about the site that can help determine the potential risk to plants and animals found at the site being studied. Information can come from a variety of sources, including a site visit, historical information, and data from previous sampling of the area. The following issues should be addressed:
- Environmental setting:
The environmental setting includes:
- Descriptions of the disturbed and undisturbed natural and developed areas;
- The past, current, and future land-uses (i.e., industrial, residential, undeveloped);
- Facilities that exist or existed at the site;
- The environmental characteristics/ecological types (wetlands, forests, grasslands, water-bodies, human-made/disturbed areas);
- Areas that are potentially, or known to be, at risk from chemical contamination;
- Has the contamination moved off-site to impact other areas;
- This information can be determined from historical data, earlier site investigations, and/or inferences based on likely sources of contaminants (e.g., obvious waste discharge outflows);
- The conceptual site model should describe how contaminants physically enter, move through, and leave the site. This includes how contaminants move through the food chain; the process of contaminant uptake by plants and animals is called bioaccumulation;
What plants, animals, or groups of plants and animals that may be adversely affected (harmed) by contaminants present at the site (endpoint selection); when making this selection, the following should be considered:
- Contact with contaminants: How the plants or animals come in contact with the contaminants (complete exposure pathways); do they ingest (eat) the contaminants; are the contaminants inhaled or do they enter the body through the skin; is the medium (soil, water, air, sediment) in which the plants or animals live contaminated;
- Effects on plants and animals (see Toxicity Effect): How the contaminants present at the site can effect plants and animals that may come in contact with those contaminants; information on specific effects by each contaminant on each type or species of plant and animals that may be affected should be included.
The site visit is part of the process by which the risk assessor attempts to determine the potential risk to the environment.
Screening Level Ecological Effects Evaluation
For this step, the risk assessor determines from a review of scientific literature at what level (concentration) various chemical contaminants will not cause adverse effects in the plants and animals that may come in contact with the contaminants present at the site. These levels are known as No-Observed-Adverse-Effects-Levels (NOAELs). The actual concentrations of the contaminants found at the site will later be compared to the respective NOAELs during risk calculations.
The plants and animals that are most sensitive to chemical contamination are considered for further study. At this step, these concentrations (NOAELs) generally come from a review of the scientific literature. There may be different sources of information with differing concentrations. Therefore, the following factors should be considered when choosing specific concentrations for comparison.
- Preferred toxicity data:
Toxicity data refers to information (at this stage it normally comes from scientific literature) about how and at what levels chemicals affect a plant or animal in a harmful way; this information can be used to compare against concentrations of contaminants found at the site to determine if there is the possibility for risk to the environment; the levels used for comparisons should be NOAELs.
- Time of exposure:
The NOAEL should be from scientific studies that exposed the plants or animals to the chemical for a long time (chronic). Short- or medium-time exposure studies are less desirable than long time studies because it might take a long period of exposure to a chemical in order for there to be any adverse effects. However, time should be measured relative to the life span of the plant or animal being studied. In other words, for a plant or animal with a short life-span, it might be only necessary to have a relatively short study (i.e., a few days); but for a plant or animal with a long life-span, it might be necessary to have a long term study (i.e., weeks or months) to discover any problems.
- Exposure route:
The risk assessor should determine how plants or animals on the site can become exposed to the contaminant. The study from which the NOAEL comes should use the same type of exposure. For example, if a fish on the site is exposed to the contaminants at the site directly from the water it is swimming in, then the NOAEL study should have looked at this type of water exposure, as opposed to a fish eating contaminated food.
- Field vs. laboratory:
The risk assessor should determine if the scientific study was performed in the laboratory or in the field. Either type of study can be used, but because they are different, the differences must be accounted for when selecting or calculating the NOAEL.
- Data conversions:
In some cases, the data from a study might need to be modified to allow the data to be used for species other than those in the study. For example, the scientific study might have looked at brown trout, but on the Superfund site, there are no brown trout, only lake trout. The brown trout data might have to be converted to lake trout data.
- Uncertainty assessment:
Professional judgment is needed to determine how accurate the scientific literature data are. The risk assessor should be consistently conservative in selecting literature values and must describe the limitations of using those data for the Superfund site. Uncertainty must be discussed before moving onto the risk calculation.