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Interpreting the PBT Profiler Results

Introduction

The PBT Profiler helps to identify potentially persistent, bioaccumulative, and toxic (PBT) chemicals using a series of computer estimation methods based on chemical structure and physical/chemical properties. The PBT Profiler uses the results of these estimation methods and compares the results to a set of well-defined criteria for each of these three areas. For a chemical to be considered a PBT, it must exceed the criteria in all 3 areas; that is, it must be persistent, bioaccumulative, and toxic. Chemicals that are persistent, bioaccumulative, and toxic are of concern because they can accumulate over time to higher concentrations that may adversely impact human health or the environment.

The PBT Profiler has three levels of output that appear on two separate pages:

The PBT Summary and Detailed Results outputs for each area (persistence, bioaccumulation, and toxicity) are provided in table format on the initial results screen. Any number of chemicals can be profiled and the results for all chemicals are provided on this page.  The user can rapidly determine which estimates exceed the EPA criteria as they appear in orange or red text; those that do not exceed the EPA criteria appear in green text.

Example Results Page for 2,3,4,6-tetrachlorophenol

Persistence
Bioaccumulation
Toxicity
58-90-2   Phenol, 2,3,4,6-tetrachloro-

PBT Profiler Estimate = PBT

Media
Half-Life
(days)
Percent in
Each Medium

BCF
Fish ChV
(mg/l)
Water 60   9% 210 0.032
Soil 120   82%
Sediment 540   8%
Air 58   0%
 

P2 Considerations and more information


(Note: These results are provided only as a representative example, and because experimental data are available for this chemical, it should not be profiled using the PBT Profiler). 

The most detailed output, the P2 Considerations, is also shown on the results page as a link to the P2 Considerations page. The P2 Considerations provides additional information on the PBT Profiler estimates. More information on interpreting the results for each type of output is provided below. Each of the important terms used by the PBT Profiler is linked to its definition. Users should be aware that the PBT Profiler estimates are available for 20 minutes after the last page is requested.


Summary Output - The PBT Profiler Estimate

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The PBT Summary output is based on the results of the individual estimates and it uses an uppercase P, B, or T to represent the persistence, bioaccumulation, and toxicity results, respectively.  It compares the estimated results to a set of defined criteria for each area.  If the estimated results exceed the criteria in any of the three areas the corresponding letter is shaded orange, if the estimated results greatly exceed the criteria the letter is shaded red; if the estimate does not exceed the criteria, it is shaded green.  In the black-and-white version, if the estimated results exceed the criteria the corresponding letter is italicized ( P ) and is not orange. If the estimated results greatly exceed the criteria the litter is underlined ( P) and is not red. If the estimated results do not exceed the criteria the letter appears in lowercase ( p ) and it is not green.

For a chemical to be considered a PBT,  it must be persistent, bioaccumulative, and toxic.  For chemicals run through the PBT Profiler, the following PBT Summary output examples are predicted to be PBTs:

In the black-and-white version, The PBT Profiler would display these PBT Summary output examples as follows:

The following PBT Summary output examples are not predicted to be PBTs:

Reviewing the PBT Summary output allows the results of the PBT Profiler's estimates on the persistence, bioaccumulation, and toxicity of a chemical substance to be readily determined.

Another result that should be noted when identifying P2 opportunities is shown when the PBT Profiler cannot estimate a chemical's aquatic toxicity:

In these PBT Summary output examples, the chemical is expected to be persistent and bioaccumulative, but the aquatic toxicity could not be estimated.  Given that persistent and bioaccumulative chemicals may eventually reach relatively high levels, chemicals with this type of estimated result should be reviewed similar to those predicted to possess moderate or high PBT characteristics when identifying P2 opportunities.

If a chemical is expected to be present in water, soil, or sediment, the PBT Profiler then determines in which environmental compartment the chemical is estimated to be most prevalent (i.e., the predominant compartment). If the half-life in the predominant compartment exceeds the persistence criteria, then the PBT Profiler will shade the persistence letter as P or P ( P or P ), indicating that this chemical is expected to persist in the environment. The PBT Profiler does not explicitly consider a chemical's fate in air in the persistence summary estimate

Detailed Results To Top
   

The Detailed Results provide numerical estimates for indicators in each of these three areas and are provided in a tabular format.  The Detailed Results for persistence are further broken down to provide information for each of the environmental compartments.

Persistence

The persistence section provides the half-life in each of the environmental media (also called environmental compartments - air, water, soil, and sediment) as well as the amount (as a percent of the total) expected to be found in each compartment.  The half-life indicates how long (in days) a chemical is expected to persist in each environmental compartment.  The percent in each medium provides an estimate of how much is found in each environmental compartment after its release (the sum of the percent of all four media = 100%).  Using this information, P2 initiatives can be identified by comparing the results to likely release scenarios throughout the life cycle of the substance.

The PBT Profiler compares the half-life in each environmental compartment to a defined set of persistence criteria.  If the half-life exceeds the persistence criteria, its value is shaded orange or red; if the criteria are not exceeded, the half-life is shaded green.  In the black-and-white version, these are indicated using italics (e.g., 60) and underlines (e.g., 180) for those values that exceed the EPA criteria. The persistence criteria in air differ from those or water, soil, and sediment and the methodology to determine the persistence in each media are slightly different.  When viewing the detailed persistence results, the user can quickly identify which environmental compartments a chemical may be persistent in by noting in which media the half-life has exceeded the EPA persistence criteria.

The percent in each medium column of the table provides an indication of the partitioning, or transport between compartments, of a chemical in the environment.  This value is provided to the user to help identify P2 initiatives by helping with possible release and exposure scenarios as well as providing information on a chemical's likely environmental fate. The values in water, soil, and sediment are used directly in the persistence summary estimate.  The persistence summary term is determined based on a chemicals half-life in the media it is predominately found in (excluding air).   The P2 Considerations results page provides narrative that helps to put the persistence results in perspective.

Bioaccumulation

The bioaccumulation detailed results provide the numerical estimate for the fish bioconcentration factor (BCF).  The BCF is a unit-less value.  In general, compounds that are found to bioconcentrate are typically found to bioaccumulate.  The PBT Profiler compares the BCF to a defined set of bioaccumulation criteria.  If the BCF exceeds the EPA bioaccumulation criteria, its value is shaded orange or red; if the criteria are not exceeded, it is shaded green.  If the BCF result for a chemical is shaded orange or red (italicized or underlined in the black-and-white version), the PBT Profiler predicts that it may be bioaccumulative.

Toxicity To Top
 

The aquatic toxicity detailed results provide the numerical estimate for the fish Chronic Value (ChV) in mg/l.  The PBT Profiler compares the ChV to a defined set of toxicity criteria.  If the ChV exceeds the EPA toxicity  criteria, its value is shaded orange or red; if the criteria are not exceeded, it is shaded green.   If the ChV result for a chemical is shaded orange or red (italicized or underlined in the black-and-white version), the PBT Profiler predicts that it may be toxic.

The PBT Profiler will flag chemicals where the maximum water solubility is estimated to be lower than the Fish ChV (in mg/l).  This is referred to as no effect at saturation.  In this situation, the chemical cannot reach a concentration high enough in environmental waters to allow the estimated aquatic toxicity effects to be expressed. The PBT Profiler results for chemicals that fall into this category should still be interpreted with caution, however,  especially if they are predicted to be persistent and bioaccumulate.  The P2 Considerations results page will help to put the results for chemicals displaying no effect at saturation into perspective.

P2 Considerations Results To Top
 

The P2 Considerations Results section, located on a separate page for each chemical, provides additional information on the PBT Profiler results on a chemical-by-chemical basis. In addition to providing the results for all of the estimation programs used by the PBT Profiler, it also contains information on how the summary output (the PBT Profiler Summary)  was generated. The individual persistence, bioaccumulation, and toxicity results are also described.  The section contains a chemical-specific discussion on partitioning and release scenarios.  Based on the chemical-specific results, it may also contain information on pollution prevention considerations that should be considered.

The bioconcentration and toxicity sections also discuss the chemical values provided in the detailed results section. A link from this page allows the user to display the complete ECOSARTM output for their compound. The toxicity section also contains structure-based information that may apply to specific chemical classes.

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Computer Resources Donated by SRC, Inc.          Ver 2.001     Last Updated September 28, 2016