Frequently Asked Questions


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What is a BSAF?

 

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Wet or Dry - Does it matter?  

  • Just remember that the BSAF is unit less, so in order for the units of concentration to cancel they have to be expressed on the same basis in the numerator and denominator.  Sediment concentration data is always dry weight, tissue may be either wet or dry, but is usually wet.   The essential point is that the normalizing base has to be expressed on the same basis as the chemical concentration.  If sediment chemical concentration is dry weight, then TOC MUST be dry weight.  If tissue concentration is wet then lipid MUST be wet, if it is dry, lipid MUST be dry.  If that is done, then the same BSAF will result whether dry weight or wet weight data are used.  However, both sediment and tissue DO NOT need to have the same units, as they cancel out of the equation.  Try it  and you'll see.

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BSAF data come from ...

  • The majority of data in the BSAF Database are extracted from published articles in scientific journals. Some gray literature data are included if the quality of the data are known. The data records are marked as either "Used? - Yes" or "Used? - No". "Used? - Yes" indicates that the article included the mean BSAF number, the error of the mean (SE, SD, CV, etc.) and the number of data points used to calculate the mean (n). Many articles provide  BSAF data, but do not have any of the supporting information.

    When viewing the data for a chemical or a specific organism, all BSAF data ("Used? - Yes" and "Used? - No") in the database are presented, however, only "Used? - Yes" data records are included in the statistical calculations (Grand Mean, etc.). This is especially true for the BSAF with statistics page. This may cause some apparent discrepancies in the presented data, so be certain to notice if you are looking at only "Used? - Yes" records or all records. 

    It is strongly recommended that the original article be read before using these data for critical decisions to make certain that these data fit your needs. 

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How Do I transfer data from the BSAF database to a spreadsheet?

  • Copying data from the BSAF database to a spreadsheet is an easy process, but it takes several steps.

    1. After you have generated the page of data you wish to copy, click the File - Save As (or Save Page As) options from your browser menu.

    2. Make certain the option to save the complete web page is selected.

    3. Type in a name for your file and a location to save it to on your local computer.

    4. Click the save button.

    After saving it on your computer, open up your spreadsheet program (Excel, Quattro Pro, etc.) and simply open up the html file you just created.  You may now manipulate the data any way you wish.

    NOTE:  This may not work on older versions of the spreadsheet programs or programs that do not support working with html files.

Why are metals (except organo tins) not found in the BSAF database?

  • BSAFs (Biota Sediment Accumulation Factors) are based on the relationship between lipid normalized tissue and total organic carbon normalized sediment. To date only non-polar organic compounds have been shown to hold to this relationship and even these chemicals show a wide variation due to numerous factors. Elemental metals provide their own unique set of problems and reliable lipid to TOC relationships have not been established. Attempts to establish BSAFs for elemental metals have yielded highly variable results. This condition does not apply to organometallic substances such as tributyltin or methylmercury in which the organic portion of the molecules provide properties conducive to yielding meaningful BSAFs.

  • When absorbed by invertebrates, many metals (cadmium, lead, and others) have been shown to form detoxification products by binding special proteins called metallothioneins (MTs) or by forming salt particulate bodies with sulfur or calcium sometimes termed metal rich granules (MRGs). When associated with MTs or MRGs, metals are thought to be removed from the toxic pool and would not  cause adverse effects to the organism. There is some evidence indicating that metals within MRGs are not available for trophic transfer to other organisms.

  • BSAF data for metals reported in some references may be in reference to organometallic substances as described above, or they may be based on variations of the BSAF equation that do not incorporate lipid and TOC normalization factors. These data are more appropriately called Bioaccumulation factors (BAFs) and are not true BSAF values.

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Why are data from many references not used?

  • Many references are not used because they do not contain the necessary data required for the database.  Some papers only present BSAF data in graphs instead of tabular form making it impossible to isolate individual values.  

  • Other papers calculate BSAF using a different formula then what we consider the "standard" way of calculating BSAF.

  • BSAF data may be placed into the database but not used for any statistical calculations because information is not presented in the paper indicating the type of calculation (Mean, median, etc.), the type of error reported (SD, SE, etc.) or the number of observations used in the mean.   These data are marked with a "Used? - NO" tag.

                            

 

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